Induction of cytokine expression in leukocytes by binding of thrombin- stimulated platelets

Background: Activated platelets tether and activate myeloid leukocytes. To investigate the potential relevance of this mechanism in acute myocardial infarction (AMI), we examined cytokine induction by leukocyte-platelet adhesion and the occurrence of leukocyte-platelet conjugates in patients with AMI. Methods and Results: We obtained peripheral venous blood samples in 20 patients with AMI before and daily for 5 days after direct percutaneous transluminal coronary angioplasty (PTCA) and in 20 patients undergoing elective PTCA. Throughout the study period, CD41 immunofluorescence of leukocytes (flow cytometry) revealed increased leukocyte-platelet adhesion in patients with AMI compared with control patients (mean±SE of fluorescence [channels] before PTCA: 77±16 versus 35±9; P=.003). In vitro, thrombin- stimulated fixed platelets bound to neutrophils and monocytes. Within 2 hours, this resulted in increased mRNA for interleukin (IL)-1β, IL-8, and monocyte chemoattractant protein (MCP)-1 in unfractionated leukocytes. After 4 hours, IL-1β and IL-8 concentration of the cell-free supernatant had increased by 268±36% and 210±7%, respectively, and cellular MCP-1 content had increased by 170±8%. Addition of activated platelets to adherent monocytes had a similar effect and was associated with nuclear factor-κB activation. Inhibition of binding by anti-P-selectin antibodies reduced the effect of activated platelets on cytokine production. Conclusions: In patients with AMI, leukocyte-platelet adhesion is increased. Binding of activated platelets induces IL-1β, IL-8, and MCP-1 in leukocytes. Our findings suggest that leukocyte-platelet adhesion contributes to the regulation of inflammatory responses in AMI.