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Antibody-dependent enhancement (ADE) of dengue virus (DENV) infection is one of the mechanisms contributing to increased severity during heterotypic, secondary infection. The complement protein C1q has been shown to reduce the magnitude of ADE in vitro. Therefore, we investigated the mechanisms of C1q modulation of ADE, focusing on processes of viral entry. Using a model of ADE of DENV-1 infection in human myeloid cell lines in the presence of monoclonal antibodies, 4G2 and 2H2, we found that C1q produced nearly a 40-fold reduction of ADE of DENV-1 in K562 cells, but had no effect in U937 cells. In K562 cells, C1q reduced adsorption of DENV-1/4G2 and exerted a dual inhibitory effect on adsorption and internalization of DENV-1/2H2. Distinct endocytic pathways in the presence of antibody corresponded to conditions where C1q produced a differential action. Also, C1q did not affect the intrinsic cell response mediated by FcγR in human myeloid cells. The modulation of ADE of DENV-1 by C1q is dependent on the FcγR expressed on immune cells and the specificity of the antibody comprising the immune complex. Understanding protective and pathogenic mechanisms in the humoral response to DENV infections is crucial for the successful design of antivirals and vaccines. [ABSTRACT FROM AUTHOR]

Antibody-dependent enhancement (ADE) has been associated with severe disease outcomes in several viral infections, including respiratory infections. In vitro and in vivo studies showed that antibody-response to SARS-CoV and MERS-CoV could exacerbate infection via ADE. Recently in SARS CoV-2, the in vitro studies and structural analysis shows a risk of disease severity via ADE. This phenomenon is partially attributed to non-neutralizing antibodies or antibodies at sub-neutralizing levels. These antibodies result in antigen-antibody complexes' deposition and propagation of a chronic inflammatory process that destroys affected tissues. Further, antigen-antibody complexes may enhance the internalization of the virus into cells through the Fc gamma receptor (FcγR) and lead to further virus replication. Thus, ADE occur via two mechanisms; 1. Antibody mediated replication and 2. Enhanced immune activation. Antibody-mediated effector functions are mainly driven by complement activation, and the first complement in the cascade is complement 1q (C1q) which binds to the virus-antibody complex. Reports say that deficiency in circulating plasma levels of C1q, an independent predictor of mortality in high-risk patients, including diabetes, is associated with severe viral infections. Complement mediated ADE is reported in several viral infections such as dengue, West Nile virus, measles, RSV, Human immunodeficiency virus (HIV), and Ebola virus. This review discusses ADE in viral infections and the in vitro evidence of ADE in coronaviruses. We outline the mechanisms of ADE, emphasizing the role of complements, especially C1q in the outcome of the enhanced disease. • Antibody-dependent enhancement (ADE) is associated with severe disease outcomes in several viral infections, including respiratory infections. • This phenomenon is partially attributed to non-neutralizing antibodies or antibodies at sub-neutralizing levels that result in: • Antigen-antibody complexes' deposition and propagation of a chronic inflammatory process that destroys affected tissues. • Antigen-antibody complexes internalization into macrophages/other cells through the Fc gamma receptor (FcγR), resulting further virus replication. • Antibody-mediated effector functions are mainly driven by complement activation, and the first complement in the cascade is complement 1q (C1q) which binds to the virus-antibody complex. • Deficiency in circulating plasma levels of C1q, an independent predictor of mortality in high-risk patients, including diabetes, is associated with severe viral infections. • This review outline the overall mechanisms of ADE, emphasizing the role of complements, especially C1q in the outcome of the enhanced disease. [ABSTRACT FROM AUTHOR]

The contribution of the complement system to non-specific host defence and maintenance of homeostasis is well appreciated. Many particulate systems trigger complement activation but the underlying mechanisms are still poorly understood. Activation of the complement cascade could lead to particle opsonisation by the cleavage products of the third complement protein and might promote inflammatory reactions. Antibody binding in a controlled manner and/or sensing of particles by the complement pattern-recognition molecules such as C1q and mannose-binding lectin can trigger complement activation. Particle curvature and spacing arrangement/periodicity of surface functional groups/ligands are two important parameters that modulate complement responses through multivalent engagement with and conformational regulation of surface-bound antibodies and complement pattern-recognition molecules. Thus, a better fundamental understanding of nanometer- and angstrom-scale parameters that modulate particle interaction with antibodies and complement proteins could portend new possibilities for engineering of particulate drug carriers and biomedical platforms with tuneable complement responses and is discussed here. [Display omitted] • Many nano−/micro-particles trigger complement activation in human plasma. • Particle curvature modulates complement responses. • Spacing arrangement/periodicity of surface moieties modulates complement responses. • Refinement of particle size and surface properties overcomes complement activation. [ABSTRACT FROM AUTHOR]

Immunohistochemical studies have identified complement component C1q in MS lesions. We aimed to compare serum (sC1q) and CSF (csfC1q) levels in a large cohort of MS patients (pwMS) (n = 222) with those of healthy controls (HC, n = 52), individuals with other immune (IND, n = 14), and non-immune neurological disorders (nIND, n = 15), and to analyze their correlation with other biomarkers. pwMS were divided into three series based on their origin. CSF samples were unavailable for HC. All three pwMS cohorts had lower sC1q levels compared to HC and IND. csfC1q was higher in one pwMS cohort, with a trend in another, and correlated with IgG, Free Kappa Light Chains, GFAP, and Chitinase-3 Like Protein-1 in CSF. Our findings suggest a significant role for C1q in MS pathophysiology, potentially serving as a biomarker for disease identification. • sC1q levels were lower in pwMS compared to both HC and patients with nIND. • There were no differences in sC1q levels between pwMS and those with other IND. • csfC1q correlated with IgG, FLKC, GFAP, and CHI3L1 in CSF, but not with NfL. • C1q levels in pwMS remained consistent irrespective of acute inflammatory activity. [ABSTRACT FROM AUTHOR]

• C1q levels increase with age but are similar between men and women. • Decreased C1q levels have been observed in several autoimmune diseases and can be caused by defective production or increased consumption. • Increased C1q levels have been reported for infectious and inflammatory diseases and is suggested to inhibit the adaptive immune response. • C1q can protect against infections via the classical pathway, and maintain tolerance by regulating adaptive immunity, likely via C1q receptors. C1q is the recognition molecule of the classical pathway of the complement system. By binding to its targets, such as antigen-bound immunoglobulins or C-reactive protein, C1q contributes to the innate defense against infections. However, C1q also plays several other roles beyond its traditional role in complement activation. Circulating levels of C1q are determined in routine diagnostics as biomarker in several diseases. Decreased C1q levels are present in several autoimmune conditions. The decreased levels reflect the consumption of C1q by complement activation and serves as a biomarker for disease activity. In contrast, increased C1q levels are present in infectious and inflammatory diseases and may serve as a diagnostic biomarker. The increased levels of C1q are still incompletely understood but are suggested to modulate the adaptive immune response as C1q is known to impact on the maturation status of antigen-presenting cells and C1q impacts directly on T cells leading to decreased T-cell activity in high C1q conditions. In this review, we provide a comprehensive overview of the current literature on circulating levels of C1q in health and disease, and discuss how C1q can both protect against infections as well as maintain tolerance by regulating adaptive immunity. [ABSTRACT FROM AUTHOR]

• Complement is a complex cascade which makes diagnostic testing complex. • To properly diagnose a patient or follow them in treatment may require many tests. • Multiplex testing holds the promise of helping to address this complexity. • There is promising work to multiplex and streamline complement diagnostics. • There is great potential in multiplex testing but there are also potential pitfalls. Complement is a complex system. This complexity becomes more obvious when looking at complement analysis in health and disease, where one presentation can require a number of measurements to understand the full role of this cascade in the disease. The current state of clinical testing requires multiple tests to cover the whole of the complement cascade. There is a clear potential for multiplex testing to help address this need for comprehensive analysis of the state of complement deficiency, activation or inhibition. Fortunately, there are a number of potential methods for multiplex analysis, each with advantages and disadvantages that need to be considered in light of the intricacy of the complement cascade and its interconnection to other systems. Despite the complexities of such methods several groups have started utilizing multiplex analysis for research and even for diagnostic testing. The potential methods, current successes, and the type of testing that needs to be streamlined are reviewed in this text. [ABSTRACT FROM AUTHOR]

