Association of Fc? receptor IIA, but not IIB and IIIA, polymorphisms with systemic lupus erythematosus: A family-based association study in Caucasians

SLE-associated risk factors affect DC function

PURPOSE OF REVIEW

Identification of function and potential pathogenic mechanisms of SLE risk genes in dendritic cells.

RECENT FINDINGS

Functional studies of individual SLE risk factors in dendritic cells were performed, and functional alterations of some risk genes in dendritic cells were observed. Recent studies confirmed the pathogenic function of known risk genes. These findings postulate novel pathogenic mechanisms made by dendritic cells. SLE is a complex disease and its etiology is not clearly understood. Dendritic cells are innate immune cells and critical for determining immune activation and immune tolerance. Genetic studies identified several new candidate genes which predispose to development of autoimmune diseases, but the mechanism of those genes has not been identified. This report updates functional implications or pathways in dendritic cells which are putatively important for the development or propagation of SLE based on genetic and functional studies performed in both human and animal models.

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.

Cross-Phenotype Association Analysis Using Summary Statistics from GWAS

For over a decade, genome-wide association studies (GWAS) have been a major tool for detecting genetic variants underlying complex traits. Recent studies have demonstrated that the same variant or gene can be associated with multiple traits, and such associations are termed cross-phenotype (CP) associations. CP association analysis can improve statistical power by searching for variants that contribute to multiple traits, which is often relevant to pleiotropy. In this chapter, we discuss existing statistical methods for analyzing association between a single marker and multivariate phenotypes, we introduce a general approach, CPASSOC, to detect the CP associations, and explain how to conduct the analysis in practice.

CPAG: software for leveraging pleiotropy in GWAS to reveal similarity between human traits links plasma fatty acids and intestinal inflammation

Meta-analyses of genome-wide association studies (GWAS) have demonstrated that the same genetic variants can be associated with multiple diseases and other complex traits. We present software called CPAG (Cross-Phenotype Analysis of GWAS) to look for similarities between 700 traits, build trees with informative clusters, and highlight underlying pathways. Clusters are consistent with pre-defined groups and literature-based validation but also reveal novel connections. We report similarity between plasma palmitoleic acid and Crohn's disease and find that specific fatty acids exacerbate enterocolitis in zebrafish. CPAG will become increasingly powerful as more genetic variants are uncovered, leading to a deeper understanding of complex traits. CPAG is freely available at www.sourceforge.net/projects/CPAG/.

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.

Polymorphism of FCGR3A gene in sarcoidosis

We showed increased level of immune complexes (ICs) with mycobacterial heat shock proteins (Mtb-hsp) and increased expression of receptors for Fc fragment of immunoglobulin G (FcγR) I-III on blood monocytes with their increased phagocytic activity, responsible for clearance of these ICs in sarcoidosis (SA). Since FcγRIIIa is the most crucial in this process, we genotyped 77 SA patients and 143 healthy controls with polymerase chain reaction for V158F polymorphism of FCGR3A gene, encoding FcγRIIIa. We revealed significantly higher percentage of 158F and 158FF and lower of 158FV variants in Stage I of SA versus controls. Conversely, in Stage II of SA, we found increase in 158VV homozygotes versus controls. We also showed significant increase of 158F and 158FF variants in Stage I vs II and of 158V in Stage II vs I. Therefore, in Stage I, 158F allele may cause decreased FcγRIIIa affinity and clearance of ICs, whereas in Stage II, 158V allele may cause effective FcγRIIIa affinity to ICs with e.g. mycobacteria, their phagocytosis, Mtb-hsp secretion with ICs formation, Mtb-hsp epitope spread and subsequent immune reaction. Thus, V158F polymorphism of FCGR3A may explain the immunocomplexemia in our patients and might serve as prognostic marker of clinical course of sarcoidosis.

