A potent antimitogenic factor from group A streptococci.

A cytoplasmic component from group A streptococci produced complete suppression of human lymphocyte transformation induced by phytohaemagglutinin or the mixed lymphocyte reaction in vitro. It also suppressed antibody-forming cells in mice against sheep erythrocytes. The active substance was eluted as second and third fractions form Sephadex G-200 chromatography of the 100,000 g supernatant of sonically ruptured group A streptococci. The antimitogenic activity was not susceptible to trypsin, pronase, RNase or DNase digestion, but the activity was completely lost when it was sequentially digested, first with RNase and DNase and then with pronase. The active substance was not antigenic nor heat-labile at 56 degrees. It may be a protein component of a nucleoprotein.