Effects of IL-8, Gro-alpha, and LTB4 on the adhesive kinetics of LFA-1 andMac-1 on human neutrophils

Firm adhesion of rolling neutrophils on inflamed endothelium is dependent o n beta (2) (CD18)-integrins and activating stimuli. LFA-1 (CD11a/CD18) appe ars to be more important than Mac-1 (CD11b/CD18) in neutrophil emigration a t inflammatory sites, but little is known of the relative binding character istics of these two integrins under conditions thought to regulate firm adh esion. The present study examined the effect of chemoattractants on the kin etics of LFA-1 and Mac-1 adhesion in human neutrophils. We found that subna nomolar concentrations of interleukin-8, Gro-alpha, and leukotriene B-4 (LT B4) induced rapid and optimal rates of LFA-1-dependent adhesion of neutroph ils to intercellular adhesion molecule (ICAM)-1-coated beads. These optimal rates of LFA-1 adhesion were transient and decayed within 1 min after chem oattractant stimulation. Mac-1 adhesion was equally rapid initially but con tinued to rise for greater than or equal to6 min after stimulation. A fourf old higher density of ICAM-1 on beads markedly increased the rate of bindin g to LFA-1 but did not change the early and narrow time window for the opti mal rate of adhesion. Using well-characterized monoclonal antibodies, we sh owed that activation of LFA-1 and Mac-1 by Gro-alpha was completely blocked by anti-CXC chemokine receptor R2, but activation of these integrins by in terleukin-8 was most effectively blocked by anti-CXC chemokine receptor R1. The topographical distribution of beads also reflected significant differe nces between LFA-1 and Mac-1. Beads bound to Mac-1 translocated to the cell uropod within 4 min, but beads bound to LFA-1 remained bound to the lamell ipodial regions at the same time. These kinetic and topographical differenc es may indicate distinct functional contributions of LFA-1 and Mac-1 on neu trophils.