Site-specific profiling of structure and function of Igµ B cell receptor glycans

Abstract

Although N-linked glycans play pivotal roles in the regulation of antibody effector functions, little is known about the composition and functional impact of glycans attached to human B cell receptors (BCR). Here, we describe the site-specific glycosylation profiles of all 4 N-linked glycosylation sites of human Ig & micro; BCRs from primary naive and memory B cells. Our data indicate that the Ig & micro; BCR glycans do not undergo structural changes during transition from naive to memory cells, as healthy donor-derived BCRs from both B cell subtypes carry similar glycans. Conversely, serum IgM antibodies display distinct glycosylation features to Ig & micro; BCRs, which are in part explained by the different molecular form of Ig & micro; BCRs and IgM antibodies. Moreover, using B cell lines expressing defined BCRs, we show that, although the absence of the Ig & micro; BCR N209 glycans reduces antigen binding, the individual glycosylation sites are nonessential for cell surface expression and BCR internalization following BCR triggering. Collectively, we show high conservation of Ig & micro; BCR glycosylation across B cell subsets and limited contribution to BCR expression and function, suggesting BCR glycans may have evolved to support IgM antibody functions.