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Since entering the stage 25 years ago as a highly specific serological biomarker for rheumatoid arthritis, anti-citrullinated protein antibodies (ACPAs) have been a topic of extensive research. This hallmark B cell response arises years before disease onset, displays interpatient autoantigen variability, and is associated with poor clinical outcomes. Technological and scientific advances have revealed broad clonal diversity and intriguing features including high levels of somatic hypermutation, variable-domain N-linked glycosylation, hapten-like peptide interactions, and clone-specific multireactivity to citrullinated, carbamylated and acetylated epitopes. ACPAs have been found in different isotypes and subclasses, in both circulation and tissue, and are secreted by both plasmablasts and long-lived plasma cells. Notably, although some disease-promoting features have been reported, results now demonstrate that certain monoclonal ACPAs therapeutically block arthritis and inflammation in mouse models. A wealth of functional studies using patient-derived polyclonal and monoclonal antibodies have provided evidence for pathogenic and protective effects of ACPAs in the context of arthritis. To understand the roles of ACPAs, one needs to consider their immunological properties by incorporating different facets such as rheumatoid arthritis B cell biology, environmental triggers and chronic antigen exposure. The emerging picture points to a complex role of citrulline-reactive autoantibodies, in which the diversity and dynamics of antibody clones could determine clinical progression and manifestations. In this Review, the authors provide an overview of the immunological, clinical and pathophysiological features of anti-citrullinated protein antibodies in rheumatoid arthritis, highlighting the latest findings regarding the complex contribution of anti-citrullinated protein antibodies to the disease. Key points: Citrulline B cell responses are diverse but share important features that might be linked to rheumatoid arthritis-associated B cell dysregulation as well as environmental triggers, antigen exposure and the evolution of chronic immune reactions. Anti-citrullinated protein antibodies (ACPAs) are extensively multireactive towards citrullinated, carbamylated and acetylated proteins, have high somatic hypermutation, and carry N-linked glycosylations in the variable regions. More than 100 patient-derived human monoclonal ACPAs have been generated from different B cell compartments and patients, providing invaluable insights into citrulline autoimmunity and antibody function. Although disease-causative autoantigens are presently unknown, ACPAs can target different synovial cells and are likely to form pathogenic immune complexes. Results from studies using human monoclonal ACPAs reveal that some clones can completely block arthritis and inflammation in mouse models, while showing moderate pathogenic properties in other settings. Different ACPA clones with different immunological features and antigen-binding patterns might mediate disease-promoting effects or have protective roles. [ABSTRACT FROM AUTHOR]

The cyclic GMP–AMP synthase (cGAS), a prominent intracellular DNA sensor in mammalian cells, controls the innate immune response and the stimulator of interferon genes (STING)‐mediated synthesis of pro‐inflammatory cytokines, such as type‐I interferon (IFN‐I). For decades, IFN‐I has been hypothesized to be essential in the development of systemic lupus erythematosus (SLE), a chronic multisystem autoimmunity characterized by immune complex (IC) deposition in small vessels. Recent findings revealed that the activation of the cGAS–STING pathway by self‐DNA would propagate the autoimmune responses via upregulating IFN‐I production in SLE. In this review, we aimed to provide a comprehensive outlook of the role of the cGAS–STING pathway in SLE pathobiology, as well as, a better understanding of current therapeutic opportunities targeting this axis. [ABSTRACT FROM AUTHOR]

A method is presented for chemiluminescence resonance energy transfer (CRET) using APTES-Fe3O4 as a highly efficient energy acceptor with strong magnetic effectiveness over extended distances, while an Au@BSA-luminol composite acts as the donor. In order to boost the chemiluminescence reactions, CuO nanoparticles were successfully employed. The distance between the donor and acceptor is a crucial factor in the occurrence of the CRET phenomenon. A sensitive and high-throughput sandwich chemiluminescence immunosensor has been developed accordingly with a linear range of 1.0 × 10–7 g/L to 6.0 × 10–5 g/L and a limit of detection of 0.8 × 10–7 g/L. The CRET-based sandwich immunosensor has the potential to be implemented to early cancer diagnosis because of its high sensitivity in detecting Nanog, fast analysis (30 min), and simplicity. Furthermore, this approach has the potential to be adapted for the recognition of other antigen–antibody immune complexes by utilizing the corresponding antigens and their selective antibodies. [ABSTRACT FROM AUTHOR]

Over the course of evolution, many proteins have undergone adaptive structural changes to meet the increasing homeostatic regulatory demands of multicellularity. Aminoacyl tRNA synthetases (aaRS), enzymes that catalyze the attachment of each amino acid to its cognate tRNA, are such proteins that have acquired new domains and motifs that enable non-canonical functions. Through these new domains and motifs, aaRS can assemble into large, multi-subunit complexes that enhance the efficiency of many biological functions. Moreover, because the complexity of multi-aminoacyl tRNA synthetase (mARS) complexes increases with the corresponding complexity of higher eukaryotes, a contribution to regulation of homeostatic functions in multicellular organisms is hypothesized. While mARS complexes in lower eukaryotes may enhance efficiency of aminoacylation, little evidence exists to support a similar role in chordates or other higher eukaryotes. Rather, mARS complexes are reported to regulate multiple and variegated cellular processes that include angiogenesis, apoptosis, inflammation, anaphylaxis, and metabolism. Because all such processes are critical components of immune homeostasis, it is important to understand the role of mARS complexes in immune regulation. Here we provide a conceptual analysis of the current understanding of mARS complex dynamics and emerging mARS complex roles in immune regulation, the increased understanding of which should reveal therapeutic targets in immunity and immune-mediated disease. [ABSTRACT FROM AUTHOR]

Porcine reproductive and respiratory syndrome (PRRS) caused by the PRRS virus (PRRSV) has been harming the pig industry worldwide for nearly 40 years. Although scientific researchers have made substantial efforts to explore PRRSV pathogenesis, the immune factors influencing PRRSV infection still need to be better understood. Infectious virus-antibody immune complexes (ICs) formed by PRRSV and sub-or non-neutralizing antibodies specific for PRRSV may significantly promote the development of PRRS by enhancing PRRSV replication through antibody-dependent enhancement. However, nothing is known about whether PRRSV infection is affected by non-infectious ICs (NICs) formed by non-pathogenic/infectious antigens and corresponding specific antibodies. Here, we found that PRRSV significantly induced the transcripts and proteins of interferon-α (IFN-α), IFN-β, IFN-γ, IFN-λ1, and tumor necrosis factor-α (TNF-α) in vitro primary porcine alveolar macrophages (PAMs) in the early stage of infection. Our results showed that NICs formed by rabbit-negative IgG (RNI) and pig anti-RNI specific IgG significantly reduced the transcripts and proteins of IFN-α, IFN-β, IFN-γ, IFN-λ1, and TNF-α in vitro PAMs and significantly elevated the transcripts and proteins of interleukine-10 (IL-10) and transforming growth factor-β1 (TGF-β1) in vitro PAMs. NICs-mediated PRRSV infection showed that NICs not only significantly decreased the induction of IFN-α, IFN-β, IFN-γ, IFN-λ1, and TNF-α by PRRSV but also significantly increased the induction of IL-10 and TGF-β1 by PRRSV and considerably enhanced PRRSV replication in vitro PAMs. Our data suggested that NICs could downregulate the production of antiviral cytokines (IFN-α/β/γ/λ1 and TNF-α) during PRRSV infection in vitro and facilitated PRRSV proliferation in its host cells by inhibiting innate antiviral immune response. This study elucidated one novel immune response to PRRSV infection, which would enhance our understanding of the pathogenesis of PRRSV. [ABSTRACT FROM AUTHOR]

