Regulation of polymorphonuclear leukocyte function by platelets

Objective: To investigate the full effect of platelet-derived constituents on various polymorphonuclear neutrophil leukocyte responses. Methods: Polymorphonuclear neutrophil leukocytes and platelets were separat ed from fresh blood of normal healthy volunteers. Platelets were then stimu lated partially, or maximally to release constituents of their alpha- or al pha- and dense granules. The effects of these: constituents on polymorphonu clear neutrophil leukocyte function (oxidase activity, degranulation and mi gration) were investigated. Results: Platelet-derived constituents were found to both enhance, and inhi bit polymorphonuclear neutrophil leukocytes-oxidant production, depending o n the incubation time, Enhancement was due to dense granule-derived nucleot ides (adenosine diphosphate and adenosine: diphosphate), while inhibition w as due to adenosine monophosphate derived from these nucleotides. by polymo rphonuclear neutrophil leukocyte surface nucleotidases. This latter inhibit ory effect was reversed by the cytokine. granulocyte-macrophage colony stim ulating factor, Moreover, platelet constituents consistently enhanced other polymorphonuclear neutrophil leukocyte responses including degranulation a nd migration regardless of the incubation period, The latter enhancement wa s due to alpha -granule constituents, most likely platelet factor 4. Conclusion: Platelets, through release of their granular constituents, are able to modulate polymorphonuclear neutrophil leukocyte function in a way t hat is physiologically beneficial.