Association of Fcgamma receptor IIb polymorphism with susceptibility to systemic lupus erythematosus in Chinese: a common susceptibility gene in the Asian populations

Fc gamma receptors: Their evolution, genomic architecture, genetic variation, and impact on human disease

Fc gamma receptors (FcγRs) are a family of receptors that bind IgG antibodies and interface at the junction of humoral and innate immunity. Precise regulation of receptor expression provides the necessary balance to achieve healthy immune homeostasis by establishing an appropriate immune threshold to limit autoimmunity but respond effectively to infection. The underlying genetics of the FCGR gene family are central to achieving this immune threshold by regulating affinity for IgG, signaling efficacy, and receptor expression. The FCGR gene locus was duplicated during evolution, retaining very high homology and resulting in a genomic region that is technically difficult to study. Here, we review the recent evolution of the gene family in mammals, its complexity and variation through copy number variation and single-nucleotide polymorphism, and impact of these on disease incidence, resolution, and therapeutic antibody efficacy. We also discuss the progress and limitations of current approaches to study the region and emphasize how new genomics technologies will likely resolve much of the current confusion in the field. This will lead to definitive conclusions on the impact of genetic variation within the FCGR gene locus on immune function and disease.

The Immunosuppressive Receptor CD32b Regulation of Macrophage Polarization and Its Implications in Tumor Progression

Macrophages, pivotal components of the immune system, orchestrate host defense mechanisms in humans and mammals. Their polarization into classically activated macrophages (CAMs or M1) and alternatively activated macrophages (AAMs or M2) dictates distinct functional roles in immunity and tissue homeostasis. While the negative regulatory role of CD32b within the FC gamma receptor (FCγR) family is recognized across various immune cell types, its influence on macrophage polarization remains elusive. This study aimed to elucidate the regulatory role of CD32b in macrophage polarization and discern the differential expression markers between the M1 and M2 phenotypes following CD32b siRNA transfection. The results revealed a decrease in the CD32b levels in lipopolysaccharide (LPS)-treated M1 and an increase in interleukin-4 (IL-4)-treated M2 macrophages, as observed in macrophage Raw264.7 cells. Furthermore, CD32b siRNA transfection significantly downregulated the M2 markers (IL-10, VEGF, Arg-1, and STAT6), while upregulating the M1 markers (IL-6, NF-κB, NOS2, and STAT1) in the Raw264.7 cells. Similar findings were recapitulated in macrophage-rich adherent cells isolated from mouse spleens. Additionally, the cytopathological analysis of pleural effusions and ascitic fluids from patients with cancer revealed a positive correlation between advanced tumor stages, metastasis, and elevated CD32b levels. In conclusion, this study highlights the regulatory influence of CD32b in suppressing M1 expression and promoting M2 polarization. Moreover, heightened M2 activation and CD32b levels appear to correlate with tumor progression. A targeted CD32b blockade may serve as a novel therapeutic strategy to inhibit M2 macrophage polarization and is promising for anti-tumor intervention.

The dualistic role of Lyn tyrosine kinase in immune cell signaling: implications for systemic lupus erythematosus

Systemic lupus erythematosus (SLE, lupus) is a debilitating, multisystem autoimmune disease that can affect any organ in the body. The disease is characterized by circulating autoantibodies that accumulate in organs and tissues, which triggers an inflammatory response that can cause permanent damage leading to significant morbidity and mortality. Lyn, a member of the Src family of non-receptor protein tyrosine kinases, is highly implicated in SLE as remarkably both mice lacking Lyn or expressing a gain-of-function mutation in Lyn develop spontaneous lupus-like disease due to altered signaling in B lymphocytes and myeloid cells, suggesting its expression or activation state plays a critical role in maintaining tolerance. The past 30 years of research has begun to elucidate the role of Lyn in a duplicitous signaling network of activating and inhibitory immunoreceptors and related targets, including interactions with the interferon regulatory factor family in the toll-like receptor pathway. Gain-of-function mutations in Lyn have now been identified in human cases and like mouse models, cause severe systemic autoinflammation. Studies of Lyn in SLE patients have presented mixed findings, which may reflect the heterogeneity of disease processes in SLE, with impairment or enhancement in Lyn function affecting subsets of SLE patients that may be a means of stratification. In this review, we present an overview of the phosphorylation and protein-binding targets of Lyn in B lymphocytes and myeloid cells, highlighting the structural domains of the protein that are involved in its function, and provide an update on studies of Lyn in SLE patients.

Serum immunoglobulin and the threshold of Fc receptor-mediated immune activation

Antibodies can mediate immune recruitment or clearance of immune complexes through the interaction of their Fc domain with cellular Fc receptors. Clustering of antibodies is a key step in generating sufficient avidity for efficacious receptor recognition. However, Fc receptors may be saturated with prevailing, endogenous serum immunoglobulin and this raises the threshold by which cellular receptors can be productively engaged. Here, we review the factors controlling serum IgG levels in both healthy and disease states, and discuss how the presence of endogenous IgG is encoded into the functional activation thresholds for low- and high-affinity Fc receptors. We discuss the circumstances where antibody engineering can help overcome these physiological limitations of therapeutic antibodies. Finally, we discuss how the pharmacological control of Fc receptor saturation by endogenous IgG is emerging as a feasible mechanism for the enhancement of antibody therapeutics.

Role of lipid nanodomains for inhibitory FcγRIIb function

The inhibitory Fcγ receptor FcγRIIb is involved in immune regulation and is known to localize to specific regions of the plasma membrane called lipid rafts. Previous studies suggested a link between the altered lateral receptor localization within the plasma membrane and the functional impairment of the FcγRIIb-I232T variant that is associated with systemic lupus erythematosus. Here, we conducted microsecond all-atom molecular dynamics simulations and IgG binding assays to investigate the lipid nano-environment of FcγRIIb monomers and of the FcγRIIb-I232T mutant within a plasma membrane model, the orientation of the FcγRIIb ectodomain, and its accessibility to IgG ligands. In contrast to previously proposed models, our simulations indicated that FcγRIIb does not favor a cholesterol- or a sphingolipid-enriched lipid environment. Interestingly, cholesterol was depleted for all studied FcγRIIb variants within a 2-3 nm environment of the receptor, counteracting the usage of raft terminology for models on receptor functionality. Instead, the receptor interacts with lipids that have poly-unsaturated fatty acyl chains and with (poly-) anionic lipids within the cytosolic membrane leaflet. We also found that FcγRIIb monomers adopt a conformation that is not suitable for binding to its IgG ligand, consistent with a lack of detectable binding of monomeric IgG in experiments on primary immune cells. However, our results propose that multivalent IgG complexes might stabilize FcγRIIb in a binding-competent conformation. We suggest differences in receptor complex formation within the membrane as a plausible cause of the altered membrane localization or clustering and the altered suppressive function of the FcγRIIb-I232T variant.

The Role of Fc Gamma Receptors in Antibody-Mediated Rejection of Kidney Transplants

For the past decades, complement activation and complement-mediated destruction of allograft cells were considered to play a central role in anti-HLA antibody-mediated rejection (AMR) of kidney transplants. However, also complement-independent mechanisms are relevant in the downstream immune activation induced by donor-specific antibodies, such as Fc-gamma receptor (FcγR)-mediated direct cellular activation. This article reviews the literature regarding FcγR involvement in AMR, and the potential contribution of FcγR gene polymorphisms to the risk for antibody mediated rejection of kidney transplants. There is large heterogeneity between the studies, both in the definition of the clinical phenotypes and in the technical aspects. The study populations were generally quite small, except for two larger study cohorts, which obviates drawing firm conclusions regarding the associations between AMR and specific FcγR polymorphisms. Although FcγR are central in the pathophysiology of AMR, it remains difficult to identify genetic risk factors for AMR in the recipient’s genome, independent of clinical risk factors, independent of the donor-recipient genetic mismatch, and in the presence of powerful immunosuppressive agents. There is a need for larger, multi-center studies with standardised methods and endpoints to identify potentially relevant FcγR gene polymorphisms that represent an increased risk for AMR after kidney transplantation.

