Temporal sequence of transcription of perforin, Fas ligand, and tumor necrosis factor-α genes in rejecting skin allografts

Background. Perforin, Fas ligand (FasL), and tumor necrosis factor-α (TNF-α) have been implicated in cytolytic T lymphocyte (CTL) effector function. However, the relative roles of these effector molecules in allograft rejection are unclear, and there has been no rigorous quantitation of transcription of the respective genes throughout the period from transplantation to rejection. Methods. We orthotopically transplanted mouse tail skin allografts and estimated the numbers of transcripts of these genes expressed by graft-infiltrating T cells with rigorous quantitative, competitive reverse transcribed PCR (QC-RT-PCR) that enabled the comparison of transcription of different genes. Results. Perforin and FasL mRNA levels correlated closely with the rejection of allografts by normal hosts over the 4 days preceding rejection. Antibody-mediated depletion of host CD4⁺ T cells retarded perforin transcription and significantly suppressed FasL transcription, suggesting FasL was not required for allograft rejection. TNF- α transcription was the highest of these genes in this time period, but these levels were dwarfed by TNF-α transcription at 24 hr posttransplant when transcription in both autografts and allografts was 30-fold higher than in allografts on the day before rejection. Elimination of the function of these single or paired genes through genetic mutation or antibody treatment had no significant effect on the speed of rejection. Conclusions. The levels of perforin and FasL transcription appeared to be related to the process of allograft rejection in normal hosts. However, TNF-α transcription was highest during the posttransplant period suggesting that the principal role of TNF-α is in wound-healing rather than the effector phase of rejection.