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Invading microbes face a myriad of cidal mechanisms of phagocytes that inflict physical damage to microbial structures. How intracellular bacterial pathogens adapt to these stresses is not fully understood. Here, we report the discovery of a virulence mechanism by which changes to the mechanical stiffness of the mycobacterial cell surface confer refraction to killing during infection. Long-term time-lapse atomic force microscopy was used to reveal a process of "mechanical morphotype switching" in mycobacteria exposed to host intracellular stress. A "soft" mechanical morphotype switch enhances tolerance to intracellular macrophage stress, including cathelicidin. Both pharmacologic treatment, with bedaquiline, and a genetic mutant lacking uvrA modified the basal mechanical state of mycobacteria into a soft mechanical morphotype, enhancing survival in macrophages. Our study proposes microbial cell mechanical adaptation as a critical axis for surviving host-mediated stressors.

Macrophages play critical protective roles as sentinels of the innate immune system against fungal infection. It is therefore important to understand the dynamics of the interaction between these phagocytes and their fungal prey. We show here that many of the hyphal apices formed by Candida albicans within the macrophage ceased elongating, and apical and sub-apical hyphal compartments became swollen. Swollen hyphal cell compartments assimilated less Lysotracker-Red than non-swollen compartments, suggesting they had enhanced viability. Staining with florescent dyes suggested that there were higher levels of β-glucan and chitin in internalized fungal filaments compared to non-internalized hyphae, suggesting active cell wall remodelling within macrophages. These observations suggest that the stresses imposed by macrophages upon the fungus lead to changes in cell wall composition, inhibition of polarised growth and the induction of swelling in hyphal compartments, and that this can prevent or delay loss of viability of hyphal cells within the phagocyte. [ABSTRACT FROM AUTHOR]

Macrophages and autophagy are intricately linked, both playing vital roles in maintaining homeostasis and responding to disease. Macrophages, known for their ‘eating’ function, rely on a sophisticated digestion system to process a variety of targets, from apoptotic cells to pathogens. The connection between macrophages and autophagy is established early in their development, influencing both differentiation and mature functions. Autophagy regulates essential immune functions, such as inflammation control, pathogen clearance, and antigen presentation, linking innate and adaptive immunity. Moreover, it modulates cytokine production, ensuring a balanced inflammatory response that prevents excessive tissue damage. Autophagy also plays a critical role in macrophage polarization, influencing their shift between pro‐inflammatory and anti‐inflammatory states. This review explores the role of autophagy in macrophages, emphasizing its impact across various tissues and pathological conditions, and detailing the cellular and molecular mechanisms by which autophagy shapes macrophage function. [ABSTRACT FROM AUTHOR]

Bone defects arising from trauma and tumors present a potential risk of infection and compromise host immune function. Within a dysfunctional microenvironment, the uncontrolled breeding of bacteria and persistent chronic inflammation exacerbate bone loss, impeding bone regeneration and repair. Macrophages function as specialized phagocytes within the immune microenvironment and the orchestrated role of distinct phenotypes during regeneration has attracted significant attention. The M1 phenotype exhibits antimicrobial activities to eliminate bacterial threats, while the M2 phenotype secretes anti‐inflammatory mediators to fine‐tune the immune microenvironment. Here, a biphasic delivery system consisting of a photothermal agent (graphene oxide, GO) coated and an immune modulator (urolithin A, UA) encapsulated in coaxial electrospun nanofibers with a dynamic regulation function of macrophage behavior is designed. It is observed that the GO coating exhibited remarkable photothermal performance within the near‐infrared window, affecting the phagocytic activity of macrophage subsets in an integrin‐RhoA‐ROCK1 dependent manner. The sustained release of UA from the core layer induced a phenotypic switch by downregulating TNF signaling and upregulating TGF signaling. This system also demonstrated a promotion of bone regeneration in vivo. Overall, this strategy achieved sequential regulation of macrophage phenotypes, effectively preventing infection and fostering bone tissue regeneration. [ABSTRACT FROM AUTHOR]

The development of novel conditional gene targeting tools is allowing us to disentangle the contribution of mononuclear phagocytes to autoimmune neuroinflammation. Microglia and border-associated macrophages are not major contributors to tissue damage but are involved in controlling inflammation and promoting tissue repair (remyelination) during experimental autoimmune encephalomyelitis, a mouse model for multiple sclerosis. Conventional dendritic cells play a dual role: they maintain tolerance to central nervous system (CNS) antigens while also facilitating the reactivation and expansion of pathogenic effector T cells within the CNS. Monocyte-derived macrophages can mediate tissue damage, although emerging evidence suggests that they may also possess tissue-protective and immunoregulatory properties. With emerging single-cell technologies and conditional gene targeting, it is evident that mammalian central nervous system (CNS)-associated phagocytes play crucial yet different and even opposing roles in neuroinflammation. Our developing understanding of their individual impact can help guide the development of more specific, effective, and safe therapies for patients suffering from neuroinflammatory diseases. A healthy mammalian central nervous system (CNS) harbors a diverse population of leukocytes including members of the mononuclear phagocyte system (MPS). Exerting their specific functions, CNS tissue-resident macrophages as well as associated monocytes and dendritic cells (DCs) maintain CNS homeostasis. Under neuroinflammatory conditions, leukocytes from the systemic immune compartment invade the CNS. This review focuses on the newly discovered roles of the MPS in autoimmune neuroinflammation elicited by encephalitogenic T cells. We propose that CNS-associated DCs act as gatekeepers and antigen-presenting cells that guide the adaptive immune response while bone marrow (BM)-derived monocytes contribute to immunopathology and tissue damage. By contrast, CNS-resident macrophages primarily support tissue function and promote the repair and maintenance of CNS functions. [ABSTRACT FROM AUTHOR]

Phagocytosis is an intensely physical process that depends on the mechanical properties of both the phagocytic cell and its chosen target. Here, we employed differentially deformable hydrogel microparticles to examine the role of cargo rigidity in the regulation of phagocytosis by macrophages. Whereas stiff cargos elicited canonical phagocytic cup formation and rapid engulfment, soft cargos induced an architecturally distinct response, characterized by filamentous actin protrusions at the center of the contact site, slower cup advancement, and frequent phagocytic stalling. Using phosphoproteomics, we identified β2 integrins as critical mediators of this mechanically regulated phagocytic switch. Macrophages lacking β2 integrins or their downstream effectors, Talin1 and Vinculin, exhibited specific defects in phagocytic cup architecture and selective suppression of stiff cargo uptake. We conclude that integrin signaling serves as a mechanical checkpoint during phagocytosis to pair cargo rigidity to the appropriate mode of engulfment. Phagocytosis is regulated by the mechanical properties of both the phagocyte and its cargo. Here, the authors show that macrophages employ β2 integrins to sense the rigidity of phagocytic cargo and then mount the appropriate form of engulfment. [ABSTRACT FROM AUTHOR]

