We have extended our studies on the role of bacterial contamination in the generation of fetal calf sera which support primary in vitro humoral responses by cultured mouse spleen cells. Gram-negative, gliding bacteria were isolated from a strongly supportive sample of fetal calf sera. Medium conditioned by the growth of these microorganisms had strong adjuvant effects in cultures of mouse spleen cells supplemented with a non supportive, deficient sera. The adjuvant and mitogenic activities of the bacterial conditioned medium were then compared to those of bacterial lipopolysaccharide from Salmonella typhosa 0901 in cultures of LPS responder and LPS nonresponder spleen cells. From the results of these comparative studies, we conclude that the active factor(s) obtained from the gliding bacteria is an adjuvant with properties very distinct from those of highly purified enteric bacterial LPS.

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This work was supported by grant NIH-AI-8817 from the National Institute of Allergy and Infectious Diseases, and Contract NIH-NCI-CB-23883 from the National Cancer Institute.

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