Allosensitization in heart transplant candidates is associated with longer transplant wait times and post-transplant complications. We summarize our experience with desensitization using carfilzomib, an irreversible proteasome inhibitor that causes plasma cell apoptosis. One cycle of desensitization consisted of plasmapheresis and carfilzomib 20 mg/m2 on days 1, 2, 8, 9, 15, and 16 with intravenous immune globulin 2 g/kg after carfilzomib on day 16. Patients underwent repeat cycles as indicated. We compare calculated panel-reactive antibody (cPRA) for neat combined Class I and II IgG and C1q pre- and post-treatment using a cutoff for cPRA entry of ≥ 4000 and 500 MFI, respectively. From June 2013 to October 2019, 9 patients underwent 20 cycles of carfilzomib-based desensitization. Each cycle resulted in an average cPRA decrease of 24% (95% CI: 6-42) for IgG and 36% (95% CI: 17-55) for C1q. From treatment start to finish, mean cPRA fell from 76% to 40% (p = 0.01) for IgG and 56% to 4% (p = 0.017) for C1q. Six of 9 patients have been transplanted with 5 of the transplanted hearts crossing preoperative donor-specific antibodies. During a median follow-up of 35.1 months, all transplanted patients have survived with only 1 occurrence of treated rejection. Side effects of desensitization included acute kidney injury (67%) and thrombocytopenia (33%) with all episodes self-resolving. A carfilzomib-based desensitization strategy among heart transplant candidates reduces the level of HLA antibodies and complement binding, facilitates successful transplantation, and is associated with excellent outcomes at 3 years. [ABSTRACT FROM AUTHOR]

• Pathogenic and protective effects of complement in flavivirus infections. • Protective role of classical pathway activation on ADE of flavivirus infections. • Binding of human IgG isotypes to C1q depends on Fc domain flexibility and conformation. • C1q modulation of ADE of flavivirus infections by different potential mechanisms. Flavivirus infections have increased dramatically in the last decades in tropical and subtropical regions of the world. Antibody-dependent enhancement of dengue virus infections has been one of the main hypotheses to explain severity of disease and one of the major challenges to safe and effective vaccine development. In the presence of cross-reactive sub-neutralizing concentrations of anti-dengue antibodies, immune complexes can amplify viral infection in mononuclear phagocytic cells, triggering a cytokine cascade and activating the complement system that leads to severe disease. The complement system comprises a family of plasma and cellular surface proteins that recognize pathogen associated molecular patterns, modified ligands and immune complexes, interacting in a regulated manner and forming an enzymatic cascade. Pathogenic as well as protective effects of complement have been reported in flavivirus infections. This review provides updated knowledge on complement activation during flavivirus infection, including antiviral effects of complement and its regulation, as well as mechanisms of complement evasion and dysregulation of complement activity during viral infection leading to pathogenesis. Particularly, insights into classical pathway activation and its protective role on antibody-dependent enhancement of flavivirus infections are highlighted. [ABSTRACT FROM AUTHOR]

Chronic lung allograft dysfunction (CLAD) is the major complication limiting long-term survival in lung transplant recipients (LTRs), with those developing donor-specific anti–human leukocyte antigen (HLA) antibodies (DSAs) previously found to have increased risk for CLAD. However, as DSA responses vary in timing of development, specificity, breadth, persistence, and complement-binding capacity, we hypothesized that these characteristics would impact CLAD and survival outcomes. We retrospectively analyzed DSA characteristics and outcomes in a single-center cohort of 582 LTRs who had serum samples collected prospectively from 2010 to 2016. Luminex-based single antigen bead assays were performed to assess DSA. DSAs were detected in 247 LTRs (42%), of which 124 (21.3%) were de novo DSAs and 53 (9.1%) were complement-binding (C1q+). CLAD developed in 208 LTRs (35.7%) during the follow-up period, with 67.8% determined as bronchiolitis obliterans syndrome phenotype and 32.2% as restrictive allograft syndrome phenotype. We found a shorter time to CLAD in LTRs with persistent DSAs (p = 0.04) and HLA-DQ–specific DSAs (p = 0.03). LTRs who developed C1q+ DSAs had significantly shorter time to CLAD (p < 0.001), with 100% of C1q+ DSAs being persistent and no differences between CLAD phenotypes. CLAD-free survival was significantly reduced in LTRs who developed C1q+ DSAs (p = 0.001), HLA-DQ–specific DSAs (p = 0.03), and multiple DSAs (p = 0.02). Together, our findings demonstrate that DSA characteristics of persistence, HLA-DQ specificity, and C1q+ DSAs are associated with shorter time to CLAD. Additionally, C1q+, HLA-DQ–specific, and multiple DSAs are associated with decreased CLAD-free survival. These characteristics may improve DSA risk stratification for deleterious outcomes in LTRs. [ABSTRACT FROM AUTHOR]

Objective: Inflammation and innate immune responses may contribute to development and progression of Osteoarthritis (OA). Chondrocytes are the sole cell type of the articular cartilage and produce extracellular-matrix molecules. How inflammatory mediators reach chondrocytes is incompletely understood. Previous studies have shown that chondrocytes express mRNA encoding complement proteins such as C1q, suggesting local protein production, which has not been demonstrated conclusively. The aim of this study is to explore C1q production at the protein level by chondrocytes.Design: We analysed protein expression of C1q in freshly isolated and cultured human articular chondrocytes using Western blot, ELISA and flow cytometry. We examined changes in mRNA expression of collagen, MMP-1 and various complement genes upon stimulation with pro-inflammatory cytokines or C1q. mRNA expression of C1 genes was determined in articular mouse chondrocytes.Results: Primary human articular chondrocytes express genes encoding C1q, C1QA, C1QB, C1QC, and secrete C1q to the extracellular medium. Stimulation of chondrocytes with pro-inflammatory cytokines upregulated C1QA, C1QB, C1QC mRNA expression, although this was not confirmed at the protein level. Extracellular C1q bound to the chondrocyte surface dose dependently. In a pilot study, binding of C1q to chondrocytes resulted in changes in the expression of collagens with a decrease in collagen type 2 and an increase in type 10. Mouse articular chondrocytes also expressed C1QA, C1QB, C1QC, C1R and C1S at the mRNA level.Conclusions: C1q protein can be expressed and secreted by human articular chondrocytes and is able to bind to chondrocytes influencing the relative collagen expression. [ABSTRACT FROM AUTHOR]

Recombinant C1q Variants rC1qB and rC1qC contain mutations in the C1q B-chain (Lys61-Ala) or C-chain (Lys58-Ala) respectively, that render them unable to interact with and and activate the classical complement pathway. They still retain the ability to modulate phagocyte responses. A region similar to the sequence identified in MBL as necessary for enhancement of phagocytosis is located below the hinge region in the C1q A-chain (). • Recombinant C1q variants were expressed that do not activate the classical complement pathway. • Recombinant C1q variants modulate phagocytosis similar to wild-type C1q. • Recombinant C1q variants modulate macrophage cytokines and chemokines similar to wild-type C1q. Complement protein C1q plays a dual role in a number of inflammatory diseases such as atherosclerosis. While in later stages classical complement pathway activation by C1q exacerbates disease progression, C1q also plays a beneficial role in early disease. Independent of its role in complement activation, we and others have identified a number of potentially beneficial interactions of C1q with phagocytes in vitro , including triggering phagocytosis of cellular and molecular debris and polarizing macrophages toward an anti-inflammatory phenotype. These interactions may also be important in preventing autoimmunity. Here, we characterize variants of recombinant human C1q (rC1q) which no longer initiate complement activation, through mutation of the C1r 2 C1s 2 interaction site. For insight into the structural location of the site of C1q that is important for interaction with phagocytes, we investigated the effect of these mutations on phagocytosis and macrophage inflammatory polarization, as compared to wild-type C1q. Phagocytosis of antibody coated sheep erythrocytes and oxidized LDL was measured in human monocytes and monocyte-derived macrophages (HMDM) respectively that had interacted with rC1q wild-type or variants. Secreted levels of cytokines were also measured in C1q stimulated HMDM. All variants of C1q increased phagocytosis in HMDM compared to controls, similar to native or wild-type rC1q. In addition, levels of certain pro-inflammatory cytokines and chemokines secreted by HMDM were modulated in cells that interacted with C1q variants, similar to wild-type rC1q and native C1q. This includes downregulation of IL-1α, IL-1β, TNFα, MIP-1α, and IL-12p40 by native and rC1q in both resting and M1-polarized HMDM. This suggests that the site responsible for C1q interaction with phagocytes is independent of the C1r 2 C1s 2 interaction site. Further studies with these classical pathway-null variants of C1q should provide greater understanding of the complement-independent role of C1q, and allow for potential therapeutic exploitation. [ABSTRACT FROM AUTHOR]