[Fcγ receptor and systemic autoimmune disease]

The systemic autoimmune disease such as systemic lupus erythematosus (SLE) is characterized by the deposition of immune complexes in multiple organs. Fcγ receptors (FcγR) recognize the Fc portion of IgG and are important in determining the response of leukocytes to deposited immune complexes. FcγR also provide positive and negative regulation of immune cell responses. The activatory FcγR including the FcR common γ chain take balance with Fcγ RIIB, the only inhibitory FcγR. Development of lupus-like autoimmune disease as well as monocytosis in BXSB mice is dependent on the activatory and inhibitory FcγR. In human SLE, dysregulated expression of FcγRIIB on memory B cells is reported and numbers of associations with genetic polymorphism are also reported. The cell-specific modulation of these activatory or inhibitory FcγRs are expected for the new therapeutic strategy in autoimmune diseases.

Genetic susceptibility to systemic lupus erythematosus in the genomic era

Our understanding of the genetic basis of systemic lupus erythematosus (SLE) has been rapidly advanced using large-scale, case-control, candidate gene studies as well as genome-wide association studies during the past 3 years. These techniques have identified more than 30 robust genetic associations with SLE including genetic variants of HLA and Fcγ receptor genes, IRF5, STAT4, PTPN22, TNFAIP3, BLK, BANK1, TNFSF4 and ITGAM. Most SLE-associated gene products participate in key pathogenic pathways, including Toll-like receptor and type I interferon signaling pathways, immune regulation pathways and those that control the clearance of immune complexes. Disease-associated loci that have not yet been demonstrated to have important functions in the immune system might provide new clues to the underlying molecular mechanisms that contribute to the pathogenesis or progression of SLE. Of note, genetic risk factors that are shared between SLE and other immune-related diseases highlight common pathways in the pathophysiology of these diseases, and might provide innovative molecular targets for therapeutic interventions.

FCGR3B copy number variation is not associated with lupus nephritis in a Chinese population

Copy number variation (CNV) is common in genomic regions encoding immune-related genes and can impact polygenic autoimmunity. FCGR3B CNV is associated with susceptibility to systemic autoimmunity in Caucasian populations. In this study, we examined FCGR3B CNV in patients with the autoimmune disease lupus nephritis (LN) in a Chinese population. The study includes 202 patients with histologically verified LN and 146 geographically matched healthy controls. To identify CNV at the FCGRB locus, quantitative polymerase chain reaction (PCR) was done with TaqMan( TM) probes and relative copy number was estimated with relative quantitative 2(-DeltaDeltaCt) method. The distribution of FCGR3B relative copy number did not differ significantly between the LN patients and the controls (1.17 +/- 0.42 for LN; 1.15 +/- 0.37 for controls; p = 0.627). The difference was still not significant when the data were stratified by gender. There was no significant difference when the LN patients were divided by pathological phenotype (proliferative LN compared with non-proliferative p = 0.511; AI < 12 compared with AI > or = 12, p = 0.401; and chronicity index (CI) < 4 compared with CI > or = 4, p = 0.058) or lupus disease activity index (SLEDAI < or = 10 compared with SLEDAI > 10, p = 0.996). The data suggest that FCGR3B CNV was not associated with LN development or progression in this Chinese population. These results were surprising given the strong in a Caucasian population.

Functional and clinical consequences of Fc receptor polymorphic and copy number variants

Receptors for immunoglobulins (Fc receptors) play a central role during an immune response, as they mediate the specific recognition of antigens of almost infinite diversity by leucocytes, thereby linking the humoral and cellular components of immunity. Indeed, engagement of Fc receptors by immunoglobulins initiates a range of immunoregulatory processes that might also play a role in disease pathogenesis. In the circulation, five main types of immunoglobulins (Ig) exist - namely IgG, IgA, IgE, IgM and IgD and receptors with the ability to recognize and bind to IgG (Fc gamma receptor family), IgE (Fc epsilon RI and CD23), IgA (CD89; Fc alpha/microR) and IgM (Fc alpha/microR) have been identified and characterized. However, it is astonishing that nearly all the known human Fc receptors display extensive genetic variation with clear implications for their function, thus representing a substantial genetic risk factor for the pathogenesis of a range of chronic inflammatory disorders.

