Monoclonal and xenoantibodies specific for HLA-DR inhibit primary responses to HLA-D but fail to inhibit secondary proliferative (PLT) responses to allogeneic cells.

Monoclonal antibodies (DA-2 and CA-2) and xenoantisera (rabbit anti-human, p23,30) specific for HLA-DR framework determinants were added to primary and secondary mixed lymphocyte cultures. Although such antisera were shown to inhibit primary MLC, primed lymphocytes were much less sensitive to the blocking effects of these antibodies. In the studies shown here, the concentration of antibody required to inhibit primary MLC reactions was 0.1-1.5 micrograms/ml).