Autoantibodies to nuclear antigens are hallmarks of systemic lupus erythematosus (SLE) where they contribute to pathogenesis. However, there remains a gap in our knowledge regarding how different isotypes of autoantibodies contribute to this autoimmune disease, including the production of the critical type I interferon (IFN) cytokines by plasmacytoid dendritic cells (pDCs) in response to immune complexes (ICs). We focused on IgA, which is the second-most prevalent isotype in serum and, along with IgG, is deposited in glomeruli in individuals with lupus nephritis. We show that individuals with SLE have serum IgA autoantibodies against most nuclear antigens, correlating with IgG against the same antigen. We investigated whether IgA autoantibodies against a major SLE autoantigen, Smith ribonucleoprotein (Sm/RNP), played a role in IC activation of pDCs. We found that pDCs expressed the IgA-specific Fc receptor, FcαR, and IgA1 autoantibodies synergized with IgG in RNA-containing ICs to generate robust primary blood pDC IFN-α responses in vitro. pDC responses to these ICs required both FcαR and FcγRIIa, showing synergy between these Fc receptors. Sm/RNP IC binding to and internalization by pDCs were greater when ICs contained both IgA1 and IgG. Circulating pDCs from individuals with SLE had higher binding of IgA1-containing ICs and higher expression of FcαR than pDCs from healthy control individuals. Although pDC FcαR expression correlated with the blood IFN-stimulated gene signature in SLE, Toll-like receptor 7 agonists, but not IFN-α, up-regulated pDC FcαR expression in vitro. Together, we show a mechanism by which IgA1 autoantibodies contribute to SLE pathogenesis. Editor's summary: Autoantibodies to nuclear antigens contribute to pathology in systemic lupus erythematosus (SLE). However, it is not understood how different isotypes of these antibodies contribute to disease. Here, Waterman et al. characterized circulating immunoglobulin A1 (IgA1) autoantibodies in individuals with SLE, showing that they reacted against many of the same self-antigens as their immunoglobulin G (IgG) counterparts, including against Smith ribonuclear proteins. The authors further showed that interferon-α (IFN-α)–producing plasmacytoid dendritic cells expressed the IgA1 receptor, Fc α receptor (FcαR), and that IgA1-containing immune complexes could drive IFN-α production by these cells in vitro. The authors showed that these responses required the presence of both IgA1 and IgG. Last, the authors showed that, in 18 individuals with SLE, interferon-stimulated gene expression positively correlated with the amount of FcαR in whole blood. Together, these results suggest that targeting FcαR could be a potential therapeutic for SLE treatment. —Brandon Berry [ABSTRACT FROM AUTHOR]

In recent decades, the poultry industry has developed rapidly. Increased demand for higher volumes, better quality and competitive prices led to industrialization, intensification and concentration of production. All this has put significant pressure on animals with genetic potential to achieve higher profits and higher efficiency, which in turn increases the risk of infectious diseases. In addition to disease control, there is pressure on producers to reduce the use of antibiotics and other chemicals, on par with the elimination of pathogens, forcing producers to seek optimal disease control methods. In this context, the principles of biosecurity and vaccination have greatly improved efforts and become important tools for disease control. The vaccine market today is quite broad and includes many vaccines developed on the basis of the latest technologies, such as immune complex vaccines, as well as the largest range of recombinant vector vaccines for poultry. However, all of them have many disadvantages and negative points in practical application, namely: different possibilities of overcoming the level of maternal antibodies (MAT), the need to collect blood serum and conduct laboratory tests to determine the exact day of vaccination, some have a high degree of tissue depletion of the bursa of Fabricius (due to destruction of lymphocytes), low percentage of protection of the bird due to incorrect drinking of the vaccine, etc. Therefore, today specialists face key questions, such as effectiveness against variations of a specific microorganism distributed in different parts of the world; compatibility between vaccines; increasing the resistance or preventing (reducing) the isolation and spread of the pathogen in the environment, which are of crucial importance for reducing the risk of the persistence of the pathogen or preventing the spread of the disease; influence or intervention of passive immunity, advantages of using one category of vaccines over others, etc. [ABSTRACT FROM AUTHOR]

The classical pathway of the complement system is activated by the binding of C1q in the C1 complex to the target activator, including immune complexes. Factor H is regarded as the key downregulatory protein of the complement alternative pathway. However, both C1q and factor H bind to target surfaces via charge distribution patterns. For a few targets, C1q and factor H compete for binding to common or overlapping sites. Factor H, therefore, can effectively regulate the classical pathway activation through such targets, in addition to its previously characterized role in the alternative pathway. Both C1q and factor H are known to recognize foreign or altered-self materials, e.g., bacteria, viruses, and apoptotic/necrotic cells. Clots, formed by the coagulation system, are an example of altered self. Factor H is present abundantly in platelets and is a well-known substrate for FXIIIa. Here, we investigated whether clots activate the complement classical pathway and whether this is regulated by factor H. We show here that both C1q and factor H bind to the fibrin formed in microtiter plates and the fibrin clots formed under in vitro physiological conditions. Both C1q and factor H become covalently bound to fibrin clots, and this is mediated via FXIIIa. We also show that fibrin clots activate the classical pathway of complement, as demonstrated by C4 consumption and membrane attack complex detection assays. Thus, factor H downregulates the activation of the classical pathway induced by fibrin clots. These results elucidate the intricate molecular mechanisms through which the complement and coagulation pathways intersect and have regulatory consequences. [ABSTRACT FROM AUTHOR]

IgA nephropathy, presently recognized as the foremost primary glomerular disorder, emerges as a principal contributor to renal failure globally, with its pathogenesis yet to be fully elucidated. Extensive research has highlighted the critical role of gut microbiome in the onset and progression of IgA nephropathy, underscoring its importance in accurately delineating the disease's etiology. For example, gut microbiome dysbacteriosis can lead to the production of nephritogenic IgA1 antibodies, which form immune complexes that deposit in the kidneys, causing inflammation and damage. The gut microbiome, a source of numerous bioactive compounds, interacts with the host and plays a regulatory role in gut-immune axis modulation, earning it the moniker of the "second brain." Recent investigations have particularly emphasized a significant correlation between IgA nephropathy and gut microbiome dysbacteriosis. This article offers a detailed overview of the pathogenic mechanisms of IgA nephropathy, specifically focusing on elucidating how alterations in the gut microbiome are associated with anomalies in the intestinal mucosal system in IgA nephropathy. Additionally, it describes the possible influence of gut microbiome on recurrent IgA nephropathy following kidney transplantation. Furthermore, it compiles potential therapeutic interventions, offering both theoretical and practical foundations for the management of IgA nephropathy. Lastly, the challenges currently faced in the therapeutic approaches to IgA nephropathy are discussed. [ABSTRACT FROM AUTHOR]

Plants rely on immune receptor complexes at the cell surface to perceive microbial molecules and transduce these signals into the cell to regulate immunity. Various immune receptors and associated proteins are often dynamically distributed in specific nanodomains on the plasma membrane (PM). However, the exact molecular mechanism and functional relevance of this nanodomain targeting in plant immunity regulation remain largely unknown. By utilizing high spatiotemporal resolution imaging and single-particle tracking analysis, we show that myosin XIK interacts with remorin to recruit and stabilize PM-associated kinase BOTRYTIS-INDUCED KINASE 1 (BIK1) within immune receptor FLAGELLIN SENSING 2 (FLS2)-containing nanodomains. This recruitment facilitates FLS2/BIK1 complex formation, leading to the full activation of BIK1-dependent defense responses upon ligand perception. Collectively, our findings provide compelling evidence that myosin XI functions as a molecular scaffold to enable a spatially confined complex assembly within nanodomains. This ensures the presence of a sufficient quantity of preformed immune receptor complex for efficient signaling transduction from the cell surface. [ABSTRACT FROM AUTHOR]

Background: Vaccine development against tuberculosis remains a global health imperative, necessitating robust immunogenicity and safety profiles. Nanoparticle-based delivery systems offer promising avenues to enhance vaccine efficacy while ensuring tolerability. This study explores the utilization of chitosan micelles as a delivery platform for immune complex vaccination against tuberculosis. Leveraging two key antigens of Mycobacterium tuberculosis, namely HspX and Mpt51, known for their relevance in latent tuberculosis and its co-infection with the human immunodeficiency virus, immune complexes were synthesized in vitro using antibodies raised against these antigens. The immune complexes were then conjugated onto chitosan micelles, characterized for their physicochemical properties, and evaluated for their biocompatibility and immunogenicity. Results: Chitosan nanoparticles conjugated with either antigen or its immune complexes were synthesized as micelles and physicochemical characterizations confirm the formation of micelles without altering the polymer composition. These immune complex-conjugated chitosan micelles were found to be safe, exhibiting no significant hemolytic and cytotoxic activity even at a higher concentration of 400 µg/ml. Peripheral blood mononuclear cells upon stimulation with immune complex-conjugated chitosan micelles showed enhanced cellular uptake and one to two-fold increased expression of key immune markers—interferon gamma and CD-86. Conclusions: These findings underscore the potential of chitosan nanoparticles as a versatile delivery platform for immune complex vaccination against tuberculosis. While limitations exist, such as including only two markers of immune modulation, this study lays a foundation for future investigations into immune complex vaccine potential in animal models. In conclusion, chitosan micelles carrying immune complexes of HspX and Mpt51 tuberculosis antigens exhibit promising immunogenicity, highlighting their potential as a platform for multi-antigenic vaccine components warranting further in vivo studies. [ABSTRACT FROM AUTHOR]