Acute Kidney Injury Induced Lupus Exacerbation Through the Enhanced Neutrophil Extracellular Traps (and Apoptosis) in Fcgr2b Deficient Lupus Mice With Renal Ischemia Reperfusion Injury

Renal ischemia is the most common cause of acute kidney injury (AKI) that might be exacerbate lupus activity through neutrophil extracellular traps (NETs) and apoptosis. Here, the renal ischemia reperfusion injury (I/R) was performed in Fc gamma receptor 2b deficient (Fcgr2b-/-) lupus mice and the in vitro experiments. At 24 h post-renal I/R injury, NETs in peripheral blood neutrophils and in kidneys were detected using myeloperoxidase (MPO), neutrophil elastase (NE) and citrullinated histone H3 (CitH3), as well as kidney apoptosis (activating caspase-3), which were prominent in Fcgr2b-/- mice more compared to wild-type (WT). After 120 h renal-I/R injury, renal NETs (using MPO and NE) were non-detectable, whereas glomerular immunoglobulin (Ig) deposition and serum anti-dsDNA were increased in Fcgr2b-/- mice. These results imply that renal NETs at 24 h post-renal I/R exacerbated the lupus nephritis at 120 h post-renal I/R injury in Fcgr2b-/- lupus mice. Furthermore, a Syk inhibitor attenuated NETs, that activated by phorbol myristate acetate (PMA; a NETs activator) or lipopolysaccharide (LPS; a potent inflammatory stimulator), more prominently in Fcgr2b-/- neutrophils than the WT cells as determined by dsDNA, PAD4 and MPO. In addition, the inhibitors against Syk and PAD4 attenuated lupus characteristics (serum creatinine, proteinuria, and anti-dsDNA) in Fcgr2b-/- mice at 120 h post-renal I/R injury. In conclusion, renal I/R in Fcgr2b-/- mice induced lupus exacerbation at 120 h post-I/R injury partly because Syk-enhanced renal NETs led to apoptosis-induced anti-dsDNA, which was attenuated by a Syk inhibitor.

A Synergy Between Endotoxin and (1→3)-Beta-D-Glucan Enhanced Neutrophil Extracellular Traps in Candida Administered Dextran Sulfate Solution Induced Colitis in FcGRIIB-/- Lupus Mice, an Impact of Intestinal Fungi in Lupus

Introduction

The translocation of organismal molecules from gut into blood circulation might worsen the disease severity of lupus through the induction of neutrophil extracellular traps (NETs).

Methods

An impact of lipopolysaccharide (LPS) and (1→3)-β-D-glucan (BG), components of gut bacteria and fungi, respectively, on NETs formation, was explored in lupus models, Fc gamma receptor IIB deficiency (FcGRIIB-/-) and Pristane injection, using Candida-administered dextran sulfate solution induced colitis (Candida-DSS) model.

Results

Severity of Candida-DSS in FcGRIIB-/- mice was more prominent than wild-type (WT) and Pristane mice as indicated by (i) colonic NETs using immunofluorescence of Ly6G, myeloperoxidase (MPO) and neutrophil elastase (NE) together with expression of PAD4 and IL-1β, (ii) colonic immunoglobulin (Ig) deposition (immunofluorescence), (iii) gut-leakage by FITC-dextran assay, endotoxemia and serum BG, (iv) systemic inflammation (neutrophilia, serum cytokines, serum dsDNA and anti-dsDNA) and (v) renal injury (proteinuria, glomerular NETs and Ig deposition).

Discussion

The formation of NETs in Candida-DSS mice was more severe than non-Candida-DSS mice and NETs in Candida-DSS were more profound in FcGRIIB-/- mice than Pristane mice. Prominent NETs in Candida-DSS FcGRIIB-/- mice might be due to the profound responses against LPS+BG in FcGRIIB-/- neutrophils compared with WT cells. These data implied an impact of the inhibitory FcGRIIB in NETs formation and an influence of gut fungi in lupus exacerbation. Hence, gut fungi in a DSS-induced gut-leakage lupus model enhanced colonic NETs that facilitated gut translocation of organismal molecules and synergistically exacerbated lupus activity.

Lipopolysaccharide-Enhanced Responses against Aryl Hydrocarbon Receptor in FcgRIIb-Deficient Macrophages, a Profound Impact of an Environmental Toxin on a Lupus-Like Mouse Model

Fc gamma receptor IIb (FcgRIIb) is the only inhibitory-FcgR in the FcgR family, and FcgRIIb-deficient (FcgRIIb^−/−) mice develop a lupus-like condition with hyper-responsiveness against several stimulations. The activation of aryl hydrocarbon receptor (Ahr), a cellular environmental sensor, might aggravate activity of the lupus-like condition. As such, 1,4-chrysenequinone (1,4-CQ), an Ahr-activator, alone did not induce supernatant cytokines from macrophages, while the 24 h pre-treatment by lipopolysaccharide (LPS), a representative inflammatory activator, prior to 1,4-CQ activation (LPS/1,4-CQ) predominantly induced macrophage pro-inflammatory responses. Additionally, the responses from FcgRIIb^−/− macrophages were more prominent than wild-type (WT) cells as determined by (i) supernatant cytokines (TNF-α, IL-6, and IL-10), (ii) expression of the inflammation associated genes (NF-κB, aryl hydrocarbon receptor, iNOS, IL-1β and activating-FcgRIV) and cell-surface CD-86 (a biomarker of M1 macrophage polarization), and (iii) cell apoptosis (Annexin V), with the lower inhibitory-FcgRIIb expression. Moreover, 8-week-administration of 1,4-CQ in 8 week old FcgRIIb^−/− mice, a genetic-prone lupus-like model, enhanced lupus characteristics as indicated by anti-dsDNA, serum creatinine, proteinuria, endotoxemia, gut-leakage (FITC-dextran), and glomerular immunoglobulin deposition. In conclusion, an Ahr activation worsened the disease severity in FcgRIIb^−/− mice possibly through the enhanced inflammatory responses. The deficiency of inhibitory-FcgRIIb in these mice, at least in part, prominently enhanced the pro-inflammatory responses. Our data suggest that patients with lupus might be more vulnerable to environmental pollutants.

Prominent Indomethacin-Induced Enteropathy in Fcgriib Defi-cient lupus Mice: An Impact of Macrophage Responses and Immune Deposition in Gut

A high dose of NSAIDs, a common analgesic, might induce lupus activity through several NSAIDs adverse effects including gastrointestinal permeability defect (gut leakage) and endotoxemia. Indomethacin (25 mg/day) was orally administered for 7 days in 24-wk-old Fc gamma receptor IIb deficient (FcgRIIb-/-) mice, an asymptomatic lupus model (increased anti-dsDNA without lupus nephritis), and age-matched wild-type (WT) mice. Severity of indomethacin-induced enteropathy in FcgRIIb-/- mice was higher than WT mice as demonstrated by survival analysis, intestinal injury (histology, immune-deposition, and intestinal cytokines), gut leakage (FITC-dextran assay and endotoxemia), serum cytokines, and lupus characteristics (anti-dsDNA, renal injury, and proteinuria). Prominent responses of FcgRIIb-/- macrophages toward lipopolysaccharide (LPS) compared to WT cells due to the expression of only activating-FcgRs without inhibitory-FcgRIIb were demonstrated. Extracellular flux analysis indicated the greater mitochondria activity (increased respiratory capacity and respiratory reserve) in FcgRIIb-/- macrophages with a concordant decrease in glycolysis activity when compared to WT cells. In conclusion, gut leakage-induced endotoxemia is more severe in indomethacin-administered FcgRIIb-/- mice than WT, possibly due to the enhanced indomethacin toxicity from lupus-induced intestinal immune-deposition. Due to a lack of inhibitory-FcgRIIb expression, mitochondrial function, and cytokine production of FcgRIIb-/- macrophages were more prominent than WT cells. Hence, lupus disease-activation from NSAIDs-enteropathy-induced gut leakage is possible.

