ROLES OF ANTIBODIES AND COMPLEMENT IN PHAGOCYTIC KILLING OF ENTEROCOCCI

The contributions of complement and antibodies to polymorphonuclear le ukocyte (PMN)-mediated killing of enterococci were investigated with p ooled normal human serum (PNHS) or immune human sera (IHS) from patien ts with serious enterococcal infections. Each IHS containing antienter ococcal antibodies demonstrated by enzyme-linked immunosorbent assay a nd Western blotting (immunoblotting) was examined with the enterococcu s strain isolated from the same patient. PNHS promoted PMN-mediated ki lting of enterococci similar to that for IHS. PMN-mediated killing was consistently abrogated after preopsonization with heat-inactivated PN HS, but some heat-inactivated IHS supported neutrophil bactericidal ac tivity. Inhibition of the classical pathway of complement by chelation of either PNHS or IHS with Mg-EGTA [Mg-ethylene glycol-bis(beta-amino ethyl ether)-N,N,N',N'-tetraacetic acid] did not alter PMN-mediated ki lling, suggesting that activation of the alternative pathway of comple ment is sufficient to promote killing of enterococci by PMNs. PMN-medi ated killing assays were also performed with normal rabbit serum and i mmune rabbit serum against enterococci. Preopsonization with heat-inac tivated immune rabbit serum resulted in PMN-mediated killing of entero cocci; which was ablatedd after adsorption of the serum with the same isolate used for immunization. The influence of different phenotypic e nterococcal traits on neutrophil-mediated killing was also investigate d. Similar kinetics of killing were observed for derivatives of Entero cccus faecalis strains regardless of resistance to antimicrobial agent s or production of p-lactamase, hemolysin, gelatinase, or surface prot eins involved in the aggregative response to pheromones. In summary, P MN-mediated killing of enterococci appears to depend primarily on comp lement activation by either the classical or the alternative pathway. Human antienterococcal antibodies generated during infection variably promoted neutrophil bactericidal activity, while antibody raised in a rabbit supported PMN-mediated killing of the organism examined. Finall y, the different phenotypic properties of E. faecalis examined did not influence the neutrophil-mediated killing of these organisms.