Inhibition by quercetin of activation of polymorphonuclear leucocyte functions. Stimulus-specific effects.

The effect of some bioflavonoids on the activation of polymorphonuclear leucocyte respiration and exocytosis was examined. At 10-5-10-4 M concentration, quercetin, but not morin and rutin, was found to inhibit the concanavalin A-induced enhancement of oxygen consumption markedly, without impairing leucocyte viability and concanavalin A binding. The inhibition could be reversed by either washing the leucocytes or adding a 10-fold molar excess of 1-anilino-8-naphthalene sulphonate. Concanavalin A-dependent cell secretion of lysozyme was also totally inhibited by 30 muM quercetin. The effect of quercetin on the activation of leucocyte respiration appeared to be stimulus specific. In fact, at a concentration of the flavonoid (75 muM) which provided a 95% inhibition of the concanavalin A-induced stimulation, the respiratory activation produced by phospholipase C was inhibited by about 50% and that caused by myristic acid and by the antibiotic Br-X537A by less than 25%. These data suggest that quercetin exerts its activity at specific sites of the plasma membrane of the leucocytes, and that this compound might be used to identify the membrane domain whereon different stimuli act to originate the initial stimulatory signal.