Abstract
Complement-stimulated granulocytes adhere to and induce significant 51Cr release from endothelial cells in vitro. Platelets were stimulated to undergo release, and these release products significantly enhanced granulocyte-endothelial cell adherence and granulocyte-induced 51Cr release from endothelial cells. Platelet serotonin appeared to mediate these phenomena because serotonin antagonists blocked both the enhanced endothelial adherence and 51Cr release. In addition, added serotonin mimicked the effect seen with the stimulated platelets upon granulocyte--endothelial cell adherence and cytotoxicity completely. This enhancement appeared to be due to serotonin effects upon both the granulocyte and endothelial cells. These data suggest that a released platelet constituent might modulate in vivo granulocyte-endothelial cell interactions in clinical disorders.