Characterization of the mitogenic and antigenic stimulatory properties of a purified streptolysin O preparation.

In vitro transformation of human peripheral blood lymphocytes was induced by a purified group A streptococcal extract rich in streptolysin O (SLO). The stimulation was shown to be largely a general mitogenic effect rather than antigen-selective as a large panel of normal blood donors responded strongly. Further support for a non-specific stimulation was obtained by experiments with cord blood lymphocytes. An antigen-specific response could also be detected as culture supernatants from the stimulation experiments contained immunoglobulins with SLO neutralizing properties. In addition, the total response could partly be inhibited by rabbit heteroantisera against HLA-DR-like antigens supporting the above contention. The stimulatory properties were found to reside in the SLO molecule although results may indicate that the determinants provoking the lymphocyte transformation differ from the determinants possessing the haemolytic properties. Peak response was found on days 4-5. Cell fractionation experiments indicated that only T lymphocytes were stimulated although co-operating B cells and/or monocytes were necessary.