While the acute inflammatory response to harmful stimuli is protective, unrestrained neutrophil swarming drives collateral tissue damage and inflammation. Biosynthesized from omega-3 essential polyunsaturated fatty acids, resolvins are a family of signaling molecules produced by immune cells within the resolution phase to orchestrate return to homeostasis. Understanding the mechanisms that govern biosynthesis of these potent molecules gives insight into stimulating endogenous resolution and offers fresh opportunities for preventing and treating excessive inflammation. In this report, using materials prepared by total synthesis and liquid chromatography and tandem mass spectrometry-based matching studies, we established the role of 7,8(S,S)-epoxytetraene intermediate in the biosynthesis of resolvin D1, resolvin D2, and the resolvin conjugate in tissue regeneration (RCTR1) by human phagocytes. We demonstrated that this 7,8(S,S)-epoxy-containing intermediate is directly converted to resolvin D2 by human M2-like macrophages and to resolvin D1 and RCTR1 by human macrophages, neutrophils, and peripheral blood mononuclear cells. In addition, both human recombinant soluble epoxide hydrolase (sEH) and the glutathione S-transferase leukotriene C4 synthase (LTC4S) each catalyze conversion of this epoxide to resolvin D1 and RCTR1, respectively. MS3 ion-trap scans and isotope incorporation of 18O from H218O with sEH indicated that the oxygen atom at C-8 in resolvin D1 is derived from water. Results from molecular docking simulations with biosynthetic precursor 17S-hydroperoxy-4,7,10,13,19-cis-15-trans-docosahexaenoic acid and the epoxy intermediate were consistent with 5-lipoxygenase production of resolvin D1. Together, these results give direct evidence for the role of resolvin 7,8(S,S)-epoxytetraene intermediate in the endogenous formation of resolution-phase mediators resolvin D1, resolvin D2, and RCTR1 by human phagocytes. [ABSTRACT FROM AUTHOR]

The process of apoptotic cell clearance by phagocytes, known as efferocytosis, plays an essential role in maintaining homeostasis. Defects in efferocytosis can lead to inflammatory diseases such as atherosclerosis and autoimmune disorders. Therefore, the maintenance and promotion of efferocytosis are considered crucial for preventing these diseases. In this study, we observed that resveratrol, a representative functional food ingredient, and its glycoside, piceid, promoted efferocytosis in both human THP-1 macrophages differentiated with phorbol 12-myristate 13-acetate and peritoneal macrophages from thioglycolate-elicited mice. Resveratrol and piceid significantly increased mRNA expression and protein secretion of MFG-E8 in THP-1 macrophages. Furthermore, the activation of efferocytosis and the increment in MFG-E8 protein secretion caused by resveratrol or piceid treatment were canceled by MFG-E8 knockdown in THP-1 macrophages. In conclusion, we have demonstrated for the first time that resveratrol and piceid promote efferocytosis through the upregulation of MFG-E8 excretion in human THP-1 macrophages. [ABSTRACT FROM AUTHOR]

Background: Andrographis paniculata (Burm. f.) Nees is a well-recognized medicinal plant known for its benefits against a multitude of ailments. The intent of the present study was to evaluate the effect of a standardized extract of A. paniculata on innate immunity. Materials and Methods: Phagocytic activity was measured in terms of phagocytic index using carbon clearance methodology in mice. In another experiment, NK cells (effector cells) were isolated from the mouse spleen after the dosing period, and NK cells-mediated lysis of target cells (YAC-1 cells) were determined using an MTT assay. Results: The phagocytic index and NK cell activity were found to be significantly (p < 0.05) different in the treated group compared to the control group in the tested animal models at a dose of 41 mg/kg. Conclusion: The results suggest the potential of A. paniculata to enhance innate immunity. [ABSTRACT FROM AUTHOR]

The immune system is divided ilito two major branches: innate and cidaptive. The iniiate immune system is the body's first line of defense and rapidly responds in a nonspecific manner to various microorganisms, foreign materials, or injuries. Phagocytes, which include tilacrophages, nionocytes, and netttrophils, are iminte immune cells tliat con surround and kill microorganisins, ingest foreign material, at:id remove dead cells. They also indirectly boost both innate and adaptive immune responses through Various activation signals. Plingocytic defects characteristically lead to filligal aild bacterial infections of the respiratory tract, lymph nodes, skill, and other organ systems, mid they are commonly associated with iii.flammatory bowel disease. This prinier-will review high-yield innate defects of phagocytic cells, inchiding defects of respiratory (oxidative) burst, defects of neutrophil migration, cyclic and severe congenital neutropenias and associated disorders, and other phagocyte defect disorders. [ABSTRACT FROM AUTHOR]

Langerhans cells (LCs) are distinct among phagocytes, functioning both as embryo-derived, tissue-resident macrophages in skin innervation and repair and as migrating professional antigen-presenting cells, a function classically assigned to dendritic cells (DCs). Here, we demonstrate that both intrinsic and extrinsic factors imprint this dual identity. Using ablation of embryo-derived LCs in the murine adult skin and tracking differentiation of incoming monocyte-derived replacements, we found intrinsic intraepidermal heterogeneity. We observed that ontogenically distinct monocytes give rise to LCs. Within the epidermis, Jagged-dependent activation of Notch signaling, likely within the hair follicle niche, provided an initial site of LC commitment before metabolic adaptation and survival of monocyte-derived LCs. In the human skin, embryo-derived LCs in newborns retained transcriptional evidence of their macrophage origin, but this was superseded by DC-like immune modules after postnatal expansion. Thus, adaptation to adult skin niches replicates conditioning of LC at birth, permitting repair of the embryo-derived LC network. Editor's summary: Langerhans cells (LCs) are specialized skin-resident antigen-presenting cells that not only share developmental origins with tissue-resident macrophages but also acquire the dendritic cell–like ability to migrate to draining lymph nodes. How this dual LC identity is imprinted and maintained is not completely understood. Using a mouse model of adult LC repopulation, Appios et al. found that both the developmental origin of repopulating monocytes and epidermal niche signaling imprint LC identity. A subset of infiltrating monocytes underwent stepwise differentiation involving loss of Zeb2-regulated macrophage identity, Jagged/Notch-dependent imprinting of LC fate, and survival signals in the epidermis. Similar developmental programs were detected among human embryo–derived LCs in postnatal skin. Together, these findings identify intrinsic and extrinsic factors guiding LC specification in the skin. —Claire Olingy [ABSTRACT FROM AUTHOR]

Introduction: Visceral leishmaniasis (VL) is an important tropical and neglected disease and represents a serious global health problem. The initial interaction between the phagocytes and the parasite is crucial to determine the pathogen's capacity to initiate infection and it shapes the subsequent immune response that will develop. While type-1 T-cells induce IL-6, IL-1β, TNF-α, and IL-12 production by monocytes/macrophages to fight the infection, type-2 T-cells are associated with a regulatory phenotype (IL-10 and TGF-β) and successful infection establishment. Recently, our group demonstrated the role of an important Th1/ Th17 T-cell population, the mucosal-associated invariant T (MAIT) cells, in VL. MAIT cells can respond to L. infantum by producing TNF-α and IFN-γ upon MR1- dependent activation. Objective and methods: Here, we describe the impact of the MR1-blockage on L. infantum internalization on the functional profile of circulating neutrophils and monocytes as well as the impact of the MR1-blockage on the soluble mediator signatures of in vitro whole blood cultures. Results: Overall, our data showed that VL patients presents higher percentage of activated neutrophils than asymptomatic and non-infected controls. In addition, MR1 blockade led to lower TNF-α and TGF-β production by non-activated neutrophils from asymptomatic individuals. Moreover, TNF-α and IL-10 production by monocytes was higher in VL patients. In the analysis of soluble mediators produced in vitro, MR1-blockade induced a decrease of IFN-γ and an increase of IL-10, IL-27 and IL-33 in the cell cultures of AS group, a cytokine pattern associated with type 2 deleterious response. Discussion and conclusion: These data corroborate the hypothesis that MR1- restricted responses are associated to a protective role during Leishmania infection. [ABSTRACT FROM AUTHOR]

