Mechanism ofS agalactiae–induced platelet activation/aggregation. (A) Effect of inhibitors on S agalactiae 6313-induced platelet aggregation. PRP (0.4 mL) was pretreated with 1 mM RGDS, abciximab (10 μg/mL), 1 μM PGE₁, or apyrase (10 U/mL) for 5 minutes or with 1 μM ASA for 20 minutes prior to the induction of platelet aggregation by 10 μM ADP (▪) or S agalactiae 6313 cells (5 × 10⁷; □). Results are expressed as percentage of aggregation performed in the absence of antagonists. Each data point is the mean ± SD of 4 experiments. (B) S agalactiae cells induce cytosolic Ca²⁺ increase in platelets. Fura-2/am-loaded platelets (8 × 10⁷ in 0.4 mL) were stimulated with 2.5 × 10⁵ or 2.5 × 10⁶ cells of S agalactiae 6313 in the presence of Fbg (3 mg/mL). Trace of Ca²⁺ increase by thrombin (1 U/mL) is shown as control. The effect of either bacteria or Fbg on Ca²⁺ increase in platelets is also reported. The arrows indicate the addition of agonist to platelets. Results are representative of 3 experiments.