Actively induced platelet-bound IgG associated with thrombocytopenia in the marmoset.

Interspecies platelet immunizations among marmosets lead to antibody formation to the donor platelets and a profound thrombocytopenia, which when associated with anemia may result in death of the animal. This actively induced immunologic thrombocytopenia closely resembles two clinical disease entities manifesting autoimmune thrombocytopenia, posttransfusion purpura and idiopathic thrombocytopenic purpura. Although antibody to donor-type platelets could be demonstrated readily, antihost activity was most often nondetectable or, when present, was in very low titer. A consistent finding was the appearance of IgG on the host’s platelets shortly after immunization and concomitant with the appearance of antidonor platelet antibody. In 3 of 13 immunized animals thrombocytopenia did not occur even though antibody was formed and the host’s platelets became lgG positive. In those animals that recovered from the induced thrombocytopenia lgG-positive platelets were found for periods ranging from 30 to greater than oo days. Splenectomy before or after immunization did not alter the sequential development of antibody formation, appearance of lgG-positive platelets, and thrombocytopenia. Eluates prepared from IgG-positive platelets contained IgG and platelet antigens; the eluted IgG could attach nonspecifically to platelets of host or donor (immunizing) type, in contrast to the species specificity demonstrated for lgG eluted from platelets that had been reacted in vitro with specific antibody. Platelets in a few normal, nonimmunized marmosets were found to have significant amounts of IgG on their surface, comparable to that observed in the immunized animal; interestingly, such IgG-positive platelets were found among imparted but not laboratory-bred marmosets.