Mycoplasma inhibition of phytohemagglutinin stimulation of lymphocytes.

Goat lymphocytes were cultured in vitro with phytohemagglutinin and nonviable mycoplasmas. Addition of the mycoplasmas, even as late as 45 hours after adding phytohemagglutinin, completely inhibited the increase in synthesis of DNA and RNA normally induced in lymphocytes by the mitogen. The suppression of synthesis did not result from killing of the cells by the mycoplasmas, combination of the organisms with phytohemagglutinin, or competition for combining sites on the cell surface, which indicates that some other mechanism of inhibition was operative. A similar depression of response to phytohemagglutinin in lymphocytes in culture has been observed in human diseases associated with an immune defect. The present demonstration that at least certain mycoplasmas can profoundly affect lymphocyte function in vitro suggests that thay may alter the immune response in vivo.