Fc gamma R expression on NK cells influences disease severity in rheumatoid arthritis

An HIV Vaccine Protective Allele in FCGR2C Associates With Increased Odds of Perinatal HIV Acquisition

In the Thai RV144 HIV-1 vaccine trial, a three-variant haplotype within the Fc gamma receptor 2C gene (FCGR2C) reduced the risk of HIV-1 acquisition. A follow-on trial, HVTN702, of a similar vaccine candidate found no efficacy in South Africa, where the predominant population is polymorphic for only a single variant in the haplotype, c.134-96C>T (rs114945036). To investigate a role for this variant in HIV-1 acquisition in South Africans, we used the model of maternal-infant HIV-1 transmission. A nested case-control study was conducted of infants born to mothers living with HIV-1, comparing children with perinatally-acquired HIV-1 (cases, n = 176) to HIV-1-exposed uninfected children (controls, n = 349). All had received nevirapine for prevention of mother-to-child transmission. The FCGR2C copy number and expression variants (c.-386G>C, c.-120A>T c.169T>C, and c.798+1A>G) were determined using a multiplex ligation-dependent probe amplification assay and the c.134-96C>T genotype with Sanger sequencing. The copy number, genotype and allele carriage were compared between groups using univariate and multivariate logistic regression. The FCGR2C c.134-96C>T genotype distribution and copy number differed significantly between HIV-1 cases and exposed-uninfected controls (P = 0.002, P _Bonf = 0.032 and P = 0.010, P _Bonf = > 0.05, respectively). The FCGR2C c.134-96T allele was overrepresented in the cases compared to the controls (58% vs 42%; P = 0.001, P _Bonf = 0.016). Adjusting for birthweight and FCGR2C copy number, perinatal HIV-1 acquisition was associated with the c.134-96C>T (AOR = 1.89; 95% CI 1.25-2.87; P = 0.003, P _Bonf = 0.048) and c.169C>T (AOR = 2.39; 95% CI 1.45-3.95; P = 0.001, P _Bonf = 0.016) minor alleles but not the promoter variant at position c.-386G>C. The c.134-96C>T variant was in strong linkage disequilibrium with the c.169C>T variant, but remained significantly associated with perinatal acquisition when adjusted for c.169C>T in multivariate analysis. In contrast to the protective effect observed in the Thai RV144 trial, we found the FCGR2C variant c.134-96T-allele associated with increased odds of perinatal HIV-1 acquisition in South African children. These findings, taken together with a similar deleterious association found with HIV-1 disease progression in South African adults, highlight the importance of elucidating the functional relevance of this variant in different populations and vaccination/disease contexts.

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.

The Human FcγRII (CD32) Family of Leukocyte FcR in Health and Disease

FcγRs have been the focus of extensive research due to their key role linking innate and humoral immunity and their implication in both inflammatory and infectious disease. Within the human FcγR family FcγRII (activatory FcγRIIa and FcγRIIc, and inhibitory FcγRIIb) are unique in their ability to signal independent of the common γ chain. Through improved understanding of the structure of these receptors and how this affects their function we may be able to better understand how to target FcγR specific immune activation or inhibition, which will facilitate in the development of therapeutic monoclonal antibodies in patients where FcγRII activity may be desirable for efficacy. This review is focused on roles of the human FcγRII family members and their link to immunoregulation in healthy individuals and infection, autoimmunity and cancer.

The Correlation of CD206, CD209, and Disease Severity in Behçet's Disease with Arthritis

The purpose of this study was to clarify the role of pattern recognition receptors in Behçet's disease (BD). The frequencies of several pattern recognition receptors (CD11b, CD11c, CD32, CD206, CD209, and dectin-1) were analyzed in patients with BD by flow cytometry, and cytokine levels, interleukin- (IL-) 18, IL-23, and IL-17A, were compared in plasma. The analysis was performed in active (n = 13) and inactive (n = 13) stages of BD patients. Rheumatoid arthritis patients (n = 19), as a disease control, and healthy control (HC) (n = 19) were enrolled. The frequencies of CD11b+ and CD32+ cells were significantly increased in active BD patients compared to HC. Disease severity score was correlated to CD11c+, CD206+, and CD209+ in whole leukocytes and CD11b+, CD11c+, CD206+, CD209+, and Dectin-1+ in granulocytes. The plasma levels of IL-17A were significantly different between HC and active BD. IL-18 showed significant difference between active and inactive BD patients. From this study, we concluded the expressions of several pattern recognition receptors were correlated to the joint symptoms of BD.

