An intracellular hemolysin of group A streptococci. III. Immunological studies.

Previous reports (Schwab, 1956a) have described the hemolytic activity of an extract of sonically disrupted group A streptococei. This is referred to as sonic extract and the hemolytic activity as intracellular hemolysin. A study comparing the hemolysin obtained by this method, with the previously described streptolysins 0 and S', indicates that the intracellular hemolysin may be a distinct streptococcal product (Schwab, 1956b). Immunological studies on the inhibition of the streptolysins were undertaken to further elucidate the relationship between the intracellular hemolysin and streptolysin S. The experiments are complicated by the facts that streptolysin S is not antigenic (Bernheimer, 1954; Humphrey, 1949a) and that serum contains a nonspecific normal inhibitor which is probably a lipoprotein (Humphrey, 1949b; Stollerman et al., 1950). The present communication also presents evidence that neutralization of the intracellular hemolysin by antibody is due to aggregation of the antigen-antibody complex. Steric hindrance by the structure of the antigen-antibody aggregate has been proposed by Cinader (1957) as one mechanism of neutralization by antibody. A study of this hemolysin-antibody system should, therefore, contribute to our understanding of the nature of antibody neutralization of toxins.