Low-affinity Fcgamma receptors, autoimmunity and infection

Low-affinity Fcgamma receptors (FcgammaRs) mediate the effects of immunoglobulin G (IgG) antibodies on leukocytes, including recruitment to inflammatory lesions, phagocytosis, antibody-dependent cellular cytotoxicity, release of inflammatory mediators and regulation of B cell activation. These functions are an important part of the mammalian response to infection, but if deployed inappropriately can cause autoimmune disease. Although most FcgammaRs are activatory, there is also an inhibitory FcgammaR that, when bound to IgG immune complexes, is able to downregulate the effects of both the activatory FcgammaRs and the B cell receptor. This review discusses the role of the low-affinity FcgammaRs in a balanced immune response and how perturbations in FcgammaR function result in susceptibility to infection or autoimmunity.

Fcgamma receptors: structure, function and role as genetic risk factors in SLE

Over 30 years ago, receptors for the Fc region of IgG (FcgammaR) were implicated in the pathogenesis of systemic lupus erythematosus (SLE). Since those pioneering studies, our knowledge of the structure and function of these FcgammaRs has increased dramatically. We now know that FcgammaR contributes to the regulation of acquired immunity and to the regulation of innate immune responses where FcgammaRs act as specific receptors for innate opsonins (CRP and SAP). Our understanding of the genomic architecture of the genes encoding the FcgammaR has also witnessed remarkable advances. Numerous functionally relevant single-nucleotide polymorphism (SNP) variants and copy number (CN) variants have been characterized in the FcgammaR genes. Many of these variants have also been shown to associate with risk to development of SLE and some have been associated with disease progression. This review will provide an overview of the FcgammaR in relation to SLE, including consideration of the role of genetic variants in FcgammaR in SLE pathogenesis. The difficulties in assessing genetic variation in these genes will be discussed. To enhance our understanding of the functional roles of these receptors in SLE, future research will need to integrate our knowledge of SNP variants, CN variants and the functional diversity of these receptors.

Fc receptor genes and the systemic lupus erythematosus diathesis

Fc receptors represent a distinct group of hematopoeitic cell surface glycoproteins that have a characterized role in affecting the efficiency of the mononuclear phagocyte system to clear IgG immune complexes. Functional genetic variations in this family of receptors have been identified as heritable susceptibility factors for SLE and lupus nephritis across diverse populations. In this review, we describe the roles of the classical Fc receptors for IgG (Fc gamma) and non-classical Fc-like receptors (FCR1-FCRL6L), Fc receptors for IgE (Fc epsilon RI) and IgA and IgM (Fc alpha/mu R) in SLE diathesis. The combined effects of these genes on SLE pathogenesis, either via linkage disequilibrium or epistasis with additional genetic or environmental factors, provide a challenge for future investigations. The pursuit of a polygenic SLE-profile that includes longitudinal evaluations of SLE and markers involved in the protean clinical manifestations associated with SLE will facilitate our understanding of the cascade of inflammatory events associated with the diathesis.

Risk alleles for multiple sclerosis identified by a genomewide study

BACKGROUND

Multiple sclerosis has a clinically significant heritable component. We conducted a genomewide association study to identify alleles associated with the risk of multiple sclerosis.

METHODS

We used DNA microarray technology to identify common DNA sequence variants in 931 family trios (consisting of an affected child and both parents) and tested them for association. For replication, we genotyped another 609 family trios, 2322 case subjects, and 789 control subjects and used genotyping data from two external control data sets. A joint analysis of data from 12,360 subjects was performed to estimate the overall significance and effect size of associations between alleles and the risk of multiple sclerosis.

