Interleukin-18 production following murine cardiac transplantation: Correlation with histologic rejection and the induction of IFN-gamma

Interleukin-18 (IL-18) and IL-12 have been shown to play an important role in the induction of interferon-gamma (IFN-gamma), IFN-gamma induces the pro liferation of T cells and natural killer (NK) cells and augments the Th1 im mune cascade. The role of IL-18 and IL-12 in the induction of IFN-gamma fol lowing allogeneic heart transplantation has not been described. We sought t o characterize the IL-12 and IL-18 response to murine allogeneic heart tran splantation, particularly with respect to IFN-gamma production and histolog ic transplant rejection. Forty-eight heterotopic heart transplants were per formed in two groups of mice: syngeneic C3H/HeN to C3H/HeN mice and allogen eic BALB/C to C3H/HeN mice. Transplants were followed out to 2, 6, 10, and 14 days. Six transplants were performed in each group, Serum and splenic sa mples were used to evaluate the cytokine response by ELISA. Explanted heart tissue was processed for evidence of histologic rejection, and RT-PCR was performed to evaluate the IL-12, IL-18, and IFN-gamma signal qualitatively. Analysis of variance (ANOVA), Fisher's projected least significant differe nce (PLSD) was used for statistical analysis. Transplant rejection occurred in the allogeneic group histologically by day 6 and clinically by day 10. Serum IFN-gamma levels rose significantly by day 6 in the allogeneic group and then continued to rise in the splenocyte cultures. Serum IL-18 also ros e significantly in the allogeneic group at day 6 compared with syngeneic gr oup. RT-PCR revealed that the allogeneic tissue contained an increased sign al for IL-12, IL-18, and IFN-gamma beginning at day 6 and peaking at day 10 after transplant. Beginning 6 days after transplantation, IL-12 and IL-18 appear to play a significant role in the induction of IFN-gamma in allogene ic heart transplants.