Macrophage Activation and Immunostimulating Activity of Sphaerotilus natans and Its Slime Fraction

The macrophage activation and immunostimulating effects of the slime of Sphaerotilus natans IAM 12068, which is an aquatic sheathed bacterium, and GF-P-1, which was isolated from the slime fraction by Sepharose 4B gel filtration and has antitumor activity against Ehrlich ascites tumor in mice, were investigated. C57BL/6 mice peritoneal exudate macrophage induced by GF-P-1, which exhibited more effective antitumor activity than slime fraction, had the strongest cytostatic activity against EL-4 leukemic cells in vitro. Addition of GF-P-1 to mouse peritoneal macrophages in vitro caused marked spreading morphology, but the slime fraction did not. Acid phosphatase activity in the peritoneal cells induced by slime and GF-P-1 was also augmented as compared with that of resident macrophages. S. natans fractions, as well as Salmonella typhimurium lipopolysaccharide, were able to induce the mitogenic response in cultured spleen cells of C57BL/6 mice. Since spleen cells pretreated with rabbit anti-mouse thymocyte antiserum showed an unaffected mitogenic response to slime, the slime may be aB-lymphocyte mitogen. When slime fraction and GF-P-1 were injected intraperitoneally into ddY mice, they exhibited an enhancing effect onantibody response in vivo. These results indicate that slime and GF-P-1 are able to activate macrophages and exhibit immunostimulating effects.