T Follicular Regulatory Cell-Derived Fibrinogen-like Protein 2 Regulates Production of Autoantibodies and Induction of Systemic Autoimmunity

T follicular regulatory (TFR) cells limit Ab responses, but the underlying mechanisms remain largely unknown. In this study, we identify Fgl2 as a soluble TFR cell effector molecule through single-cell gene expression profiling. Highly expressed by TFR cells, Fgl2 directly binds to B cells, especially light-zone germinal center B cells, as well as to T follicular helper (TFH) cells, and directly regulates B cells and TFH in a context-dependent and type 2 Ab isotype-specific manner. In TFH cells, Fgl2 induces the expression of Prdm1 and a panel of checkpoint molecules, including PD1, TIM3, LAG3, and TIGIT, resulting in TFH cell dysfunction. Mice deficient in Fgl2 had dysregulated Ab responses at steady-state and upon immunization. In addition, loss of Fgl2 results in expansion of autoreactive B cells upon immunization. Consistent with this observation, aged Fgl2^-/- mice spontaneously developed autoimmunity associated with elevated autoantibodies. Thus, Fgl2 is a TFR cell effector molecule that regulates humoral immunity and limits systemic autoimmunity.

Follicular Dendritic Cells Modulate Germinal Center B Cell Diversity through FcγRIIB

Follicular dendritic cells (FDCs), a rare and enigmatic stromal cell type in the B cell follicles of secondary lymphoid organs, store and present antigen to B cells. While essential for germinal center (GC) responses, their exact role during GC B cell selection remains unknown. FDCs upregulate the inhibitory IgG Fc receptor FcγRIIB during GC formation. We show that the stromal deficiency of FcγRIIB does not affect GC B cell frequencies compared to wild-type mice. However, in the absence of FcγRIIB on FDCs, GCs show aberrant B cell selection during autoreactive and selective foreign antigen responses. These GCs are more diverse as measured by the AidCre^ERT2 -confetti system and show the persistence of IgM⁺ clones with decreased numbers of IgH mutations. Our results show that FDCs can modulate GC B cell diversity by the upregulation of FcγRIIB. Permissive clonal selection and subsequent increased GC diversity may affect epitope spreading during autoimmunity and foreign responses.

van der Poel et al. show that follicular dendritic cells (FDCs) can regulate germinal center diversity through FcγRIIB. In the absence of this receptor, germinal centers appear more diverse. In addition, the loss of FcγRIIB on FDCs leads to the persistence of IgM clones with decreased levels of somatic hypermutation.

An Overlapping Case of IgG4-related Disease and Klinefelter Syndrome with Lupus-like Serological and Neurological Features: A Case Report and Literature Review

A 46-year-old man with Klinefelter syndrome (KS) presented with obliterative phlebitis of the lower legs with a deteriorated renal function, and elevated serum alkaline phosphatase and ataxia levels. Examinations demonstrated tubulointerstitial nephritis, obliterative phlebitis and lymphadenopathy with IgG4+ plasma cell infiltrate and sclerosing cholangitis. Although the serological profile and central nerve system involvement were compatible for systemic lupus erythematosus (SLE), a definite diagnosis of SLE was difficult to make. IgG4-related disease (IgG4-RD) with KS was finally diagnosed, and high dose prednisolone with intravenous cyclophosphamide was initiated and thereafter the patient demonstrated a prompt improvement. This is the first known case demonstrating overlapping IgG4-RD with lupus-like serological and neurological features in a patient with KS, thus highlighting the pathogenic role with the genomic background for IgG4-RD and SLE.

Syk Inhibitor Attenuates Polymicrobial Sepsis in FcgRIIb-Deficient Lupus Mouse Model, the Impact of Lupus Characteristics in Sepsis

The impact of spleen tyrosine kinase (Syk) signaling might be prominent in lupus because (i) Syk is a shared downstream signaling molecule among circulating immune complex, LPS, and (1→3)-β-D-glucan (BG), and (ii) all of these factors are detectable in the serum of Fc gamma receptor IIb-deficient (FcgRIIb-/-) mice with sepsis. As a proof of concept study, we activated macrophages with BG combined with LPS (BG + LPS). We found that BG + LPS predominantly upregulated Syk expression and proinflammatory cytokines in FcgRIIb-/- macrophages compared with wild-type (WT) macrophages. Syk inhibition downregulated several inflammatory pathways in FcgRIIb-/- macrophages activated with BG + LPS, as determined by RNA sequencing analysis, suggesting the potential anti-inflammatory impact of Syk inhibitors in lupus. Indeed, administration of a Syk inhibitor prior to cecal ligation and puncture (CLP) sepsis in FcgRIIb-/- mice reduced baseline lupus-induced proinflammatory cytokines and attenuated sepsis severity as evaluated by mortality, organ injury, serum LPS, and post-sepsis serum cytokines. In conclusion, it was easier to induce Syk expression in FcgRIIb-/- macrophages than in WT macrophages. This might be because of the loss of inhibitory signaling, which might be responsible for prominent Syk abundance in the spleens of 40-week-old FcgRIIb-/- mice and the potent effect of Syk inhibitor in lupus mice compared with WT.

Relation between FCGRIIB rs1050501 and HSV-1 specific IgG antibodies in Alzheimer's disease

Background

Alzheimer’s Disease (AD) is a chronic neurodegenerative disorder characterized by extracellular plaques, intracellular neurofibrillary tangles and neuronal loss in the central nervous system (CNS). Pathogens are suspected to have a role in the development of AD; herpes simplex virus type 1 (HSV-1), in particular, is suggested to be a risk factor for the disease. The gamma receptor for the Fc portion of IgG molecules (FCGRs) plays a crucial role in regulating immune responses, and among FCGRs, FCGRIIB is endowed with an inhibitory function. Notably, the rs1050501 polymorphism of FCGRIIB gene associates with autoimmune diseases and with neuronal uptake and interneuronal accumulation of amyloid beta in animal AD models.

Methods

Genotype and allelic distribution of ApoE4 and FCGRIIB rs1050501 were evaluated in a case–control population of 225 AD patients, 93 MCI individuals and 201 sex and age matched healthy controls (HC). HSV-1 total IgG titers and IgG subclasses were detected and quantified in a subgroup of the main study population by ELISA.

Results

Genotype and allelic distribution of FCGRIIB was comparable in the study population. HSV-1-specific antibody titers were significantly higher in AD and MCI compared to HC (p < 0.01 for both); IgG3 titers, in particular, were increased in MCI compared to AD (p = 0.04). Analyses of possible correlations between the FCGRIIB rs1050501 genotype polymorphism and IgG subclasses showed that the presence of IgG3 was more frequent in MCI carrying the FCGRIIB TT (94.1%) compared to those carrying the CT genotype (63.6%) (p = 0.03).

Conclusion

Results herein show an association between humoral immune response against HSV-1 and FCGRIIB rs1050501 genetic variation in the first stage of the disease.

Syk inhibitor attenuates inflammation in lupus mice from FcgRIIb deficiency but not in pristane induction: the influence of lupus pathogenesis on the therapeutic effect

Macrophages are responsible for the recognition of pathogen molecules. The downstream signalling of the innate immune responses against pathogen molecules, lipopolysaccharide (LPS) and (1→3)-β-D-glucan (BG), and the adaptive immune response to antibodies, Fc gamma receptor (FcgR), is spleen tyrosine kinase (Syk). Because pathogen molecules and antibodies could be presented in lupus, impact of Syk and macrophages in lupus is explored. FcgR-IIb deficient (FcgRIIb^-/-) mice, a model of inhibitory signalling loss, at 40 weeks old, but not pristane mice (a chemical induction lupus model) demonstrated spontaneous elevation of LPS and BG in serum from gut translocation despite the similarity in faecal microbiome analysis. Syk abundance in FcgRIIb^-/- mice was higher than in pristane mice, possibly due to several Syk activators (anti-dsDNA, LPS and BG), and Syk inhibitor-attenuated proteinuria and serum cytokines only in FcgRIIb^-/- mice. In addition, LPS + BG enhanced the expression of activating FcgRs, NF-κB and Syk, together with supernatant TNF-α predominantly in FcgRIIb^-/- compared to wild-type macrophages. The inhibitors against Dectin-1, Syk and nuclear factor kappa B, but not anti-Raf-1, reduced supernatant TNF-α in LPS+BG-activated macrophages, implying Syk-dependent signalling. The pathogen molecules enhanced activating-FcgRs, without inhibition, through Syk, a shared downstream innate and adaptive signalling, is responsible for the hyper-responsiveness in FcgRIIb^-/- macrophages. In conclusion, Syk inhibitor attenuated inflammation in FcgRIIb^-/- but not in pristane mice, implying the influence of a lupus genetic background in treatment modalities.

