Target platelet antigen in homosexual men with immune thrombocytopenia.

A syndrome of isolated immune thrombocytopenic purpura (ITP) has recently been described in homosexual men. We have identified an antiplatelet antibody in the serum of 29 of 30 homosexual men with isolated ITP. The antibody binds to a platelet membrane antigen of 25,000 daltons, and binding is effected by the F(ab)2 portion of the immunoglobulin. Similar antibody activity was not detected in serum from 30 nonhomosexual patients with either ITP or nonimmune thrombocytopenia. The 25,000-dalton antigen was not found on other hematopoietic cells, and it was distinct from the core protein of the AIDS-associated retrovirus. In contrast, serum antibody reacted with a 25,000-dalton antigen associated with cultured herpes simplex virus Types I and II. In these experiments the antigen appeared to be derived from green-monkey kidney cells in which the herpes simplex viruses were grown. Identical antigenic activity was also demonstrated in uninfected human skin fibroblasts. We conclude that ITP in homosexual men is accompanied by a serum antibody directed against a platelet antigen of 25,000 daltons. The nature of the antigen and the relation of the serum antibody to ITP require further study.