Although antibody-mediated lung damage is a major factor in transfusionrelated acute lung injury (ALI), autoimmune lung disease (for example, coatomer subunit α [COPA] syndrome), and primary graft dysfunction following lung transplantation, the mechanism by which antigen-antibody complexes activate complement to induce lung damage remains unclear. In this issue of the JCI, Cleary and colleagues utilized several approaches to demonstrate that IgG forms hexamers with MHC class I alloantibodies. This hexamerization served as a key pathophysiological mechanism in alloimmune lung injury models and was mediated through the classical pathway of complement activation. Additionally, the authors provided avenues for exploring therapeutics for this currently hard-to-treat clinical entity that has several etiologies but a potentially focused mechanism. [ABSTRACT FROM AUTHOR]

The constraints imposed by natural antibody affinity maturation often culminate in antibodies with suboptimal binding affinities, thereby limiting their therapeutic efficacy. As such, the augmentation of antibody binding affinity is pivotal for the advancement of efficacious antibody-based therapies. Classical experimental paradigms for antibody engineering are financially and temporally prohibitive due to the extensive combinatorial space of sequence variations in the complementarity-determining regions (CDRs). The advent of computational techniques presents a more expeditious and economical avenue for the systematic design and optimization of antibodies. In this investigation, we assess the performance of AlphaFold2 coupled with the binder hallucination technique for the computational refinement of antibody sequences to elevate the binding affinity of pre-existing antigen-antibody complexes. These methodologies exhibit the capability to predict protein tertiary structures with remarkable fidelity, even in the absence of empirically derived data. Our results intimate that the proposed approach is adept at designing antibodies with improved affinities for antigen-antibody complexes unrepresented in AlphaFold2's training dataset, underscoring its potential as a robust and scalable strategy for antibody engineering. [ABSTRACT FROM AUTHOR]

Simple Summary: Complement system is an ancient immune pathway that protects us against harmful invaders. Meanwhile, mitochondria, widely known as the powerhouse of the cell, are essential for producing energy and maintaining healthy cells. Bridging past and present studies, this review aims to elucidate an underexplored yet essential connection between the complement system and mitochondria. These interactions are implicated in different diseases across various tissues and organs, such as Alzheimer's disease and cancer, that are in critical need of cure. Mitochondria release signals that impact the activation of the complement system, leading to tissue damage and inflammation; while the complement system alters mitochondrial functions, forming a vicious cycle. This cycle exacerbates disease progression and health outcomes. We hope to highlight potential targets to alleviate societal healthcare burdens by bringing scientists' attention to this novel bidirectional interaction. Mitochondria serve an ultimate purpose that seeks to balance the life and death of cells, a role that extends well beyond the tissue and organ systems to impact not only normal physiology but also the pathogenesis of diverse diseases. Theorized to have originated from ancient proto-bacteria, mitochondria share similarities with bacterial cells, including their own circular DNA, double-membrane structures, and fission dynamics. It is no surprise, then, that mitochondria interact with a bacterium-targeting immune pathway known as a complement system. The complement system is an ancient and sophisticated arm of the immune response that serves as the body's first line of defense against microbial invaders. It operates through a complex cascade of protein activations, rapidly identifying and neutralizing pathogens, and even aiding in the clearance of damaged cells and immune complexes. This dynamic system, intertwining innate and adaptive immunity, holds secrets to understanding numerous diseases. In this review, we explore the bidirectional interplay between mitochondrial dysfunction and the complement system through the release of mitochondrial damage-associated molecular patterns. Additionally, we explore several mitochondria- and complement-related diseases and the potential for new therapeutic strategies. [ABSTRACT FROM AUTHOR]

Over the past century, multichannel fluorescence imaging has been pivotal in myriad scientific breakthroughs by enabling the spatial visualization of proteins within a biological sample. With the shift to digital methods and visualization software, experts can now flexibly pseudocolor and combine image channels, each corresponding to a different protein, to explore their spatial relationships. We thus propose psudo, an interactive system that allows users to create optimal color palettes for multichannel spatial data. In psudo, a novel optimization method generates palettes that maximize the perceptual differences between channels while mitigating confusing color blending in overlapping channels. We integrate this method into a system that allows users to explore multi‐channel image data and compare and evaluate color palettes for their data. An interactive lensing approach provides on‐demand feedback on channel overlap and a color confusion metric while giving context to the underlying channel values. Color palettes can be applied globally or, using the lens, to local regions of interest. We evaluate our palette optimization approach using three graphical perception tasks in a crowdsourced user study with 150 participants, showing that users are more accurate at discerning and comparing the underlying data using our approach. Additionally, we showcase psudo in a case study exploring the complex immune responses in cancer tissue data with a biologist. [ABSTRACT FROM AUTHOR]

Nonylphenol is an aromatic organic compound that has an estrogen-like effect and has a negative effect on the human endocrine system. A method has been developed for the competitive determination of nonylphenol using magnetic particles, rabbit antiserum, nonylphenol conjugate with soybean trypsin inhibitor (STI) and biotin. The principle of the analysis is the formation of immune complexes on the surface of magnetite particles due to covalent immobilization of protein G through the oriented immobilization of polyclonal antibodies from rabbit serum during a competitive reaction between the free analyte (nonylphenol) and the bound one (as part of the nonylphenol-STI-biotin conjugate) for the binding sites of specific antibodies. The detection of formed immune complexes is proposed to be carried out using a streptavidin-polyperoxidase conjugate, which makes it possible to achieve a nine-fold gain in the level of the analytical signal. The developed ELISA using magnetite particles allows us to achieve a detection limit of nonylphenol at the level of 3.8 ng/mL, which is 14.5 times lower in comparison with the classic competitive ELISA (55 ng/mL). Based on the results of the experimental work, the optimized volume of the test sample was 500 μL, which makes it possible to concentrate low-contaminated samples by 17 times. [ABSTRACT FROM AUTHOR]

Doxorubicin (DOX) is a commonly used chemotherapeutic drug, from the anthracycline class, which is genotoxic to neoplastic cells via a DNA intercalation mechanism. It is effective and universal; however, it also causes numerous side effects. The most serious of them are cardiotoxicity and a decrease in the number of myeloid cells. For this reason, targeted DOX delivery systems are desirable, since they would allow lowering the drug dose and therefore limiting systemic side effects. Recently, synthetic dyes, in particular Congo red (CR), have been proposed as possible DOX carriers. CR is a planar molecule, built of a central biphenyl moiety and two substituted naphthalene rings, connected with diazo bonds. In water, it forms elongated ribbon-shaped supramolecular structures, which are able to selectively interact with immune complexes. In our previous studies, we have shown that CR aggregates can intercalate DOX molecules. In this way, they preclude DOX precipitation in water solutions and increase its uptake by MCF7 breast cancer cells. In the present work, we further explore the interactions between DOX, CR, and their aggregates (CR/DOX) with phospholipid membranes. In addition to neutral molecules, the protonated doxorubicin form, DXP, is also studied. Molecular dynamics simulations are employed to study the transfer of CR, DOX, DXP, and their aggregates through POPC bilayers. Interactions of CR, DOX, and CR/DOX with model monolayers are studied with Langmuir trough measurements. This study shows that CR may support the transfer of doxorubicin molecules into the bilayer. Both electrostatic and van der Waals interactions with lipids are important in this respect. The former promote the initial stages of the insertion process, the latter keep guest molecules inside the bilayer. [ABSTRACT FROM AUTHOR]

Cardiomyopathy is a severe cardiac condition characterized by complex immune regulatory mechanisms. While the role of immune genes is recognized, the specifics of their regulation in cardiomyopathy are not fully understood. Recent studies highlight the significance of transposable elements (TEs) in various diseases, particularly their potential to modulate immune responses. This paper utilizes publicly available databases to explore the role of TEs in myocarditis: RNA Seq data and single-cell sequencing data were analyzed, with a focus on the mouse model of experimental autoimmune myocarditis (EAM). The RNA-Seq analysis revealed substantial upregulation of a range of immune genes in cardiac tissue. Further investigation using single-cell sequencing of cardiac immune cells identified specific expression of certain transposable elements (TEs) across different types of immune cells in the heart. Additionally, there was an overall increase in the expression of the ERVB7-1. LTR-MM transposon across various cells in the EAM model, suggesting a widespread impact of this transposon on the immune response in this disease context. The findings of this study highlight the intricate interplay between transposable elements and the immune system in cardiomyopathy, providing new insights into the molecular mechanisms underlying this condition. The discovery of specific TEs expression in cardiac immune cells and the overall increase in ERVB7-1. LTR-MM expression across the EAM model underscore the potential of these elements in modulating immune responses and contribute to our understanding of cardiomyopathy's pathogenesis. These observations open avenues for further research into the role of TEs in cardiac disases and may lead to novel therapeutic strategies. [ABSTRACT FROM AUTHOR]

