Endotoxins derived from several species of Gram-negative bacteria, while inducing non-specific resistance to typhoid bacilli in mice, failed to increase the resistance of these animals to infection with virulent strains of Group A streptococci. However, if administration of endotoxin was followed by injection of minute amounts of type-specific antiserum, a substantial degree of protection against the streptococcal pathogen was obtained. The same amount of type-specific antiserum given to the animals by itself did not have any effect on the outcome of the streptococcal infection. Fresh rabbit blood, obtained from animals pretreated with endotoxin, together with anti-M protein immune serum, was found strongly bactericidal for streptococci. These observations suggest that, at least with regard to streptococcal infection, both humoral and cellular factors are required for induction of non-specific resistance.

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