In the present study we report a novel interaction of human C1q, a primary activator of the Complement system, with human Galectin-3 (Gal-3). We investigated the potential recognition between C1q and Gal-3 on a solid hydrophobic surface by ELISA, by fluorescence spectroscopy, molecular docking and molecular dynamics (MD). The data showed that C1q and Gal-3 had a pronounced affinity for protein-protein interaction and supramolecular binding, locating the binding sites within the globular domains of C1q (gC1q) and on the backside of the carbohydrate recognition domain (CRD) of Gal-3. Fluorescence spectroscopy gave quantitative assessment of the recognition with K D value of 0.04 μM. MD analysis showed that when the active AAs of the two proteins interacted, electrostatic attraction, aided by a large number of hydrogen bonds, was dominant for the stabilization of the complex. When the contact of C1q and Gal-3 was not limited to active residues, the complex between them was stabilized mainly by Van der Waals interactions and smaller in number but stronger hydrogen bonds. This is the first report analyzing the interaction of Gal-3 with C1q, which could open the way to new applications of this protein-protein complex. [Display omitted] [ABSTRACT FROM AUTHOR]

Axotomized spinal motoneurons (MNs) lose presynaptic inputs following peripheral nerve injury; however, the cellular mechanisms that lead to this form of synapse loss are currently unknown. Here, we delineate a critical role for neuronal kinase dual leucine zipper kinase (DLK)/MAP3K12, which becomes activated in axotomized neurons. Studies with conditional knockout mice indicate that DLK signaling activation in injured MNs triggers the induction of phagocytic microglia and synapse loss. Aspects of the DLK-regulated response include expression of C1q first from the axotomized MN and then later in surrounding microglia, which subsequently phagocytose presynaptic components of upstream synapses. Pharmacological ablation of microglia inhibits the loss of cholinergic C boutons from axotomized MNs. Together, the observations implicate a neuronal mechanism, governed by the DLK, in the induction of inflammation and the removal of synapses. [Display omitted] • DLK signaling in axotomized neurons triggers the loss of upstream synaptic inputs • DLK regulates the expression of secreted proteins from injured motoneurons • The activation of complement following nerve injury requires neuronal DLK • Microglial phagocytosis of synapses is regulated by DLK Following peripheral nerve injury, microglia hug the cell bodies of axotomized motoneurons, which lose their upstream synaptic inputs. Asghari Adib et al. demonstrate that the phagocytosis of synaptic components by microglia is governed by the DLK kinase, which becomes activated in injured neurons. [ABSTRACT FROM AUTHOR]

Persistent extracellular tissue-dwelling pathogens face the challenge of antibody-dependent activation of the classical complement pathway (CCP). A prime example of this situation is the larva of the cestode Echinococcus granulosus sensu lato , causing cystic echinococcosis. This tissue-dwelling, bladder-like larva is bounded by a cellular layer protected by the outermost acellular "laminated layer" (LL), to which host antibodies bind. The LL is made up of a mucin meshwork and interspersed nano-deposits of calcium inositol hexakisphosphate (calcium Ins P 6). We previously reported that calcium Ins P 6 bound C1q, apparently initiating CCP activation. The present work dissects CCP activation on the LL. Most of the C1 binding activity in the LL corresponded to calcium Ins P 6 , and this binding was enhanced by partial proteolysis of the mucin meshwork. The remaining C1 binding activity was attributable to host antibodies, which included CCP-activating IgG isotypes. Calcium Ins P 6 made only a weak contribution to early CCP activation on the LL, suggesting inefficient C1 complex activation as reported for other polyanions. CCP activation on calcium Ins P 6 gave rise to a dominant population of C3b deposited onto calcium Ins P 6 itself that appeared to be quickly inactivated. Apparently as a result of inefficient initiation plus C3b inactivation, calcium Ins P 6 made no net contribution to C5 activation. We propose that the LL protects the underlying parasite cells from CCP activation through the combined effects of inefficient permeation of C1 through the mucins and C1 retention on calcium Ins P 6. This mechanism does not result in C5 activation, which is known to drive parasite-damaging inflammation. [ABSTRACT FROM AUTHOR]

• Soluble defense collagens are secreted proteins containing short collagen domains. • High-order oligomerization is integral to the biological functions of these proteins. • They are involved in clearing the extracellular space of dying cells and pathogens. • They modulate macrophages toward an anti-inflammatory resolving phenotype. • They are key factors for macrophage-driven repair programs that restore homeostasis. Soluble defense collagens form a group of secreted proteins that are primarily involved in host defense. All defense collagens contain a globular recognition domain contiguous to a collagen-like triple helical domain. They are oligomeric proteins, assembled in multiples of three subunits due to their collagen domains. Members of this group include collectins such as surfactant protein A and D (SP-A, SP-D), and mannan-binding lectin; C1q, the first component of the complement system; adiponectin; and ficolins. All are secreted to tissue cavities or serum. Soluble defense collagens are specialized to respond to infection, triggering the initiation of the complement cascade and/or enhancing phagocytosis of pathogens by macrophages. However, once inflammation is established, C1q, collectins, ficolins, or adiponectin can influence macrophage responses, thereby contributing to resolve the inflammation. In addition, some members of this group of proteins (SP-A, C1q, and adiponectin) modulate tissue-repair functions of macrophages. This review will focus on the molecular mechanisms by which these proteins efficiently defend against immune threats and contribute to tissue repair. [ABSTRACT FROM AUTHOR]

Nanodiamonds are promising nanomedicines for diagnostic and therapeutic applications. As nanodiamonds are mainly administered intravenously, it is critical to understand the humoral immune response upon exposure to nanodiamonds. Here, we report the interactions of pristine, oxidized, and PEG-functionalized nanodiamonds with human complement, an important part of our humoral innate immunity. In particular, we report the nanodiamond binding properties of the recognition protein of the classical complement pathway: C1q, which also takes part in many other physiological and pathological processes. Our results show similar trends in the effects of C1q on the three types of nanodiamonds. Complement activation assays using human serum show that the nanodiamonds trigger slight activities via the alternative pathway and no response via the classical pathway. Nevertheless, surface plasmon resonance shows that C1q binds the nanodiamonds and transmission electron microscopy reveals their agglutination. Studies with macrophages further show that C1q attachment affects their phagocytosis and cytokine response. The multifunctional protein C1q bound unmodified, oxidized, and PEG-functionalized nanodiamonds (NDs), causing agglutination. Whereas the three types of NDs induced different macrophage responses due to their different surface structure and chemistry, the effect of C1q binding on phagocytosis and cytokine secretion of the macrophages was similar. Attraction of C1q molecules onto the NDs may affect the many physiological processes involving C1q and may alter the effect of ND in biomedical applications. Unlabelled Image [ABSTRACT FROM AUTHOR]