Conventional microfluidic systems that rely on capillary force have a fixed structure and limited sensitivity, which cannot meet the demands of clinical applications. Herein, we propose a dual-drive microfluidic device for sensitive and flexible detection of multiple pathogenic microorganisms antigens/antibodies. The device comprises a portable microfluidic analyzer and a dual-drive microfluidic chip. Along with capillary force, a second active driving force is provided by a removable self-driving valve in the waste chamber. The interval between these two driving forces can be adjusted to control the reaction time in the microchannel, optimizing the formation of antigen-antibody complexes and enhancing sensitivity. Moreover, the material used in the self-driving valve can be changed to adjust the active force strength needed for different tests. The device offers quantitative analysis for respiratory syncytial virus antigen and SARS-CoV-2 antigen using a 35 μL sample, delivering results within 5 min. The detection limits of the system were 1.121 ng/mL and 0.447 ng/mL for respiratory syncytial virus recombinant fusion protein and SARS-CoV-2 recombinant nucleoprotein, respectively. Although the dual-drive microfluidic device has been used for immunoassay for respiratory syncytial virus and SARS-CoV-2 in this study, it can be easily adapted to other immunoassay applications by changing the critical reagents. [ABSTRACT FROM AUTHOR]

Activated lung ILC2s produce large quantities of IL-5 and IL-13 that contribute to eosinophilic inflammation and mucus production following respiratory syncytial virus infection (RSV). The current understanding of ILC2 activation during RSV infection, is that ILC2s are activated by alarmins, including IL-33, released from airway epithelial cells in response to viral-mediated damage. Thus, high levels of RSV neutralizing maternal antibody generated from maternal immunization would be expected to reduce IL-33 production and mitigate ILC2 activation. Here we report that lung ILC2s from mice born to RSV-immunized dams become activated despite undetectable RSV replication. We also report, for the first time, expression of activating and inhibitory Fcgamma receptors on ILC2s that are differentially expressed in offspring born to immunized versus unimmunized dams. Alternatively, ex vivo IL-33-mediated activation of ILC2s was mitigated following the addition of antibody: antigen immune complexes. Further studies are needed to confirm the role of Fcgamma receptor ligation by immune complexes as an alternative mechanism of ILC2 regulation in RSVassociated eosinophilic lung inflammation. [ABSTRACT FROM AUTHOR]

Introduction: Canine leishmaniosis (CanL) is a systemic disease that affects dogs. When multiplication of the parasite cannot be controlled, dogs consistently show high levels of antigen and IgG antibodies, which lead to the formation of circulating immune complexes (CIC). Timely intervention to reduce the parasite load and CIC levels is crucial for preventing irreversible organ damage. However, a diagnostic test to quantify CIC levels is currently lacking. Methods: In this real-world study, we aimed to examine the performance of a new ELISA to measure CIC levels in dogs naturally infected with Leishmania infantum. Thirty-four dogs were treated according to their clinical condition and followed for 360 days. Before (day 0) and after treatment (days 30, 90, 180, 270, and 360), all dogs underwent a physical examination, and blood samples were obtained for CBC, biochemical profile, serum protein electrophoresis and IFAT. Serum PEG-precipitated CIC were determined by ELISA. Results: Our results indicate higher CIC levels in dogs in advanced disease stages showing higher antibody titres (p < 0.0001, r = 0.735), anemia (p < 0.0001), dysproteinemia (p < 0.0001), and proteinuria (p = 0.004). Importantly, dogs responding well to treatment exhibited declining CIC levels (p < 0.0001), while in poor responders and those experiencing relapses, CIC were consistently elevated. CIC emerged as a robust discriminator of relapse, with an area under the curve (AUC) of 0.808. The optimal cut-off to accurately identify relapse was an optical density of 1.539. Discussion: Our findings suggest that declining CIC levels should be expected in dogs showing a favorable treatment response. Conversely, in dogs displaying a poor response and recurrent clinical relapses, CIC levels will be high, emphasizing the need for vigilant monitoring. These findings suggest that CIC could serve as a valuable biomarker for disease progression, treatment efficacy, and relapse detection in CanL. Our study contributes to enhancing diagnostic approaches for CanL and underscores the potential of CIC as a complementary tool in veterinary practice. As we move forward, larger studies will be essential to confirm these findings and establish definitive cut-offs for clinical application. [ABSTRACT FROM AUTHOR]

Through enabling whole blood detection in point-of-care testing (POCT), sedimentation-based plasma separation promises to enhance the functionality and extend the application range of lateral flow assays (LFAs). To streamline the entire process from the introduction of the blood sample to the generation of quantitative immune-fluorescence results, we combined a simple plasma separation technique, an immunoreaction, and a micropump-driven external suction control system in a polymer channel-based LFA. Our primary objective was to eliminate the reliance on sample-absorbing separation membranes, the use of active separation forces commonly found in POCT, and ultimately allowing finger prick testing. Combining the principle of agglutination of red blood cells with an on-device sedimentation-based separation, our device allows for the efficient and fast separation of plasma from a 25-µL blood volume within a mere 10 min and overcomes limitations such as clogging, analyte adsorption, and blood pre-dilution. To simplify this process, we stored the agglutination agent in a dried state on the test and incorporated a filter trench to initiate sedimentation-based separation. The separated plasma was then moved to the integrated mixing area, initiating the immunoreaction by rehydration of probe-specific fluorophore-conjugated antibodies. The biotinylated immune complex was subsequently trapped in the streptavidin-rich detection zone and quantitatively analyzed using a fluorescence microscope. Normalized to the centrifugation-based separation, our device demonstrated high separation efficiency of 96% and a yield of 7.23 µL (= 72%). Furthermore, we elaborate on its user-friendly nature and demonstrate its proof-of-concept through an all-dried ready-to-go NT-proBNP lateral flow immunoassay with clinical blood samples. [ABSTRACT FROM AUTHOR]

Mammalian innate immunity is regulated by pattern-recognition receptors (PRRs) and guard proteins, which use distinct strategies to detect infections. PRRs detect bacterial molecules directly, whereas guards detect host cell manipulations by microbial virulence factors. Despite sensing infection through different mechanisms, both classes of innate immune sensors can activate the inflammasome, an immune complex that can mediate cell death and inflammation. Inflammasome-mediated immune responses are crucial for host defense against many bacterial pathogens and prevent invasion by non-pathogenic organisms. In this review, we discuss the mechanisms by which inflammasomes are stimulated by PRRs and guards during bacterial infection, and the strategies used by virulent bacteria to evade inflammasome-mediated immunity. [Display omitted] Inflammasomes are a central regulator of the innate immune response to bacteria. Jastrab and Kagan review the mammalian receptors and guard proteins that trigger inflammasome formation upon sensing the presence of bacteria, discuss bacterial mechanisms of inflammasome evasion, and consider how inflammasome-directed immunity contributes to the pathogenesis of bacterial infections. [ABSTRACT FROM AUTHOR]

Antibodies play a central role in the adaptive immune response of vertebrates through the specific recognition of exogenous or endogenous antigens. The rational design of antibodies has a wide range of biotechnological and medical applications, such as in disease diagnosis and treatment. However, there are currently no reliable methods for predicting the antibodies that recognize a specific antigen region (or epitope) and, conversely, epitopes that recognize the binding region of a given antibody (or paratope). To fill this gap, we developed ImaPEp, a machine learning-based tool for predicting the binding probability of paratope–epitope pairs, where the epitope and paratope patches were simplified into interacting two-dimensional patches, which were colored according to the values of selected features, and pixelated. The specific recognition of an epitope image by a paratope image was achieved by using a convolutional neural network-based model, which was trained on a set of two-dimensional paratope–epitope images derived from experimental structures of antibody–antigen complexes. Our method achieves good performances in terms of cross-validation with a balanced accuracy of 0.8. Finally, we showcase examples of application of ImaPep, including extensive screening of large libraries to identify paratope candidates that bind to a selected epitope, and rescoring and refining antibody–antigen docking poses. [ABSTRACT FROM AUTHOR]