Dysregulation of Lipid Metabolism in Macrophages Is Responsible for Severe Endotoxin Tolerance in FcgRIIB-Deficient Lupus Mice

FcgRIIB dysfunction is commonly found in patients with lupus, especially in Asia. LPS-tolerance is prominent in FcgRIIB–/– lupus mice. LPS-tolerant macrophages demonstrate cell energy depletion, which might affect lipid metabolism. Therefore, to explore lipid metabolism, LPS-tolerance was induced twice by LPS administration in macrophages and in mice. LPS-tolerant FcgRIIB–/– macrophages demonstrated lesser mitochondrial DNA (mtDNA), more severe ATP depletion, lower cytokine production, and higher lipid accumulation (oil red O staining) compared to LPS-tolerant WT cells. Mass-spectrometry-based lipidomic analysis demonstrated a higher abundance of phosphatidylethanolamine (PE) phospholipid in LPS-tolerant FcgRIIB–/– macrophages than WT cells. This was at least in part due to the lower expression of phosphatidylethanolamine N-methyltransferase (pemt), an enzyme that converts PE to phosphatidylcholine (PC). Aminoimidazole-4-carboxamide ribonucleotide (AICAR), a pemt inhibitor, worsens LPS-tolerance in WT macrophages and supports the impact of pemt upon LPS-tolerant FcgRIIB–/– macrophages. Additionally, phosphorylated AMP-activated protein kinase (AMPK-p), a molecule for ATP-restoration associated with pemt, and phosphorylated acetyl CoA carboxylase, a downstream signaling of AMPK-p, were higher in LPS-tolerant FcgRIIB–/– macrophages than WT. Furthermore, Compound C, an AMPK inhibitor, attenuated LPS-tolerance in both FcgRIIB–/– macrophages and mice. Taken together, the intense decrease in cytokine production after the second LPS stimulation (LPS-tolerance) in FcgRIIB–/– macrophages was possibly due to the impact of an immense cytokine synthesis after the first dose of LPS. This includes using up PEMT, an enzyme of phospholipid synthesis during cytokine production, and AMPK-p induction in response to profound ATP-depletion. Therefore, the manipulation of the AMPK/PEMT axis provides a novel therapeutic candidate for the treatment of severe LPS-tolerance in lupus.

FcγR2B B2.4 haplotype predicts increased risk of red blood cell alloimmunization in sickle cell disease patients

BACKGROUND

Red blood cell (RBC) alloimmunization is an important transfusion complication which is prevalent among sickle cell disease (SCD) patients. Autoimmune diseases are a known risk factor for RBC alloimmunization, suggesting that autoimmunity and post-transfusion alloantibody development occur through similar physiopathological pathways. Polymorphisms in the FcγR2B gene have already been associated with several autoimmune disorders and hypothetically could be associated with RBC alloimmunization. Our goal was to evaluate if important polymorphisms of FcγR2B have an impact on the risk of RBC alloimmunization among SCD patients.

STUDY DESIGN AND METHODS

This was a case-control study in which alloimmunized and non-alloimmunized SCD patients were compared in terms of the genotype frequency of the FcγR2B polymorphisms -386G/C, -120 T/A, and 695C/T, genotyped through direct Sanger sequencing.

RESULTS

A total of 237 patients met the eligibility criteria, 120 cases (alloimmunized) and 117 controls (non-alloimmunized). RBC alloimmunization was associated with female sex (p < 0.001), lifetime number of RBC units transfused (p = 0.002) and 120 T/A FcγR2B genotype (p = 0.031). The FcγR2B promoter region haplotype 2B.4 (386C120A) was positively associated with RBC alloimunization (p = 0.045). The logistic regression (LR) model identified female sex (OR 10.03, CI 95% 5.16-19.49; p < 0.001) and FcγR2B 2B.4 haplotype (OR 4.55, CI95% 1.1118.65; p = 0.035) as independent predictors of RBC alloimmunization in SCD patients.

CONCLUSION

SCD patients with the FcγR2B 2B.4 haplotype had over a fourfold higher risk for RBC alloimmunization. This highlights the role played by FcγR2B on RBC alloimmunization and may be helpful in identifying the immune responders.

Gene Expression Analysis of the Pre-Diabetic Pancreas to Identify Pathogenic Mechanisms and Biomarkers of Type 1 Diabetes

Type 1 Diabetes (T1D) occurs as a result of the autoimmune destruction of pancreatic β-cells by self-reactive T cells. The etiology of this disease is complex and difficult to study due to a lack of disease-relevant tissues from pre-diabetic individuals. In this study, we performed gene expression analysis on human pancreas tissues obtained from the Network of Pancreatic Organ Donors with Diabetes (nPOD), and showed that 155 genes were differentially expressed by ≥2-fold in the pancreata of autoantibody-positive (AA+) at-risk individuals compared to healthy controls. Only 48 of these genes remained changed by ≥2-fold in the pancreata of established T1D patients. Pathway analysis of these genes showed a significant association with various immune pathways. We were able to validate the differential expression of eight disease-relevant genes by QPCR analysis: A significant upregulation of CADM2, and downregulation of TRPM5, CRH, PDK4, ANGPL4, CLEC4D, RSG16, and FCGR2B was confirmed in the pancreata of AA+ individuals versus controls. Studies have already implicated FCGR2B in the pathogenesis of disease in non-obese diabetic (NOD) mice. Here we showed that CADM2, TRPM5, PDK4, and ANGPL4 were similarly changed in the pancreata of pre-diabetic 12-week-old NOD mice compared to NOD.B10 controls, suggesting a possible role for these genes in the pathogenesis of both T1D and NOD disease. The loss of the leukocyte-specific gene, FCGR2B, in the pancreata of AA+ individuals, is particularly interesting, as it may serve as a potential whole blood biomarker of disease progression. To test this, we quantified FCGR2B expression in peripheral blood samples of T1D patients, and AA+ and AA- first-degree relatives of T1D patients enrolled in the TrialNet Pathway to Prevention study. We showed that FCGR2B was significantly reduced in the peripheral blood of AA+ individuals compared to AA- controls. Together, these findings demonstrate that gene expression analysis of pancreatic tissue and peripheral blood samples can be used to identify disease-relevant genes and pathways and potential biomarkers of disease progression in T1D.

The Complex Association of FcγRIIb With Autoimmune Susceptibility

FcγRIIb is the only inhibitory Fc receptor and controls many aspects of immune and inflammatory responses. The observation 19 years ago that Fc γ RIIb ^-/- mice generated by gene targeting in 129 derived ES cells developed severe lupus like disease when backcrossed more than 7 generations into C57BL/6 background initiated extensive research on the functional understanding of this strong autoimmune phenotype. The genomic region in the distal part of Chr1 both in human and mice in which the Fc γ R gene cluster is located shows a high level of complexity in relation to the susceptibility to SLE. Specific haplotypes of closely linked genes including the Fc γ RIIb and Slamf genes are associated with increased susceptibility to SLE both in mice and human. Using forward and reverse genetic approaches including in human GWAS and in mice congenic strains, KO mice (germline and cell type specific, on different genetic background), knockin mice, overexpressing transgenic mice combined with immunological models such as adoptive transfer of B cells from Ig transgenic mice the involved genes and the causal mutations and their associated functional alterations were analyzed. In this review the results of this 19 years extensive research are discussed with a focus on (genetically modified) mouse models.