Highlights • Complement factor H expression was upregulated in the hippocampus of methamphetamine induced behavioral sensitization mice. • C1q expression decreased in mossy fiber of hippocampus in behavioral sensitization mice. • We detected the changes and distribution of various small molecules by MALDI-MS imaging in brain regions of behavioral sensitization mice. Abstract Background At present, the harm of new-type drug, methamphetamine (METH), has gradually exceeded that of the traditional opioid drugs, and METH abuse has become a serious public health and social problem. In our previous study, complement factor H (CFH) was found to be upregulated in the sera of METH-addicted patients and rats and in certain brain regions in the rats. Methods We used ELISA and immunofluorescence to confirm the changes in CFH in the serum and hippocampus of a METH behavioral sensitization mouse model, and C1q expression was also detected by immunofluorescence in the hippocampus. We aimed to elucidate the involvement of CFH and C1q in the mechanism of METH addiction. We also detected the distribution of various small molecules by matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) in select brain regions: the nucleus accumbens, the hippocampus and the ventral tegmental area. Results The expression of CFH was upregulated in the serum and hippocampus of METH behavioral sensitization model mice, consistent with our previous research on conditioned place preference rats. In contrast, C1q decreased dramatically in the mossy fibers of the hippocampus. The results of small-molecule imaging by MALDI-MSI showed that the levels of K+, antioxidants, neurotransmitters, and ATP metabolism-related molecules were altered in different regions. Conclusions These results indicate the involvement of the complement system in the mechanism of METH addiction and validate the presence of oxidative stress, energy metabolism changes during addiction. This suggests the utility of further investigation into the above aspects. [ABSTRACT FROM AUTHOR]

Abstract Complement 1q-binding protein (gC1qR), a multi-functional cellular protein, is able to bind the globular head region of C1q molecule (gC1q), playing an important role in regulation of immune response and host defense against bacterial infection. In this study, the full length of a gC1qR ortholog (OngC1qR) was identified and characterized from Nile tilapia (Oreochromis niloticus). The cDNA of OngC1qR ORFs consisted of 870 bp of nucleotide sequence encoding a 289 amino acid residue polypeptide. The deduced amino acid sequence is highly homologous to teleost, containing a MAM33p domain, two potential glycosylation sites, and a putative cell adhesion site EGD (Glu-Gly-Asp). Spatial mRNA expression analysis revealed that the OngC1qR was expressed ubiquitously in all examined tissues, with a high expression in the liver. The OngC1qR expression was significantly up-regulated in liver, spleen and head kidney following in vivo challenges with Streptococcus agalactiae. A high up-regulation was also detected in head kidney leukocytes in vitro stimulation with Streptococcus agalactiae. In addition, immunofluorescence detection illustrated that the OngC1qR was located at the cell surface of leukocytes. Recombinant OngC1qR protein was able to not only bind LPS, LTA, S. agalactiae and Aeromonas hydrophila , but also possess binding capability with the ligand OnC1qs. Taken together, the results indicated that OngC1qR might be involved in host defense against bacterial infection in Nile tilapia. Highlights • Full-length cDNA of gC1qR was identified and characterized in Nile tilapia. • Expressions of OnC1qR were significantly up-regulated upon LPS and bacterial challenges. • OnC1qR was located on the surface of leukocytes. • Recombinant OnC1qR was able to bind bacteria and ligand OnC1qs. [ABSTRACT FROM AUTHOR]

Activated microglia and subsequent release of pro-inflammatory cytokines result in neuroinflammatory status which further damage neurological function including cognitive impairments in various neurological conditions. However, the underlying molecular mechanisms during these pathological processing remain unknown. In the current study, mice received intraperitoneal administrations of LPS (0.5 mg/kg, daily, Escherichia coli O55:B5) for seven consecutive days and their different cohorts were used for behavioral assessment with open field, Y maze, and novel object recognition test or for electrophysiology recordings of mEPSC, LFP or LTP in in vivo or ex vivo preparation. The hippocampus from some cohorts were harvested for immunostaining or Western blotting of c1q, Iba-1, CD68, PSD95 and dendritic spine density or for transcriptome and proteomics analysis. Repeated LPS injections induced an up-regulation of complement system protein c1q and distinct microglial phenotype with an enrichment of the complement–phagosome pathway. Microglial synaptic engulfment and profound synaptic loss were found. These pathological changes were accompanied with the significantly decreased excitatory synaptic transmission, disturbed theta oscillations, impaired hippocampal long-term potentiation, and cognitive impairments. Notably, neutralization of c1q signaling robustly prevented these changes. Collectively, our data provide evidence that activated microglia and complement cascade c1q signaling in the hippocampus may account for synaptic loss and cognitive impairments in a mouse model of neuroinflammation induced by repeated LPS injections. Our work implicates that complement system may be a therapeutic target for developing therapies to prevent or treat cognitive disorders related to neuroinflammation or other disease conditions including neurodegenerative disease per se. • LPS injections induced up-regulation of C1q and synaptic loss in the CA1. • Microglia might engulf synaptic material through a C1q-dependent manner. • Neutralization of C1q signaling prevented synaptic and cognitive impairments. [ABSTRACT FROM AUTHOR]

Abstract Atherosclerosis is the predominant underlying pathology of many types of cardiovascular disease and is one of the leading causes of death worldwide. It is characterized by the retention of oxidized low-density lipoprotein (ox-LDL) in lipid-rich macrophages (foam cells) in the intima of arteries. Autoantigens derived from oxLDL can be used to vaccinate against atherosclerosis. However, a major challenge is the induction of antigen-specific Tregs in a safe and effective way. Here we report that liposomes containing the anionic phospholipid 1,2-distearoyl-sn-glycero-3-phosphoglycerol (DSPG) induce Tregs that are specific for the liposomes' cargo. Mechanistically, we show a crucial role for the protein corona that forms on the liposomes in the circulation, as uptake of DSPG-liposomes by antigen-presenting cells is mediated via complement component 1q (C1q) and scavenger receptors (SRs). Vaccination of atherosclerotic mice on a western-type diet with DSPG-liposomes encapsulating an LDL-derived peptide antigen significantly reduced plaque formation by 50% and stabilized the plaques, and reduced serum cholesterol concentrations. These results indicate that DSPG-liposomes have potential as a delivery system in vaccination against atherosclerosis. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Summary The gut microbiota is strongly influenced by environmental factors, although host contribution is far less understood. We leveraged macrophage-deficient interferon regulatory factor irf8 zebrafish mutants to investigate the role of macrophages in this process. In conventionally raised adult irf8 -deficient mutants, we found a significant loss of intestinal macrophages associated with a strikingly altered gut microbiota when compared to co-housed siblings. The destabilization of the gut commensal microbiota was associated with a severe reduction in complement C1q genes and outgrowth of a rare bacterial species. Consistent with a critical function of irf8 in adult intestinal macrophages, irf8 is abundantly expressed in these cells normally, and restoring macrophage irf8 expression in irf8 mutants was sufficient to recover commensal microbes and C1q genes expression. This study reports an important subpopulation of intestinal macrophages that requires irf8 to establish in the gut, ensure normal colonization of gut microbes, and prevent immune dysregulation. Graphical Abstract Highlights • irf8 is required for a subset of adult intestinal macrophages in zebrafish • irf8 mutants have disrupted gut commensal microbiota and gut C1q genes expression • Macrophage rescue of irf8 mutants recovers commensal microbiota and C1q expressions • Intestinal macrophages are critical for normal colonization of commensal microbiota Whether intestinal macrophages shape adult gut microbiota has not been demonstrated. Shiau et al. show that a severe loss of intestinal macrophages in adult zebrafish irf8 mutants can cause destabilization of gut commensal microbiota and a reduction of C1q expressions. Macrophage-specific rescue of irf8 mutants can reverse these effects. [ABSTRACT FROM AUTHOR]

