Glycoprotein V-specific platelet-associated antibodies in thrombocytopenicpatients

In autoimmune thrombocytopenia, platelet-associated IgG (PA-IgG) frequently displays specificity against glycoprotein (GPI) IIbIIIa and/or GP IbIX. Be cause in a high proportion of patients positive PA-IgG may not be explained by these GP specificities, studies on other target proteins are needed. We studied the presence of GP V-specific PA-IgG by direct monoclonal antibody -specific immobilization of platelet antigens (MAIPA) with the monoclonal a ntibody SW16. We focused on 69 consecutive random patients with histories o f thrombocytopenia who were strongly positive for PA-IgG detected by the di rect platelet immunofluorescence test (PIFT). PA-IgG against GP V (ratio gr eater than or equal to 1.5) was noted in 15 (22%) patients. The degree of P A-IgG measured by PIFT, and of GP IIbIIIa-and/or GP IbIX-specific PA-IgG me asured by direct MAIPA. correlated directly with the GP V-specific PA-IgG ( P < 0.001). In one patient, GP V-specific antibodies were associated with q uinidine-induced thrombocytopenia. Although this patient had strongly posit ive GP V-specific PA-IgG, she remained negative in GP IIbIIIa- and GP IbIX- specific direct MAIPA. Two patients studied because of thrombocytopenia ass ociated with gold therapy had strongly positive GP V-specific PA-IgG. In on e patient with rheumatoid arthritis and severe gold-induced thrombocytopeni a, the amount of GP V-specific PA-IgG decreased during the recovery phase. Thus, GP V may represent an important target antigen in autoimmune-mediated thrombocytopenia, especially in drug-induced thrombocytopenia.