Interaction of rat platelets with Listeria monocytogenes

Listeria monocytogenes induced aggregation of rat platelets in vitro and stimulated the nonlytic release of [3H]serotonin. Listeria-induced platelet aggregation and serotonin release required the presence of intact Listeria, was maximal at a 1:1 Listeria/platelet ratio, required a plasma cofactor, and was not inhibited by indomethacin, acetylsalicylic acid, or apyrase. Aggregation either of platelets in platelet-rich plasma with adenosine diphosphate or of washed platelets with thrombin resulted in the release of a listericidin from the platelets; however, direct interaction of L. monocytogenes with platelet-rich plasma did not kill Listeria. The ability of rats to clear an intravenous challenge of L. monocytogenes (0.005 50% lethal dose), as determined by the recovery of viable L. monocytogenes from the spleen and liver, was unaffected by prior treatment with antiplatelet serum.