RESULTS

A transmission disequilibrium test of 334,923 single-nucleotide polymorphisms (SNPs) in 931 family trios revealed 49 SNPs having an association with multiple sclerosis (P<1x10(-4)); of these SNPs, 38 were selected for the second-stage analysis. A comparison between the 931 case subjects from the family trios and 2431 control subjects identified an additional nonoverlapping 32 SNPs (P<0.001). An additional 40 SNPs with less stringent P values (<0.01) were also selected, for a total of 110 SNPs for the second-stage analysis. Of these SNPs, two within the interleukin-2 receptor alpha gene (IL2RA) were strongly associated with multiple sclerosis (P=2.96x10(-8)), as were a nonsynonymous SNP in the interleukin-7 receptor alpha gene (IL7RA) (P=2.94x10(-7)) and multiple SNPs in the HLA-DRA locus (P=8.94x10(-81)).

CONCLUSIONS

Alleles of IL2RA and IL7RA and those in the HLA locus are identified as heritable risk factors for multiple sclerosis.

Physiopathologie du lupus érythémateux systémique

Innate immunity is directly implicated in the pathophysiology of lupus through the dendritic cell system and the activation by immune complexes of some toll-like receptors (TLR). Interferon-alpha plays a key role in the pathophysiology of lupus and represents a promising target for immune therapy. Dendritic cells are activated and able to capture large quantities of nuclear antigen-containing bodies to stimulate specific adaptive immune response.

The involvement of Fc gamma receptor gene polymorphisms in Kawasaki disease

Kawasaki disease is an acute febrile syndrome in infancy, characterized by vasculitis of medium-sized arteries. Without treatment the disease can lead to coronary artery lesions (CAL) in approximately 25% of the children. Therapy consists of intravenous immunoglobulins (IVIG), leading to a decrease of complications to 5-16%. Little is known about the working mechanisms of IVIG. In this study we evaluated the involvement of Fcgamma receptors (FcgammaRs) in Kawasaki disease by the determination of the frequency of known single nucleotide polymorphisms (SNPs) in the genes coding for the FcgammaRs and compared this with frequencies in a cohort of healthy controls. There was no difference in the distribution of the functionally relevant genotypes for FcgammaRIIa-131H/R, FcgammaRIIb-232I/T, FcgammaRIIIa-158 V/F and FcgammaRIIIb-NA1/NA2 between the patient group and the healthy controls. Furthermore, there were no polymorphisms linked to the disease severity as indicated by the absence or development of CAL during the disease. Altered transcription or expression of FcgammaR on specific cell types of the immune system may still play a role in susceptibility and treatment success, but at a level different from the functional SNPs in FcgammaR genes tested in this study.

Lack of association between FCRL3 and FcγRII polymorphisms in Japanese type 1 autoimmune hepatitis

Autoimmune hepatitis (AIH) is an organ-specific autoimmune disease characterized by chronic inflammation of the liver. Although the HLA-DRB1*0405 allele is associated with type 1 AIH in Japanese, the exact genetic etiology of AIH remains undefined. Recently, polymorphisms of Fcgamma receptors (FcgammaR) and Fc receptor-like gene 3 (FCRL3) were linked to a variety of autoimmune diseases, and may be at least partially responsible for susceptibility to AIH. In this study, we genotyped FcgammaRIIA, FcgammaRIIB, and four FCRL3 polymorphisms in 87 Japanese patients with type 1 AIH and 97 ethnically matched controls using the TaqMan assay. Although we were able to detect significantly lower serum IgG concentrations in AIH patients specifically with the FCRL3-110A/A genotype, we observed no difference in the distribution of the genotypes between patients and controls, implying that susceptibility to type 1 AIH in Japanese patients is not influenced by FcgammaRIIA, FcgammaRIIB, or FCRL3 polymorphisms.

