['To explore the mechanism of PTA1 monoclonal antibody (McAb) induced human platelet aggregation and its effect on intra-cytoplasmic Ca2+ level.', "Platelet aggregation, ATP releasing assay and Pollock's test were used.", "PTA1 McAb induced human platelet aggregation in vitro, which could be completely inhibited by EGTA and PGI2. F(ab')2 of PTA1 McAb had no effect on CD9 or CD41 induced platelet activation and aggregation. PTA1 McAb enhanced platelet intra-cytoplasmic Ca2+ elevation."] Does [ PTA1 monoclonal antibody induce human platelet aggregation and intra-cytoplasmic Ca2+ elevation ]?