Genetic Variation in Low-To-Medium-Affinity Fcγ Receptors: Functional Consequences, Disease Associations, and Opportunities for Personalized Medicine

Fc-gamma receptors (FcγR) are the cellular receptors for Immunoglobulin G (IgG). Upon binding of complexed IgG, FcγRs can trigger various cellular immune effector functions, thereby linking the adaptive and innate immune systems. In humans, six classic FcγRs are known: one high-affinity receptor (FcγRI) and five low-to-medium-affinity FcγRs (FcγRIIA, -B and -C, FcγRIIIA and -B). In this review we describe the five genes encoding the low-to-medium -affinity FcγRs (FCGR2A, FCGR2B, FCGR2C, FCGR3A, and FCGR3B), including well-characterized functionally relevant single nucleotide polymorphisms (SNPs), haplotypes as well as copy number variants (CNVs), which occur in distinct copy number regions across the locus. The evolution of the locus is also discussed. Importantly, we recommend a consistent nomenclature of genetic variants in the FCGR2/3 locus. Next, we focus on the relevance of genetic variation in the FCGR2/3 locus in auto-immune and auto-inflammatory diseases, highlighting pathophysiological insights that are informed by genetic association studies. Finally, we illustrate how specific FcγR variants relate to variation in treatment responses and prognosis amongst autoimmune diseases, cancer and transplant immunology, suggesting novel opportunities for personalized medicine.

Lipocalin-2 (Lcn-2) Attenuates Polymicrobial Sepsis with LPS Preconditioning (LPS Tolerance) in FcGRIIb Deficient Lupus Mice

In patients with active lupus, spontaneous endotoxemia and possibly tolerance to lipopolysaccharide (LPS) is a potentially adverse complication. Similarly, previous reports have demonstrated that FcGRIIb deficient mice (FcGRIIb-/-; a lupus mouse model) are susceptible to LPS tolerance-induced decreased cytokine responses that inadequate for the organismal control. Thus, understanding the relationship between FcGRIIb and LPS tolerance could improve the therapeutic strategy for lupus. LPS tolerance can be induced through sequential LPS stimulations in either cells or a model organism. In RAW264.7 (a mouse macrophage cell-line), sequential LPS stimulation induced the secretion of Lipocalin-2 (Lcn-2) despite reduced cytokine secretion and severe energy depletion, as measured by the extracellular flux analysis, typical of LPS tolerance. In contrast, treatment with recombinant Lcn-2 (rLcn-2) attenuated LPS tolerance, as shown by an increase in secreted cytokines and altered macrophage polarization toward M1 (increased iNOS and TNF-α) in RAW264.7 cells. These results suggest a role of Lcn-2 in LPS tolerance attenuation. In bone marrow derived macrophages, Lcn-2 level was similar in LPS tolerant FcGRIIb-/- and wild-type (WT) cells despite the increased LPS tolerance of FcGRIIb-/- cells, suggesting relatively low basal levels of Lcn-2 produced in FcGRIIb-/- cells. In addition, attenuation of LPS tolerance effectuated by granulocyte-monocyte colony stimulating factor (GM-CSF) reduced Lcn-2 in both cell types, implying an inverse correlation between Lcn-2 and the severity of LPS tolerance. Consequently, rLcn-2 improved LPS tolerance only in FcGRIIb-/- macrophages and attenuated disease severity of cecal ligation and puncture (CLP) sepsis pre-conditioning with sequential LPS injection (LPS-CLP model) only in FcGRIIb-/- mice, but not in WT mice. To summarize, inadequate Lcn-2 production in FcGRIIb-/- macrophage might, at least in part, be responsible for the inordinate LPS tolerance compared with WT cells. Additionally, supplementation of rLcn-2 attenuates LPS tolerance in FcGRIIb-/- macrophages in vitro, and in FcGRIIb-/- mice with LPS-CLP sepsis in vivo. In conclusion, Lcn-2 secreted by macrophages is possibly an autocrine signal to counter the reduced cytokine secretion in LPS tolerance.

FcγRIIB-I232T polymorphic change allosterically suppresses ligand binding

FcγRIIB binding to its ligand suppresses immune cell activation. A single-nucleotide polymorphic (SNP) change, I232T, in the transmembrane (TM) domain of FcγRIIB loses its suppressive function, which is clinically associated with systemic lupus erythematosus (SLE). Previously, we reported that I232T tilts FcγRIIB’s TM domain. In this study, combining with molecular dynamics simulations and single-cell FRET assay, we further reveal that such tilting by I232T unexpectedly bends the FcγRIIB’s ectodomain toward plasma membrane to allosterically impede FcγRIIB’s ligand association. I232T substitution reduces in situ two-dimensional binding affinities and association rates of FcγRIIB to interact with its ligands, IgG1, IgG2 and IgG3 by three to four folds. This allosteric regulation by an SNP provides an intrinsic molecular mechanism for the functional loss of FcγRIIB-I232T in SLE patients.

Left unchecked the immune system can cause devastating damage to healthy tissue. To prevent this from happening, immune cells have built-in off switches that dampen their activation. One such switch is a protein called FcγRIIB that sits on the outer surface of immune cells and binds to proteins known as antibodies, which are produced as part of the immune response. Its role is to act as a brake on the immune system, and stop it from getting out of control.

Overactive immune cells can lead to autoimmune diseases such as systemic lupus erythematosus, also known as SLE for short, which causes damage to the skin, joints and other organs. Previous work suggests that SLE is correlated with a specific mutation in the FcγRIIB gene, but it is unclear how the mutation and the disease are connected.

Proteins are made out of building blocks called amino acids, which have different chemical properties. A swap of one amino acid for another can have big consequences for the structure of a protein. In the case of FcγRIIB, the mutation that correlates with SLE changes an amino acid called isoleucine for another called threonine. Isoleucine does not mix well with water and is commonly found buried in the middle of proteins or inside cell membranes. Threonine, on the other hand, can readily interact with the hydrogen atoms in water and other amino acids.

Hu, Zhang, Sun et al. used computer simulations and imaged single human cells to find out how the isoleucine to threonine change causes immune cells to become over-activated. The experiments revealed that threonine interacts with a nearby amino acid, putting a kink in the FcγRIIB protein. This kink causes the outer part of the FcγRIIB protein to bend towards the immune cell membrane, stopping it from binding to antibodies, and putting a break on immune cells that have become hyper-activated.

There is currently no cure for SLE, but understanding its causes could take us a step closer to better management of the disease. Small molecule drug treatments often target the three-dimensional shape of certain proteins, so understanding the effect of mutations at the molecular level could help with the design of new treatments in the future.

FcγRIIb differentially regulates pre-immune and germinal center B cell tolerance in mouse and human

Several tolerance checkpoints exist throughout B cell development to control autoreactive B cells and prevent the generation of pathogenic autoantibodies. FcγRIIb is an Fc receptor that inhibits B cell activation and, if defective, is associated with autoimmune disease, yet its impact on specific B cell tolerance checkpoints is unknown. Here we show that reduced expression of FcγRIIb enhances the deletion and anergy of autoreactive immature B cells, but in contrast promotes autoreactive B cell expansion in the germinal center and serum autoantibody production, even in response to exogenous, non-self antigens. Our data thus show that FcγRIIb has opposing effects on pre-immune and post-immune tolerance checkpoints, and suggest that B cell tolerance requires the control of bystander germinal center B cells with low or no affinity for the immunizing antigen.

The inhibitory receptor, FcγRIIb, is reported to limit autoimmune B cell response. Here the authors show that FcγRIIb has a dual role in both human and mouse, with reduced FcγRIIb expression or function associated with enhanced pre-immune B cell tolerance, yet defective control of mature autoreactive B cells in the germinal center.

Decreased Protein Kinase C-β Type II Associated with the Prominent Endotoxin Exhaustion in the Macrophage of FcGRIIb-/- Lupus Prone Mice is Revealed by Phosphoproteomic Analysis

Dysfunction of FcGRIIb, the only inhibitory receptor of the FcGR family, is commonly found in the Asian population and is possibly responsible for the extreme endotoxin exhaustion in lupus. Here, the mechanisms of prominent endotoxin (LPS) tolerance in FcGRIIb−/− mice were explored on bone marrow-derived macrophages using phosphoproteomic analysis. As such, LPS tolerance decreased several phosphoproteins in the FcGRIIb−/− macrophage, including protein kinase C-β type II (PRKCB), which was associated with phagocytosis function. Overexpression of PRKCB attenuated LPS tolerance in RAW264.7 cells, supporting the role of this gene in LPS tolerance. In parallel, LPS tolerance in macrophages and in mice was attenuated by phorbol 12-myristate 13-acetate (PMA) administration. This treatment induced several protein kinase C families, including PRKCB. However, PMA attenuated the severity of mice with cecal ligation and puncture on LPS tolerance preconditioning in FcGRIIb−/− but not in wild-type cells. The significant reduction of PRKCB in the FcGRIIb−/− macrophage over wild-type cell possibly induced the more severe LPS-exhaustion and increased the infection susceptibility in FcGRIIb−/− mice. PMA induced PRKCB, improved LPS-tolerance, and attenuated sepsis severity, predominantly in FcGRIIb−/− mice. PRKCB enhancement might be a promising strategy to improve macrophage functions in lupus patients with LPS-tolerance from chronic infection.

