SYNERGISTIC EFFECT OF TYPE-II PHOSPHOLIPASE A(2) AND PLATELET-ACTIVATING-FACTOR ON MAC-1 SURFACE EXPRESSION AND EXOCYTOSIS OF GELATINASE GRANULES IN HUMAN NEUTROPHILS - EVIDENCE FOR THE 5-LIPOXYGENASE-DEPENDENT MECHANISM

Stimulation of human neutrophils with inflammatory mediators such as T NF-alpha or platelet-activating factor (PAF) induces translocation of adhesion molecule Mac-1 (CD11b/CD18) from secretory vesicles to the pl asma membrane, Type II phospholipase A(2) (PLA(2)-II) also induces tra nslocation of Mac-1 from secretory vesicles. However, there are more M ac-1 molecules in gelatinase granules and specific granules than in se cretory vesicles. Therefore, different combinations of PLA(2)-II and o ther mediators were examined for their ability to induce gelatinase gr anules and specific granules to induce Mac-1 surface expression. The c ombination of PLA(2)-II and PAF synergistically increased Mac-1 surfac e expression, and the effect was greater than the combinations of PLA( 2)-II with TNF-alpha, IL-8, or FMLP, Additionally, the combination of PLA(2)-II and PAF induced exocytosis of both secretory vesicles and ge latinase granules, which did not occur with either PLA(2)-II alone or PAF alone. The induction was accompanied by marked production of leuko triene B-4. AA861, an inhibitor of 5-lipoxygenase, did not inhibit exo cytosis of secretory vesicles but did inhibit exocytosis of gelatinase granules and decrease Mac-1 surface expression. It was also found tha t Ca2+ influx is essential for 5-lipoxygenase activation, because Ni2, which blocks the influx of extracellular Ca2+, inhibited the product ion of leukotriene B-4. These results suggest that stimulation by the combination of PLA(2)-II and PAF, unlike stimulation by each mediator alone, causes exocytosis of gelatinase granules via the 5-lipoxygenase pathway, resulting in a synergistic increase in neutrophil Mac-1 surf ace expression during inflammatory processes.