Summary: Splenectomised β‐thalassaemia/haemoglobin E (HbE) patients have increased levels of circulating microparticles or medium extra‐cellular vesicles (mEVs). The splenectomised mEVs play important roles in thromboembolic complications in patients since they can induce platelet activation and endothelial cell dysfunction. However, a comprehensive understanding of the mechanism of mEV generation in thalassaemia disease has still not been reached. Thalassaemic mEVs are hypothesised to be generated from cellular oxidative stress in red blood cells (RBCs) and platelets. Therefore, a proteomic analysis of mEVs from splenectomised and non‐splenectomised β‐thalassaemia/HbE patients was performed by liquid chromatography with tandem mass spectrometry. A total of 171 proteins were identified among mEVs. Interestingly, 72 proteins were uniquely found in splenectomised mEVs including immunoglobulin subunits and cytoskeleton proteins. Immunoglobulin G (IgG)‐bearing mEVs in splenectomised patients were significantly increased. Furthermore, complement C1q was detected in both mEVs with IgG binding and mEVs without IgG binding. Interestingly, the percentage of mEVs generated from RBCs with IgG binding was approximately 15–20 times higher than the percentage of RBCs binding with IgG. This suggested that the vesiculation of thalassaemia mEVs could be a mechanism of RBCs to eliminate membrane patches harbouring immune complex and may consequently prevent cells from phagocytosis and lysis. [ABSTRACT FROM AUTHOR]

IgA nephropathy (IgAN) is characterized by glomerular deposition of immune complexes (ICs) consisting of IgA1 with O-glycans deficient in galactose (Gd-IgA1) and Gd-IgA1-specific IgG autoantibodies. These ICs induce kidney injury, and in the absence of diseasespecific therapy, up to 40% of patients with IgAN progress to kidney failure. IgA1 with its clustered O-glycans is unique to humans, which hampered development of small-animal models of IgAN. Here, we used a model wherein engineered ICs (EICs) formed from human Gd-IgA1 and recombinant human IgG autoantibody are injected into nude mice to induce glomerular injury mimicking human IgAN. In this model, we assessed the protective effects of sparsentan, a single-molecule dual endothelin angiotensin receptor antagonist (DEARA) versus vehicle on EIC-induced glomerular proliferation and dysregulation of gene expression in the kidney. Oral administration of sparsentan (60 or 120 mg/kg daily) to mice intravenously injected with EIC attenuated the EIC-induced glomerular hypercellularity. Furthermore, analysis of changes in the whole kidney transcriptome revealed that key inflammatory and proliferative biological genes and pathways that are upregulated in this EIC model of IgAN were markedly reduced by sparsentan, including complement genes, integrin components, members of the mitogen-activated protein kinase family, and Fc receptor elements. Partial overlap between mouse and human differentially expressed genes in IgAN further supported the translational aspect of the immune and inflammatory components from our transcriptional findings. In conclusion, our data indicate that in the mouse model of IgAN, sparsentan targets immune and inflammatory processes leading to protection from mesangial hypercellularity. [ABSTRACT FROM AUTHOR]

Background: To identify specific human neutrophil antigen (HNA) antibodies, assays using neutrophils such as monoclonal antibody‐specific immobilization of granulocyte antigens (MAIGA) are recommended. However, these assays are limited by labor‐intensive neutrophil preparation and varying antigen expression levels. Methods: We evaluated a newly developed immunocomplex capture fluorescence assay (ICFA) for identifying HNA‐1 antibodies and compared it to MAIGA and LABScreen Multi (LABM), which utilizes recombinant HNA‐coated Luminex beads. For ICFA, HNA‐1a or HNA‐1b transfected cells replaced neutrophils. Cells incubated with serum were lysed, and immune complexes were captured using five CD16 monoclonal antibody‐conjugated Luminex beads. Nine antisera with known specificity and 26 samples suspected of containing HNA antibodies were analyzed by ICFA and MAIGA using neutrophils or transfected cells (ICFA‐N or ICFA‐T, and MAIGA‐N or MAIGA‐T, respectively). Results: ICFA‐T and MAIGA‐N accurately determined the specificity of all antibodies in the nine antiserum samples. The ICFA‐T detection limit was 2048‐fold for anti–HNA‐1a and 256‐fold for anti‐HNA‐1b; the limits of MAIGA‐T, MAIGA‐N, and LABM were 32‐, 4 ~ 64‐, and 128‐fold for anti‐HNA‐1a and 64‐, 16 ~ 64‐, and 32‐fold for anti–HNA‐1b, respectively. Twelve and 7 of the remaining 26 samples tested negative and positive, respectively, in both ICFA‐T and MAIGA‐N. Antibody specificity against HNA‐1a or HNA‐1b determined using ICFA‐T agreed with that determined using MAIGA‐N and LABM. Another seven samples tested positive in ICFA‐T but negative in MAIGA‐N. Conclusion: The novel ICFA is highly sensitive and exhibits specificity similar to MAIGA and LABM for detecting HNA‐1 antibodies. [ABSTRACT FROM AUTHOR]

Systemic lupus erythematosus (SLE) is a complex autoimmune disease of unknown etiology. It is marked by the production of pathogenic autoantibodies and the deposition of immune complexes. Lupus nephritis (LN) is a prevalent and challenging clinical complications of SLE. Cortex Moutan contains paeonol as its main effective component. In this study, using the animal model of SLE induced by R848, it was found that paeonol could alleviate the lupus-like symptoms of lupus mouse model induced by R848 activating TLR7, reduce the mortality and ameliorate the renal damage of mice. In order to explore the mechanism of paeonol on lupus nephritis, we studied the effect of paeonol on the polarization of Raw264.7 macrophages in vitro. The experimental results show that paeonol can inhibit the polarization of macrophages to M1 and promote their polarization to M2, which may be related to the inhibition of MAPK and NF-κB signaling pathways. Our research provides a new insight into paeonol in the treatment of lupus nephritis, which is of great importance for the treatment of systemic lupus erythematosus and its complications. • Paeonol can inhibit the polarization of macrophages to M1 and promote their polarization to M2. • MAPK and NF-κB signaling pathway may be an important way to regulate M1/M2 polarization of macrophages. • Feasibility analysis of intervention of paeonol in lupus nephritis. [ABSTRACT FROM AUTHOR]

Key Clinical Message: Non‐lupus full house nephropathy is a rare entity that is still poorly understood. It can complicate post‐transplant kidneys and result in a de novo process. Treatment is difficult but can be possibly achieved with optimization of immune suppression. Non‐lupus full house nephropathy is a rare entity with an unclear incidence. It describes the kidney biopsy findings of positive deposits for IgG, IgA, IgM, C3, and C1q on immunofluorescence in the absence of the classical diagnostic features of systemic lupus nephritis. This disease entity is becoming more recognized but further studies are still needed to evaluate the incidence, etiologies, and management of this condition. Transplant glomerulopathy is a major cause for renal graft loss. It can present with a wide variety of manifestations; it can cause AKI, CKD, or glomerular inflammations through an immune complex or autoimmune‐mediated damage. [ABSTRACT FROM AUTHOR]

Background: Post-streptococcal glomerulonephritis (PSGN) is a consequence of the infection by group A beta-hemolytic streptococcus. During this infection, various immunological processes generated by streptococcal antigens are triggered, such as the induction of antibodies and immune complexes. This activation of the immune system involves both innate and acquired immunity. The immunological events that occur at the renal level lead to kidney damage with chronic renal failure as well as resolution of the pathological process (in most cases). Summary: Angiotensin II (Ang II) is a molecule with vasopressor and pro-inflammatory capacities, being an important factor in various inflammatory processes. During PSGN some events are defined that make Ang II conceivable as a molecule involved in the inflammatory processes during the disease. Conclusion: This review is focused on defining which reported events would be related to the presence of this hormone in PSGN. [ABSTRACT FROM AUTHOR]

