Bactericidal activity of fractionated granule contents from human polymorphonuclear leukocytes: antagonism of granule cationic proteins by lipopolysaccharide

Abstract

Granule extracts from human polymorphonuclear leukocytes (PMN) were prepared with 0.2 M (pH 4.0) acetate. A fraction (valley AB) with distinctive bactericidal activity against cell wall mutants of Salmonella typhimurium LT-2 was obtained after fractionation of the granule extracts by Sephadex G-100 column chromatography. The smooth parent LT-2 strain was less sensitive to the bactericidal action. Susceptibility of the rough mutants to bactericidal action increased as sugar residues decreased in the lipopolysaccharide (LPS) (Re > Rd2 > Rd1 > Rc > Ra). Cationic protein(s) responsible for bactericidal activity could be selectively removed from the fraction by absorption with whole LT-2 cells or purified LPS. Loss of cationic protein species was confirmed by cationic polyacrylamide gel electrophoresis. Purified LPS from LT-2 or the deep rough mutant TA2168 inhibited the anti-microbial activity of the killing fraction in in vitro assays. A minor protein species (vAB1) from the valley AB fraction had an apparent MW 36,000-37,000 and represented a major bactericidal activity of the fraction. Small amounts of the isolated vAB1 protein were bactericidal for the smooth parent LT-2 strain.