inhibition by antihla class ii monoclonal antibodies of monocytedependent t cell proliferation induced by monoclonal antibody okt3 the inhibitory effect of monoclonal antibodies mab to monomorphic locusrestricted and locusshared and polymorphic determinants of hla class ii antigens on the monocytedependent proliferation of t cells stimulated with mab okt3 has been studied the effect appears to be specific dose dependent is not mediated by the fc portion of mab and reflects their interaction with the corresponding determinants the antihla class ii mab do not have to be present in the culture throughout the incubation period but are essential in early phases of mab okt3 t cell activation both monocytes and t cells are the targets of the inhibition exerted by the antihla class ii mab their inhibitory effect involves several steps in the sequence of events which leads to t cell proliferation including interleukin il 1 and 2 secretion and il2 receptor expression