Macrophage response to bacteria and bacterial products: modulation of Fc gamma receptors and secretory and cellular activities.

The ability of bacteria and bacterial products to modulate the expression of Fc gamma receptors and major histocompatibility complex (MHC) class II molecules in resting rat bone marrow-derived mononuclear phagocytes (BMM phi) was determined by means of flow cytometry (FCM). Binding of IgG via Fc gamma receptors was considerably enhanced by most microbial agents; bacterial lipopolysaccharide, lipoteichoic acid and some intact bacteria proved to be as active as interferon-gamma (IFN-gamma) and augmented binding of IgG via high- and low-affinity Fc gamma receptors. In contrast, expression of MHC class II molecules by BMM phi was only slightly affected by the microbial agents. Additional findings attest that resting unprimed rat BMM phi are able to respond directly to Gram-negative and Gram-positive bacteria and to some of their products with the expression of marked secretory [in particular tumour necrosis factor-alpha (TNF-alpha) and nitrite] and cellular activities (TNF-alpha-independent tumoricidal activity). This extensive, direct type of macrophage activation may substantially amplify the capability of these cells to cope with these infectious agents in first-line, non-specific host defence.