Highlights • Complement has critical functional roles in embryonic brain development. • C1, C4, C2, C3 and CR3 are critical in synaptic refinement during brain maturation. • Complement activation contributes to excessive synaptic pruning in CNS disorders. • Determination of the molecular triggers of complement involvement will direct the pharmacologic development of interventions for currently intractable disorders of the CNS. Abstract While the mechanisms underlying the functions of the complement system in the central nervous system (CNS) and systemically, namely opsonization, chemotaxis, membrane lysis, and regulation of inflammation are the same, the plethora of functions that complement orchestrates in the central nervous system (CNS) is complex. Strictly controlled expression of complement effector molecules, regulators and receptors across the gamut of life stages (embryogenesis, development and maturation, aging and disease) dictate fascinating contributions for this ancient system. Furthermore, it is becoming apparent that complement functions differ widely across distinct brain regions. This review provides a comprehensive overview of the newly identified roles for complement in the brain, including its roles in CNS development and function, during aging and in the processes of neurodegeneration. The diversity and selectively of beneficial and detrimental activities of complement, while challenging, should lead to precision targeting of specific components to provide disease modifying treatments for devastating psychiatric and neurodegenerative disorders that are still without effective treatment. [ABSTRACT FROM AUTHOR]

Background Although complement activation is believed to be important in mediating PMN, the pathways involved and clinical consequences remain controversial. Many cases of idiopathic or primary membranous nephropathy (PMN) present with subepithelial C1q deposits along with IgG and C3 on glomerular capillary walls but without deposits of IgA or IgM (“full house”) by immunofluorescence or any causes of secondary MN. We sought to define the clinical and pathological significance of these C1q deposits in PMN by comparing a variety of clinical parameters, outcomes and other serum and urine factors in patients with and without significant glomerular C1q deposits. Methods Two-hundred eighty-eight patients with biopsy-proven PMN were enrolled. We compared the clinical and pathological features, treatment responses and kidney outcomes, between patients with and without C1q deposition. Circulating anti-PLA2R antibodies and complement components in plasma and urine were detected by ELISA. Results Glomerular C1q deposition was detected on capillary walls by immunofluorescence in 66/288 (22.9%) patients. C1q-positive patients presented with lower concentrations of serum IgG (5.3 ± 3.1 vs. 6.6 ± 3.5 g/l, p = 0.008), a higher frequency of IgA (37.9% vs. 15.8%, p < 0.001), IgM (48.5% vs. 31.5%, p = 0.011) and C3c (100% vs. 88.3%, p = 0.004) deposits in glomeruli and more stage III of MN (24.2% vs. 11.7%, p < 0.001) by pathologic criteria. Other features, including gender, age, anti-PLA2R antibody positivity and concentrations, proteinuria, albumin and serum creatinine, were not different between the patients with and without C1q deposition (p > 0.05). The IgG subclasses of anti-PLA2R antibodies in circulation or in glomeruli showed no difference (p > 0.05). C1q deposition, and C1q concentrations in circulation and urine had no apparent effect on the treatment responses or kidney outcomes (p > 0.05). Conclusion The classical pathway of complement is activated in some patients with PMN, but may not play an essential role in mediating the kidney injury seen in this disease. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate how the size of nanosized surface features affect classical immune complement activation through adsorption of IgG and the following binding of C1q. By using model surfaces with immobilized SiO 2 nanoparticles of different sizes (8, 32 and 68 nm in diameter), three different curvatures with the same chemistry was systematically studied and analyzed using the acoustic sensing technique; Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D). Circular Dichroism (CD) was employed to study any changes in the secondary structure of IgG using a methodology with stacked functionalized substrates. Our results show that the amount of IgG adsorption increased slightly with nanoparticle size, but also showed a strong size/curvature-dependent effect on the following C1q binding, with the highest binding to IgG adsorbed on the largest nanoparticles and a smooth control surface, indicating that classical immune complement activation possibly increase with decreasing curvature. We conclude that the difference in C1q binding was not due to changes in the secondary structure of IgG, suggesting that geometrical arrangement of adsorbed IgG is the determining factor. Statement of Significance We have shown that small changes at the topographical nanoscale can give large effects on the initiation of the classical immune complement cascade, an important immunological reaction that take place when a foreign material is inserted in the body. By developing a methodology using silicon dioxide nanoparticles with three different sizes, to systematically study their impact on the secondary structure and binding of human immunoglobulin G (IgG) to the initiator protein C1q of the classical complement cascade, we have shown that the initiation of the classical immune complement is hampered by the sharp curvature of the smaller nanoparticles. We conclude that this is not mediated by changes in the secondary structure of the adsorbed proteins, but rather an effect of curvature-induced spatial mismatch. The results provide a possible mechanistic explanation on how nanotopography may effect protein adsorption and protein cascade events. [ABSTRACT FROM AUTHOR]

Polydiacetylene (pDA) micelles have been demonstrated to be effective drug carriers for cancer therapy in mouse model. However, little is known about their interaction with the human complement system, which constitutes an important part of the innate immune system and can cause severe hypersensitivity reactions. Herein, we investigate the influence of micelle surface charge on the binding of complement protein C1q, the target recognition unit that activates the classical complement pathway and performs a range of other important physiological functions. Besides the classical pathway, we also investigate the surface charge effect on complement activities through the other activation pathways, namely, the MBL-dependent lectin pathway and the alternative pathway. We synthesized three samples of pDA micelles bearing neutral, anionic, and cationic surface charge motifs, respectively. Surface plasmon resonance showed that none of these micelles interacted with C1q. Results from serum complement activation assays indicated that all micelles were inert to complement, except for the anionic pDA micelles, which activated the alternative pathway. [ABSTRACT FROM AUTHOR]

In several types of antigen-presenting cells (APCs), Cathepsin S (CatS) plays a crucial role in the regulation of MHC class II surface expression and consequently influences antigen (Ag) presentation of APCs to CD4 + T cells. During the assembly of MHC class II-Ag peptide complexes, CatS cleaves the invariant chain p10 (Lip10) – a fragment of the MHC class II-associated invariant chain peptide. In this report, we used a selective, high-affinity CatS inhibitor to suppress the proteolytic activity of CatS in lymphoid and myeloid cells. CatS inhibition resulted in a concentration-dependent Lip10 accumulation in B cells from both healthy donors and patients with systemic lupus erythematosus (SLE). Furthermore, CatS inhibition led to a decreased MHC class II expression on B cells, monocytes, and proinflammatory macrophages. In SLE patient-derived peripheral blood mononuclear cells, CatS inhibition led to a suppressed secretion of IL-6, TNFα, and IL-10. In a second step, we tested the effect of CatS inhibition on macrophages being exposed to patient-derived autoantibodies against C1q (anti-C1q) that are known to be associated with severe lupus nephritis. As shown previously, those SLE patient-derived high-affinity anti-C1q bound to immobilized C1q induce a proinflammatory phenotype in macrophages. Using this human in vitro model of autoimmunity, we found that CatS inhibition reduces the inflammatory responses of macrophages as demonstrated by a decreased secretion of proinflammatory cytokines, the downregulation of MHC class II and CD80. In summary, we can show that the used CatS inhibitor is able to block Lip10 degradation in healthy donor- and SLE patient-derived B cells and inhibits the induction of proinflammatory macrophages. Thus, CatS inhibition seems to be a promising future treatment of SLE. [ABSTRACT FROM AUTHOR]

The single antigen test is widely used in the field of transplantation to determine the specificity of HLA antibodies. It will be beneficial to standardize the procedure of the single antigen test among HLA laboratories. It is not uncommon that single antigen testing on native sera fails to detect antibodies with very high concentrations. It has been shown that cleavage products of activated complement components may mask strongly binding antibodies in single antigen testing. To overcome inhibition by the activated complement products, sera are pretreated with ethylenediaminetetraacetic acid (EDTA), dithiothreitol (DTT), or heat inactivation before single antigen testing. However, no studies have been published to systemically compare the impact of these treatments on single antigen testing. The aim of this study is to understand the different effects these treatments may have on single antigen test results. We found that mean fluorescence intensity (MFI) obtained from sera treated with EDTA and heat inactivation were nearly identical, while DTT treatment was less potent to remove the inhibition. In addition, sera dilution did not further increase MFI of antibodies after EDTA treatment. Our results provide guidance to choose a pretreatment reagent for single antigen testing, and to compare studies obtained from laboratories using different treatments. [ABSTRACT FROM AUTHOR]