Helicobacter pylori Infection Increased Anti-dsDNA and Enhanced Lupus Severity in Symptomatic FcγRIIb-Deficient Lupus Mice

The defect on Fc gamma receptor IIb (FcγRIIb), the only inhibitory FcγR, has been identified as one of the genetic factors increasing susceptibility to lupus. The prevalence of Helicobacter pylori (HP) and FcγRIIb dysfunction-polymorphisms are high among Asians, and their co-existence is possible. Unfortunately, the influence of HP against lupus progression in patients with lupus is still controversial. In this study, the interactions between these conditions were tested with HP infection in 24-week-old FcγRIIb-/- mice (symptomatic lupus). HP induced failure to thrive, increased stomach bacterial burdens and stomach injury (histology and cytokines) in both wild-type and FcγRIIb-/- mice. While the severity of HP infection, as determined by these parameters, was not different between both strains, antibodies production (anti-HP, anti-dsDNA and serum gammaglobulin) were higher in FcγRIIb-/- mice compared to wild-type. Accordingly, HP infection also accelerated the severity of lupus as determined by proteinuria, serum creatinine, serum cytokines, renal histology, and renal immune complex deposition. Although HP increased serum cytokines in both wild-type and FcγRIIb-/- mice, the levels were higher in FcγRIIb-/- mice. As such, HP also increased spleen weight and induced several splenic immune cells responsible for antibody productions (activated B cell, plasma cell and follicular helper T cell) in FcγRIIb-/- mice, but not in wild-type. These data describe the different systemic responses against localized HP infection from diverse host genetic background. In conclusion, the mutual interactions between HP and lupus manifestations of FcγRIIb-/-mice were demonstrated in this study. With the prominent immune responses from the loss of inhibitory signaling in FcγRIIb-/- mice, HP infection in these mice induced intense chronic inflammation, increased antibody production, and enhanced lupus severity. Thus, the increased systemic inflammatory responses due to localized HP inducing gastritis in some patients with lupus may enhance lupus progression. More studies are needed.

Transmembrane domain dependent inhibitory function of FcγRIIB

FcγRIIB, the only inhibitory IgG Fc receptor, functions to suppress the hyper-activation of immune cells. Numerous studies have illustrated its inhibitory function through the ITIM motif in the cytoplasmic tail of FcγRIIB. However, later studies revealed that in addition to the ITIM, the transmembrane (TM) domain of FcγRIIB is also indispensable for its inhibitory function. Indeed, recent epidemiological studies revealed that a non-synonymous single nucleotide polymorphism (rs1050501) within the TM domain of FcγRIIB, responsible for the I232T substitution, is associated with the susceptibility to systemic lupus erythematosus (SLE). In this review, we will summarize these epidemiological and functional studies of FcγRIIB-I232T in the past few years, and will further discuss the mechanisms accounting for the functional loss of FcγRIIB-I232T. Our review will help the reader gain a deeper understanding of the importance of the TM domain in mediating the inhibitory function of FcγRIIB and may provide insights to a new therapeutic target for the associated diseases.

Nonclassical FCGR2C haplotype is associated with protection from red blood cell alloimmunization in sickle cell disease

Red blood cell (RBC) transfusions are of vital importance in patients with sickle cell disease (SCD). However, a major complication of transfusion therapy is alloimmunization. The low-affinity Fcγ receptors, expressed on immune cells, are important regulators of antibody responses. Genetic variation in FCGR genes has been associated with various auto- and alloimmune diseases. The aim of this study was to evaluate the association between genetic variation of FCGR and RBC alloimmunization in SCD. In this case-control study, DNA samples from 2 cohorts of transfused SCD patients were combined (France and The Netherlands). Cases had a positive history of alloimmunization, having received ≥1 RBC unit. Controls had a negative history of alloimmunization, having received ≥20 RBC units. Single nucleotide polymorphisms and copy number variation of the FCGR2/3 gene cluster were studied in a FCGR-specific multiplex ligation-dependent probe amplification assay. Frequencies were compared using logistic regression. Two hundred seventy-two patients were included (130 controls, 142 cases). The nonclassical open reading frame in the FCGR2C gene (FCGR2C.nc-ORF) was strongly associated with a decreased alloimmunization risk (odds ratio [OR] 0.26, 95% confidence [CI] 0.11-0.64). This association persisted when only including controls with exposure to ≥100 units (OR 0.30, CI 0.11-0.85) and appeared even stronger when excluding cases with Rh or K antibodies only (OR 0.19, CI 0.06-0.59). In conclusion, SCD patients with the FCGR2Cnc-ORF polymorphism have over a 3-fold lower risk for RBC alloimmunization in comparison with patients without this mutation. This protective effect was strongest for exposure to antigens other than the immunogenic Rh or K antigens.

Identification of Fc Gamma Receptor Glycoforms That Produce Differential Binding Kinetics for Rituximab

Fc gamma receptors (FcγR) bind the Fc region of antibodies and therefore play a prominent role in antibody-dependent cell-based immune responses such as ADCC, CDC and ADCP. The immune effector cell activity is directly linked to a productive molecular engagement of FcγRs where both the protein and glycan moiety of antibody and receptor can affect the interaction and in the present study we focus on the role of the FcγR glycans in this interaction. We provide a complete description of the glycan composition of Chinese hamster ovary (CHO) expressed human Fcγ receptors RI (CD64), RIIa_{Arg131/His131} (CD32a), RIIb (CD32b) and RIIIa_{Phe158/Val158} (CD16a) and analyze the role of the glycans in the binding mechanism with IgG. The interactions of the monoclonal antibody rituximab with each FcγR were characterized and we discuss the CHO-FcγRIIIa_{Phe158/Val158} and CHO-FcγRI interactions and compare them to the equivalent interactions with human (HEK293) and murine (NS0) produced receptors. Our results reveal clear differences in the binding profiles of rituximab, which we attribute in each case to the differences in host cell-dependent FcγR glycosylation. The glycan profiles of CHO expressed FcγRI and FcγRIIIa_{Phe158/Val158} were compared with the glycan profiles of the receptors expressed in NS0 and HEK293 cells and we show that the glycan type and abundance differs significantly between the receptors and that these glycan differences lead to the observed differences in the respective FcγR binding patterns with rituximab. Oligomannose structures are prevalent on FcγRI from each source and likely contribute to the high affinity rituximab interaction through a stabilization effect. On FcγRI and FcγRIIIa large and sialylated glycans have a negative impact on rituximab binding, likely through destabilization of the interaction. In conclusion, the data show that the IgG1-FcγR binding kinetics differ depending on the glycosylation of the FcγR and further support a stabilizing role of FcγR glycans in the antibody binding interaction.