Highly Expression of CD11b and CD32 on Peripheral Blood Mononuclear Cells from Patients with Adult-Onset Still's Disease

BACKGROUND

We investigated the potential role of several pattern-recognition receptors (PRRs; CD11b, CD11c, CD32, CD206, CD209, and dectin-1) in adult-onset Still's disease (AOSD).

METHODS

The study included 13 untreated AOSD patients, 19 rheumatoid arthritis (RA) patients (as a disease control), and 19 healthy controls (HCs). The PRRs were quantified in peripheral blood using flow cytometry. The serum levels of interleukin-17 (IL-17), IL-18, and IL-23 were measured by enzyme-linked immunosorbent assay.

RESULTS

Significantly higher mean frequencies of cells presenting CD11b and CD32 from whole blood were observed in patients with AOSD than in patients with RA or HC. The levels of IL-17, IL-18, and IL-23 were elevated in AOSD patients compared to HCs. CD11b frequencies from whole cells correlated with systemic scores, lactate dehydrogenase (LDH) levels, aspartate transaminase levels, interleukin-23 (IL-23) levels, and IL-18. Frequencies of CD209 from granulocytes were significantly correlated with systemic scores, and the erythrocyte sedimentation rate and levels of C-reactive protein, ferritin, LDH, IL-23, and interleukin-18 (IL-18).

CONCLUSIONS

Elevated frequencies of circulating CD11b-positive cells and positive correlations with disease activity markers suggest that circulating CD11b-positive cells contribute to the pathogenesis of AOSD.

Sustained Immune Complex-Mediated Reduction in CD16 Expression after Vaccination Regulates NK Cell Function

Cross-linking of FcγRIII (CD16) by immune complexes induces antibody-dependent cellular cytotoxicity (ADCC) by natural killer (NK) cells, contributing to control of intracellular pathogens; this pathway can also be targeted for immunotherapy of cancerous or otherwise diseased cells. However, downregulation of CD16 expression on activated NK cells may limit or regulate this response. Here, we report sustained downregulation of CD16 expression on NK cells in vivo after intramuscular (but not intranasal) influenza vaccination. CD16 downregulation persisted for at least 12 weeks after vaccination and was associated with robust enhancement of influenza-specific plasma antibodies after intramuscular (but not intranasal) vaccination. This effect could be emulated in vitro by co-culture of NK cells with influenza antigen and immune serum and, consistent with the sustained effects after vaccination, only very limited recovery of CD16 expression was observed during long-term in vitro culture of immune complex-treated cells. CD16 downregulation was most marked among normally CD16^high CD57⁺ NK cells, irrespective of NKG2C expression, and was strongly positively associated with degranulation (surface CD107a expression). CD16 downregulation was partially reversed by inhibition of ADAM17 matrix metalloprotease, leading to a sustained increase in both CD107a and CD25 (IL-2Rα) expression. Both the degranulation and CD25 responses of CD57+ NK cells were uniquely dependent on trivalent influenza vaccine-specific IgG. These data support a role for CD16 in early activation of NK cells after vaccination and for CD16 downregulation as a means to modulate NK cell responses and maintain immune homeostasis of both antibody and T cell-dependent pathways.

Fcγ receptor IIIa single-nucleotide polymorphisms and haplotypes affect human IgG binding and are associated with lupus nephritis in African Americans

OBJECTIVE

To investigate whether the Fcγ receptor IIIa-66L/R/H (FcγRIIIa-66L/R/H) polymorphism influences net effective receptor function and to assess if the FCGR3A combined genotypes formed by FcγRIIIa-66L/R/H and FcγRIIIa-176F/V, as well as copy number variation (CNV), confer risk of developing systemic lupus erythematosus (SLE) and lupus nephritis.

METHODS

FcγRIIIa variants, expressed on A20 IIA1.6 cells, were used in flow cytometry-based human IgG-binding assays. Using Pyrosequencing methodology, FCGR3A single-nucleotide polymorphism and CNV genotypes were determined in a cohort of 1,728 SLE patients and 2,404 healthy controls.