Analysis of Fcgamma receptor haplotypes in rheumatoid arthritis: FCGR3A remains a major susceptibility gene at this locus, with an additional contribution from FCGR3B

The Fcγ receptors play important roles in the initiation and regulation of many immunological and inflammatory processes, and genetic variants (FCGR) have been associated with numerous autoimmune and infectious diseases. The data in rheumatoid arthritis (RA) are conflicting and we previously demonstrated an association between FCGR3A and RA. In view of the close molecular proximity with FCGR2A, FCGR2B and FCGR3B, additional polymorphisms within these genes and FCGR haplotypes were examined to refine the extent of association with RA. Biallelic polymorphisms in FCGR2A, FCGR2B and FCGR3B were examined for association with RA in two well characterized UK Caucasian and North Indian/Pakistani cohorts, in which FCGR3A genotyping had previously been undertaken. Haplotype frequencies and linkage disequilibrium were estimated across the FCGR locus and a model-free analysis was performed to determine association with RA. This was followed by regression analysis, allowing for phase uncertainty, to identify the particular haplotype(s) that influences disease risk. Our results reveal that FCGR2A, FCGR2B and FCGR3B were not associated with RA. The haplotype with the strongest association with RA susceptibility was the FCGR3A–FCGR3B 158V-NA2 haplotype (odds ratio 3.18, 95% confidence interval 1.13–8.92 [P = 0.03] for homozygotes compared with all genotypes). The association was stronger in the presence of nodules (odds ratio 5.03, 95% confidence interval 1.44–17.56; P = 0.01). This haplotype was also more common in North Indian/Pakistani RA patients than in control individuals, but not significantly so. Logistic regression analyses suggested that FCGR3A remained the most significant gene at this locus. The increased association with an FCGR3A–FCGR3B haplotype suggests that other polymorphic variants within FCGR3A or FCGR3B, or in linkage disequilibrium with this haplotype, may additionally contribute to disease pathogenesis.

Role of B cell inhibitory receptor polymorphisms in systemic lupus erythematosus: a negative times a negative makes a positive

B lymphocytes play a pivotal role in the pathogenesis of systemic lupus erythematosus (SLE). Here, we will review our studies on the role of polymorphisms of two genes coding for B cell inhibitory receptors, FCGR2B and CD72. In FCGR2B, a single nucleotide polymorphism leading to a nonsynonymous substitution, Ile232Thr, within the transmembrane domain was identified, and a significant association of the 232Thr/Thr genotype with SLE was observed in Japanese, Thai and Chinese populations, while this allele was found to be rare in Caucasians. On the other hand, the association of FCGR2B promoter polymorphism with SLE in Caucasians has been reported by two independent groups, but this allele was not found to be present in Japanese. These observations demonstrate that the association of FCGR2B polymorphisms with SLE is common to multiple populations, but the alleles associated with SLE depend upon the genetic background of each population. Functional analyses using a human B cell line lacking endogenous FcgammaRIIb revealed that SLE-associated 232Thr allele product was partially excluded from membrane lipid rafts under resting conditions and after coligation with B cell receptor, and was significantly less potent at inhibiting B cell activation. Two haplotypes were identified in CD72, one of which was associated with increased production of an alternative splicing isoform that substantially alters the extracellular region of CD72. Interestingly, the presence of the haplotype significantly decreased the risk of SLE conferred by FCGR2B-232Thr in an epistatic manner. These observations emphasize the need to understand human immune system diversity if we are to improve our understanding of the pathogenesis of autoimmune diseases.

Fcgamma receptors: old friends and new family members

Although cellular receptors for immunoglobulins were first identified nearly 40 years ago, their central role in the immune response was discovered only in the last decade. They are key players in both the afferent and efferent phase of an immune response, setting thresholds for B cell activation, regulating the maturation of dendritic cells, and coupling the exquisite specificity of the antibody response to innate effector pathways, such as phagocytosis, antibody-dependent cellular cytotoxicity, and the recruitment and activation of inflammatory cells. Moreover, because of their general presence as receptor pairs consisting of activating and inhibitory molecules on the same cell, they have become a paradigm for studying the balance of positive and negative signals that ultimately determine the outcome of an immune response. This review will summarize recent results in Fc-receptor biology with an emphasis on data obtained in in vivo model systems.

