Conservation of FcepsilonRI gamma chain coding region in normals and in SLE patients

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.

Association of three sets of high-affinity IgE receptor (FcepsilonR1) polymorphisms with aspirin-intolerant asthma

BACKGROUND AND OBJECTIVE

The high-affinity IgE receptor comprises a tetramer of the ligand-binding alpha chain, a signal-augmenting beta chain, and a signal-transducing gamma chain dimer on mast cells. We hypothesized that the three subsets of the FCER1 gene may play a role in the development of the aspirin-intolerant asthma (AIA) phenotype and analyzed these genetic polymorphisms in association with clinical parameters in AIA patients.

SUBJECTS AND METHODS

Six polymorphisms of FCER1 (FCERIA-344C>T, FCER1A-95T>C, MS4A2-109T>C, MS4A2 E237G, FCER1G-237A>G, FCER1G-54G>T) were genotyped in 126 AIA patients compared to 177 patients with aspirin-tolerant asthma (ATA) and 222 normal health controls (NC).

RESULTS

A significant difference in the genotype frequencies of FCER1G-237A>G was detected between AIA and ATA patients (p<0.05) both in co-dominant and recessive analysis models, whereas no significant relationships were identified between the frequencies of the other five single-nucleotide polymorphisms and AIA, ATA, and NC subjects. In addition, AIA patients carrying the homozygous AA genotype of FCER1G-237A>G exhibited significantly higher total serum IgE levels than did those with the GG/AG genotype (p=0.012). AIA patients expressing the CT/TT genotype at FCERIA-344C>T showed a higher prevalence of serum IgE specific to Staphylococcal enterotoxin A than did those with the CC genotype (p=0.008).

CONCLUSION

The FCER1G-237A>G and FCERIA-344C>T polymorphisms may contribute to the development of AIA in a Korean population.

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.

Genetic variability of the high-affinity IgE receptor alpha subunit (Fc epsilon RI alpha) is related to total serum IgE levels in allergic subjects

Known susceptibility genes to atopy and asthma have been identified by linkage or associations with clinical phenotypes, including total serum IgE levels. IgE-mediated sensitivity reactions require a high-affinity IgE receptor (FcepsilonRI), which immobilizes the immunoglobulin on the surface of the effector cells, mostly mast cells and basophils. In this mini-review, recent findings are presented on genetic variation of this receptor, as related to atopy. Transcription of FCER1A gene encoding the receptor alpha subunit can be initiated from two separate promoters, the proximal one and the distal one, which results in a transcript containing two novel untranslated exons (1A, 2A). Our knowledge on the role of this mechanism in allergic diseases is still at an infancy stage. Within regulatory elements of FCER1A some common single nucleotide polymorphisms have functional associations, which were recently reported and replicated in different ethnical groups. Interestingly, these associations do not confer susceptibility to allergic diseases, but rather modulate serum concentrations of IgE. Similarly to the previously investigated beta subunit of the receptor, FCER1A is a good candidate for a quantitative trait locus (QTL) in allergic diseases, and appears to participate in the systemic regulation of IgE levels.

IgE and FcepsilonRI regulation

The high-affinity immunoglobulin (Ig)E receptor, FcepsilonRI, regulates the action of mast cells and basophils and therefore, regulates the expression of atopic disease. There have been several recent observations that demonstrate new behaviors for this receptor. The control of FcepsilonRI expression, control of cell function by FcepsilonRI, and expression of FcepsilonRI on other cell types are important new areas of understanding currently being explored.

IgE and Fc{epsilon}RI regulation

A central feature of allergic reactions is the aggregation of the high-affinity IgE receptor, FcepsilonRI, to initiate a change in the behavior of the cell expressing the receptor. It is now clear that a number of cell types can express this receptor, which broadens the biology that revolves around IgE antibody. It is also quite clear that the presence of monomeric IgE antibody alters the expression of FcepsilonRI. There remains considerable uncertainty about the importance of independent regulation of the FcepsilonRIbeta subunit or its splice variant beta(T), in terms of regulating both expression and function of FcepsilonRI. There is also only primitive understanding of the role of various polymorphisms in the subunit genes on the atopic phenotype. There are, however, many efforts being made to resolve these issues and to discover other factors that regulate expression of this receptor. Of particular interest for understanding the variation in expression in atopy among patients, the role of this receptor on non-mast cell/basophils will be important to elucidate.

Fc receptor homologs: newest members of a remarkably diverse Fc receptor gene family

Newfound relatives of the classical Fc receptors (FcR) have been provisionally named the Fc receptor homologs (FcRH). The recent identification of eight human and six mouse FcRH genes substantially increases the size and functional potential of the FcR family. The extended family of FcR and FcRH genes spans approximately 15 Mb of the human chromosome 1q21-23 region, whereas in mice this family is split between chromosomes 1 and 3. The FcRH genes encode molecules with variable combinations of five subtypes of immunoglobulin (Ig) domains. The presence of a conserved sequence motif in one Ig domain subtype implies Ig Fc binding capability for many FcRH family members that are preferentially expressed by B lineage cells. In addition, most FcRH family members have consensus tyrosine-based activating and inhibitory motifs in their cytoplasmic domains, while the others lack features typical of transmembrane receptors. The FcRH family members, like the classical FcRs, come in multiple isoforms and allelic variations. The unique individual and polymorphic properties of the FcR/FcRH members indicate a remarkably diverse Fc receptor gene family with immunoregulatory function.