A Surface Component in Group A, C, and G Streptococci with Non-Immune Reactivity for Immunoglobulin G

Abstract

Fifty-seven strains of streptococci belonging to groups A, C, and G were tested for γ-globulin Fc-reactivity with sensitized sheep red cells. Twenty-six per cent of the strains were positive. Forty-four per cent of the strains produced a soluble factor with similar γ-globulin reactivity. With a radioimmunologic assay to detect streptococcal reactivity, human IgG was found to be positive, whereas human IgA, IgM, IgD, and IgE were negative. The reactivity was detected in heavy chain preparations but not in light chains, F(ab′)2 fragments nor in Fc fragments. Experiments using isolated myeloma globulins representing the four IgG subclasses indicated that streptococci might react not only with IgG1-, IgG2-, and IgG4-like protein A but also with IgG3 molecules. One of the two IgG3 myeloma globulins studied did react with a group A streptococcus and both myeloma globulins did react with a group G streptococcus. Serum samples from 14 selected animal species also indicated differences between the γ-globulin reactivity of protein A and streptococci. Marsupials as well as the Rhea bird were non-reactive with streptococci. The results obtained with eleven other species indicated that the group A and G streptococcal reactivities were similar but differed significantly from staphylococcal protein A reactivity.