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

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 Igµ BCRs from primary naive and memory B cells. Our data indicate that the Igµ 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 Igµ BCRs, which are in part explained by the different molecular form of Igµ BCRs and IgM antibodies. Moreover, using B cell lines expressing defined BCRs, we show that, although the absence of the Igµ 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 Igµ 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.