Monoclonal antibodies against HLA class I antigens inhibit human lymphocyte proliferation but do not affect mitogen dependent second messenger generation

The mechanism through which anti HLA class I monoclonal antibodies inhibit human lymphocyte proliferation induced by the policlonal mitogen phytohemoagglutinin was investigated. Anti HLA class I monoclonal antibodies inhibited mitogen stimulated DNA synthesis even when added several hours after phytohemoagglutinin. The extent of inhibition depended on the duration of the exposure of lymphocytes to the monoclonal antibodies. Anti HLA class I monoclonal Antibodies neither affected the rise in cytosolic fee Ca2+ concentration nor the production of inositol phosphates induced by phytohemoagglutinin. These results demonstrate that anti HLA class I monoclonal antibodies inhibit lymphocyte proliferation at a step downhill of second messenger generation.