Early innate immune responses play an important role in determining the protective outcome of Mycobacterium tuberculosis (Mtb) infection. Nuclear factor κB (NF-κB) signaling in immune cells regulates the expression of key downstream effector molecules that mount early antimycobacterial responses. Using conditional knockout mice, we studied the effect of abrogation of NF-κB signaling in different myeloid cell types and its impact on Mtb infection. Our results show that the absence of IKK2-mediated signaling in all myeloid cells resulted in increased susceptibility to Mtb infection. In contrast, the absence of IKK2-mediated signaling in CD11c+ myeloid cells induced early proinflammatory cytokine responses, enhanced the recruitment of myeloid cells, and mediated early resistance to Mtb. Abrogation of IKK2 in MRP8-expressing neutrophils did not affect disease pathology or Mtb control. Thus, we describe an early immunoregulatory role for NF-κB signaling in CD11c-expressing phagocytes and a later protective role for NF-κB in LysM-expressing cells during Mtb infection. [ABSTRACT FROM AUTHOR]

Cystatin F (CstF) is a protease inhibitor of cysteine cathepsins, including those involved in activating the perforin/granzyme cytotoxic pathways. It is targeted at the endolysosomal pathway but can also be secreted to the extracellular milieu or endocytosed by bystander cells. CstF was shown to be significantly increased in tuberculous pleurisy, and during HIV coinfection, pleural fluids display high viral loads. In human macrophages, our previous results revealed a strong upregulation of CstF in phagocytes activated by interferon γ or after infection with Mycobacterium tuberculosis (Mtb). CstF manipulation using RNA silencing led to increased proteolytic activity of lysosomal cathepsins, improving Mtb intracellular killing. In the present work, we investigate the impact of CstF depletion in macrophages during the coinfection of Mtb-infected phagocytes with lymphocytes infected with HIV. The results indicate that decreasing the CstF released by phagocytes increases the major pro-granzyme convertase cathepsin C of cytotoxic immune cells from peripheral blood-derived lymphocytes. Consequently, an observed augmentation of the granzyme B cytolytic activity leads to a significant reduction in viral replication in HIV-infected CD4+ T-lymphocytes. Ultimately, this knowledge can be crucial for developing new therapeutic approaches to control both pathogens based on manipulating CstF. [ABSTRACT FROM AUTHOR]

Staphylococcus aureus is a prevalent pathogen in pneumonia and harbors glycolipids, which may serve as molecular patterns in Mincle (macrophage-inducible C-type lectin)–dependent pathogen recognition. We examined the role of Mincle in lung defense against S aureus in wild-type (WT), Mincle knockout (KO), and Mincle transgenic (tg) mice. Two glycolipids, glucosyl-diacylglycerol (Glc-DAG) and diglucosyl-diacylglycerol (Glc2-DAG), were purified, of which only Glc-DAG triggered Mincle reporter cell activation and professional phagocyte responses. Proteomic profiling revealed that Glc2-DAG blocked Glc-DAG–induced cytokine responses, thereby acting as inhibitor of Glc-DAG/Mincle signaling. WT mice responded to S aureus with a similar lung pathology as Mincle KO mice, most likely due to Glc2-DAG–dependent inhibition of Glc-DAG/Mincle signaling. In contrast, ectopic Mincle expression caused severe lung pathology in S aureus –infected mice, characterized by bacterial outgrowth and fatal pneumonia. Collectively, Glc2-DAG inhibits Glc-DAG/Mincle–dependent responses in WT mice, whereas sustained Mincle expression overrides Glc2-DAG–mediated inhibitory effects, conferring increased host susceptibility to S aureus. [ABSTRACT FROM AUTHOR]

Cell death is an important process in the body, as it occurs throughout every tissue during development, disease, and tissue regeneration. Phagocytes are responsible for clearing away dying cells and are typically characterized as either professional or nonprofessional phagocytes. Professional phagocytes, such as macrophages, are found in nearly every part of the body while nonprofessional phagocytes, such as epithelial cells, are found in every tissue type. However, there are organs that are considered “immune-privileged” as they have little to no immune surveillance and rely on nonprofessional phagocytes to engulf dying cells. These organs are surrounded by barriers to protect the tissue from viruses, bacteria, and perhaps even immune cells. The Drosophila ovary is considered immune-privileged, however the presence of hemocytes, the macrophages of Drosophila, around the ovary suggests they may have a potential function. Here we analyze hemocyte localization and potential functions in response to starvation-induced cell death in the ovary. Hemocytes were found to accumulate in the oviduct in the vicinity of mature eggs and follicle cell debris. Genetic ablation of hemocytes revealed that the presence of hemocytes affects oogenesis and that they phagocytose ovarian cell debris and in their absence fecundity decreases. Unpaired3, an IL-6 like cytokine, was found to be required for the recruitment of hemocytes to the oviduct to clear away obsolete follicle cells. These findings demonstrate a role for hemocytes in the ovary, providing a more thorough understanding of phagocyte communication and cell clearance in a previously thought immune-privileged organ. [ABSTRACT FROM AUTHOR]

The rising prevalence of fungal infections is a significant and growing public health threat, and this risk is further underscored by our incomplete understanding of why organs like the kidney are so susceptible to systemic candidiasis. To combat the high mortality of such infections, we urgently need to advance our understanding of fungal pathogenesis and how it articulates with human immune response. Now, a recent landmark study has illuminated a crucial role of the complement system in the response to candidiasis and determined the stepwise local response of phagocytes within the kidney during infection. These fundamental discoveries provide crucial insights that can be leveraged to improve the care and outcome for patients with fungal infections. [ABSTRACT FROM AUTHOR]

(1) Background: Macrophagic myofasciitis (MMF) is an inflammatory histopathological lesion demonstrating long-term biopersistence of vaccine-derived aluminum adjuvants within muscular phagocytic cells. Affected patients suffer from widespread myalgia and severe fatigue consistent with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), a poorly understood disorder suspected to result from chronic immune stimulation by infectious and inorganic particles. (2) Methods: In this study we determined the immuno-metabolic properties of MMF phagocytic cells compared to controls, at rest and upon exposure to aluminum oxyhydroxide adjuvant, with or without adsorbed antigens, using protein quantification and an oxygen consumption assay. (3) Results: MMF and control cells similarly internalized the adjuvant and vaccine but MMF cells specifically expressed Rubicon and Nox2, two molecules unique to the LC3-associated phagocytosis (LAP) machinery, a non-canonical autophagic pathway able to downregulate canonical autophagy. MMF cells exhibited an altered inflammatory secretome, producing more pain-inducing CXC chemokines and less TNF-α than controls, consistent with chronic myalgia and exhaustion of the immune system previously documented in ME/CFS. MMF cells exhibited mitochondrial metabolism dysfunction, with exacerbated reaction to adjuvanted vaccine, contrasting with limited spare respiratory capacity and marked proton leak weakening energy production. (4) Conclusions: MMF phagocytes seemingly use LAP to handle aluminum oxyhydroxide vaccine particles, secrete pain-inducing molecules, and exhibit exacerbated metabolic reaction to the vaccine with limited capacity to respond to ongoing energetic requests. [ABSTRACT FROM AUTHOR]