Immunoglobulin E (IgE)-mediated food allergy is a rapidly growing public health problem. The interaction between allergens and IgE is at the core of the allergic response. One of the best ways to understand this interaction is through structural characterization. This review focuses on animal-derived food allergens, overviews allergen structures determined by X-ray crystallography, presents an update on IgE conformational epitopes, and explores the structural features of these epitopes. The structural determinants of allergenicity and cross-reactivity are also discussed. Animal-derived food allergens are classified into limited protein families according to structural features, with the calcium-binding protein and actin-binding protein families dominating. Progress in epitope characterization has provided useful information on the structural properties of the IgE recognition region. The data reveals that epitopes are located in relatively protruding areas with negative surface electrostatic potential. Ligand binding and disulfide bonds are two intrinsic characteristics that influence protein structure and impact allergenicity. Shared structures, local motifs, and shared epitopes are factors that lead to cross-reactivity. The structural properties of epitope regions and structural determinants of allergenicity and cross-reactivity may provide directions for the prevention, diagnosis, and treatment of food allergies. Experimentally determined structure, especially that of antigen-antibody complexes, remains limited, and the identification of epitopes continues to be a bottleneck in the study of animal-derived food allergens. A combination of traditional immunological techniques and emerging bioinformatics technology will revolutionize how protein interactions are characterized. [ABSTRACT FROM AUTHOR]

Glutamic acid decarboxylase antibody (GADAb) has emerged as a significant biomarker for clinical diagnosis and prognosis in type 1 diabetes (T1D). In this study, we investigated the potential utilization of glass capillary solid-state nanopores as a cost-effective and easily preparable platform for the detection of individual antigens, antibodies, and antigen-antibody complexes without necessitating any modifications to the nanopores. Our findings revealed notable characteristic variations in the translocation events of glutamic acid decarboxylase (GAD65) through nanopores under different voltage conditions, discovered that anomalous phenomenon of protein translocation events increasing with voltage may potentially be caused by the crowding of multiple proteins in the nanopores, and demonstrated that there are multiple components in the polyclonal antibodies (GADAb-poly). Furthermore, we achieved successful differentiation between GAD65, GADAb, and GADAb-GAD65 complexes. These results offer promising prospects for the development of a rapid and reliable GADAb detection method, which holds the potential to be applied in patient serum samples, thereby facilitating a label-free, cost-effective, and early diagnosis of type I diabetes. [ABSTRACT FROM AUTHOR]

IgA nephropathy is a mucosally driven disease and new therapeutic approaches are specifically targeting the mucosal production of IgA in the hope that this will lead to a reduction in circulating IgA immune complexes and mesangial IgA deposition. In this lecture, I discuss the rationale for targeting the mucosal immune system of the gut and the existing data from clinical trials supporting such an approach as a disease modifying treatment for IgA nephropathy. [ABSTRACT FROM AUTHOR]

This article explores the pathogenesis of IgA nephropathy (IgAN), a kidney disease characterized by abnormal production of immunoglobulin A (IgA). The source and triggers for the production of pathogenic IgA in IgAN are still unknown. The article discusses the structure and function of IgA, highlighting the differences between mucosal and circulatory IgA. It suggests that the pathogenic IgA in IgAN may originate from the mucosal immune system, specifically from cells in the mucosal associated lymphoid tissue or the bone marrow. However, emerging data also suggest that IgA-producing cells from the mucosal compartment may migrate to other locations in the body. Further research is needed to fully understand the nature and source of pathogenic IgA in IgAN. [Extracted from the article]

Summary at a glance: Complement plays a vital role in the pathogenesis of IgA nephropathy. Kidney biopsies with IgA nephropathy show glomerular immune complex deposits with evidence of complement activation by the alternative pathway and in a subset of cases the mannose binding lectin pathway. The recent development of specific drugs targeting these complement pathways represent a potentially important new approach to treating IgA nephropathy. [ABSTRACT FROM AUTHOR]

Visceral leishmaniasis (VL) is an infectious disease caused by Leishmania infantum. Clinically, VL evolves with systemic impairment, immunosuppression and hyperactivation with hypergammaglobulinemia. Although renal involvement has been recognized, a dearth of understanding about the underlying mechanisms driving acute kidney injury (AKI) in VL remains. We aimed to evaluate the involvement of immunoglobulins (Igs) and immune complexes (CIC) in the occurrence of AKI in VL patients. Fourteen VL patients were evaluated between early treatment and 12 months post-treatment (mpt). Anti-Leishmania Igs, CIC, cystatin C, C3a and C5a were assessed and correlated with AKI markers. Interestingly, high levels of CIC were observed in VL patients up to 6 mpt. Concomitantly, twelve patients met the criteria for AKI, while high levels of cystatin C were observed up to 6 mpt. Plasmatic cystatin C was positively correlated with CIC and Igs. Moreover, C5a was correlated with cystatin C, CIC and Igs. We did not identify any correlation between amphotericin B use and kidney function markers in VL patients, although this association needs to be further explored in subsequent studies. Our data reinforce the presence of an important renal function impairment during VL, suggesting the involvement of Igs, CIC, and C5a in this clinical condition. [ABSTRACT FROM AUTHOR]

Background: Asparaginase (ASNase) is a crucial part of acute leukemia treatment, but immune responses to the agent can reduce its effectiveness and increase the risk of relapse. Currently, no reliable and validated biomarker predicts ASNaseinduced hypersensitivity reactions during therapy. We aimed to identify predictive biomarkers and determine immune cells responsible for anaphylaxis using a murine model of ASNase hypersensitivity. Methods: Our preclinical study uses a murine model to investigate predictive biomarkers of ASNase anaphylaxis, including anti-ASNase antibody responses, immune complex (IC) levels, ASNase-specific binding to leukocytes or basophils, and basophil activation. Results: Our results indicate that mice immunized to ASNase exhibited dynamic IgM, IgG, and IgE antibody responses. The severity of ASNase-induced anaphylaxis was found to be correlated with levels of IgG and IgE, but not IgM. Basophils from immunized mice were able to recognize and activate in response to ASNase ex vivo, and the extent of recognition and activation also correlated with the severity of anaphylaxis observed. Using a multivariable model that included all biomarkers significantly associated with anaphylaxis, independent predictors of ASNase-induced hypersensitivity reactions were found to be ASNase IC levels and ASNase-specific binding to leukocytes or basophils. Consistent with our multivariable analysis, we found that basophil depletion significantly protected mice from ASNase-induced hypersensitivity reactions, supporting that basophils are essential and can be used as a predictive marker of ASNase-induced anaphylaxis. Conclusions: Our study demonstrates the need for using tools that can detect both IC- and IgE-mediated hypersensitivity reactions to mitigate the risk of ASNase-induced hypersensitivity reactions during treatment. [ABSTRACT FROM AUTHOR]

Data on the course of viral infections revealed severe inflammation as a consequence of antiviral immune response. Despite extensive research, there are insufficient data on the role of innate immune cells in promoting inflammation mediated by immune complexes (IC) of viral antigens and their specific antibodies. Recently, we demonstrated that antigens of human polyomaviruses (PyVs) induce an inflammatory response in macrophages. Here, we investigated macrophage activation by IC. We used primary murine macrophages as a cell model, virus-like particles (VLPs) of PyV capsid protein as antigens, and a collection of murine monoclonal antibodies (mAbs) of IgG1, IgG2a, IgG2b subclasses. The inflammatory response was investigated by analysing inflammatory chemokines and activation of NLRP3 inflammasome. We observed a diverse pattern of chemokine secretion in macrophages treated with different IC compared to VLPs alone. To link IC properties with cell activation status, we characterised the IC by advanced optical and acoustic techniques. Ellipsometry provided precise real-time kinetics of mAb-antigen interactions, while quartz crystal microbalance measurements showed changes in conformation and viscoelastic properties during IC formation. These results revealed differences in mAb-antigen interaction and mAb binding parameters of the investigated IC. We found that IC-mediated cell activation depends more on IC characteristics, including mAb affinity, than on mAb affinity for the activating Fc receptor. IC formed by the highest affinity mAb showed a significant enhancement of inflammasome activation. This may explain the hyperinflammation related to viral infection and vaccination. Our findings demonstrate that IC promote the viral antigen-induced inflammatory response depending on antibody properties. [ABSTRACT FROM AUTHOR]

The biosynthesis of C-reactive protein (CRP) in the liver is increased in inflammatory diseases including rheumatoid arthritis. Previously published data suggest a protective function of CRP in arthritis; however, the mechanism of action of CRP remains undefined. The aim of this study was to evaluate the effects of human CRP on the development of collagen-induced arthritis (CIA) in mice which is an animal model of autoimmune inflammatory arthritis. Two CRP species were employed: wild-type CRP which binds to aggregated IgG at acidic pH and a CRP mutant which binds to aggregated IgG at physiological pH. Ten CRP injections were given on alternate days during the development of CIA. Both wild-type and mutant CRP reduced the incidence of CIA, that is, reduced the number of mice developing CIA; however, CRP did not affect the severity of the disease in arthritic mice. The serum levels of IL-17, IL-6, TNF-α, IL-10, IL-2 and IL-1β were measured: both wild-type and mutant CRP decreased the level of IL-17 and IL-6 but not of TNF-a, IL-10, IL-2 and IL-1β. These data suggest that CRP recognizes and binds to immune complexes, although it was not clear whether CRP functioned in its native pentameric or in its structurally altered pentameric form in the CIA model. Consequently, ligand-complexed CRP, through an as-yet undefined mechanism, directly or indirectly, inhibits the production of IL-17 and eventually protects against the initiation of the development of arthritis. The data also suggest that IL-17, not TNF-a, is critical for the development of autoimmune inflammatory arthritis. [ABSTRACT FROM AUTHOR]

