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Biological Activities of Lipopolysaccharide‐Like Substance (LLS) Extracted from Leptospira interrogans Serovar canicola Strain Moulton

The biological activities of lipopolysaccharide‐like substance (LLS) extracted from Leptospira interrogans serovar canicola strain Moulton by the hot phenol‐water method were studied in mice. The addition of 12.5 μg/ml or more of LLS fraction increased the incorporation of [3H] thymidine into in vitro cultured spleen cells of C57BL/6 mice, while the activity of the LLS fraction was about 20 times weaker than that of Salmonella typhimurium lipopolysaccharide (LPS). Pretreatment of murine spleen cells with rabbit anti‐mouse thymocyte antiserum did not diminish the mitogenic activity of leptospiral LLS, and the LLS could not increase the incorporation of [3H] thymidine into thymocytes, suggesting that LLS acts on a B‐lymphocyte population of lymphocytes. When sheep erythrocytes and LLS fraction were injected intraperitoneally into BALB/c mice, LLS exhibited an enhancing effect on antibody response in vivo. However, lethal toxicity of the LLS fraction was about 500 times lower than that of LPS in C57BL/6 mice loaded with galactosamine. No antitumor activity of leptospiral LLS (250–1,000 μg/mouse) against the ascites form of Ehrlich carcinoma in ddY mice was observed. The biological activities of the LLS fraction from the organism were weaker than those of gram‐negative bacterial LPS, suggesting that Leptospira possesses no typical LPS.