Redox regulation of β2-integrin CD11b / CD18 activation

Although the central role of beta2-integrin CD11b / CD18 in neutrophil functions is well recognized, signaling pathway that regulate integrin activation remain to be elucidated. We analyzed the contribution of oxido-reduction mechanisms in this signaling. Exogenously added H(2)O(2) induced CD11b/CD18-dependent neutrophil adhesion and expression of an integrin activation neoepitope recognized by monoclonal antibody (mAb) clone 24. H(2)O(2)-triggered beta2-integrin activation was inhibited by tyrosine kinase inhibitors and by complexing sulfhydryl groups with phenylarsine oxide (PAO). CD11b/CD18-dependent adhesion and mAb 24 antigen expression triggered by physiological agonists such as TNF-alpha were inhibited by diphenylene iodonium (DPI, an inhibitor of flavoprotein oxidoreductase), by free radical scavengers, by tyrosine kinase inhibitors and by PAO. No inhibition was observed when adhesion was induced by the integrin-activating KIM 185 mAb. Taken together, these results emphasize the importance of an oxidative S-thiolation step(s) in the tyrosine kinase-dependent signaling pathway leading to beta2-integrin activation. H(2)O(2) would directly mediate this oxidative reaction and bypass the initial agonist/receptor pathway to promote integrin-dependent adhesion. The putative oxidase(s) involved in this process is not NADPH oxidase, since adhesion of neutrophils from patients with chronic granulomatous disease was normal and inhibited by scavengers and DPI. These data shed a new light on the regulation of integrin activation required for cell migration into inflamed organs.