Objectives: In addition to various immunosuppressive agents, belimumab and anifrolumab became available in Japan. We aimed to investigate glucocorticoid-free clinical remission in a single-centre retrospective cohort in October 2023. Methods: Our cohort included patients with SLE who needed to start or increase glucocorticoids for disease activity and were followed up for more than 1 year. We investigated the rate of achievement of clinical remission off corticosteroids (CR off C), defined as no clinical score on the SLEDAI-2K without glucocorticoids, baseline predictors of CR off C, medications used when CR off C was achieved, and flare rates following CR off C. Results: Out of the 60 patients followed for an average of 5.4 (±2.6) years, 17 (28.3%) achieved CR off C in 3.6 (±1.2) years after enrolment. Use of belimumab and anifrolumab accounted for eight (47.1%) of the achievers. Among the baseline data, male sex, recent enrolment, high glucocorticoid dose, and detection of immune complex (IC) significantly predicted CR off C, while lupus nephritis (LN) and a low C3 level tended to predict it. In the multivariate analysis, IC detection was the only predictor of CR off C. Clinical flares were observed in 5.9% of the achievers during a median 1.2 years after achievement of CR off C. Conclusion: In the era of biologics, CR off C was achieved in 28.3% of the patient cohort requiring the start or increase of glucocorticoids for disease activity, with a relatively low rate of flares, suggesting that glucocorticoid-free clinical remission is an achievable target in SLE. IC disease, represented by male sex or nephritis, is likely to benefit from currently available medications. [ABSTRACT FROM AUTHOR]

Background and Purpose: Millions of patients with inflammatory diseases are treated with tumour necrosis factor (TNF) inhibitors (TNFi). Individual treatment response varies, in part related to variable drug clearance. The role of TNF–TNFi complexes in clearance of the different TNFi is controversial. Moreover, mechanistic insight into the structural aspects and biological significance of TNF–TNFi complexes is lacking. We hypothesized a role for Fc‐mediated clearance of TNF–TNFi immune complexes. Therefore, we investigated circulating TNF–TNFi complexes upon treatment with certolizumab—lacking Fc tails—in comparison with adalimumab, golimumab, infliximab and etanercept. Experimental Approach: Drug‐tolerant ELISAs were developed and used to quantify TNF during adalimumab, golimumab, etanercept, certolizumab and infliximab treatment in patients with inflammatory arthritis or ulcerative colitis for a maximum follow‐up of 1 year. Effects on in vitro TNF production and Fc‐mediated uptake of TNF–TNFi complexes were investigated for all five TNFi. Key Results: Circulating TNF concentrations were >20‐fold higher during certolizumab treatment compared with adalimumab, reaching up to 23.1 ng·ml−1. Internalization of TNF–TNFi complexes by macrophages depended on Fc valency, with efficient uptake for the full antibody TNFi (three Fc tails), but little or no uptake for etanercept and certolizumab (one and zero Fc tail, respectively). TNF production was not affected by TNFi. Total TNF load did not affect clearance rate of total TNFi. Conclusions and Implications: Differences in TNFi structure profoundly affect clearance of TNF, while it is unlikely that TNF itself significantly contributes to target‐mediated drug disposition of TNFi. [ABSTRACT FROM AUTHOR]

Dendritic cell (DC)-targeted vaccination is a new mode of antigen delivery that relies on the use of monoclonal antibodies (mAb) to target antigen to specific DC subsets. The neonatal Fc receptor (FcRn) is a non-classical Fc receptor that binds to immunoglobulin G (IgG) in acidified endosomes and controls its intracellular transport and recycling. FcRn is known to participate in the antigen presentation of immune complexes, however its contribution to DC-targeted vaccination has not previously been examined. Here we have investigated the role of FcRn in antigen presentation using antigen conjugated to IgG mAb which target specific DC receptors, including DEC205 and Clec9A expressed by the conventional DC 1 (cDC1) subset. We show that FcRn is expressed at high levels by cDC1, both at steady-state and following activation and plays a significant role in MHC I cross-presentation and MHC II presentation of antigens that are targeted to cDC1 via mAb specific for DEC205. This effect of FcRn is intrinsic to cDC1 and FcRn impacts the efficacy of anti-DEC205-mediated vaccination against B cell lymphoma. In contrast, FcRn does not impact presentation of antigens targeted to Clec9A and does not regulate presentation of cell-associated antigen. These data highlight a new and unique role of FcRn in controlling the immunogenicity of anti-DEC205-based vaccination, with consequences for exploiting this pathway to improve DC-targeted vaccine outcomes. [ABSTRACT FROM AUTHOR]

Background: Myelin oligodendrocyte glycoprotein antibody (MOG) immunoglobulin G (IgG)-associated disease (MOGAD) has clinical and pathophysiological features that are similar to but distinct from those of aquaporin-4 antibody (AQP4-IgG)-positive neuromyelitis optica spectrum disorders (AQP4-NMOSD). MOG-IgG and AQP4-IgG, mostly of the IgG1 subtype, can both activate the complement system. Therefore, we investigated whether the levels of serum complement components, regulators, and activation products differ between MOGAD and AQP4-NMOSD, and if complement analytes can be utilized to differentiate between these diseases. Methods: The sera of patients with MOGAD (from during an attack and remission; N=19 and N=9, respectively) and AQP4-NMOSD (N=35 and N=17), and healthy controls (N=38) were analyzed for C1q-binding circulating immune complex (CIC-C1q), C1 inhibitor (C1-INH), factor H (FH), C3, iC3b, and soluble terminal complement complex (sC5b-9). Results: In attack samples, the levels of C1-INH, FH, and iC3b were higher in the MOGAD group than in the NMOSD group (all, p<0.001), while the level of sC5b-9 was increased only in the NMOSD group. In MOGAD, there were no differences in the concentrations of complement analytes based on disease status. However, within AQP4-NMOSD, remission samples indicated a higher C1-INH level than attack samples (p=0.003). Notably, AQP4-NMOSD patients on medications during attack showed lower levels of iC3b (p<0.001) and higher levels of C3 (p=0.008), C1-INH (p=0.004), and sC5b-9 (p<0.001) compared to those not on medication. Among patients not on medication at the time of attack sampling, serum MOG-IgG cell-based assay (CBA) score had a positive correlation with iC3b and C1-INH levels (rho=0.764 and p=0.010, and rho=0.629 and p=0.049, respectively), and AQP4-IgG CBA score had a positive correlation with C1-INH level (rho=0.836, p=0.003). Conclusions: This study indicates a higher prominence of complement pathway activation and subsequent C3 degradation in MOGAD compared to AQP4-NMOSD. On the other hand, the production of terminal complement complexes (TCC) was found to be more substantial in AQP4-NMOSD than in MOGAD. These findings suggest a strong regulation of the complement system, implying its potential involvement in the pathogenesis of MOGAD through mechanisms that extend beyond TCC formation. [ABSTRACT FROM AUTHOR]

Most host-microbiota interactions occur within the intestinal barrier, which is essential for separating the intestinal epithelium from toxins, microorganisms, and antigens in the gut lumen. Gut inflammation allows pathogenic bacteria to enter the blood stream, forming immune complexes which may deposit on organs. Despite increased circulating immune complexes (CICs) in patients with inflammatory bowel disease (IBD) and discussions among IBD experts regarding their potential pathogenic role in extra-intestinal manifestations, this phenomenon is overlooked because definitive evidence demonstrating CICinduced extra-intestinal manifestations in IBD animal models is lacking. However, clinical observations of elevated CICs in newly diagnosed, untreated patients with IBD have reignited research into their potential pathogenic implications. Musculoskeletal symptoms are the most prevalent extra-intestinal IBD manifestations. CICs are pivotal in various arthritis forms, including reactive, rheumatoid, and Lyme arthritis and systemic lupus erythematosus. Research indicates that intestinal barrier restoration during the pre-phase of arthritis could inhibit arthritis development. In the absence of animal models supporting extra-intestinal IBD manifestations, this paper aims to comprehensively explore the relationship between CICs and arthritis onset via a multifaceted analysis to offer a fresh perspective for further investigation and provide novel insights into the interplay between CICs and arthritis development in IBD. [ABSTRACT FROM AUTHOR]