RESULTS

The FcγRIIIa-66L/R/H (rs10127939) polymorphism influenced ligand binding capacity in the presence of the FcγRIIIa-176V (rs396991) allele. There was a trend toward an association of the low-binding FcγRIIIa-176F allele with lupus nephritis among African Americans (P = 0.0609) but not among European Americans (P > 0.10). Nephritis among African American patients with SLE was associated with FcγRIIIa low-binding haplotypes containing the 66L/R/H and 176F variants (P = 0.03) and with low-binding genotype combinations (P = 0.002). No association was observed among European American patients with SLE. The distribution of FCGR3A CNV was not significantly different among controls and SLE patients with or without nephritis.

CONCLUSION

FcγRIIIa-66L/R/H influences ligand binding. The low-binding haplotypes formed by 66L/R/H and 176F confer enhanced risk of lupus nephritis in African Americans. FCGR3A CNVs are not associated with SLE or lupus nephritis in either African Americans or European Americans.

Allelic-dependent expression of an activating Fc receptor on B cells enhances humoral immune responses

B cells are pivotal regulators of acquired immune responses, and recent work in both experimental murine models and humans has demonstrated that subtle changes in the regulation of B cell function can substantially alter immunological responses. The balance of negative and positive signals in maintaining an appropriate B cell activation threshold is critical in B lymphocyte immune tolerance and autoreactivity. FcγRIIb (CD32B), the only recognized Fcγ receptor on B cells, provides immunoglobulin G (IgG)-mediated negative modulation through a tyrosine-based inhibition motif, which down-regulates B cell receptor-initiated signaling. These properties make FcγRIIb a promising target for antibody-based therapy. We report the discovery of allele-dependent expression of the activating FcγRIIc on B cells. Identical to FcγRIIb in the extracellular domain, FcγRIIc has a tyrosine-based activation motif in its cytoplasmic domain. In both human B cells and B cells from mice transgenic for human FcγRIIc, FcγRIIc expression counterbalances the negative feedback of FcγRIIb and enhances humoral responses to immunization in mice and to BioThrax vaccination in a human anthrax vaccine trial. Moreover, the FCGR2C-ORF allele is associated with the risk of development of autoimmunity in humans. FcγRIIc expression on B cells challenges the prevailing paradigm of unidirectional negative feedback by IgG immune complexes via the inhibitory FcγRIIb, is a previously unrecognized determinant in human antibody/autoantibody responses, and opens the opportunity for more precise personalized use of B cell-targeted antibody-based therapy.

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.

CD19 and CD32b differentially regulate human B cell responsiveness

B cell activation is regulated by a variety of signals. CD19 positively regulates B cell activation, augmenting signals delivered through the BCR complex. In contrast, CD32b contains an ITIM and negatively regulates BCR signaling. Importantly, there are drugs currently in clinical trials and preclinical development that cross-link CD32b to molecules within the BCR complex. We wanted to address how single engagement versus cotargeting these molecules affects human B cell function. When B cells from healthy individuals were activated by signals that mimic a T cell response (IL-21 costimulation), ligation of CD32b, but not CD19, inhibited B cell expansion and plasma cell (PC) differentiation. In contrast, when B cells were activated through TLR, anti-CD19, but not anti-CD32b, blunted the response. However, when both CD19 and CD32b were coengaged by a bispecific anti-CD19×CD32b Ab, both types of stimuli were potently inhibited. Cross-linking CD19 with CD32b also inhibited Ab-independent functions of B cells, such as HLA upregulation, cytokine production, and the ability of B cells to prime CD4(+) T cells. Finally, although cross-linking CD19 and CD32b inhibited PC differentiation of primary B cells, it did not alter Ig production from pre-established PCs. These data elucidate the mechanism by which a complex set of signals determines the fate of B cell responsiveness. Although signals through CD19 influence TLR-driven activation, CD32b impacts the magnitude of the response following IL-21 costimulation. Therefore, simultaneous targeting of multiple surface molecules may be a necessary approach to comprehensively modulate B cell activation in vivo.

FCGR2C genotyping by pyrosequencing reveals linkage disequilibrium with FCGR3A V158F and FCGR2A H131R polymorphisms in a Caucasian population

The FCGR3A-V158F and FCGR2A-H131R polymorphisms are associated with clinical responses to therapeutic mAbs and with immune thrombocytopenic purpura (ITP). The FCGR2C-ORF/STOP polymorphism, controlling FcγRIIC expression on natural killer cells and therefore FcγRIIC-mediated antibody dependent cell-mediated cytotoxicity, is also associated with ITP. Using a new pyrosequencing assay to determine this polymorphism in a control population, we observed the expected allele frequencies (ORF:12.6%) and percentages of individuals with a single copy (10.0%) or 3 copies (12.1%) of FCGR2C, or with at least one FCGR2C-ORF allele (20.1%). No association of FCGR2C copy number variations with the FCGR3A-V158F or FCGR2A-H131R genotype was detected. More importantly, our results demonstrate a strong and a weaker linkage disequilibrium associating the FCGR2C-ORF allele with the FCGR3A-158V and the FCGR2A-131H allele, respectively.