The role of macrophages in the susceptibility of Fc gamma receptor IIb deficient mice to Cryptococcus neoformans

Dysfunctional polymorphisms of FcγRIIb, an inhibitory receptor, are associated with Systemic Lupus Erythaematosus (SLE). Cryptococcosis is an invasive fungal infection in SLE, perhaps due to the de novo immune defect. We investigated cryptococcosis in the FcγRIIb-/- mouse-lupus-model. Mortality, after intravenous C. neoformans-induced cryptococcosis, in young (8-week-old) and older (24-week-old) FcγRIIb-/- mice, was higher than in age-matched wild-types. Severe cryptococcosis in the FcγRIIb-/- mice was demonstrated by high fungal burdens in the internal organs with histological cryptococcoma-like lesions and high levels of TNF-α and IL-6, but not IL-10. Interestingly, FcγRIIb-/- macrophages demonstrated more prominent phagocytosis but did not differ in killing activity in vitro and the striking TNF-α, IL-6 and IL-10 levels, compared to wild-type cells. Indeed, in vivo macrophage depletion with liposomal clodronate attenuated the fungal burdens in FcγRIIb-/- mice, but not wild-type mice. When administered to wild-type mice, FcγRIIb-/- macrophages with phagocytosed Cryptococcus resulted in higher fungal burdens than FcγRIIb+/+ macrophages with phagocytosed Cryptococcus. These results support, at least in part, a model whereby, in FcγRIIb-/- mice, enhanced C. neoformans transmigration occurs through infected macrophages. In summary, prominent phagocytosis, with limited effective killing activity, and high pro-inflammatory cytokine production by FcγRIIb-/- macrophages were correlated with more severe cryptococcosis in FcγRIIb-/- mice.

Fc gamma receptor IIIa polymorphism is not associated with susceptibility to systemic lupus erythematosus in Brazilian patients

We evaluated the possible association between FCGR3A V/F (158) polymorphism and SLE susceptibility and clinical phenotype in 305 sequentially retrieved SLE patients and 300 healthy controls from the southeastern part of Brazil by allele-specific polymerase chain reaction. Our results showed no association between FCGR3A 158V/F alleles and susceptibility to SLE in this series of patients albeit the heterozygous genotype was strongly associated with the disease.

Impairment on the lateral mobility induced by structural changes underlies the functional deficiency of the lupus-associated polymorphism FcγRIIB-T232

Xu et al. show that the lupus-associated polymorphism FcγRIIB-T232 has structural changes of the TM domain that reduces lateral mobility and inhibitory functions.

FcγRIIB functions to suppress the activation of immune cells. A single-nucleotide polymorphism in the transmembrane (TM) domain of FcγRIIB, FcγRIIB-T232, is associated with lupus. In this study, we investigated the pathogenic mechanism of FcγRIIB-T232 at both functional and structural levels. Our results showed that FcγRIIB-T232 exhibited significantly reduced lateral mobility compared with FcγRIIB-I232 and was significantly less enriched into the microclusters of immune complexes (ICs) after stimulation. However, if sufficient responding time is given for FcγRIIB-T232 to diffuse and interact with the ICs, FcγRIIB-T232 can restore its inhibitory function. Moreover, substituting the FcγRIIB-T232 TM domain with that of a fast floating CD86 molecule restored both the rapid mobility and the inhibitory function, which further corroborated the importance of fast mobility for FcγRIIB to function. Mechanistically, the crippled lateral mobility of FcγRIIB-T232 can be explained by the structural changes of the TM domain. Both atomistic simulations and nuclear magnetic resonance measurement indicated that the TM helix of FcγRIIB-T232 exhibited a more inclined orientation than that of FcγRIIB-I232, thus resulting in a longer region embedded in the membrane. Therefore, we conclude that the single-residue polymorphism T232 enforces the inclination of the TM domain and thereby reduces the lateral mobility and inhibitory functions of FcγRIIB.

Recapitulation of Candidate Systemic Lupus Erythematosus-Associated Variants in Koreans

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease that affects multiple organ systems. Although the etiology of SLE remains unclear, it is widely accepted that genetic factors could be involved in its pathogenesis. A number of genome-wide association studies (GWASs) have identified novel single-nucleotide polymorphisms (SNPs) associated with the risk of SLE in diverse populations. However, not all the SNP candidates identified from non-Asian populations have been validated in Koreans. In this study, we aimed to replicate the SNPs that were recently discovered in the GWAS; these SNPs have not been validated in Koreans or have only been replicated in Koreans with an insufficient sample size to conclude any association. For this, we selected five SNPs (rs1801274 in FCGR2A and rs2286672 in PLD2, rs887369 in CXorf21, rs9782955 in LYST, and rs3794060 in NADSYN1). Through the replication study with 656 cases and 622 controls, rs1801274 in FCGR2A was found to be significantly associated with SLE in Koreans (odds ratio, 1.26, 95% confidence interval, 1.06 to 1.50; p = 0.01 in allelic model). This association was also significant in two other models (dominant and recessive). The other four SNPs did not show a significant association. Our data support that FCGR polymorphisms play important roles in the susceptibility to SLE in diverse populations, including Koreans.

FcγRIIB and autoimmunity

Autoimmune diseases are characterized by adaptive immune responses against self-antigens, including humoral responses resulting in the production of autoantibodies. Autoantibodies generate inflammation by activating complement and engaging Fcγ receptors (FcγRs). The inhibitory receptor FcγRIIB plays a central role in regulating the generation of autoantibodies and their effector functions, which include activation of innate immune cells and the cellular arm of the adaptive immune system, via effects on antigen presentation to CD4 T cells. Polymorphisms in FcγRIIB have been associated with susceptibility to autoimmunity but protection against infections in humans and mice. In the last few years, new mechanisms by which FcγRIIB controls the adaptive immune response have been described. Notably, FcγRIIB has been shown to regulate germinal center B cells and dendritic cell migration, with potential impact on the development of autoimmune diseases. Recent work has also highlighted the implication of FcγRIIB on the regulation of the innate immune system, via inhibition of Toll-like receptor- and complement receptor-mediated activation. This review will provide an update on the role of FcγRIIB in adaptive immune responses in autoimmunity, and then focus on their emerging function in innate immunity.

Comprehensive Assessment of the Association between FCGRs polymorphisms and the risk of systemic lupus erythematosus: Evidence from a Meta-Analysis

We performed a meta analysis to assess the relationship of FCGRs polymorphisms with the risk of SLE. Thirty-five articles (including up to 5741 cases and 6530 controls) were recruited for meta-analysis. The strongest association was observed between FCGR2B rs1050501 and SLE under the recessive genotypic model of C allele in the overall population (CC vs CT/TT, OR = 1.754, 95%CI: 1.422–2.165, P = 1.61 × 10⁻⁷) and in Asian population (CC vs CT/TT, OR = 1.784, 95%CI; 1.408–2.261, P = 1.67 × 10⁻⁶). We also found that FCGR3A rs396991 were significant association with the susceptibility to SLE in overall population in recessive model of T allele (TT vs TG/GG, OR = 1.263, 95%CI: 1.123–1.421, P = 9.62 × 10⁻⁵). The results also showed that significant association between FCGR2A rs1801274 and SLE under the allelic model in the overall population (OR = 0.879 per A allele, 95%CI: 0.819–0.943, P = 3.31 × 10⁻⁴). The meta-analysis indicated that FCGR3B copy number polymorphism NA1·NA2 was modestly associated with SLE in overall population (OR = 0.851 per NA1, 95%CI: 0.772–0.938, P = 1.2 × 10⁻³). We concluded that FCGR2B rs1050501 C allele and FCGR3A rs396991 T allele might contribute to susceptibility and development of SLE, and were under recessive association model. While, FCGR2A rs1801274 A allele and FCGR3B NA1 were associated with SLE and reduced the risk of SLE.

FcγRIIB Gene Polymorphisms Are Associated with Disease Risk and Clinical Manifestations of Systemic Lupus Erythematosus in Koreans

Systemic lupus erythematosus (SLE) is chronic autoimmune disease with various autoantibodies, which are involved in tissue damage. Fc gamma receptors (FcγRs) bind the constant region of the immunoglobulin G and transmit stimulatory or inhibitory signal to immune cells. The FcγR genes map to 1q23, a susceptible locus for SLE. We have screened single nucleotide polymorphisms (SNPs) in one of FcγR gene, FcγRIIB, which is the only inhibitory receptor, after considering gene map and reported SNPs. There were 3 SNPs in FcγRIIB: 10849 T>C (rs1050501) in exon 5 and 10950 T>G (rs6666965) and 11045 G>T (rs12117530) in intron 5 in Koreans. The frequency of the minor allele (T) of rs12117530 was significantly higher in SLE patients (50 patients, 20.4%) than healthy controls (17 patients, 12%, p = 0.041). Leukopenia occurred more frequently in SLE patients carrying the minor allele (T) of rs12117530 (p = 0.032). Among 5 haplotypes, the frequency of decreased complement was significantly lower in SLE patients with haplotype 1 [TTG] (p = 0.045). Nephritis, lymphopenia and anti-dsDNA antibody were significantly less frequent in SLE patients with haplotype 2 [TGG] (p = 0.046, p = 0.018, p = 0.002, respectively). The frequency of thrombocytopenia and anti-dsDNA antibody was significantly higher in SLE patients with haplotype 3 [CTG] (p < 0.001, p = 0.04, respectively). These data reveal that genetic polymorphisms within FcγRIIB are associated with disease susceptibility and phenotypes of SLE in Koreans. Furthermore, FcγRIIB rs12117530 polymorphism (T allele) may be an important risk factor in SLE.

