Stimulation of lymphocyte proliferation by killed mycobacteria and other bacterial species.

Killed mycobacteria and some mycobacterial fractions induced spleen cells from normal C3H mice to incorporate tritiated thymidine to a relatively high degree. Thymocytes under the same conditions were not activated. However, incorporation of thymidine was significantly increased when mixtures of thymus and spleen cells were cultured in the presence of the inducers. A similar activation of spleen cells was displayed in the presence of gram-positive and gram-negative non-mycobacterial species.