Signal transduction during in vitro lymphocyte homing

Lymphocyte binding to endothelium is a necessary prerequisite for lymphocyte homing through endothelium. This is mediated by the binding of ligands on endothelial cells to lymphocyte surface homing receptors. We show in this paper that the intracellular second messenger pathways involved in interferon gamma-induced intercellular adhesion molecule 1 upregulation on endothelial cells are protein kinase C and calcium dependent. Lymphocyte binding to endothelial cells is enhanced by both platelet activating factor and interleukin 1 alpha. Platelet activating factor added to endothelial cultures increases lymphocyte binding within 10 min and operates via protein kinase C but not via cAMP. On the other hand interleukin 1 alpha increases binding within 4 hr and operates via cAMP but not via protein kinase C. These results imply that different mediators of inflammation can activate different signal transduction pathways but lead to similar increases in lymphocyte binding.