Anti-HLA class I antibody inhibits Staphylococcus enterotoxin A (SEA)-induced proliferation of human PBMC

The antigen-presenting role of major histocompatibility complex (MHC) Class I molecules in the activation of appropriately restricted T cells is well documented. Now growing evidence indicates that MHC Class I molecules can, in addition, exert a regulatory effect and influence the resulting immune responses. In this report we show that a monoclonal antibody (mAb) directed against a conserved region of the human leukocyte antigens (HLA)-A, -B, and -C was able to inhibit proliferation of human peripheral blood mononuclear cells induced by the superantigen, Staphylococcus enterotoxin A. While anti-HLA inhibition was associated with a decrease in IL-2 receptor (IL-2R) expression, the addition of exogenous IL-2 did not restore the proliferative response in the presence of anti-HLA mAb. The inhibition of DNA synthesis was also associated with a decrease in the expression of the early activation marker CD69. These results suggest a critical role for HLA Class I molecules in the early events of human lymphocyte activation and proliferation as well as in their expression of the IL-2R.