Specific changes to the B lymphocyte glycocalyx and relevant glycosyltransferasemRNA abundances accompany differential activation in vitro

Glycosylation is critical to the proper function of the immune system as evidenced from transgenic and knockout mice deficient in specific glycosyltransferases (Hennet, 1998 and Priatel, 2000). However, the exact molecular mechanisms by which glycosylation facilitates immune function remain largely unknown. The present study lays key groundwork for future functionality studies by characterizing the changes in the glycocalyx glycotype that accompany various model systems for murine B lymphocyte activation. Of particular interest are the changes in terminal galactose and sialic acid content that are induced during in vitro activation. It is generally accepted that B cells are hyposialylated following activation (Krieger et al. 1988, and Tedder, et al 1997), yet convincing data demonstrating a general desialylation following activation have yet to be published. While an increase in Galβ1,3GalNAc is observed on activated B cells, this study demonstrates that activated B cells undergo a general increase in sialic acid linked α2,3 and α2,6 on substrates other than Galβ1,3GalNAc and may in fact be hypersialylated relative to resting cells.; In an effort to determine the level at which the observed changes in glycotype are regulated, relative mRNA abundances for the galactose-active sialyltransferases were quantitated. The present study demonstrates that the general increases in sialic acid content of the B cell glycocalyx during activation are accompanied by corresponding increases in most of the relevant sialyltransferases. Furthermore, the observed increase in terminal Galβ1,3GalNAc is correlated to decreases in specific Galβ1,3GalNAc-active glycosyltransferases.