Mitogenic activity of extracellular cationic products produced by group A streptococci; analysis of the lymphocyte...

The cationic fraction (isoelectric point greater than 8.5) of supernatant products of group A streptococcal cultures exerted a strong mitogenic effect on human peripheral lymphocytes at concentrations as low as 1 ng/well. Incorporation rates were highest at concentrations of 1-10 micrograms; rabbit peripheral lymphocytes also responded strongly, only a weak response was seen with mouse peripheral lymphocytes and rabbit thymocytes. Purified OKT4 positive (T helper) and OKT8 positive (T suppressor) lymphocyte subpopulations both responded, the former more strongly. Although accessory cells (monocytes) were not absolutely necessary, in their presence higher incorporation of 3H-thymidine was observed. Isolated B cells did not respond.