Perforin and granzyme B: Cytolytic proteins up-regulated during rejection of rat small intestine allografts

Perforin and granzyme B are 2 cytolytic proteins specific to activated killer cells, particularly CTL. We have studied the mRNA expression of these 2 proteins by a reverse transcriptase polymerase chain reaction method in a unidirectional model of rat small intestine transplant rejection. The allograft group consisted of Lewis x Brown Norway FI donors into Lewis recipients. The isograft controls were Lewis donors into Lewis recipients. Grafts were placed heterotopically and no immunosuppression was given. Five animals in each group were killed at postoperative days (POD) 3, 5, 7, 8, 9, 10, 12, and 14. mRNA was extracted and a semiquantitative reverse transcriptase polymerase chain reaction was performed. For the semiquantitative analysis, we compared scintillation counts from excised bands. Results were expressed as a percent activity compared with /3-actin. From the same tissue samples, a histologic evaluation was made and rejection was graded according to severity. The isograft controls showed no evidence of histologic rejection and a very low expression of mRNA for perforin and granzyme B from POD 3-14. In contrast, the allograft group began to show histologic evidence of mild rejection on POD 5. By day 7, rejection was moderately severe and associated with a significant up-regulation of perforin and granzyme B in the allografts compared with the controls (P&0.01), which persisted through POD 14. Peak expression for perforin and granzyme B was on POD 10 and 8, respectively. We conclude that the up-regulation of perforin and granzyme B in rat small intestine transplant allografts is a useful marker of clinically important rejection.