As the practice of medicine becomes more reliant on imaging and laboratory tests, medical decisions will be increasingly based on numbers. Accordingly, following the introduction of solid-phase testing to the HLA testing repertoire, laboratory directors and physicians have employed preset mean fluorescence intensity (MFI) thresholds as the basis for decisions in the management of transplant patients. However, what do MFI values mean? The literature is rife with reports detailing numerous factors that influence antibody assessment including (but not limited to) sensitization history of the patient, level of mismatch between donor and recipient, presence of interfering substances in the serum, whether the antigen on multiplex beads is native or denatured, day-to-day and technologist variability, and the historical performance of an assay in a given institution. How are these variables incorporated into the interpretation of MFI values? Herein, the pitfalls and complexities of single antigen bead (SAB) testing and interpretation are discussed with specific attention to what can and cannot be inferred by MFI. [ABSTRACT FROM AUTHOR]

Background Complement-binding assays are proposed to better stratify the risk of antibody-mediated rejection associated-graft failure. Despite promising clinical results, some have suggested that the MFI of anti-HLA antibodies may influence these tests. Methods We investigated the impact of Abs MFI reduction, induced by plasmapheresis, on C1q- and C3d-binding assays. Sera provided from 7 sensitized kidney transplant patients were analyzed. Results Four hundreds and thirty-three SABs were analyzed. Before plasmapheresis, when compared to C1q− SABs, C1q+ SABs had a higher median MFI [17397 (IQR: 14851–18794) vs. 2745 (IQR: 1125–6476), p < 0.01 ]. SABs that remained C1q+ after plasmapheresis had a higher median MFI. Regarding the C3d assay, results were strictly comparable. MFI value was a powerful predictor of both C1q and C3d positivity [AUC 0.97 (CI95% 0.95–0.99) and 0.96, (CI95% 0.93–0.98), respectively]. Conclusion Our data suggest that both C1q- and C3d-binding assays are intimately linked to the MFI of anti-HLA Abs. [ABSTRACT FROM AUTHOR]

Most of the complement proteins in circulation are, by and large, synthesized in the liver. However data accumulated over the past several decades provide incontrovertible evidence that some if not most of the individual complement proteins are also synthesized extrahepatically by activated as well as non-activated cells. The question that is finally being addressed by various investigators is: are the locally synthesized proteins solely responsible for the myriad of biological functions in situ without the contribution of systemic complement? The answer is probably “yes”. Among the proteins that are synthesized locally, C1q takes center stage for several reasons. First, it is synthesized predominantly by potent antigen presenting cells such as monocytes, macrophages and dendritic cells (DCs), which by itself is a clue that it plays an important role in antigen presentation and/or DC maturation. Second, it is transiently anchored on the cell surface via a transmembrane domain located in its A chain before it is cleaved off and released into the pericellular milieu. The membrane-associated C1q in turn, is able to sense danger patterns via its versatile antigen-capturing globular head domains. More importantly, locally synthesized C1q has been shown to induce a plethora of biological functions through the induction of immunomodulatory molecules by an autocrine- or paracrine- mediated signaling in a manner that mimics those of TNFα. These include recognition of pathogen- and danger- associated molecular patterns, phagocytosis, angiogenesis, apoptosis and induction of cytokines or chemokines that are important in modulating the inflammatory response. The functional convergence between C1q and TNFα in turn is attributed to their shared genetic ancestry. In this paper, we will infer to the aforementioned “local-synthesis-for-local function” paradigm using as an example, the role played by locally synthesized C1q in autoimmunity in general and in systemic lupus erythematosus in particular. [ABSTRACT FROM AUTHOR]

Complement component C1q is one of the recognition molecules of the complement system which can serve several functions unrelated to complement activation. This molecule is produced at foeto-maternal interface by macrophages as wells as by decidual endothelial cells and invading trophoblast. Foetal trophoblast cells migrating through the decidua in the early stages of pregnancy synthesize and express C1q on their surface, which is actively involved in promoting trophoblast endovascular and interstitial invasion of the decidua. These functions are mediated by two cell surface receptors, gC1qR and α4β1 integrin, which promote trophoblast adhesion and migration through the activation of ERK1/2 MAPKs. C1q −/− mice manifest increased frequency of foetal resorption, reduced foetal weight, and smaller litter size when compared to their wild-type counterparts, suggesting that defective local production of C1q may be involved in pregnancy disorders, such as pre-eclampsia. C1q acts also as a strong angiogenic factor and promotes neovascularization. These studies suggest novel and unexpected roles of this complement component in physiological and pathological pregnancies. [ABSTRACT FROM AUTHOR]

C1q is the initiation molecule of the classical pathway of the complement system and is produced by macrophages and immature dendritic cells. As mast cells share the same myeloid progenitor cells, we have studied whether also mast cells can produce and secrete C1q. Mast cells were generated in vitro from CD34+ progenitor cells from buffy coats or cord blood. Fully differentiated mast cells were shown by both RNA sequencing and qPCR to express C1QA, C1QB and C1QC. C1q produced by mast cells has a similar molecular make-up as serum C1q. Reconstituting C1q depleted serum with mast cell supernatant in haemolytic assays, indicated that C1q secreted by mast cells is functionally active. The level of C1q in supernatants produced under basal conditions was considerably enhanced upon stimulation with LPS, dexamethasone in combination with IFN- γ or via FcεRI triggering. Mast cells in human tissues stained positive for C1q in both healthy and in inflamed tissue. Moreover, mast cells in healthy and diseased skin appear to be the predominant C1q positive cells. Together, our data reveal that mast cells are able to produce and secrete functional active C1q and indicate mast cells as a local source of C1q in human tissue. [ABSTRACT FROM AUTHOR]

Using a previously described retinal explant culture system as an acute injury model, we here explore the role of C1q, the initiator of the classical complement pathway, in neuronal cell survival and retinal homeostasis. Full-thickness adult rat retinal explants were divided into four groups, receiving the following supplementation: C1q (50 nM), C1-inhibitor (C1-inh; Berinert; 500 mg/l), C1q + C1-inh, and no supplementation (culture controls). Explants were kept for 12 h or 2 days after which they were examined morphologically and with a panel of immunohistochemical markers. C1q supplementation protects ganglion cells from degeneration within the explant in vitro system. This effect is correlated to an attenuated endogenous production of C1q, and a quiesced gliotic response. [ABSTRACT FROM AUTHOR]

Presensitized kidney transplant recipients are at high-risk for early antibody-mediated rejection. We studied the impact of pre- and post-transplant donor-specific human leukocyte antigen (HLA) antibodies (DSA) and T-cell-activation on the occurrence of antibody-mediated rejection episodes (AMR) and graft loss (AMR-GL) in a unique cohort of 80 desensitized high-risk kidney transplant recipients. Patients with pre-transplant DSA demonstrated more AMR episodes than patients without DSA, but did not show a significantly increased rate of AMR-GL. The rates of AMR and AMR-GL were not significantly increased in patients with complement split product (C1q)-binding pre-transplant DSA. Pre-transplant C1q-DSA became undetectable post-transplant in 11 of 13 (85%) patients; 2 (18%) of these 11 patients showed AMR but no AMR-GL. In contrast, the post-transplant presence of C1q-DSA was associated with significantly higher rates of AMR (86 vs 33 vs 0%; P<0.001) and AMR-GL (86 vs 0 vs 0%; log-rank P<0.001) compared with post-transplant DSA without C1q-binding or the absence of DSA. Patients with both pre-transplant DSA and evidence of pre-transplant T-cell-activation as indicated by soluble CD30-positivity showed a significantly increased risk for AMR-GL [HR=11.1, 95% confidence interval (CI)=1.68-73.4; log-rank P=0.013]. In these high-risk patients, AMR-GL was associated with total DSA in combination with T-cell-activation pre-transplant, and de novo or persistent C1q-binding DSA post-transplant. [ABSTRACT FROM AUTHOR]

