The interaction of macrophages and bacteria: Escherichia coli species, bacterial lipopolysaccharide, and lipid A differ in their ability to induce tumoricidal activity and the secretion of reactive nitrogen intermediates in macrophages

Abstract

The ability of nine Escherichia coli strains, and of bacterial lipopolysaccharide (LPS) 3 3 Abbreviations used: BMMø, bone marrow-derived mononuclear phagocytes; FCS, fetal calf serum; IFN, Interferon; IMDM, Iscove's modified Dulbecco medium; KDO, 2-keto-3-deoxyoctulosonic acid; LPS, lipopolysaccharide; NMMA, N G-monomethyl- l-arginine; NO, nitric oxide; NO − 2 , nitrite; RNI, reactive nitrogen intermediates. and lipid A preparations, to elicit in a pure population of bone marrow-derived mononuclear phagocytes (BMMø) tumoricidal activity and/or the generation of reactive nitrogen intermediates (RNI) was compared. Generally, low concentrations of E. coli organisms were able to trigger the generation of RNI; however, for induction of tumoricidal activity, higher concentrations were required. Nonisogenic E. coli species exhibited different ability; isogenic E. coli organisms that differed only in the expression of K antigen exhibited similar ability to elicit the macrophage activities. LPS proved to be highly efficient in triggering the secretion of reactive nitrogen intermediates; lipid A was clearly less potent, but evidence is presented to suggest that this was due to the diminished solubility of these reagents. On the other hand, all LPS and lipid A samples were very poor inducers of tumoricidal activity. Although RNI secretion and expression of tumoricidal activity are both strongly dependent on l-arginine, various evidence suggests that the two functions are not closely correlated and are induced by different bacterial structures.