Macrophage nitric oxide synthase (NOS) activation by Nocardia opaca fractions and 15- and 56-kD isolated antigens

The Gram-positive bacterium, Nocardia opaca, is a source of substances with adjuvant effect, ability to stimulate macrophages and natural killer cells for enhanced cytotoxity and cytokine production and B lymphocytes for polyclonal immunoglobulin secretion. We determined the immunogenicity of isolated N. opaca fractions and prepared MoAbs against immunogenic water-soluble mitogen (NWSM). Two main proteins of molecular mass 15 and 56 kD were detected in western blot analysis and isolated by affinity chromatography using anti-NWSM MoAb B7/7. Both these isolated nocardial antigens were found to stimulate mouse peritoneal macrophage NOS. The effect of 5 micrograms NWSM was comparable to that of 5 micrograms lipopolysaccharide (LPS) or 20 U of interferon-gamma (IFN-gamma) added to cell cultures. The MoAb B7/7 decreased No2- production induced by NWSM or by isolated nocardial antigens, but did not significantly influence the production elicited by LPS or IFN-gamma. On the other hand, NOS activation by NWSM was not affected by anti-IFN-gamma MoAb. The possible independent pathway for IFN-gamma and NWSM macrophage activation is discussed.