A role for beta(2) integrin (CD11/CD18)-mediated tyrosine signaling in extravasation of human polymorphonuclear neutrophils

During the recruitment of human polymorphonuclear neutrophils (PMN) to site s of inflammation; leukocyte adhesion molecules of the beta (2) integrin (C D11/CD18) family mediate. firm adhesion of these cells to the endothelial c ell monolayer lining the vessel wall. This process is a prerequisite for sh ape change and spreading of PMN on the endothelium which eventually allows PMN emigration into;the extravascular space. In order to elucidate the mole cular mechanisms which mediate this sequence of events, intracellular prote in tyrosine signaling was studied subsequent to beta (2) integrin-mediated ligand binding. Using western blotting technique, beta (2) integrin-mediate d adhesion was found to induce tyrosine phosphorylation of different protei ns. The effect was absent in PMN derived from CD18-deficient mice which lac k any beta (2) integrin expression on the cell surface demonstrating the sp ecificity of the observed response. Inhibition of a integrin-mediated tyros ine signaling by herbimycin A almost completely inhibited adhesion, shape c hange, and subsequent spreading of PMN. Herbimycin A also diminished chemot actic migration of these cells in response to the soluble mediator N-formyl -Met-Leu-Phe (fMLP): In contrast, treatment of PMN with cytochalasin D had no substantial effect on beta (2) integrin-mediated signaling or adhesion b ut inhibited shape change, spreading, and chemotactic migration of PMN. Thi s suggests that the signaling capacity exerted by beta (2) integrins upon l igand binding was independent of an intact cytoskeleton. Moreover, the beta (2) integrin-mediated activation of intracellular signal transduction path ways was critical for firm adhesion of PMN, the prerequisite subsequent sha pe change and spreading, which allows emigration of PMN into the extravascu lar space.