C5a-induced bronchoconstriction: absence of a role of circulating white blood cells and platelets.

C5a causes an intense bronchoconstriction when injected intravenously into the guinea pig. The present study was designed to determine if circulating white blood cells or platelets were important target cells for the induction of bronchoconstriction on intravenous injection of C5a. To accomplish this, we examined the effect of C5a on numbers of circulating cells as well as the effect of depletion of various circulating cell populations on C5a-induced bronchoconstriction. Intravenous injection of C5a caused a precipitous drop in circulating granulocytes which preceded the maximum bronchoconstrictor response. The levels of circulating platelets and mononuclear cells were unchanged by intravenous injection of C5a. Depletion of either white blood cells or platelets did not significantly alter either the maximum bronchoconstrictor response to C5a or the time course of the response. Thus, these studies suggest that C5a-induced bronchoconstriction in the guinea pig is not dependent on an interaction of C5a with circulating white blood cells or platelets.