The data presented in this study suggest that Group A streptococci produce two distinct pyrogenic toxins: one primarily an intracellular toxin and the other mainly an extracellular toxin.

Both of these toxins are not extractable by the conventional methods, phenol and TCA, used for isolation of Gram-negative bacterial endotoxin. Their chemical composition, therefore, differs from that of Gram-negative bacterial endotoxin.

On the basis of tolerance studies it appears that similar non-specific host factors may be involved in the detoxification of both the streptococcal intracellular pyrogenic toxin and the Gram-negative bacterial endotoxin. Detoxification of streptococcal exotoxin requires a more immunologically specific mechanism.

Because all the Group A sonic extracts studied elicited reciprocal tolerance to one another, it is suggested that tolerance to the intracellular pyrogenic toxin is not correlated with type-specificity.

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