IgG+ platelets in the marmoset: their induction, maintenance, and survival

Abstract

Immunization of marmosets with platelets from another species of marmoset leads to antibody formation to the donor platelets, deposition of IgG on the host's platelets, and thrombocytopenia. This disease closely resembles posttransfusion purpura of man, which may develop after one or two transfusions of whole blood. The mode of immunization in the marmoset was found to be important: intravenous (i.v.) inoculations were without effect, while intramuscular (i.m.) immunizations led to the disease. Intramuscular inoculations were characterized by formation of 7S antibodies, as measured by indirect immunofluorescent (IF) and complement-dependent platelet cytotoxicity (PC) tests; in contrast, i.v. immunizations, while leading to 7S antibodies by the IF test, yielded only 19S antibodies reactive in the PC assay. The titers were also consistently higher with i.m. immunizations. Antibody was not limited to the donor platelets, but auto- or host-type reactivity was also present; this antibody was in very low titer and could be found only when the animal was thrombocytopenic. A primary finding was the ability to maintain increased deposition of IgG on the host's platelets in the absence of thrombocytopenia by biweekly or monthly inoculations of the donor platelet antigen. The amount of IgG found on platelets of normal and immunized marmosetsmore » was comparable to that reported for normal humans and patients with cinical immune thrombocytopenia. Finally, platelet survival studies in animals with IgG+ platelets and normal platelet counts indicated a rapid turnover, suggesting operation of a compensatory mechanism to maintain platelet levels.« less