T cells can be cytotoxic without making interleukin 2: a model of separate pathways of induction.

The thoracic duct lymphocytes from rats previously injected with ultraviolet-light-irradiated allogeneic lymphocytes were grown for 4 days with alloantigen, with or without Con A-induced lymphokine factors, and then for 3 days with the lymphokines alone. They were then tested for their cytoxicity and for their capacity to make interleukin 2 (IL-2) in response to antigen. The results show that T helper cells specific for both class I and class II antigens of the major histocompatibility complex were removed from the circulation by the injection of ultraviolet-irradiated alloantigen. However, precursors of cytotoxic cells remained and appeared to lose their OX-19 markers during activation. We have interpreted the results by using a speculative model that involves separate pathways of induction to cytotoxicity and IL-2 synthesis. We propose that the OX-19 marker is associated with the interleukin 1 receptor and that the latter is required for the IL-2 production pathway but not for activation to cytotoxicity.