ROLE OF TNF-ALPHA IN CD8-LYMPHOCYTE-MEDIATED LYSIS( CYTOTOXIC T)

The possibility that lymphokines such as TNF-alpha produced by CD8+ CT L are responsible for acute (short term) target cell damage induced by CTL has been debated for many years. However, the slow kinetics of TN F-induced target cell death stands in sharp contrast to the rapid targ et cell lysis mediated by CTL. We find that cloned CD8+ CTL activated through their TCR secrete TNF-alpha. On the other hand, our cloned CTL also have a membrane form of TNF-alpha, and they kill TNF-alpha-sensi tive target cells not recognized through the TCR in a slow (18-h) lyti c reaction using this surface-associated TNF-alpha. There is no secret ed TNF-alpha release during this interaction. Cyclosporin A and protei n synthesis inhibitors block TNF-alpha secretion, but have no effect o n slow lysis mediated by the CTL. On the other hand, TNF-alpha-resista nt variants are greatly resistant to slow lysis, and antibodies to TNF -alpha strongly inhibit this slow lysis. Thus, although secreted TNF-a lpha does not seem to be the mechanism behind slow lysis, some form of TNF-alpha, most likely the membrane-associated form, must be involved . Not only does surface TNF-alpha appear to be biologically active in these CTL, but its expression is enhanced severalfold upon activation of the CTL through the TCR. This may be important in vivo, where surfa ce TNF-alpha could preserve the localized nature of cytolysis and endo w a CTL with an additional, albeit slower, mechanism of cell lysis. Fi nally, we find that although activated CTL clearly use the membrane fo rm of TNF-alpha in slow lysis, they appear not to use TNF-alpha, in an y form, during acute lysis, even under conditions in which degranulati on and perforin assembly are blocked.