Ex vivo expansion of human CD34+ hematopoietic stem and progenitor cells remains a challenge due to rapid differentiation after detachment from the bone marrow niche. In this study, we assessed the capacity of an inducible fusion protein to enable sustained ex vivo proliferation of hematopoietic precursors and their capacity to differentiate into functional phagocytes. We fused the coding sequences of an FK506-Binding Protein 12 (FKBP12)-derived destabilization domain (DD) to the myeloid/lymphoid lineage leukemia/eleven nineteen leukemia (MLL-ENL) fusion gene to generate the fusion protein DD-MLL-ENL and retrovirally expressed the protein switch in human CD34+ progenitors. Using Shield1, a chemical inhibitor of DD fusion protein degradation, we established large-scale and long-term expansion of late monocytic precursors. Upon Shield1 removal, the cells lost self-renewal capacity and spontaneously differentiated, even after 2.5 y of continuous ex vivo expansion. In the absence of Shield1, stimulation with IFN-Y, LPS, and GM-CSF triggered terminal differentiation. Gene expression analysis of the obtained phagocytes revealed marked similarity with naive monocytes. In functional assays, the novel phagocytes migrated toward CCL2, attached to VCAM-1 under shear stress, produced reactive oxygen species, and engulfed bacterial particles, cellular particles, and apoptotic cells. Finally, we demonstrated FcY receptor recognition and phagocytosis of opsonized lymphoma cells in an antibody-dependent manner. Overall, we have established an engineered protein that, as a single factor, is useful for large-scale ex vivo production of human phagocytes. Such adjustable proteins have the potential to be applied as molecular tools to produce functional immune cells for experimental cell-based approaches. [ABSTRACT FROM AUTHOR]

Mycobacterium avium subsp. paratuberculosis (Map) is the etiological agent of paratuberculosis (PTB), a chronic intestinal inflammatory disease that causes high economical losses in dairy livestock worldwide. Due to the absence of widely available preventive or therapeutical treatments, new alternative therapies are needed. In this study, the effect of a probiotic alone or in combination with a commercial vaccine has been evaluated in a rabbit model. Vaccination enhanced the humoral response, exerted a training effect of peripheral polymorphonuclear neutrophils (PMNs) against homologous and heterologous stimuli, stimulated the release of pro-inflammatory cytokines by gut-associated lymphoid tissue (GALT) macrophages, and reduced the bacterial burden in GALT as well. However, the administration of the probiotic after vaccination did not affect the PMN activity, increased metabolic demand, and supressed pro-inflammatory cytokines, although humoral response and bacterial burden decrease in GALT was maintained similar to vaccination alone. The administration of the probiotic alone did not enhance the humoral response or PMN activity, and the bacterial burden in GALT was further increased compared to the only challenged group. In conclusion, the probiotic was able to modulate the immune response hampering the clearance of the infection and was also able to affect the response of innate immune cells after vaccination. This study shows that the administration of a probiotic can modulate the immune response pathways triggered by vaccination and/or infection and even exacerbate the outcome of the disease, bringing forward the importance of verifying treatment combinations in the context of each particular infectious agent. [ABSTRACT FROM AUTHOR]

Phagocytes maintain homeostasis in a healthy brain. Upon injury, they are essential for repairing damaged tissue, recruiting other immune cells, and releasing cytokines as the first line of defense. However, there seems to be a delicate balance between the beneficial and detrimental effects of their activation in a seizing brain. Blocking the infiltration of peripheral phagocytes (macrophages) or their depletion can partially alleviate epileptic seizures and prevent the death of neurons in experimental models of epilepsy. However, the depletion of resident phagocytes in the brain (microglia) can aggravate disease outcomes. This review describes the role of resident microglia and peripheral infiltrating monocytes in animal models of acutely triggered seizures and epilepsy. Understanding the roles of phagocytes in ictogenesis and the time course of their activation and involvement in epileptogenesis and disease progression can offer us new biomarkers to identify patients at risk of developing epilepsy after a brain insult, as well as provide novel therapeutic targets for treating epilepsy. [ABSTRACT FROM AUTHOR]

Transmembrane protein 268 (TMEM268) is a novel, tumor growth-related protein first reported by our laboratory. It interacts with the integrin subunit β4 (ITGB4) and plays a positive role in the regulation of the ITGB4/PLEC signaling pathway. Here, we investigated the effects and mechanism of TMEM268 in anti-infectious immune response in mice. Tmem268 knockout in mice aggravated cecal ligation and puncture-induced sepsis, as evidenced by higher bacterial burden in various tissues and organs, congestion, and apoptosis. Moreover, Tmem268 deficiency in mice inhibited phagocyte adhesion and migration, thus decreasing phagocyte infiltration at the site of infection and complement-dependent phagocytosis. Further findings indicated that TMEM268 interacts with CD11b and inhibits its degradation via the endosome–lysosome pathway. Our results reveal a positive regulatory role of TMEM268 in β2 integrin-associated anti-infectious immune responses and signify the potential value of targeting the TMEM268–CD11b signaling axis for the maintenance of immune homeostasis and immunotherapy for sepsis and related immune disorders. Synopsis: TMEM268 interacts with the β2 integrin subunit CD11b and attenuates its degradation via the endosome–lysosome pathway, thereby promoting phagocyte adhesion, migration, phagocytosis and bacterial clearance during sepsis. Tmem268 -deficiency impairs bacterial clearance and aggravates CLP-induced sepsis. Tmem268 -deficiency suppresses phagocyte adhesion, migration and phagocytosis by downregulating CD11b. Tmem268 knockout promotes CD11b degradation via the endosomal–lysosomal pathway. TMEM268 interacts with the β2 integrin subunit CD11b and attenuates its degradation via the endosome–lysosome pathway, thereby promoting phagocyte adhesion, migration, phagocytosis and bacterial clearance during sepsis. [ABSTRACT FROM AUTHOR]

Hepatocellular carcinoma (HCC) acquires an immunosuppressive microenvironment, leading to unbeneficial therapeutic outcomes. Hyaluronan-mediated motility receptor (HMMR) plays a crucial role in tumor progression. Here, we found that aberrant expression of HMMR could be a predictive biomarker for the immune suppressive microenvironment of HCC, but the mechanism remains unclear. We established an HMMR-/- liver cancer mouse model to elucidate the HMMR-mediated mechanism of the dysregulated "don't eat me" signal. HMMR knockout inhibited liver cancer growth and induced phagocytosis. HMMRhigh liver cancer cells escaped from phagocytosis via sustaining CD47 signaling. Patients with HMMRhighCD47high expression showed a worse prognosis than those with HMMRlowCD47low expression. HMMR formed a complex with FAK/SRC in the cytoplasm to activate NF-ΰB signaling, which could be independent of membrane interaction with CD44. Notably, targeting HMMR could enhance anti-PD-1 treatment efficiency by recruiting CD8+ T cells. Overall, our data revealed a regulatory mechanism of the "don't eat me" signal and knockdown of HMMR for enhancing anti-PD-1 treatment. [ABSTRACT FROM AUTHOR]

