Anti-F(ab')2 antibodies in thrombocytopenic patients at risk for acquired immunodeficiency syndrome

22 homosexual or narcotic addict patients at risk for acquired immunodeficiency syndrome (AIDS) or with AIDS, were studied for the presence of antiimmunoglobulin antibodies and circulating immune complexes (20 were thrombocytopenic, 6 had AIDS). Circulating immune complex levels were 10-fold higher than levels in normal subjects. IgG anti-F(ab')2 antibodies were noted in homosexual as well as narcotic addict patients. Of 16 homosexual patients, 7 had IgG anti-F(ab')2 antibody of moderate to marked titer with broad reactivity against autologous, homologous, and control F(ab')2 fragments. Three others demonstrated limited reactivity against one or two F(ab')2 fragments. The remaining six patients were negative. Six of six narcotic addict patients had IgG anti-F(ab')2 antibody, five with limited reactivity, one with broad reactivity. In contrast, neither elevated circulating immune complexes nor anti-F(ab')2 antibodies were detectable in six autoimmune thrombocytopenic patients. Anti-F(ab')2 antibody could be affinity purified from serum or circulating immune complexes. Anti-F(ab')2 reactivity correlated with circulating immune complex levels, r = 0.83, P less than 0.01.