Role of Fc gamma receptor IIb polymorphism in the genetic background of systemic lupus erythematosus: insights from Asia

FCGR2B codes for an inhibitory receptor expressed in B cells and monocytes. Polymorphisms of Fcgr2b in mice have been shown to be associated with autoimmune diseases including systemic lupus erythematosus (SLE) and targeted disruption of Fcgr2b renders mice susceptible to induced or spontaneous autoimmunity, depending on the genetic background. Polymorphism screening of FCGR2B has been hampered by the complexity and extreme homology among FCGR family members. We established a specific genotyping system, detected a SNP that changes position 232 amino acid in the transmembrane region from Ile to Thr and found a significant association of 232Thr with SLE in the Japanese, Thai and Chinese populations. In contrast, promoter polymorphism of FCGR2B, but not Ile232Thr, was shown to be associated with SLE in Caucasians. Linkage disequilibrium was observed among FCGR2A, 2B, 3A and 3B genes with varying degrees, but in the Asian populations, each of FCGR2B, 3A and 3B genes was suggested to contribute to the susceptibility to SLE. These results indicate that FCGR2B is a susceptibility gene to SLE in the context of a genetic background, both in humans and mice.

Fc receptors and their role in immune regulation and autoimmunity

The activation threshold of cells in the immune system is often tuned by cell surface molecules. The Fc receptors expressed on various hematopoietic cells constitute critical elements for activating or downmodulating immune responses and combines humoral and cell-mediated immunity. Thus, Fc receptors are the intelligent sensors of the immune status in the individual. However, impaired regulation by Fc receptors will lead to unresponsiveness or hyperreactivity to foreign as well as self-antigens. Murine models for autoimmune disease indicate the indispensable roles of the inhibitory Fc receptor in the suppression of such disorders, whereas activating-type FcRs are crucial for the onset and exacerbation of the disease. The development of many autoimmune diseases in humans may be caused by impairment of the human Fc receptor regulatory system. This review is aimed at providing a current overview of the mechanism of Fc receptor-based immune regulation and the possible scenario of how autoimmune disease might result from their dysfunction.

Genetics of susceptibility and severity in systemic lupus erythematosus

PURPOSE OF REVIEW

The genetic basis of systemic lupus erythematosus, a complex genetic trait, may provide important insights into autoimmune disease. Innovation in both practical and theoretical approaches will assist in accelerating the pace of discovery and our understanding of pathogenesis.

RECENT FINDINGS

Significant progress has been made in the last year with respect to the refinement of genetic intervals to promising candidate genes involved in systemic lupus erythematosus pathogenesis and specific phenotype susceptibility. This review highlights these discoveries and suggests platforms that may affect the future of analysis of this complex disease.

SUMMARY

Understanding the genetic basis for systemic lupus erythematosus disease and sub-phenotype susceptibility will have a substantial effect on the therapeutic interventions used to care for patients.

FcγRIIB Ile232Thr transmembrane polymorphism associated with human systemic lupus erythematosus decreases affinity to lipid rafts and attenuates inhibitory effects on B cell receptor signaling

The B cell inhibitory receptor FcgammaRIIB plays crucial roles in the maintenance of self-tolerance. We have identified a polymorphism FCGR2B c.695T>C that results in the non-conservative replacement of 232Ile at the transmembrane helix to Thr and demonstrated the association of the polymorphism with susceptibility to systemic lupus erythematosus (SLE) in Asians. In this study, we examined the impact of FCGR2B c.695T>C on the functional properties of FcgammaRIIB by expressing each allele product in a human B cell line ST486 lacking endogenous FcgammaRIIB. FcgammaRIIB 232Thr was found to be significantly less potent than wild-type 232Ile in inhibiting B cell receptor (BCR)-mediated phosphatidylinositol-3,4,5-trisphosphate accumulation, Akt and PLCgamma2 activation and calcium mobilization, and to display decreased levels of tyrosine phosphorylation and SH2-containing 5'-inositolphosphate phosphatase recruitment compared with 232Ile after IgG Fc-mediated coligation with BCR. Notably, a quantitative analysis of the subcellular distribution of FcgammaRIIB using 125I-labeled anti-FcgammaRIIB revealed that FcgammaRIIB 232Thr is less effectively distributed to detergent-insoluble lipid rafts than 232Ile, findings in accordance with the importance of the transmembrane amino acid residues, in particular large hydrophobic amino acids including Ile, in the association of membrane proteins with lipid rafts. Given the crucial roles of lipid rafts in integrating BCR signaling, decreased association of FcgammaRIIB 232Thr could contribute to its impaired inhibitory potential. Collectively, the present findings indicate that the Ile232Thr substitution affects the localization and function of FcgammaRIIB and that the molecular mechanism may link the polymorphism and susceptibility to SLE.

