Expansion of the IgD class switched B cell population in carriers of the autoimmune disease associated risk haplotype in BLK (HUM2P.332)

Abstract

Abstract Polymorphisms in BLK are associated with numerous autoimmune diseases including rheumatoid arthritis and lupus. BLK (B lymphocyte kinase) is a tyrosine kinase involved in signaling through the B cell receptor (BCR). The disease risk haplotype is known to be associated with reduced expression of BLK transcript and the most significant association of reduced BLK transcript is with a candidate causal SNP rs922483. We have previously shown that expression of BLK is reduced in cord blood B cells from carriers of rs922483 risk alleles (HMG 2012). B cell development is perturbed in blk transgenic and knockout mice, and B cells from these mice are hyper-responsive to BCR stimulation. To determine if reduced BLK expression affects the function of primary human B cells we measured CD86 expression in cells stimulated by anti-IgM. As in mice, cord blood B cells from risk allele carriers are hyper-responsive to BCR stimulation. We also assessed if BLK risk variants convey any variation on the composition of circulating B cell populations of healthy adults. We observed that subjects with BLK risk variants have an expansion in the proportion and number of IgD class-switched B cells, and an increase in the total number of class-switched memory B cells. These results suggest that BLK risk haplotypes confer autoimmune disease susceptibility by reducing a negative regulatory effect of BLK, making B cells more likely to receive help from CD4 T cells and to undergo class switch recombination.