FcγRIIA and Src and Syk tyrosine kinases mediate bacteria-induced platelet activation. (A) Effect of anti-FcγRIIA mAb IV.3 on bacteria-induced platelet aggregation. PRP was incubated for 10 minutes with mAb IV.3 (10 μg/mL) or vehicle prior to addition of bacteria or protease-activated receptor 1 agonist TRAP, and platelet aggregation was monitored by light transmission aggregometry (see also supplemental Figure 2B). (B) Effect of anti-FcγRIIA mAb IV.3 on platelet dense granule secretion in response to bacteria. Reactions were performed as in panel A; supernatants were collected at time of full aggregation, or a parallel time point in the case of inhibition. Supernatants were analyzed for ATP release by luciferin-luciferase assay. ATP levels released by S sanguinis 133-79–stimulated platelets were used to normalize data. (C) Effect of the Src tyrosine kinase inhibitor dasatinib in bacteria-induced platelet aggregation in plasma. PRP was incubated for 2 minutes with dasatinib (4 μM) prior to addition of bacteria or agonists, and platelet aggregation was monitored (see also supplemental Figure 2C). (D) Effect of Syk tyrosine kinase inhibitor PRT-060318 in bacteria-induced platelet aggregation in plasma. PRP was incubated for 2 minutes with PRT-060318 (10 μM) or vehicle prior to addition of bacteria or agonist, and platelet aggregation was monitored (see also supplemental Figure 2D). Results are shown as mean ± SD of 3 independent experiments; *P < .05.