Differential glycosylation of MHC class II molecules on gastric epithelial cells: implications in local immune responses.

Class II major histocompatibility complex (MHC) expression is a hallmark of antigen presenting cells (APC). Human gastric epithelial cells (GEC) express class II MHC and this expression increases during infection with Helicobacter pylori as does the number of CD4 T cells found adjacent or in between epithelial cells. These observations suggested that human GEC act as APCs. To characterize and compare class II MHC complexes with those present in conventional APC, immunoprecipitated class II MHC from GEC and B cells, as prototypic APC, were separated by two-dimensional electrophoresis. Although the composition of class II MHC from both cell phenotypes was similar, their electrophoretic mobility differed. Methodical elimination of carbohydrates, either enzymatically with endoglycosidase-H or blocking with tunicamycin, revealed that the deviations were due to differences in glycosylation in both cell phenotypes. When deglycosylated class II MHC alpha chains, beta chains, and the invariant chain from both cell phenotypes were mixed and run in the same gel, the core proteins had identical migration patterns. Because differences in glycosylation of class II MHC proteins may affect peptide selection and/or recognition by T cells, the noted differences in glycosylation of class II MHC expressed by GEC could be important in considering their potential role as APC locally.