Cytolytic activity of Ia-restricted T cell clones and hybridomas: evidence for a cytolytic mechanism independent of interferon-gamma, lymphotoxin, and tumor necrosis factor-alpha.

Ten different helper T cell (Th) hybridomas that are specific to Ia or antigen plus Ia were found to express nonspecific cytolytic activity toward the cytotoxin (CT)-resistant P815 cells upon activation with either Con A or a monoclonal anti-T3 antibody (T3-mAb). In contrast to cytolytic Th1 clones which secrete high levels of interferon-gamma (IFN-gamma) and cytotoxin (CT) (lymphotoxin (LT, also known as TNF-beta) or tumor necrosis factor-alpha (TNF-alpha], these Th hybridomas produce low or undetectable levels of IFN-gamma and CT. No inhibitory activity of IFN-gamma and CT was observed in culture supernatants of activated Th hybridomas. Double-chamber experiments demonstrated that CT-sensitive L929 cells when physically separated from activated Th1 clones were killed by membrane-permeable CT. Under identical experimental conditions, lysis of P815 cells did not occur. Moreover, activation of Th hybridomas directly in wells containing the CT-sensitive L929 cells failed to induce target cell lysis. This confirms that these Th hybridomas produce little CT and argues against high local concentrations of CT being responsible for Th hybridoma-mediated killing of P815 cells. Finally, a polyclonal rabbit antiserum to rTNF-alpha, which strongly and specifically inhibited CT-mediated and Th1 clone-mediated killing of L929 cells, failed to inhibit P815 lysis by activated Th1 clones and Th hybridomas. These observations establish that a cytolytic mechanism independent of IFN-gamma, LT, and TNF-alpha is responsible for lysis of CT-resistant target cells.