Mycoplasma-dependent activation of normal mouse lymphocytes: requirement for functional T lymphocytes in the cytotoxicity reaction mediated by Mycoplasma arthritidis.

Syngeneic and allogeneic target cells were killed in the presence of CBA mouse lymphocytes and viable Mycoplasma arthritidis. Medium supplementation had no effect on the response. Nonviable M. arthritidis was also capable of stimulating lymphocytotoxicity, although to a much lesser extent. Cytotoxicity was shown to be largely dependent upon the lymphocytes, since lymphocytes preincubated with mycoplasmas and treated to remove remaining organisms were highly toxic to target cells, whereas supernatants prepared from lymphocyte/mycoplasma mixtures exhibited minimal effects. A 6-h exposure of lymphocytes to mycoplasmas at a ratio of 100:1 was sufficient for commitment to target cell killing. Functional lymphocytes were required for the reaction, since gamma-irradiated lymphocytes did not develop cytotoxic potential despite the fact that the mycoplasmas replicated equally well in the presence of these and untreated lymphocytes. Furthermore, lymphocytes already activated with mycoplasmas lost cytotoxic potential after disruption. The kinetics and degree of lymphocytotoxicity induced by M. arthritidis and phytohemagglutinin toward 51Cr-labeled syngeneic fibroblasts were similar. Removal of most B cells and other adherent cells by column separation did not abrogate the cytotoxic effect. Lymphocyte suspensions treated with anti-Thy 1 antiserum and complement exhibited a marked decrease in their cytotoxic potential when added to labeled target cells in the presence of M. arthritidis. We conclude that the cytotoxic reaction is dependent upon the T-lymphocyte subpopulation.