Human Blood Platelets, PMN Leukocytes and Their Interactions . Responses to Selective and Non-selective Stimuli

Using simultaneous recording of aggregation and chemiluminescence, responses of human polymorphonuclear leukocytes, blood platelets and their mixture were investigated after stimulation by specific as well as non-specific stimuli for each cell. In our experimental settings, aggregation of platelets and PMN leukocytes was increased in the following order of stimuli: PMA<A23187<thrombin and FMLP<A23187<PMA, respectively. FMLP selective for PMN leukocytes did not activate platelet aggregation, and, on the other hand, aggregation of PMN leukocytes was not induced by thrombin. The presence of PMN leukocytes decreased aggregatory responses of platelets to all the stimuli applied. Luminol amplified chemiluminescence of PMN leukocytes was increased in the order: thrombin<FMLP< A23187<PMA, but platelets alone did not show detectable chemiluminescence response to any stimulation. Platelets significantly decreased chemiluminescence of PMN leukocytes and their inhibitory effect did not depend on the type of stimulation. These observations suggest that under defined experimental conditions human PMN leukocytes and platelets might decrease mutually their dominant responses in vitro. The inhibitory effect was dependent either on the selectivity of stimuli, or on cell to cell contact before stimulus addition.