Redox regulation of beta 2-integrin CD11b/CD18 activation

Although the central role of beta 2-integrin CD11b/CD18 in neutrophil funct ions is well recognized, signaling pathway that regulate integrin activatio n remain to be elucidated. We analyzed the contribution of oxide-reduction mechanisms in this signaling. Exogenously added H2O2 induced CD11b/CD18-dep endent neutrophil adhesion and expression of an integrin activation neoepit ope recognized by monoclonal antibody (mAb) clone 24. H2O2-triggered beta 2 -integrin activation was inhibited by tyrosine kinase inhibitors and by com plexing sulfhydryl groups with phenylarsine oxide (PAO). CD11b/CD18-depende nt adhesion and mAb 24 antigen expression triggered by physiological agonis ts such as TNF-alpha were inhibited by diphenylene iodonium (DPI, an inhibi tor of flavoprotein oxidoreductase), by free radical scavengers, by tyrosin e kinase inhibitors and by PAO. No inhibition was observed when adhesion wa s induced by the integrin-activating KIM 185 mAb. Taken together, these res ults emphasize the importance of an oxidative S-thiolation step(s) in the t yrosine kinase-dependent signaling pathway leading to beta 2-integrin activ ation. H2O2 would directly mediate this oxidative reaction and bypass the i nitial agonist/receptor pathway to promote integrin-dependent adhesion. The putative oxidase(s) involved in this process is not NADPH oxidase, since a dhesion 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 inf lamed organs.