Evolutionary history of copy-number-variable locus for the low-affinity Fcγ receptor: mutation rate, autoimmune disease, and the legacy of helminth infection

Both sequence variation and copy-number variation (CNV) of the genes encoding receptors for immunoglobulin G (Fcγ receptors) have been genetically and functionally associated with a number of autoimmune diseases. However, the molecular nature and evolutionary context of this variation is unknown. Here, we describe the structure of the CNV, estimate its mutation rate and diversity, and place it in the context of the known functional alloantigen variation of these genes. Deletion of Fcγ receptor IIIB, associated with systemic lupus erythematosus, is a result of independent nonallelic homologous recombination events with a frequency of approximately 0.1%. We also show that pathogen diversity, in particular helminth diversity, has played a critical role in shaping the functional variation at these genes both between mammalian species and between human populations. Positively selected amino acids are involved in the interaction with IgG and include some amino acids that are known polymorphic alloantigens in humans. This supports a genetic contribution to the hygiene hypothesis, which states that past evolution in the context of helminth diversity has left humans with an array of susceptibility alleles for autoimmune disease in the context of a helminth-free environment. This approach shows the link between pathogens and autoimmune disease at the genetic level and provides a strategy for interrogating the genetic variation underlying autoimmune-disease risk and infectious-disease susceptibility.

Phenotypic variation in IgG receptors by nonclassical FCGR2C alleles

The balance between activating and inhibitory signals from the different FcγRs for IgG ensures homeostasis of many inflammatory responses. FCGR2C is the product of an unequal crossover of the FCGR2A and FCGR2B genes encoding the activating FcγRIIa (CD32a) and inhibitory FcγRIIb (CD32b), respectively. A single nucleotide polymorphism (SNP) in exon 3 of FCGR2C results in either expression of the activating FcγRIIc (CD32c) (FCGR2C-open reading frame [ORF]) or its absence because of a stop codon (FCGR2C-Stop). Two additional variations in FcγRIIb/c expression on leukocytes have now been identified. In case of "nonclassical" FCGR2C-ORF alleles, FcγRIIc expression was unexpectedly absent, because of novel splice site mutations near exon 7 leading to another stop codon. In some individuals with FCGR2C-Stop alleles FcγRIIb was detected on NK cells, which normally are devoid of this protein. Individuals with these nonclassical FCGR2C-Stop alleles carried a deletion of FCGR2C-FCGR3B that extends into the promoter region of the adjacent FCGR2B gene and probably deletes a negative regulatory element in the FCGR2B promoter in NK cells. FcγRIIb expression on NK cells effectively inhibited killing mediated by FcγRIIIa (CD16a) in Ab-dependent cytotoxicity tests. Our findings demonstrate a more extensive and previously unnoticed variation in FcγR expression with relevance to immunity and inflammation.

Association of variation in Fcgamma receptor 3B gene copy number with rheumatoid arthritis in Caucasian samples

OBJECTIVE

There is increasing evidence that variation in gene copy number (CN) influences clinical phenotype. The low-affinity Fcgamma receptor 3B (FCGR3B) located in the FCGR gene cluster is a CN polymorphic gene involved in the recruitment to sites of inflammation and activation of polymorphonuclear neutrophils (PMNs). Given recent evidence that low FCGR3B CN is a risk factor for systemic but not organ-specific autoimmune disease and the potential importance of PMN in the pathophysiology of rheumatoid arthritis (RA), the authors hypothesised that FCGR3B gene dosage influences susceptibility to RA.

METHODS

FCGR3B CN was measured in 643 cases of RA and 461 controls from New Zealand (NZ), with follow-up analysis in 768 cases and 702 controls from the Netherlands and 250 cases and 211 controls from the UK. All subjects were of Caucasian ancestry.

