Activation of guinea pig platelets by a monoclonal antibody.

We herein describe the characterization of a monoclonal anti-guinea pig platelet antibody, termed GT2-12, which causes aggregation, ATP and [3H]serotonin release, and platelet protein phosphorylation. GT2-12 can bind to platelets and megakaryocytes in guinea pig bone marrow cells. A protein of 34,000 daltons was detected by immunoprecipitation of platelet lysates with GT2-12. Incubation of 32P-labeled guinea pig platelets with GT2-12 resulted in rapid phosphorylation of proteins of 40,000 and 20,000 daltons. GT2-12-induced aggregation and protein phosphorylation of platelets were inhibited by diltiazem, TMB-8 and dibutyryl cAMP and partially inhibited by indomethacin. The F(ab')2 fragment of GT2-12 IgG also induced platelet aggregation, indicating that activation is not mediated by Fc receptors. This type of antibody should be useful for studying platelet function in the guinea pig model.