Involvement of immunoglobulin FcgammaRIIA and FcgammaRIIIB gene polymorphisms in susceptibility to rheumatic fever

OBJECTIVES

To assess the impact of the human FcgammaRIIA and FcgammaRIIIB gene polymorphisms on the risk of rheumatic fever (RF).

DESIGNS AND METHODS

FcgammaRIIA-R/H-131 and FcgammaRIIIB-NA1/NA2 genotypes were determined using polymerase chain reaction in 66 RF cases and 117 healthy controls in this case control study.

RESULTS

Compared with healthy controls, the RR genotype was enriched in the entire group of RF cases (odds ratio [OR] 4.98, 95% confidence interval [95% CI] 1.81-13.70). RF patients were more frequently HR heterozygotes rather than HH homozygotes (OR 3.09 vs. 0.11). The results of this study show that patients who have RF are more likely to have the RR and HR genotypes than control children. These probabilities show that RR is associated with the greatest risk for rheumatic fever and HR is associated with an intermediate risk. For the distribution of FcgammaRIIIB NA2 genotypes, a nonsignificant increase was found in RF patients (39.31% vs. 51.51%; OR 1.64, P = 0.1226).

CONCLUSION

The FcgammaRIIA-R/H-131 polymorphism may be an important marker in determining predisposition to RF.

CD72 polymorphisms associated with alternative splicing modify susceptibility to human systemic lupus erythematosus through epistatic interaction with FCGR2B

We previously reported association of FCGR2B-Ile232Thr with systemic lupus erythematosus (SLE) in three Asian populations. Because polymorphism of CD72, another inhibitory receptor of B cells, was associated with murine SLE, we identified human CD72 polymorphisms, tested their association with SLE and examined genetic interaction with FCGR2B in the Japanese (160 SLE, 277 controls), Thais (87 SLE, 187 controls) and Caucasians (94 families containing SLE members). Four polymorphisms and six rare variations were detected. The former constituted two major haplotypes that contained one or two repeats of 13 nucleotides in intron 8 (designated as *1 and *2, respectively). Although association with susceptibility to SLE was not detected, the *1 allele was significantly associated with nephritis among the Japanese patients (P=0.024). RT-PCR identified a novel alternatively spliced (AS) transcript that was expressed at the protein level in COS-7 transfectants. The ratio of AS/common isoforms was strikingly increased in individuals with *2/*2 genotype when compared with *1/*1 (P=0.000038) or *1/*2 (P=0.0085) genotypes. Using the two Asian cohorts, significant association of FCGR2B-232Thr/Thr with SLE was observed only in the presence of CD72-*1/*1 genotype (OR 4.63, 95% CI 1.47-14.6, P=0.009 versus FCGR2B-232Ile/Ile plus CD72-*2/*2). Minigene assays demonstrated that the 13-nucleotide repeat and 4 bp deletion within the same haplotype of intron 8 could regulate alternative splicing. The AS isoform lacks exon 8, and is deduced to contain 49 amino acid changes in the membrane-distal portion of the extracellular domain, where considerable amino acid changes are known in CD72(c) allele associated with murine SLE. These results indicated that the presence of CD72-*2 allele decreases risk for human SLE conferred by FCGR2B-232Thr, possibly by increasing the AS isoform of CD72.