NEUTROPHIL ADHERENCE TO RAT CARDIAC MYOCYTE BY PROINFLAMMATORY CYTOKINES

Cytokine induction of intercellular adhesion molecule-1 (ICAM-1) in cardiac myocytes may be a critical step in inflammation associated with ischemia-reperfusion injury. We investigated the involvement of tumor necrosis factor-alpha (TNF-alpha), interleukin 6 (IL-6), and interleukin 8 (IL-8) on neutrophil-myocyte adhesion; These cytokines are increased in plasma of patients with acute myocardial infarction (AMI). ICAM-1 expression on cultured neonatal rat cardiac myocytes was determined through immunohistochemical and enzyme-linked immunosorbent assay (ELISA) analysis. ICAM-1 mRNA expression in myocytes was investigated by Northern blot hybridization. Rat neutrophils isolated from peripheral blood (PB) were used for adherence assay. In immunohistochemical study, cultured neonatal rat cardiac myocytes constitutively expressed ICAM-1 molecules. In ELISA analysis, ICAM-1 molecule expression on myocytes was significantly stimulated by TNF-alpha (100 U/ml), but not by IL-6 (100 U/ml) or IL-8 (100 ng/ml) dose dependently. The effect of TNF-alpha was observed as early as 6 h after stimulation. Levels of ICAM-1 mRNA were very low or almost undetectable in unstimulated myocytes, but its expression was markedly induced after exposure to TNF-alpha for 3 h. IL-6 and IL-8 showed no effect on ICAM-1 mRNA accumulation. Adhesion of rat neutrophils to myocytes was stimulated by TNF-alpha, and the effect of TNF-alpha on adherence was significantly inhibited by an anti-ICAM-1 monoclonal antibody (MoAb). These results show that TNF-alpha, but not IL-6 and IL-8, promotes neutrophil-myocyte adhesion through ICAM-1 expression, suggesting involvement of TNF-alpha in inflammation associated with ischemia-reperfusion injury.