Essential for reactive oxygen species (EROS) protein is a recently identified molecular chaperone of NOX2 (gp91phox), the catalytic subunit of phagocyte NADPH oxidase. Deficiency in EROS is a recently identified cause for chronic granulomatous disease, a genetic disorder with recurrent bacterial and fungal infections. Here, we report a cryo-EM structure of the EROS-NOX2-p22phox heterotrimeric complex at an overall resolution of 3.56Å. EROS and p22phox are situated on the opposite sides of NOX2, and there is no direct contact between them. EROS associates with NOX2 through two antiparallel transmembrane (TM) α-helices and multiple β-strands that form hydrogen bonds with the cytoplasmic domain of NOX2. EROS binding induces a 79° upward bend of TM2 and a 48° backward rotation of the lower part of TM6 in NOX2, resulting in an increase in the distance between the two hemes and a shift of the binding site for flavin adenine dinucleotide (FAD). These conformational changes are expected to compromise superoxide production by NOX2, suggesting that the EROS-bound NOX2 is in a protected state against activation. Phorbol myristate acetate, an activator of NOX2 in vitro, is able to induce dissociation of NOX2 from EROS with concurrent increase in FAD binding and superoxide production in a transfected COS-7 model. In differentiated neutrophil-like HL-60, the majority of NOX2 on the cell surface is dissociated with EROS. Further studies are required to delineate how EROS dissociates from NOX2 during its transport to cell surface, which may be a potential mechanism for regulation of NOX2 activation. [ABSTRACT FROM AUTHOR]

Aim: Cystic fibrosis (CF) is an autosomal recessive disorder. Although it is considered as an epithelial disease due to impaired chloride transport, its pathogenesis remains unclear. CF is classified as a syndrome with congenital defects of phagocyte in recent human inborn errors of immunity phenotypic classifications. Neutrophils are the most effective cells in the eradication of bacterial infections such as Pseudomonas aeruginosa. The aim of the present study was to investigate the phagocyte functions in pseudomonas colonized CF patients. Materials and Methods: A total number of 26 pseudomonas colonized CF patients and 21 healthy controls (gender and age matched) were included in this study. Absolute neutrophil counts (ANC), immunoglobulin values (Ig), the Migratest to evaluate chemotaxis in neutrophils and monocytes, CD11A/CD18/CD15 S (b2 integrin) adhesion molecules, and the Phagoburst test for intracellular bacterial killing were analyzed by flow cytometer. Results: ANC, CD15S expression on neutrophils and IgG, IgA and IgM levels were higher in the CF patients than the control group (p<0.01). The neutrophils oxidative burst activity and the chemotactic ability of the CF patients did not differ from those of the controls. Patients with allergic bronchopulmonary aspergillosis and those with a mutation of 2183AA>G had significantly lower chemotaxis indexes than the others (p=0.01, p=0.01 respectively). Conclusion: Our results from a small group of patients does not support impaired functions such as migration and phagocytosis of neutrophils in patients with CF. Further studies involving more CF patients are needed to make a definitive interpretation. [ABSTRACT FROM AUTHOR]

Vomocytosis, also known as nonlytic exocytosis, is a process whereby fully phagocytosed microbes are expelled from phagocytes without discernible damage to either the phagocyte or microbe. Although this phenomenon was first described in the opportunistic fungal pathogen Cryptococcus neoformans in 2006, to date, mechanistic studies have been hampered by an inability to reliably stimulate or inhibit vomocytosis. Here we present the fortuitous discovery that macrophages lacking the scavenger receptor MAcrophage Receptor with COllagenous domain (MARCO), exhibit near‐total vomocytosis of internalised cryptococci within a few hours of infection. Marco−/− macrophages also showed elevated vomocytosis of a yeast‐locked C. albicans strain, suggesting this to be a broadly relevant observation. We go on to show that MARCO's role in modulating vomocytosis is independent of its role as a phagocytic receptor, suggesting that this protein may play an important and hitherto unrecognised role in modulating macrophage behaviour. [ABSTRACT FROM AUTHOR]

Brucella spp. are facultatively intracellular bacteria that can infect, survive, and multiply in various host cell types in vivo and/or in vitro. The genus Brucella has markedly expanded in recent years with the identification of novel species and hosts, which has revealed additional information about the cell and tissue tropism of these pathogens. Classically, Brucella spp. are considered to have tropism for organs that contain large populations of phagocytes such as lymph nodes, spleen, and liver, as well as for organs of the genital system, including the uterus, epididymis, testis, and placenta. However, experimental infections of several different cultured cell types indicate that Brucella may actually have a broader cell tropism than previously thought. Indeed, recent studies indicate that certain Brucella species in particular hosts may display a pantropic distribution in vivo. This review discusses the available knowledge on cell and tissue tropism of Brucella spp. in natural infections of various host species, as well as in experimental animal models and cultured cells.

Efferocytosis is defined as the highly effective phagocytic removal of apoptotic cells (ACs) by professional or non-professional phagocytes. Tissue-resident professional phagocytes ("efferocytes"), such as macrophages, have high phagocytic capacity and are crucial to resolve inflammation and aid in homeostasis. Recently, numerous exciting discoveries have revealed divergent (and even diametrically opposite) findings regarding metabolic immune reprogramming associated with efferocytosis by macrophages. In this review, we highlight the key metabolites involved in the three phases of efferocytosis and immune reprogramming of macrophages under physiological and pathological conditions. The next decade is expected to yield further breakthroughs in the regulatory pathways and molecular mechanisms connecting immunological outcomes to metabolic cues as well as avenues for "personalized" therapeutic intervention. [ABSTRACT FROM AUTHOR]

Macrophages and microglia are professional phagocytes that sense and migrate toward "eat-me" signals. The role of phagocytic cells is to maintain homeostasis by engulfing senescent or apoptotic cells, debris, and abnormally aggregated macromolecules. Usually, dying cells send out "find-me" signals, facilitating the recruitment of phagocytes. Healthy cells can also promote or inhibit the phagocytosis phenomenon of macrophages and microglia by tuning the balance between "eat-me" and "don't-eat-me" signals at different stages in their lifespan, while the "don't-eat-me" signals are often hijacked by tumor cells as a mechanism of immune evasion. Using a combination of bioinformatic analysis and spatial profiling, we delineate the balance of the "don't-eat-me" CD47/SIRPα and "eat-me" CALR/STC1 ligand–receptor interactions to guide therapeutic strategies that are being developed for glioblastoma sequestered in the central nervous system (CNS). [ABSTRACT FROM AUTHOR]

