Differential inside-out activation of beta sub(2)-integrins by leukotriene B sub(4) and fMLP in human neutrophils

We have investigated how LTB sub(4), an endogenous chemoattractant encountered early in the inflammatory process, and fMLP, a bacteria-derived chemotactic peptide emanating from the site of infection, mediate inside-out regulation of the beta sub(2)-integrin. The role of the two chemoattractants on beta sub(2)- integrin avidity was investigated by measuring their effect on beta sub(2)- integrin clustering and surface mobility, whereas their effect on beta sub(2)- integrin affinity was measured by the expression of a high affinity epitope, a ligand-binding domain on beta sub(2)-integrins, and by integrin binding to s- ICAM. We find that the two chemoattractants modulate the beta sub(2)-integrin differently. LTB sub(4) induces an increase in integrin clustering and surface mobility, but only a modest increase in integrin affinity. fMLP evokes a large increase in beta sub(2)-integrin affinity as well as in clustering and mobility. Lipoxin, which acts as a stop signal for the functions mediated by pro- inflammatory agents, was used as a tool for further examining the inside-out mechanisms. While LTB sub(4)-induced integrin clustering and mobility were inhibited by lipoxin, only a minor inhibition of fMLP-induced beta sub(2)- integrin avidity and no inhibition of integrin affinity were detected. The different modes of the inside-out regulation of beta sub(2)-integrins suggest that distinct mechanisms are involved in the beta sub(2)-integrin modulation induced by various chemoattractants.