Differential induction of NO synthesis by Gram-positive and Gram-negative bacteria and their components in bovine monocyte-derived macrophages

The ability of Gram-positive and Gram-negative bacteria to promote the indu ction of NO synthesis in bovine monocyte-derived macrophages (MDM) was test ed. Heat-killed Gram-negative organisms induced NO synthesis at low concent rations (optimum 0.2 to 2 mu g/ml wet weight), regardless of the strain, an d the response was only moderately enhanced by co-administration of recombi nant bovine interferon-gamma (rbolFN-gamma). The activity was largely, but not exclusively, due to lipopolysaccharide (LPS), since it was largely abro gated by co-incubation with polymyxin-B. Diphosphoryl-lipid-A and rough-str ain LPS were two orders of magnitude more active than monophosphoryl-lipid A, but two orders of magnitude less active than smooth-strain LPS, suggesti ng that O side chains contribute to increasing the affinity of LPS or to ac t as a costimulus. Gram-positive bacteria as single stimuli were four order s of magnitude less potent in inducing NO synthesis than Gram-negative orga nisms, but upon costimulation with rboIFN-gamma, some of them were excellen t inducers of NO synthesis. A similar rboIFN-gamma-enhanced NO synthesis in duction was also observed for zymosan, muramyl dipeptide, lipoteichoic acid and lipoarabinomannan, although to a lesser extent than for the whole heat -inactivated prototypic organisms. Thus, bovine macrophages exposed to rbol FN-gamma have mechanisms by which they universally react to bacterial compo unds distinct from LPS by induction of NO synthesis. (C) 1999 Academic Pres s.