Introduction: The California purple sea urchin, Strongylocentrotus purpuratus, relies solely on an innate immune system to combat the many pathogens in the marine environment. One aspect of their molecular defenses is the SpTransformer (SpTrf) gene family that is upregulated in response to immune challenge. The gene sequences are highly variable both within and among animals and likely encode thousands of SpTrf isoforms within the sea urchin population. The native SpTrf proteins bind foreign targets and augment phagocytosis of a marine Vibrio. A recombinant (r)SpTrf-E1-Ec protein produced by E. coli also binds Vibrio but does not augment phagocytosis. Methods: To address the question of whether other rSpTrf isoforms function as opsonins and augment phagocytosis, six rSpTrf proteins were expressed in insect cells. Results: The rSpTrf proteins are larger than expected, are glycosylated, and one dimerized irreversibly. Each rSpTrf protein cross-linked to inert magnetic beads (rSpTrf::beads) results in different levels of surface binding and phagocytosis by phagocytes. Initial analysis shows that significantly more rSpTrf::beads associate with cells compared to control BSA::beads. Binding specificity was verified by pre-incubating the rSpTrf::beads with antibodies, which reduces the association with phagocytes. The different rSpTrf::beads show significant differences for cell surface binding and phagocytosis by phagocytes. Furthermore, there are differences among the three distinct types of phagocytes that show specific vs. constitutive binding and phagocytosis. Conclusion: These findings illustrate the complexity and effectiveness of the sea urchin innate immune system driven by the natSpTrf proteins and the phagocyte cell populations that act to neutralize a wide range of foreign pathogens. [ABSTRACT FROM AUTHOR]

Inhibitory natural killer (NK) cell receptors recognize MHC class I (MHC-I) in trans on target cells and suppress cytotoxicity. Some NK cell receptors recognize MHC-I in cis, but the role of this interaction is uncertain. Ly49Q, an atypical Ly49 receptor expressed in non-NK cells, binds MHC-I in cis and mediates chemotaxis of neutrophils and type I interferon production by plasmacytoid dendritic cells. We identified a lipid-binding motif in the juxtamembrane region of Ly49Q and found that Ly49Q organized functional membrane domains comprising sphingolipids via sulfatide binding. Ly49Q recruited actin-remodeling molecules to an immunoreceptor tyrosine-based inhibitory motif, which enabled the sphingolipid-enriched membrane domain to mediate complicated actin remodeling at the lamellipodia and phagosome membranes during phagocytosis. Thus, Ly49Q facilitates integrative regulation of proteins and lipid species to construct a cell type-specific membrane platform. Other Ly49 members possess lipid binding motifs; therefore, membrane platform organization may be a primary role of some NK cell receptors. [ABSTRACT FROM AUTHOR]

Purpose: Behçet's disease (BD) is an autoimmune chronic systemic inflammatory disease characterized by a versatile clinical spectrum. Growth arrest specific protein 6 (GAS6)/soluble AXL (sAXL) signaling pathway draws attention in the resolution of inflammation, and its deficiency is associated with chronic inflammatory, autoimmune diseases, as well as clearance of apoptotic cells by phagocytes - efferocytosis. In this study, it was aimed to investigate whether GAS6/sAXL, interleukin (IL)-10, nitric oxide (NO), and BCL-2 levels were associated with inflammation and efferocytosis contributes to the pathogenesis of BD. Methods: A total of 37 Behçet patients with ocular involvement and 30 healthy control subjects were included in this study. GAS6, sAXL, IL-10, NO, and BCL-2 levels were quantified using enzyme-linked immunosorbent assay (ELISA) method. Results: Serum GAS6, sAXL, IL-10, NO, and BCL-2 levels were significantly lower in patients with BD compared to the controls (P < 0.005, P < 0.001, P < 0.001, P < 0.001, and P < 0.001, respectively). In correlation analysis, research parameters decreased in patients with BD was significantly correlated with each other: GAS6-IL-10 (r = 0.585, P < 0.001), GAS6-BCL-2 (r = 0.541, P < 0.001), sAXL-BCL-2 (r = 0.696, P < 0.001), IL-10-NO (r = 0.717, P < 0.001), IL-10-BCL-2 (r = 0.759, P < 0.001), and NO-BCL-2 (r = 0.541, P < 0.001). Conclusion: In conclusion, decreased serum BCL-2 level may be an indicator of increased apoptosis in these patients and decreased levels of GAS6/sAXL, IL-10, and NO may indicate insufficient clearance of apoptotic bodies released as a result of increased apoptosis in BD patients. [ABSTRACT FROM AUTHOR]

Staphylococcus aureus, the principal causative agent of osteomyelitis, can be internalized by osteoblasts and thereby escape from immune phagocytes and many kinds of antibiotics. To deliver antibiotics into osteoblasts to kill S. aureus in the intracellular environment, we developed gentamicin-loaded chitosan nanoparticles and evaluated their intracellular bactericidal effect. We found decreased numbers of S. aureus cells in infected osteoblasts treated with gentamicin-loaded chitosan nanoparticles. The cytotoxicity of the nanoparticles was evaluated by CCK-8 assay. There was no significant viability decrease at all tested concentrations. In conclusion, our results provide evidence for the potential use of gentamicin-loaded chitosan nanoparticles to enhance the delivery of gentamicin into cells and for their antibacterial effect against internalized S. aureus in the intracellular environment of osteoblasts. [ABSTRACT FROM AUTHOR]

Background: People with alcohol use disorder (AUD) have an increased risk of developing pneumonia and pulmonary diseases. Alveolar macrophages (AMs) are immune cells of the lower respiratory tract that are necessary for clearance of pathogens. However, alcohol causes AM oxidative stress, mitochondrial damage and dysfunction, and diminished phagocytic capacity, leading to lung injury and immune suppression. Methods: AMs were isolated by bronchoalveolar lavage from people with AUD and male and female C57BL/6J mice given chronic ethanol (20% w/v, 12 weeks) in drinking water. The peroxisome proliferator‐activated receptor γ ligand, pioglitazone, was used to treat human AMs ex vivo (10 μM, 24 h) and mice in vivo by oral gavage (10 mg/kg/day). Levels of AM mitochondrial superoxide and hypoxia‐inducible factor‐1 alpha (HIF‐1α) mRNA, a marker of oxidative stress, were measured by fluorescence microscopy and RT‐qPCR, respectively. Mouse AM phagocytic ability was determined by internalized Staphylococcus aureus, and mitochondrial capacity, dependency, and flexibility for glucose, long‐chain fatty acid, and glutamine oxidation were measured using an extracellular flux analyzer. In vitro studies used a murine AM cell line, MH‐S (±0.08% ethanol, 72 h) to investigate mitochondrial fuel oxidation and ATP‐linked respiration. Results: Pioglitazone treatment decreased mitochondrial superoxide in AMs from people with AUD and ethanol‐fed mice and HIF‐1α mRNA in ethanol‐fed mouse lungs. Pioglitazone also reversed mouse AM glutamine oxidation and glucose or long‐chain fatty acid flexibility to meet basal oxidation needs. In vitro, ethanol decreased the rate of AM mitochondrial and total ATP production, and pioglitazone improved changes in glucose and glutamine oxidation. Conclusions: Pioglitazone reversed chronic alcohol‐induced oxidative stress in human AM and mitochondrial substrate oxidation flexibility and superoxide levels in mouse AM. Decreased ethanol‐induced AM HIF‐1α mRNA with pioglitazone suggests that this pathway may be a focus for metabolic‐targeted therapeutics to improve morbidity and mortality in people with AUD. [ABSTRACT FROM AUTHOR]

