The macrophage response to bacteria: flow of L-arginine through the nitric oxide and urea pathways and induction of tumoricidal activity.

The consequences of the interaction of heat-killed bacteria and lipopolysaccharide (LPS) with a pure population of bone marrow-derived mononuclear phagocytes (BMMø) were investigated, utilizing changes in the flow of L-arginine and expression of tumoricidal activity as parameters of macrophage (mø) function. Gram negative bacteria and LPS proved potent in inducing the flow of L-arginine through the nitric oxide and the urea pathways but were mostly poor in eliciting tumoricidal activity. Gram positive bacteria affected the metabolism of L-arginine only little but were often efficient in triggering tumoricidal activity. The findings show that the mø response to bacteria, which may determine the outcome of their interaction with the host, may differ considerably depending on the type of bacteria.