ACTIVATION OF HUMAN NEUTROPHIL LFA-1 (CD11A) BY LEUKOTRIENE-B4

Homotypic aggregation (HA) of human neutrophils by the potent leukotac tic factor, leukotriene B4 (LTB4), and phorbol myristate acetate (PMA) was evaluated by recording the net decrease in absorbency at 650 nm o f suspensions of 10(7) neutrophils/ml in a microtiter plate reader, wh ich was found to correlate with microscopic evidence of aggregation. L TB4-elicited HA was increased maximally by approximately one third abo ve HA in buffer at 30 min, whereas PMA-induced HA reached a maximal le vel more than 2 1/2-fold higher than buffer control at 60 min. The inv olvement of LFA-1 in LTB4-induced HA of neutrophils was suggested init ially by the inhibitory effect of monoclonal anti-CD18 and anti-CD11a antibodies. The binding to neutrophils of a monoclonal anti-LFA-1 anti body (NK1-L16) specific for an activation epitope of CD11a was increas ed a maximum of 28-fold and sixfold, respectively, after 1 and 5 min o f preincubation with 10 nM LTB4 and fivefold after 5 min with PMA. Thu s, both LTB4 and PMA induce an activating conformational change in the CD11 a adherence receptor of human neutrophils.