Background: Retinal degeneration results from disruptions in retinal homeostasis due to injury, disease, or aging and triggers peripheral leukocyte infiltration. Effective immune responses rely on coordinated actions of resident microglia and recruited macrophages, critical for tissue remodeling and repair. However, these phagocytes also contribute to chronic inflammation in degenerated retinas, yet the precise coordination of immune response to retinal damage remains elusive. Recent investigations have demonstrated that phagocytic cells can produce extracellular traps (ETs), which are a source of self-antigens that alter the immune response, which can potentially lead to tissue injury. Methods: Innovations in experimental systems facilitate real-time exploration of immune cell interactions and dynamic responses. We integrated in vivo imaging with ultrastructural analysis, transcriptomics, pharmacological treatments, and knockout mice to elucidate the role of phagocytes and their modulation of the local inflammatory response through extracellular traps (ETs). Deciphering these mechanisms is essential for developing novel and enhanced immunotherapeutic approaches that can redirect a specific maladaptive immune response towards favorable wound healing in the retina. Results: Our findings underscore the pivotal role of innate immune cells, especially macrophages/monocytes, in regulating retinal repair and inflammation. The absence of neutrophil and macrophage infiltration aids parenchymal integrity restoration, while their depletion, particularly macrophages/monocytes, impedes vascular recovery. We demonstrate that macrophages/monocytes, when recruited in the retina, release chromatin and granular proteins, forming ETs. Furthermore, the pharmacological inhibition of ETosis support retinal and vascular repair, surpassing the effects of blocking innate immune cell recruitment. Simultaneously, the absence of ETosis reshapes the inflammatory response, causing neutrophils, helper, and cytotoxic T-cells to be restricted primarily in the superficial capillary plexus instead of reaching the damaged photoreceptor layer. Conclusions: Our data offer novel insights into innate immunity's role in responding to retinal damage and potentially help developing innovative immunotherapeutic approaches that can shift the immune response from maladaptive to beneficial for retinal regeneration. [ABSTRACT FROM AUTHOR]

Introduction: Modern fish farming faces challenges in sourcing feed ingredients, most related with their prices, 21 availability, and specifically for plant protein sources, competition for the limited cultivation space for 22 vegetable crops. In that sense, halophytes have the added value of being rich in valuable bioactive compounds and salt tolerant. This study assessed the inclusion of non-food fractions of S. ramosissima in European seabass diets. Methods: Different levels (2.5%, 5%, and 10%) were incorporated into seabass diets, replacing wheat meal (diets ST2.5, ST5, and ST10) or without inclusion (CTRL). Experimental diets were administered to seabass juveniles (8.62 ± 0.63 g) for 34 and 62 days and subsequent inflammatory responses to a heat-inactivated Photobacterium damselae subsp. piscicida (Phdp) were evaluated in a time-course manner (4, 24, 48, and 72 h after the challenge). At each sampling point, seabass haematological profile, plasma immune parameters, and head-kidney immune-related gene expression were evaluated. Results: After both feeding periods, most parameters remained unaltered by S. ramosissima inclusion; nonetheless, seabass fed ST10 showed an upregulation of macrophage colony-stimulating factor 1 receptor 1 (mcsf1r1) and cluster of differentiation 8 (cd8β) compared with those fed CTRL after 62 days of feeding. Regarding the inflammatory response, seabass fed ST10 showed lower plasma lysozyme levels than their counterparts fed ST2.5 and ST5 at 24 h following injection, while 4 h after the inflammatory stimulus, seabass fed ST10 presented higher numbers of peritoneal leucocytes than fish fed CTRL. Moreover, at 4 h, fish fed ST2.5, ST5, and ST10 showed a higher expression of interleukin 1β (il1β), while fish fed ST5 showed higher levels of ornithine decarboxylase (odc) than those fed CTRL. An upregulation of macrophage colony-stimulating factor 1 receptor 1 (mcsf1r1) and glutathione peroxidase (gpx) was also observed at 72 h in fish fed ST10 or ST5 and ST10 compared with CTRL, respectively. Discussion: In conclusion, incorporating up to 10% of the non-food fraction S. ramosissima in feed did not compromise seabass growth or immune status after 62 days, aligning with circular economy principles. However, S. ramosissima inclusion improved the leucocyte response and upregulated key immune-related genes in seabass challenged with an inactivated pathogen. [ABSTRACT FROM AUTHOR]

Disulfiram (DSF), an anti-alcoholism medicine, exerts treatment effects in patients suffering from persistent Borreliosis and also exhibits anti-cancer effects through its copper chelating derivatives and induction of oxidative stress in mitochondria. Since chronic/persistent borreliosis is characterized by increased amounts of pro-inflammatory macrophages, this study investigated opsonin-independent phagocytosis, migration, and surface marker expression of in vivo activated and in vitro cultured human monocyte-derived phagocytes (macrophages and dendritic cells) with and without DSF treatment. Phagocytosis of non-opsonized Dynabeads® M-450 and migration of macrophages and dendritic cells were monitored using live cell analyzer Juli™ Br for 24 h, imaging every 3.5 min. To simultaneously monitor phagocyte function, results were analyzed by a newly developed software based on the differential phase contrast images of cells before and after ingestion of Dynabeads. DSF decreased the phagocytic capacities exhibited by in vitro enriched and long-lived phagocytes. Although no chemotactic gradient was applied to the test system, vigorous spontaneous migration was observed. We therefore set up an algorithm to monitor and quantify both phagocytosis and migration simultaneously. DSF not only reduced phagocytosis in a majority of these long-lived phagocytes but also impaired their migration. Despite these selective effects by DSF, we found that DSF reduced the expression densities of surface antigens CD45 and CD14 in all of our long-lived phagocytes. In cells with a high metabolic activity and high mitochondrial contents, DSF led to cell death corresponding to mitochondrial oxidative stress, whereas metabolically inactive phagocytes survived our DSF treatment protocol. In conclusion, DSF affects the viability of metabolically active phagocytes by inducing mitochondrial stress and secondly attenuates phagocytosis and migration in some long-lived phagocytes. [ABSTRACT FROM AUTHOR]

Summary: Since their description by Metchnikoff in 1905, phagocytes have been increasingly recognized to be the entities that traffic to sites of infection and inflammation, engulf and kill infecting organisms, and clear out apoptotic debris all the while making antigens available and accessible to the lymphoid organs for future use. Therefore, phagocytes provide the gateway and the first check in host protection and immune response. Disorders in killing and chemotaxis lead not only to infection susceptibility, but also to autoimmunity. We aim to describe chronic granulomatous disease and the leukocyte adhesion deficiencies as well as myeloperoxidase deficiency and G6PD deficiency as paradigms of critical pathways. [ABSTRACT FROM AUTHOR]

Human fungal pathogens are a deadly and underappreciated risk to global health that most severely affect immunocompromised individuals. A virulence attribute shared by some of the most clinically relevant fungal species is their ability to survive inside macrophages and escape from these immune cells. In this review, we discuss the mechanisms behind intracellular survival and elaborate how escape is mediated by lytic and non‐lytic pathways as well as strategies to induce programmed host cell death. We also discuss persistence as an alternative to rapid host cell exit. In the end, we address the consequences of fungal escape for the host immune response and provide future perspectives for research and development of targeted therapies. [ABSTRACT FROM AUTHOR]

