EFFECTS OF FIBRONECTIN ON ACTIN ORGANIZATION AND RESPIRATORY BURST ACTIVITY IN NEUTROPHILS, MONOCYTES, AND MACROPHAGES

Previous studies have shown that fibronectin (Fn) enhances phagocytosi s and killing of antibody-coated bacteria by neutrophils and macrophag es. In an attempt to understand the mechanism of this enhancement, we have investigated the effects of Fn on phagocytosis-related actin orga nization as well as respiratory burst activity in neutrophils, monocyt es and culture-derived macrophages. Employing an NBD-phallacidin flow cytometric analysis of filamentous actin formation, we found that Fn p romotes rapid actin polymerization within 30 seconds in neutrophils, m onocytes, and macrophages, but not lymphocytes. Enhancement of actin p olymerization by Fn was concentration-dependent and mediated by a pert ussis toxin- but not cholera toxin- sensitive C protein. Inhibition or protein kinase C by sphingosine (20 mu M), calcium influx by verapami l (0.1 mM), or intracellular calcium mobilization by 8-(N,N-diethyl-am ino) octyl-3,4,5-trimethoxybenzoate HCl (TMB-8; 0.1 mM) did not block Fn-enhanced actin polymerization in phagocytes. Incubation of neutroph ils and macrophages on microtiter plates precoated with Fn suppressed superoxide (O-2(-)) production induced by IgG- and IgA- opsonized grou p B streptococci. In contrast, Fn significantly enhanced IgA- and IgG- mediated O-2(-) production by freshly isolated monocytes. These data s uggest that Fn enhances phagocytosis, presumably through G protein-cou pled cytoskeleton reorganization and augments O-2(-) production by cir culating monocytes. In contrast, it appears to suppress O-2(-) product ion by the active phagocytic cells, neutrophils and macrophages. This may result in enhanced phagocytosis and intracellular killing of micro organisms without damaging interstitial tissues.