Background The virtual crossmatch relies on the assignment of unacceptable antigens (UAs) to identify compatible donors. The purpose of our study was to identify an algorithm for assignment of UAs such that a negative complement-dependent cytotoxicity (CDC) crossmatch and concomitant negative or weakly positive flow cytometric crossmatch (FXM) are obtained. Methods We used 4 antibody methods: (1) Luminex single antigen (LSA), (2) LSA with a 1:8 serum dilution, (3) C1q LSA, and (4) CDC panel. The UAs were prioritized in the following order: (1) all C1q+/CDC+, (2) LSA 1:8 >7,500 median fluorescence intensity, and (3) LSA >10,000 median fluorescence intensity. Results Of 295 heart transplants that were performed at our center, 69 (23%) recipients had detectable human leukocyte antigen specific antibody at the time of transplant. All donor specific antibodies (DSAs) were avoided for 44 of 69 (64%) (DSA−). There were 25 recipients who had DSA at the time of transplant: 12 (48%) had negative FXM (DSA+/FXM−), and 13 (52%) had positive T-cell and/or B-cell FXM (DSA+/FXM+). Lower freedom from antibody-mediated rejection was observed for the DSA+/FXM+ group compared with the DSA− group ( p < 0.0001). DSA remained detectable after transplant in the sera of 14 recipients, and de novo DSA was detected in 32 recipients. Freedom from antibody-mediated rejection was comparable for both groups ( p = 0.53) but was lower than the DSA− group ( p < 0.0001). Survival was comparable for all groups at 1,200 days post-transplant. Conclusions Strategic prioritization of UA assignment has allowed transplantation of highly sensitized patients across the DSA barrier with survival rates comparable to DSA− heart transplant recipients. [ABSTRACT FROM AUTHOR]

Deficiencies in the classical pathway of complement activation have some common features but show also great differences. Deficiencies of each of the components (C1q, C1s, C1r, C4 and C2) imply increased susceptibility to bacterial infections. They are also associated with increased risk to develop systemic lupus erythematosus where deficiency of C1q is strongly associated to the disease while C4 less and C2 much less. Deficiency of C1q affects only activation of the classical pathway while deficiency of C4 and C2 also prevent activation of the lectin pathway. Bypass mechanisms may result in complement activation also in absence of C2 but not in absence of C1q or C4. The genes for C2 and C4 isotypes are closely located within the MHC class III region on chromosome 6p and the genes for the 3 C1q chains are on chromosome 1p. Deficiencies of C1q and of C4 show genetic heterogeneity while deficiency of C2 in the great majority of cases is caused by a specific deletion. The production of C4 and C2 is mainly by the hepatocytes in the liver while C1q is produced by monocytic bone marrow derived cells. This has implications for the possibility to treat the deficiency and hematopoietic stem cell transplantation has been tried in C1q deficiency. [ABSTRACT FROM AUTHOR]

The complement system has long been known for its role in combating infections. More recently the complement system is becoming increasingly appreciated for its role in processes that range from waste transport, immune tolerance and shaping of the adaptive immune response. Antibodies represent the humoral part of the adaptive immune response and the complement system interacts with antibodies in several ways. Activated complement fragments impact on the production of antibodies, the complement system gets activated by antibodies and complement proteins can be the target of (auto)antibodies. In this review, written to celebrate the contributions of Prof. Dr. M.R. Daha to the field of immunology and especially complement, we will focus on C1q and its various interactions with antibodies. We will specifically focus on the mechanisms by which C1q will interact with monomeric IgG versus polymerized IgG and fluid-phase IgM versus solid-phase IgM. In addition in this review we will discuss in detail how C1q itself is targeted by autoantibodies and how these autoantibodies are currently considered to play a role in human disease. [ABSTRACT FROM AUTHOR]

Interaction between the complement system and carbon nanotubes (CNTs) can modify their intended biomedical applications. Pristine and derivatised CNTs can activate complement primarily via the classical pathway which enhances uptake of CNTs and suppresses pro-inflammatory response by immune cells. Here, we report that the interaction of C1q, the classical pathway recognition molecule, with CNTs involves charge pattern and classical pathway activation that is partly inhibited by factor H, a complement regulator. C1q and its globular modules, but not factor H, enhanced uptake of CNTs by macrophages and modulated the pro-inflammatory immune response. Thus, soluble complement factors can interact differentially with CNTs and alter the immune response even without complement activation. Coating CNTs with recombinant C1q globular heads offers a novel way of controlling classical pathway activation in nanotherapeutics. Surprisingly, the globular heads also enhance clearance by phagocytes and down-regulate inflammation, suggesting unexpected complexity in receptor interaction. From the Clinical Editor Carbon nanotubes (CNTs) maybe useful in the clinical setting as targeting drug carriers. However, it is also well known that they can interact and activate the complement system, which may have a negative impact on the applicability of CNTs. In this study, the authors functionalized multi-walled CNT (MWNT), and investigated the interaction with the complement pathway. These studies are important so as to gain further understanding of the underlying mechanism in preparation for future use of CNTs in the clinical setting. [ABSTRACT FROM AUTHOR]

Surfactant proteins SP-A and SP-D, and complement protein C1q are soluble innate immune pattern recognizing molecules. SP-A, SP-D and C1q have an overall similar structure composed of an N-terminal triple-helical collagen region that is followed by a trimeric globular domain. While SP-A and SP-D belong to the collectin family (collagen containing lectin), C1q is the first recognition subcomponent of the classical pathway of the complement system. Recently, SP-A, SP-D and C1q have been considered to play important roles in early and late pregnancy. However, their expression in early human decidua has not been examined. Here, we investigated whether SP-A, SP-D and C1q are expressed within first trimester decidua in humans and their expression is associated with trophoblasts and decidual stromal cells. Decidual samples from women undergoing elective vaginal termination of pregnancy during first trimester were obtained from 25 subjects. Immunohistochemical studies using anti-human SP-A, anti-human SP-D and anti-human C1q antibodies were performed on decidual tissue sections along with anti-vimentin and cytokeratin-7 antibodies to identify stromal cells and trophoblasts. The expression was also examined by immunostaining and PCR using decidual and stromal cells. C1q expression was significantly higher when compared to SP-A and SP-D in the first trimester human decidua. Double immunostaining revealed that all stromal cells and trophoblasts expressed SP-A, SP-D and C1q, while only few invasive trophoblasts expressed C1q. Thus, expression of SP-A, SP-D and C1q in human decidua during first trimester suggests potential role of SP-A, SP-D and C1q during the early stages of pregnancy including implantation, trophoblast invasion and placental development. [ABSTRACT FROM AUTHOR]

Detection of donor-specific anti-HLA antibodies (DSA) has been associated with graft rejection in all forms of transplantation. The mechanism by which DSA increase the risk of graft failure remains unclear. We hypothesized that complement-binding DSA are associated with engraftment failure in hematopoietic stem cell transplantation (HSCT) and analyzed 122 haploidentical transplant recipients tested prospectively for DSA. Retrospective analysis to detect C1q binding DSA (C1q+DSA) was performed on 22 allosensitized recipients. Twenty-two of 122 patients (18%) had DSA, 19 of which were women (86%). Seven patients with DSA (32%) rejected the graft. Median DSA level at transplant for patients who failed to engraft was 10,055 mean fluorescence intensity (MFI) versus 2065 MFI for those who engrafted ( P = .007). Nine patients with DSA were C1q positive in the initial samples with median DSA levels of 15,279 MFI (range, 1554 to 28,615), compared with 7 C1q-negative patients with median DSA levels of 2471 MFI (range, 665 to 12,254) ( P = .016). Of 9 patients who were C1q positive in the initial samples, 5 patients remained C1q positive at time of transplant (all with high DSA levels [median, 15,279; range, 6487 to 22,944]) and experienced engraftment failure, whereas 4 patients became C1q negative pretransplant and all engrafted the donor cells ( P = .008). In conclusion, patients with high DSA levels (>5000 MFI) and complement-binding DSA antibodies (C1q positive) appear to be at much higher risk of primary graft failure. The presence of C1q+DSA should be assessed in allosensitized patients before HSCT. Reduction of C1q+DSA levels might prevent engraftment failure in HSCT. [ABSTRACT FROM AUTHOR]

