Suppression of antibody response by group A streptococcal pyrogenic exotoxin and characterization of the cells involved.

The effect of purified streptococcal pyrogenic exotoxins (SPE) on the antibody response to sheep erythrocytes was studied in cultures of mouse spleen cells. Purified SPE types A, B, and C shared the ability to suppress the day 4 direct plaque-forming cell response when added to cultures. SPE A and C were most suppressive at concentrations of 0.1 to 1 ng per culture, while SPE B was active at 1 microgram per culture. Pretreatment of mice with SPE A, 3 h before removal of their spleens for culture, also produced suppression. Cell populations were separated from spleens of normal and toxin-treated mice and recombined in culture to test the cellular site of action of SPE immunosuppression. When nonadherent cells (lymphocytes) and adherent cells (macrophages) from control and SPE-treated mice were separated and recombined, the plaque-forming cell response depended on the source of lymphocytes. Macrophages from toxin-treated mice functioned normally in the presence of control lymphocytes. In a further experiment, toxin pretreatment failed to suppress the plaque-forming cell response of spleen cells that were T-cell depleted and reconstituted with control thymocytes. When the T lymphocytes were removed from toxin-treated spleen cell suspensions, the remaining cells were able to respond normally to antigen if normal helper T cells were provided. The results suggest that the suppressive activity of SPE on antibody production is mediated by altered activity of T lymphocytes.