RESULTS

Significant evidence for an association between CN <2 and RA was observed in the Dutch cohort (OR 2.01 (95% CI 1.37 to 2.94), p=3 x 10-4) but not in the two smaller cohorts (OR 1.45 (95% CI 0.92 to 2.26), p=0.11 and OR 1.33 (95% CI 0.58 to 3.02), p=0.50 for the NZ and UK populations, respectively). The association was evident in a meta-analysis which included a previously published Caucasian sample set (OR 1.67 (95% CI 1.28 to 2.17), p=1.2 x 10-4).

CONCLUSIONS

One possible mechanism to explain the association between reduced FCGR3B CN and RA is the reduced clearance of immune complex during inflammation. However, it is not known whether the association between RA and FCGR3B CN is aetiological or acts as a proxy marker for another biologically relevant variant. More detailed examination of genetic variation within the FCGR gene cluster is required.

A novel subset of NK cells expressing high levels of inhibitory FcgammaRIIB modulating antibody-dependent function

NK cells can kill antibody-coated target cells following engagement of FcgammaRIIIA, the major activating FcgammaR expressed by these cells. The presence of FcgammaRIIC (CD32C) has also been reported, but its contribution to the FcgammaR-dependent effector functions of NK cells remains debated. We demonstrate here that inhibitory FcgammaRIIB is also expressed by a small subset of CD56+/NKp46+ NK cells and can efficiently down-modulate their FcgammaR-dependent effector function. Immunofluorescence analyses of NK cells from 52 healthy donors showed the presence of CD56bright/FcgammaRII(-) (5.2%+/-3.4), CD56dim/FcgammaRII(lo/-) (94.1%+/-3.4), and CD56dim/FcgammaRIIbright (0.64%+/-0.72) cells. QRT-PCR and protein analyses performed on isolated FcgammaRIIbright NK cells indicated that FcgammaRIIB is strongly expressed by these cells but not by FcgammaRII(lo/-) cells. In addition, FcgammaRIIbright cells showed a weaker antibody-dependent degranulation when incubated with IgG-coated target cells compared with FcgammaRII(lo/-) NK cells, although a strong FcgammaRIIIA expression was detected in both cells. Furthermore, the addition of anti-FcgammaRII Fab paralleled a higher degranulation of FcgammaRIIbright NK cells, indicating a direct role for FcgammaRIIB in this down-modulating effect. Thus, it is proposed that FcgammaRIIBbright NK cells represent a new NK cell compartment able to down-modulate NK cell functions triggered by the engagement of activating FcgammaR.

Possible therapeutic applications of single-chain antibodies in systemic autoimmune diseases

B cells participate in the induction and maintenance of systemic autoimmune diseases, such as rheumatoid arthritis and systemic lupus erythematosus, via production of pathogenic autoantibodies, contributing to the formation of immune complexes. Immune complex deposition in the kidney and joints causes inflammation and organ destruction, and chemokine production enhances T cell activation and tissue damage. The development of the disorder depends on several factors, for example, genetic susceptibility, environmental factors or immune dysregulation. Traditional therapies, which aimed at the alleviation of symptoms, are giving way to biological therapies with the potential of disrupting disease progression. This article focuses on antibody therapies, especially on the applications of single-chain antibodies, as new biological agents for the treatment of systemic autoimmune disorders.

FcgammaRII and multi-system autoimmune disease

The FcR are a crucial link in the immune response between humoral and cellular immunity and cell-based effector systems, mediating a wide variety of physiological and biochemical responses. The FcR for IgG (FcgammaR) and in particular the most widely expressed of these, FcgammaRII, are important in regulating adaptive immunity. Disruption of their function is a key factor in the development of autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA), which are characterized by chronic, multi-organ inflammation. Studies of the FcgammaRII include structure/function relationships, investigation of the associations between FcR polymorphisms and human disease and animal studies using knockout or transgenic mouse models. These investigations showed that the various forms of FcgammaRII interact with immune complexes to either initiate or inhibit inflammation. In conjunction with environmental antigens and genotype, the FcgammaRII activating and inhibitory receptors determine the nature and magnitude of response to antigens. In this review, the structure and function of the FcgammaRIIs and their role in immune complex-mediated auto-immunity are discussed.

Potassium channels, memory T cells, and multiple sclerosis

Multiple sclerosis is a chronic inflammatory autoimmune disease of the central nervous system characterized by demyelination and axonal damage that result in disabling neurological deficits. Here the authors explain the rationale for the use of inhibitors of the Kv1.3 K+ channel in immune cells as a therapy for multiple sclerosis and other autoimmune disorders.