Expression of the tumor necrosis factor locus is not necessary for the cytolytic activity of T lymphocytes

In order to test whether tumor necrosis factors α (TNF-α) or β (TNF-β, also known as lymphotoxin) are involved in the lysis of target cells by cytolytic T lymphocytes, we probed for the presence of the TNF mRNAs in several quiescent and activated CTL clones. No TNF mRNA could be found in constitutively cytolytic Lyt-2⁺ clones, and only two out of three clones tested accumulated TNF mRNA after stimulation with phorbol myristate acetate and ionomycin. Of two L3T4⁺ clones that can be induced to become cytolytic by a combination of antigen and IL-1, only one accumulated TNF-β mRNA in the process. The PC60 rat x mouse T cell hybrid, which becomes cytolytic in response to a combination of IL-1 and IL-2, also failed to accumulate TNF mRNA after stimulation with these agents. Our results strongly suggest that TNF-α or -β are not necessary agents of the cytolytic activity exhibited by antigen-specific T lymphocytes.