Anti-PF4 disorders are a group of platelet-consumptive disorders characterized by platelet-activating antibodies against platelet factor 4 (PF4), thrombocytopenia and an increased risk of thrombosis. PF4 is a chemokine released by platelet alpha granules upon activation, which can form immune complexes with negatively charged substances, such as heparin, cartilage components, nucleic acids, and viral and bacterial agents. Antibodies formed in response to PF4-polyanion complexes may display platelet-activating properties and cause pancellular activation, leading to the marked prothrombotic state of anti-PF4 disorders. In recent years, the landscape of anti-PF4 disorders has evolved to include classic heparin-induced thrombocytopenia (cHIT), autoimmune HIT (aHIT), spontaneous HIT (SpHIT), vaccine-induced immune thrombotic thrombocytopenia (VITT), and the newly recognized spontaneous VITT (SpVITT). These disorders have garnered increased attention due to their association with severe clinical outcomes. Recent discoveries have expanded the understanding of these conditions, highlighting the role of various triggers, such as upper respiratory tract infections and monoclonal gammopathy of undetermined significance, in their development. Compared to cHIT, the less common anti-PF4 disorders VITT, aHIT, SpHIT and SpVITT generally appear more severe, with aggressive disease courses, more severe thrombocytopenia and a higher frequency of bleeding, thrombosis at unusual sites, involvement of the central nervous system and of multiple vascular beds. Clinical suspicion and knowledge of the less well-known triggers of anti-PF4 disorders are pivotal to ordering the appropriate laboratory tests and initiating the necessary treatments. Herein, we will review cHIT, aHIT, SpHIT and VITT, focusing on their clinical presentation and therapeutic management. [ABSTRACT FROM AUTHOR]

In peanut allergy, Arachis hypogaea 2 (Ara h 2) and Arachis hypogaea 6 (Ara h 6) are two clinically relevant peanut allergens with known structural and sequence homology and demonstrated cross-reactivity. We have previously utilized X-ray crystallography and epitope binning to define the epitopes on Ara h 2. We aimed to quantitatively characterize the cross-reactivity between Ara h 2 and Ara h 6 on a molecular level using human monoclonal antibodies (mAbs) and structural characterization of allergenic epitopes. We utilized mAbs cloned from Ara h 2 positive single B cells isolated from peanut-allergic, oral immunotherapy–treated patients to quantitatively analyze cross-reactivity between recombinant Ara h 2 (rAra h 2) and Ara h 6 (rAra h 6) proteins using biolayer interferometry and indirect inhibitory ELISA. Molecular dynamics simulations assessed time-dependent motions and interactions in the antibody–antigen complexes. Three epitopes—conformational epitopes 1.1 and 3, and the sequential epitope KRELRNL/KRELMNL—are conserved between Ara h 2 and Ara h 6, while two more conformational and three sequential epitopes are not. Overall, mAb affinity was significantly lower to rAra h 6 than it was to rAra h 2. This difference in affinity was primarily due to increased dissociation of the antibodies from rAra h 6, a phenomenon explained by the higher conformational flexibility of the Ara h 6–antibody complexes in comparison to Ara h 2–antibody complexes. Our results further elucidate the cross-reactivity of peanut 2S albumins on a molecular level and support the clinical immunodominance of Ara h 2. We utilized monoclonal antibodies cloned from peanut-allergic, oral immunotherapy–treated patients to probe the cross-reactivity between clinically relevant peanut allergens Ara h 2 and Ara h 6 on a molecular level. Graphical Abstract [ABSTRACT FROM AUTHOR]

The histopathological lesions, minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) are entities without immune complex deposits which can cause podocyte injury, thus are frequently grouped under the umbrella of podocytopathies. Whether MCD and FSGS may represent a spectrum of the same disease remains a matter of conjecture. Both frequently require repeated high-dose glucocorticoid therapy with alternative immunosuppressive treatments reserved for relapsing or resistant cases and response rates are variable. There is an unmet need to identify patients who should receive immunosuppressive therapies as opposed to those who would benefit from supportive strategies. Therapeutic trials focusing on MCD are scarce, and the evidence used for the 2021 Kidney Disease: Improving Global Outcomes (KDIGO) guideline for the management of glomerular diseases largely stems from observational and pediatric trials. In FSGS, the differentiation between primary forms and those with underlying genetic variants or secondary forms further complicates trial design. This article provides a perspective of the Immunonephrology Working Group (IWG) of the European Renal Association (ERA) and discusses the KDIGO 2021 Clinical Practice Guideline for the Management of Glomerular Diseases focusing on the management of MCD and primary forms of FSGS in the context of recently published evidence, with a special emphasis on the role of rituximab, cyclophosphamide, supportive treatment options and ongoing clinical trials in the field. [ABSTRACT FROM AUTHOR]

Membranous nephropathy (MN) is a common cause of nephrotic syndrome in adults. MN is characterized by subepithelial accumulation of immune complexes along the glomerular basement membrane. The immune complexes are composed of immunoglobulin G and a target antigen. PLA2R is the target antigen in approximately 60% of MN cases, and MN is traditionally classified as PLA2R-positive or PLA2R-negative MN. Over the last 7 years, additional target antigens have been identified, which have specific disease associations, distinctive clinical and pathologic findings, and therapeutic implications. The newly discovered target antigens include NELL1, EXT1/EXT2, NCAM1, SEMA3B, PCDH7, FAT1, CNTN1, NTNG1, PCSK6 and NDNF. To group all these antigens into a generic 'PLA2R-negative' MN group is imprecise and un-informative. We propose a logical approach for detection of the target antigen which includes (i) currently available serology-based testing to detect anti-PLA2R and anti-THSD7A antibodies; and (ii) kidney biopsy testing to detect the target antigens. Determination of the antigen on kidney biopsy can be done by immunohistochemistry or immunofluorescence studies. Alternatively, laser capture microdissection (LCM) of glomeruli followed by mass spectrometry (MS) can be used to identify a target antigen. LCM/MS has the advantage of being a one-stop test and is particularly useful for detection of rare target antigens. At the current time, while it is possible to detect the newer antigens by immunohistochemistry/immunofluorescence/LCM/MS, serology-based tests to detect serum antibodies to the new antigens are not yet available. It is critical that serology-based tests should be developed not just for accurate diagnosis, but as a guide for treatment. We review the current methodology and propose an algorithm for diagnosis and detection of target antigens in MN that may shape the current practice in the future. Membranous nephropathy (MN) results from accumulation of subepithelial immune complexes along the glomerular basement membrane. PLA2R is the most common target antigen, but newly discovered target antigens have filled the void of PLA2R-negative MN. MN associated with the newly discovered target antigens have distinctive clinical and pathologic findings, treatment and prognostic implications. These include NELL1, EXT1/EXT2, NCAM1, PCDH7, SEMA3B, CNTN1, FAT1, NDNF and PCSK6. Immunohistochemistry/immunofluorescence methodology is currently in use for detecting target antigens in kidney biopsy tissue, although we anticipate laser capture microdissection of glomeruli followed by mass spectrometry will become available soon. Serologic testing is currently available for only detecting antibodies to PLA2R and THSD7A. It is critical that serologic tests become available for detecting antibodies to the newly discovered antigens. [ABSTRACT FROM AUTHOR]

Research into the neonatal Fc receptor (FcRn) has increased dramatically ever since Simister and Mostov first purified a rat version of the receptor. Over the years, FcRn has been shown to function not only as a receptor that transfers immunity from mother to fetus but also performs an array of different functions that include transport and recycling of immunoglobulins and albumin in the adult. Due to its important cellular roles, several clinical trials have been designed to either inhibit/enhance FcRn function or develop of non-invasive therapeutic delivery system such as fusion of drugs to IgG Fc or albumin to enhance delivery inside the cells. Here, we report the accidental identification of several FcRn alternatively spliced variants in both mouse and human cells. The four new mouse splice variants are capable of binding immunoglobulins' Fc and Fab portions. In addition, we have identified FcRn-specific vesicles in which immunoglobulins and albumin can be stored and that are involved in the endosomal–lysosomal system. The complexity of FcRn functions offers significant potential to design and develop novel and targeted therapeutics. [ABSTRACT FROM AUTHOR]