TARGET CELL-DIRECTED DEGRADATION OF PERFORIN MESSENGER-RNA IN CTL - LACK OF CORRELATION WITH LOSS OF PROTEIN AND LYTIC ABILITY

We have previously shown that CTL and NK cells rapidly down regulate p erforin mRNA and become functionally inactive within 4-6 hr after expo sure to sensitive target cells (TC). We report here for the first time that CTL also down regulate perforin mRNA upon exposure to resistant, but binding, TC. When three separate human MHC-restricted CTL lines w ere exposed to resistant TC, perforin mRNA was rapidly degraded. Remov al of both extracellular Ca++ and Mg++ prevented perforin message down regulation, whereas removal of Ca++ alone did not, indicating that CT L: TC binding was required. Unlike the response of CTL exposed to sens itive TC, resistant TC did not trigger serine esterase (SE) release, s uggesting distinct signalling pathways for perforin mRNA down regulati on and granule exocytosis. Moreover, using western analysis, we showed that there was limited (< 10%) perforin protein release after CTL: TC interaction, suggesting that CTL loss of lytic activity after exposur e to sensitive TC is not due to massive depletion of perforin. Treatme nt of CTL with mAb to CD2, CD3, CD2 + CD3, CD8, Class I and LFA-1 did not induce perforin mRNA down regulation. Furthermore, mAb to CD2, CD3 , CD8, Class I, Class II, CD54 and LFA-1 did not block TC-mediated per forin mRNA down regulation although lysis of TC was inhibited.