IntroductionVisceral leishmaniasis (VL) is an important tropical and neglected disease and represents a serious global health problem. The initial interaction between the phagocytes and the parasite is crucial to determine the pathogen’s capacity to initiate infection and it shapes the subsequent immune response that will develop. While type-1 T-cells induce IL-6, IL-1β, TNF-α, and IL-12 production by monocytes/macrophages to fight the infection, type-2 T-cells are associated with a regulatory phenotype (IL-10 and TGF-β) and successful infection establishment. Recently, our group demonstrated the role of an important Th1/Th17 T-cell population, the mucosal-associated invariant T (MAIT) cells, in VL. MAIT cells can respond to L. infantum by producing TNF-α and IFN-γ upon MR1-dependent activation.Objective and methodsHere, we describe the impact of the MR1-blockage on L. infantum internalization on the functional profile of circulating neutrophils and monocytes as well as the impact of the MR1-blockage on the soluble mediator signatures of in vitro whole blood cultures.ResultsOverall, our data showed that VL patients presents higher percentage of activated neutrophils than asymptomatic and non-infected controls. In addition, MR1 blockade led to lower TNF-α and TGF-β production by non-activated neutrophils from asymptomatic individuals. Moreover, TNF-α and IL-10 production by monocytes was higher in VL patients. In the analysis of soluble mediators produced in vitro, MR1-blockade induced a decrease of IFN-γ and an increase of IL-10, IL-27 and IL-33 in the cell cultures of AS group, a cytokine pattern associated with type 2 deleterious response.Discussion and conclusionThese data corroborate the hypothesis that MR1-restricted responses are associated to a protective role during Leishmania infection.

Pseudomonas aeruginosa is a Gram‐negative bacterium and an opportunistic pathogen ubiquitously present throughout nature. LecB, a fucose‐, and mannose‐binding lectin, is a prominent virulence factor of P. aeruginosa, which can be expressed on the bacterial surface but also be secreted. However, the LecB interaction with human immune cells remains to be characterized. Neutrophils comprise the first line of defense against infections and their production of reactive oxygen species (ROS) and release of extracellular traps (NETs) are critical antimicrobial mechanisms. When profiling the neutrophil glycome we found several glycoconjugates on granule and plasma membranes that could potentially act as LecB receptors. In line with this, we here show that soluble LecB can activate primed neutrophils to produce high levels of intracellular ROS (icROS), an effect that was inhibited by methyl fucoside. On the other hand, soluble LecB inhibits P. aeruginosa‐induced icROS production. In support of that, during phagocytosis of wild‐type and LecB‐deficient P. aeruginosa, bacteria with LecB induced less icROS production as compared with bacteria lacking the lectin. Hence, LecB can either induce or inhibit icROS production in neutrophils depending on the circumstances, demonstrating a novel and potential role for LecB as an immunomodulator of neutrophil functional responses. [ABSTRACT FROM AUTHOR]

Streptococcus uberis is frequently isolated from milk collected from dairy cows with mastitis. According to the host's immunity, bacterial virulence, and their interaction, infection with some strains can induce persistent subclinical inflammation, while infection with others induces severe inflammation and transient mastitis. This study compared the inflammatory response of milk-isolated white blood cells (mWBCs) to persistent and transient S. uberis strains. Quarter milk samples were collected aseptically for bacterial culture from all lactating cows once a week over a 10-week period. A transient and noncapsular strain with a 1-week intramammary infection duration was selected from this herd, while a persistent and capsular S. uberis strain with an intramammary infection longer than 2 months from our previous study was selected based on an identical pulse field gel electrophoresis pattern during the IMI episode. Cellular and molecular responses of mWBCs were tested, and the data were analyzed using repeated analysis of variance. The results showed a higher response in migration, reactive oxygen species generation, and bacterial killing when cells were stimulated with transient S. uberis. In contrast, the persistent strain led to increased neutrophil extracellular trap release. This study also highlighted several important molecular aspects of mWBCs. Gene expression analyses by real-time RT-PCR revealed a significant elevation in the expression of Toll-like receptors (TLR-1, TLR-2, TLR-6) and proinflammatory cytokines (tumor necrosis factor-alpha or TNF-α) with the transient strain. Additionally, Streptococcus uberis capsule formation might contribute to the capability of these strains to induce different immune responses. Altogether, these results focus on the immune function of activated mWBCs which demonstrate that a transient strain can elicit a stronger local immune response and, subsequently, lead to rapid recovery from mastitis. [ABSTRACT FROM AUTHOR]

Ingestion and killing of bacteria by phagocytic cells are critical processes to protect the human body from bacterial infections. In addition, some immune cells (neutrophils, NK cells) can release microbicidal molecules in the extracellular medium to eliminate non‐ingested microorganism. Molecular mechanisms involved in the resulting intracellular and extracellular killing are still poorly understood. In this study, we used the amoeba Dictyostelium discoideum as a model phagocyte to investigate the mechanisms allowing intracellular and extracellular killing of Pseudomonas aeruginosa. When a D. discoideum cell establishes a close contact with a P. aeruginosa bacterium, it can either ingest it and kill it in phagosomes, or kill it extracellularly, allowing a direct side‐by‐side comparison of these two killing modalities. Efficient intracellular destruction of P. aeruginosa requires the presence of the Kil2 pump in the phagosomal membrane. On the contrary, extracellular lysis is independent on Kil2 but requires the expression of the superoxide‐producing protein NoxA, and the extracellular release of the AplA bacteriolytic protein. These results shed new light on the molecular mechanisms allowing elimination of P. aeruginosa bacteria by phagocytic cells. [ABSTRACT FROM AUTHOR]

Rapid removal of apoptotic cells by phagocytes, a process known as efferocytosis, is key for the maintenance of tissue homeostasis, the resolution of inflammation, and tissue repair. However, impaired efferocytosis can result in the accumulation of apoptotic cells, subsequently triggering sterile inflammation through the release of endogenous factors such as DNA and nuclear proteins from membrane permeabilized dying cells. Here, we review the molecular basis of the three key phases of efferocytosis, that is, the detection, uptake, and degradation of apoptotic materials by phagocytes. We also discuss how defects in efferocytosis due to the alteration of phagocytes and dying cells can contribute to the low-grade chronic inflammation that occurs during aging, described as inflammaging. Lastly, we explore opportunities in targeting and harnessing the efferocytic machinery to limit aging-associated inflammatory diseases. [ABSTRACT FROM AUTHOR]

Introduction: Looking into the literature, many articles accuse bacterial persister cells as important causes of infection relapse/recalcitrance. This opinion paper, highlights the knowledge gaps and scientific misconceptions in experimental procedures regarding the role of persisters in relapse/recalcitrance of infections and recommends a roadmap for investigations in this field. Conclusion: It is debated in this paper, that unless the queries and missing points are addressed clearly, persisters cannot be stigmatized as the culprit of infection relapse/recalcitrance. [ABSTRACT FROM AUTHOR]