Regulation of T-cell differentiation by IL-4Rα-chain single nucleotide polymorphisms

Chronic inflammation in rheumatoid arthritis (RA) is mediated by repeatedly activated proinflammatory Th1 cells. In contrast, Th2 cells that might downmodulate the chronic autoimmune response are rarely found in RA. It has been previously documented that RA T cells are severely impaired in their ability to differentiate into Th2 effectors while exerting enhanced Th1 differentiation. The mechanisms underlying this functional abnormality, however, have not been delineated. As IL-4 is a most critical determinant in regulating immune responses by promoting Th2 cell development and inhibiting Th1 cell differentiation, we analyzed the role of single nucleotide polymorphisms (SNP) in the IL-4 receptor α-chain, which is critical for binding of IL-4 and for IL-4 signal transduction, in the differentiation of human T cells. Naive and memory CD4 T cells were isolated from the peripheral blood of 348 healthy individuals and genotyped by allele-specific PCR for the two IL-4R α-chain SNPs that are located in functionally important regions of the IL-4R α-chain – the I50 V SNP50 and the Q551R SNP551 in the IL-4-binding and STAT6-binding domains, respectively. To analyze the functional role of IL-4R α-chain SNPs for T-cell differentiation, CD4-positive T cells were purified from the peripheral blood from the individuals who were homozygous for either allele at SNP50 and SNP551, and primed for 5 days with mAbs to CD28 and/or CD3 in the presence or absence of exogenous IL-4. The phenotype of the resulting differentiated effector cells was then analyzed by flow cytometric analysis of cytoplasmic cytokines. The SNP551 alleles did not significantly affect T-cell differentiation. In marked contrast, the inhibitory effect of IL-4 on Th1 cell differentiation was significantly diminished in CD4 T cells that were homozygous for the mutated allele at SNP50 (50 V) as compared with those with the wild-type allele (I50). Likewise, the augmenting effect of IL-4 on Th2 cell differentiation was markedly enhanced on T cells that were homozygous for the wild-type allele as compared with T cells expressing the mutant allele. The data indicate that the mutated allele of the IL-4R α-chain SNP50 is associated with a decreased T-cell response to IL-4. Thus, SNP50 of the IL-4R α-chain might regulate T-cell differentiation by altering T-cell responses to IL-4 and contribute to the development of unbalanced Th subset activation, as characteristic for autoimmune diseases, such as RA.