Variability at the FCGR locus: characterization in Black South Africans and evidence for ethnic variation in and out of Africa

This study set out to comprehensively investigate all known functional FcγR variants in South African Black and Caucasian individuals. Population diversity was further assessed using data from the 1000 Genomes Project. In our cohort, Black South Africans neither possessed the haplotypes previously associated with increased surface densities of FcγRIIb and FcγRIIIa nor the FCGR2C haplotype recently associated with increased vaccine efficacy in the RV144 HIV-1 vaccine trial (despite 48.7% bearing the c.134-96T tag allele). Moreover, Africans (South Africans, Luhya Kenyans and Yoruba Nigerians) lack the FCGR2C c.798+1G splice-site allele required for the expression of functional FcγRIIc. Although the presence or absence of surface FcγRIIc did not affect natural killer cell-mediated antibody-dependent cellular cytotoxicity capability, this may be significant for other FcγRIIc-mediated functions. Overall, allele distribution and linkage disequilibrium in Africans and Caucasians differed in a manner that would suggest a differentially maintained balance of FcγR-mediated cell activation in these populations. Finally, significant variation observed among different African populations precludes the use of any one African population as a proxy for FcγR diversity in Africans. In conclusion, the findings of this study highlight further ethnic variation at the FCGR gene locus, in particular for FCGR2C, a gene with increasingly recognized clinical significance.

Association of FCGR3A and FCGR3B copy number variations with systemic lupus erythematosus and rheumatoid arthritis in Taiwanese patients

Objective

To determine whether copy number variations (CNVs) in FCGR3A and FCGR3B are associated with systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) in Taiwanese individuals.

Methods

FCGR3A and FCGR3B CNV genotypes were determined in 846 patients with SLE, 948 patients with RA, and 1,420 healthy control subjects, using custom TaqMan CNV assays. The FCGR3A and FCGR3B CNV genotypes were compared between healthy control subjects and patients and among patients stratified according to clinical characteristics.

Results

A low (<2) FCGR3A copy number was significantly associated with SLE (for <2 copies versus 2 copies, P = 5.06 × 10⁻⁴, false discovery rate–corrected P [P_FDR] = 0.001, odds ratio [OR] 3.26, 95% confidence interval [95% CI] 1.68−6.35) and RA (for <2 copies versus 2 copies, P = 5.83 × 10⁻⁴, P_FDR = 0.0012, OR 2.82, 95% CI 1.56−5.1). A low FCGR3B copy number was also significantly associated with SLE (for <2 copies versus 2 copies, P = 0.0032, P_FDR = 0.0032, OR 1.59, 95% CI 1.17−2.18). Notably, a high (>2) FCGR3A copy number was also associated with SLE (for >2 copies versus 2 copies, P = 0.003, P_FDR = 0.0061, OR 1.6, 95% CI 1.17−2.18). Additionally, the FCGR3A low copy number genotype was significantly enriched in subsets of patients with SLE (those with ulcer, arthritis, rash, discoid rash, photosensitivity, nephritis, leukopenia, thrombocytopenia, depressed complement levels, and autoantibody positivity) and patients with RA (those positive for rheumatoid factor) compared with healthy control subjects. The FCGR3B low copy number genotype was also significantly enriched in SLE patients with ulcer, rash, discoid rash, photosensitivity, ascites, nephritis, complement level depression, and anti–double-stranded DNA antibody positivity compared with control subjects. However, FCGR3B CNVs were not associated with RA susceptibility (for <2 copy numbers versus 2 copy numbers, P = 0.3584, OR 1.15, 95% CI 0.85–1.55) and clinical characteristics.

Conclusion

In Taiwanese individuals, a low FCGR3A copy number is a common risk factor for SLE and RA, while a low FCGR3B copy number confers a risk of SLE but not RA.

An evolutionary perspective of how infection drives human genome diversity: the case of malaria

Infection with malaria parasites has imposed a strong selective pressure on the human genome, promoting the convergent evolution of a diverse range of genetic adaptations, many of which are harboured by the red blood cell, which hosts the pathogenic stage of the Plasmodium life cycle. Recent genome-wide and multi-centre association studies of severe malaria have consistently identified ATP2B4, encoding the major Ca(2+) pump of erythrocytes, as a novel resistance locus. Evidence is also accumulating that interaction occurs among resistance loci, the most recent example being negative epistasis among alpha-thalassemia and haptoglobin type 2. Finally, studies on the effect of haemoglobin S and C on parasite transmission to mosquitoes have suggested that protective variants could increase in frequency enhancing parasite fitness.

Human FcR polymorphism and disease

Fc receptors play a central role in maintaining the homeostatic balance in the immune system. Our knowledge of the structure and function of these receptors and their naturally occurring polymorphisms, including single nucleotide polymorphisms and/or copy number variations, continues to expand. Through studies of their impact on human biology and clinical phenotype, the contributions of these variants to the pathogenesis, progression, and/or treatment outcome of many diseases that involve immunoglobulin have become evident. They affect susceptibility to bacterial and viral pathogens, constitute as risk factors for IgG or IgE mediated inflammatory diseases, and impact the development of many autoimmune conditions. In this chapter, we will provide an overview of these genetic variations in classical FcγRs, FcRLs, and other Fc receptors, as well as challenges in achieving an accurate and comprehensive understanding of the FcR polymorphisms and genomic architecture.

Sweet and sour: the role of glycosylation for the anti-inflammatory activity of immunoglobulin G

The importance of immunoglobulin G (IgG) molecules for providing long-term sterile immunity as well as their major contribution to tissue inflammation during autoimmune diseases is generally accepted. In a similar manner, studies over the last years have elucidated many details of the molecular and cellular pathways underlying this protective activity in vivo, emphasizing the role of cellular recognizing the constant antibody fragment. In contrast, the active anti-inflammatory activity of IgG, despite being known and actually identified in human autoimmune patients more than 30 years ago, is much less defined. Recent evidence from several independent model systems suggests that IgG glycosylation is critical for the immunomodulatory activity of IgG and that both monomeric IgG as well as IgG immune complexes can diminish Fc receptor and complement dependent inflammatory processes. Moreover, there is increasing evidence that IgG molecules also modulate B and T cell responses, which may suggest that IgG is centrally involved in the establishment and maintenance of immune homeostasis.

Association of FcγRIIB and FcγRIIA R131H gene polymorphisms with renal involvement in Egyptian systemic lupus erythematosus patients

Identification of the genetic basis of systemic lupus erythematosus (SLE) may contribute to the discovery of effective drugs before renal involvement. Our aim of this study was to estimate the association between Fc gamma receptor (FcγR) polymorphisms and SLE and renal involvement in Egyptian patients. FcγRIIB and FcγRIIA R131H gene polymorphisms were genotyped in 180 Egyptian adults. Genotyping for FcγRIIA R131H was performed using allele-specific PCR and FcγRIIB-Ile232 Thr polymorphism was genotyped using polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP). The study showed that the homozygous genotype (Thr/Thr) of FcγRIIB significantly increased in all SLE patients (90 patients) and in SLE patients complicated with nephritis (61 patients). The Thr allele was significantly associated with an increased risk of the disease in all the patients and in patients complicated with nephritis. Our study demonstrated an association of FcγRIIB polymorphisms with SLE and lupus nephritis and a lack of association of FcγRIIA polymorphisms with SLE in the Egyptian patients.