H2-O inhibits presentation of bacterial superantigens, but not endogenous self antigens

H2-O/HLA-DO are MHC class II accessory molecules that modulate exogenous Ag presentation. Most class II accessory molecules are expressed in all profe ssional APC; however, H2-O is only expressed in B cells and medullary thymi c epithelial cells. Because B cells present exogenous Ags and superantigens (SAgs), and medullary thymic epithelial cells are specialized APC for self Ags during negative selection in the thymus, we have hypothesized that H2- O might play a role in MHC class II-restricted SAg and self Ag presentation . In this study, we demonstrate that H2-O expression inhibits presentation of the bacterial SAgs staphylococcal enterotoxins A and B to four SAg-react ive T hybridoma cells. In contrast, H2-O has no effect on presentation of e ndogenous self Ags, as measured by tumorigenicity in vivo and Ag presentati on to three self Ag-specific T hybridoma cells. Additional experiments sugg est that H2-O inhibits presentation of exogenous Ags by both newly synthesi zed and recycling MHC class II molecules. These data suggest H2-O may have a physiological role in tolerance induction and SAg-mediated toxic shock.