C1q domain-containing (C1qDC) proteins are regarded as important players in the innate immunity of bivalve mollusks and other invertebrates and their highly adaptive binding properties indicate them as efficient pathogen recognition molecules. Although experimental studies support this view, the molecular data available at the present time are not sufficient to fully explain the great molecular diversification of this family, present in bivalves with hundreds of C1q coding genes. Taking advantage of the fully sequenced genome of the Pacific oyster Crassostrea gigas and more than 100 transcriptomic datasets, we: (i) re-annotated the oyster C1qDC loci, thus identifying the correct genomic organization of 337 C1qDC genes, (ii) explored the expression pattern of oyster C1qDC genes in diverse developmental stages and adult tissues of unchallenged and experimentally treated animals; (iii) investigated the expansion of the C1qDC gene family in all major bivalve subclasses. Overall, we provide a broad description of the functionally relevant features of oyster C1qDC genes, their comparative expression levels and new evidence confirming that a gene family expansion event has occurred during the course of Bivalve evolution, leading to the diversification of hundreds of different C1qDC genes in both the Pteriomorphia and Heterodonta subclasses. [ABSTRACT FROM AUTHOR]

Inflammation plays a key role in the pathophysiology of Glioblastoma Multiforme (GBM). Here we focus on the contribution of the so far largely ignored complement system. ELISA and immunohistochemistry were combined to assess levels and localization of critical components of the initiation- and effector pathways of the complement cascade in sera and tumor tissue from GBM patients and matched controls. Serum levels of factor-B were decreased in GBM patients whereas C1q levels were increased. C1q and factor-B deposited in the tumor tissue. Deposition of C3 and C5b-9 suggests local complement activation. MBL deficiency, based on serum levels, was significantly less frequent among GBM patients compared to controls (14% vs. 33%). Therefore low levels of MBL may protect against the initiation/progression of GBM. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) have promised a range of applications in biomedicine. Although influenced by the dispersants used, CNTs are recognized by the innate immune system, predominantly by the classical pathway of the complement system. Here, we confirm that complement activation by the CNT used continues up to C3 and C5, indicating that the entire complement system is activated including the formation of membrane-attack complexes. Using recombinant forms of the globular regions of human C1q (gC1q) as inhibitors of CNT-mediated classical pathway activation, we show that C1q, the first recognition subcomponent of the classical pathway, binds CNTs via the gC1q domain. Complement opsonisation of CNTs significantly enhances their uptake by U937 cells, with concomitant downregulation of pro-inflammatory cytokines and up-regulation of anti-inflammatory cytokines in both U937 cells and human monocytes. We propose that CNT-mediated complement activation may cause recruitment of cellular infiltration, followed by phagocytosis without inducing a pro-inflammatory immune response. [ABSTRACT FROM AUTHOR]

Abstract: Introduction: Complement system is an important effector component of the innate immune system. More than 30 plasma proteins undergo a cascade of enzymatic reactions to produce effector molecules to clear infectious microbes, immune complexes, post apoptotic cellular debris and thus participate in prevention of autoimmunity. Absolute deficiency of individual complement components and selective deficiency of classical pathway complement components are reported to be associated with severe infections and a high risk for lupus like syndromes. Genetic defects in gene encoding for complement components were reported to be associated with complement deficiency. This study was carried out to investigate whether C1q and C2 polymorphisms are risk factors for SLE in south Indian Tamils. Materials and methods: Three hundred SLE patients fulfilling ACR criteria for SLE and 460 age and sex similar ethnicity matched individuals were included as patients and healthy controls respectively. The genomic DNA obtained from both the groups was screened for two polymorphisms including a C/T transition in exon 2 of C1qA (rs121909581) by PCR-RFLP and a 28bp deletion in sixth exon of C2 gene by PCR. Results: C1q exon 2 C/T polymorphism analysis revealed that homozygous CC was the most common genotype in patients and controls. A single SLE patient was found to have heterozygous variant (CT). None of the patients or healthy controls were found to have 28bp deletion variant of C2 gene. Conclusion: The C/T polymorphism in exon 2 of C1qA and a 28bp deletion in sixth exon of C2 gene were found to be rare in south Indian Tamil SLE patients. They do not appear to be susceptibility factors for SLE in Indian Tamils. [Copyright &y& Elsevier]

Highlights: [•] We identified a homologue of mammalian C1q in hagfish serum. [•] Hagfish C1q bound to various microbes in a Ca2+ dependent manner. [•] Hagfish C1q bound to peptidoglycan in a Ca2+ dependent manner. [•] Hagfish C1q bound to agarobiose but not to monosaccharide. [•] High density of agarobiose was necessary for stable binding of Hagfish C1q. [Copyright &y& Elsevier]

Highlights: [•] C1q binds to dengue envelope protein of all 4 serotypes. [•] C1q binds to dengue serotype 2 virus. [•] Dengue serotype 2 virus bound to C1q is less infective to THP-1, a human monocytic leukemia cell line. [•] The levels of transcription of immunoregulatory molecules in such infected THP-1 cells is altered. [Copyright &y& Elsevier]

Abstract: The complement system represents a major component of our innate immune defense. Although the physiological contribution of the complement system is beneficial, it can cause tissue damage when inappropriately activated or when it is a target of an autoantibody response. Autoantibodies directed against a variety of individual complement components, convertases, regulators and receptors have been described. For several autoantibodies the functional consequences are well documented and clear associations exist with clinical presentation, whereas for other autoantibodies targeting complement components this relation is currently insufficiently clear. Several anti-complement autoantibodies can also be detected in healthy controls, indicating that a second hit is required for such autoantibodies to induce or participate in pathology or alternatively that these antibodies are part of the natural antibody repertoire. In the present review, we describe autoantibodies against complement components and their functional consequences and discuss about their clinical relevance. [Copyright &y& Elsevier]

Abstract: Of the many mysteries that surround the brain, few surpass the awe-inspiring complexity of its development. The intricate wiring of the brain at both the system and molecular level is both spatially and temporally regulated in perfect synchrony. How such a delicate, yet elegant, system arises from an embryo's most basic cells remains at the forefront of neuroscientific research. At the cellular level, the competitive dance between synapses struggling to gain dominance seems to be refereed by both neurons themselves and microglia, the innate immune cells of the nervous system. Additionally, the unexpected complement cascade, a major effecter arm of the innate immune system, is almost certainly involved in synaptic remodeling by tagging destined neurons and synapses for destruction. As suddenly as they appear, the mechanisms of neurogenesis recede entering into adulthood. However, with age and insult, these mechanisms boisterously return, resulting in neurodegeneration. This review describes some of the mechanisms involved in synaptogenesis and wiring of the brain from the point of view of the innate immune system and then covers how similar molecular processes return with age and disease, specifically in the context of Alzheimer's disease. [Copyright &y& Elsevier]

Abstract: Objective: Adiponectin, an adipocyte-derived protein, has potential antiatherogenic properties. Low levels of serum total-adiponectin (Total-APN) correlate with diabetes and coronary artery disease (CAD). Adiponectin and C1q form a protein complex in blood, and serum C1q-binding adiponectin (C1q-APN) can be measured. We investigated the correlation between C1q-APN and CAD in patients with type 2 diabetes mellitus (T2DM). Methods: The study subjects were 107 outpatients with T2DM who underwent evaluation for CAD. Blood C1q, Total-APN, high-molecular weight-adiponectin (HMW-APN) and C1q-APN were measured by enzyme-linked immunosorbent assays. Results: Serum levels of C1q-APN/Total-APN ratio were higher in patients diagnosed with CAD (10.47±0.59, mean±SEM, n=54) than those without CAD (8.88±0.60, n=53, p=0.0482). Age- and sex-adjusted logistic regression analysis identified serum C1q-APN/Total-APN ratio and hypertension as significant and independent determinants of CAD. A high serum C1q-APN/Total-APN ratio was associated with 3.965-fold increase in CAD prevalence. Conclusions: High serum C1q-APN/Total-APN ratio correlates with CAD in T2DM. [Copyright &y& Elsevier]