AN INTRACELLULAR HEMOLYSIN OF GROUP A STREPTOCOCCI III

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Abstract
Serum from rabbits immunized with an extract of sonically disrupted group A streptococci contains an antibody specific for an intracellular hemolysin present in the extract. The antibody occurs in low concentration but has been isolated and concentrated in the gamma-globulin fraction by both alcohol fractionation and ultracentrifugation. The specific antibody is distinguishable from the normal serum inhibitor which is a [beta]-globulin and neutralizes both the intracellular hemolysin and streptolysin S'' after a short incubation. Neutralization of intracellular hemolysin by its antibody is detectable only after prolonged incubation and centrifugation. This is interpreted to be an example of steric hindrance by an antigen-antibody aggregate. Sixty samples of human serum were also studied and one was found to have a very high titer of inhibitor specific for intracellular hemolysin. These serological studies support the concept that the intracellular hemolysin is distinct from streptolysin S.