The immune response to allogeneic rat platelets; Ag-B antigens in matrix form lacking Ia

Allogeneic rat platelets fail to induce either primary antibody or cell-mediated immune responses despite repeated injections. Platelets bear Ag-B epitopes which are capable of being recognized by antigen-reactive T and B cells since primed rats develop secondary responses after challenge with allogeneic platelets. The secondary responses induced decrease rather than increase on repeated injection of platelets. Repeated injection of allogeneic platelets into nonprimed rats leads to a state of specific, partial non-reactivity; recipients given such treatment show marked depression of cytotoxic antibody responses, but normal cellular immunity after challenge with viable lymphoid cells taken from the platelet-donor strain. Injection of normal rats with allogeneic platelets mixed with 3rd party, viable lymphoid cells, does not provoke an anti-platelet Ag-B antibody response.