Stimulation of phagocytosis in bone marrow-derived mouse macrophages by bacterial lipopolysaccharide: correlation with biochemical and functional parameters.

Abstract

It has been shown that low concentrations of E. coli lipopolysaccharides (LPS) greatly and selectively stimulate phagocytosis and related functions in mouse bone marrow-derived macrophages. Culture in the presence of 50 ng/ml LPS induced on average a 10-fold enhancement of phagocytosis of IgG-coated sheep erythrocytes. Activation was in two stages--a small increase observed during the first 8 to 12 hr, and the major increase noted between 16 and 24 hr. Phagocytic activity remained at the maximal level for 24 hr and then declined progressively. Stimulation by LPS was dose-dependent; significant effects could be observed at 0.8 ng/ml and the maximum was reached at 10 ng/ml. LPS-treated cells also showed a markedly increased tendency to form colonies. All these effects could be prevented by the addition of 100 ng/ml polymyxin B together with LPS, indicating that the active principle is lipid A. The LPS-dependent increase in phagocytic activity is probably mediated by increased Fc receptor capacity because both parameters were influenced in parallel by the stimulus. Phagocytosis-related events, such as enhanced hexose monophosphate shunt activity, H2O2 formation, and nitroblue tetrazolium reduction were also stimulated by LPS. By contrast, pinocytosis was unaffected. Measurements of cell-associated enzyme activities showed that lactate dehydrogenase, acid phosphatase, and cathepsin D were significantly increased. Beta-glucuronidase, beta-galactosidase, alkaline phosphodiesterase, and aminopeptidase were unchanged and NAD nucleosidase was markedly decreased after LPS treatment. 5'-Nucleotidase and glucosamine uptake were undetectable both in control and LPS-stimulated cells. LPS treatment induced a significant increase in cell-associated protein, but did not result in cell proliferation or increased cell loss as shown by the DNA content that remained constant. LPS-induced changes were dependent on de novo protein synthesis; cycloheximide prevented enhancement of phagocytosis, Fc receptor capacity, and colony formation.