Nonspecific resistance to infection induced in mice by a water-soluble adjuvant derived from Mycobacterium smegmatis.

The effect of a nontoxic, water-soluble adjuvant (Neo-WSA) from delipidated cells of Mycobacterium smegmatis on the susceptibility of mice to infection with four challenge organisms was studied. An intravenous dose of 1 mg of Neo-WSA per mouse 24 hr before challenge enhanced resistance to infection with a fungus (Candida albicans), a gram-negative bacterium (Klebsiella pneumoniae), and a gram-positive bacterium (Streptococcus pneumoniae). Protection by Neo-WSA was not significant when the mice were challenged with a malarial parasite. Plasmodium berghei. When 1 mg of Neo-WSA was given intravenously to mice 10 min before challenge with C. albicans, protection was significant, but when the same dose was given two or six days prior to challenge, mice were not protected. The concentration of iron in serum had not changed significantly 1 or 24 hr after the intravenous injection of 1 mg of Neo-WSA. Thus Neo-WSA is capable of inducing nonspecific resistance to certain experimental infections in mice. The protection afforded by administration of Neo-WSA 10 min before challenge, the lack of protection afforded by administration of Neo-WSA six days before challenge, and the lack of significant change in the serum iron concentration clearly separate this compound from bacterial endotoxins, which are classical inducers of nonspecific resistance to infection.