THE RELATIONSHIP BETWEEN ACUTE REJECTION AND CHRONIC REJECTION IS HIGHLY DEPENDENT ON SPECIFIC MHC MATCHING

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Abstract
The impact of acute rejection, immunosuppression, and infection, specifically cytomegalovirus infection, on the development of chronic rejection in the cardiac allograft, has been the subject of a large number of investigations. One of the difficulties in finding associations has been the marked immunologic heterogeneity of the patient population coupled with the lack of the ability to HLA match. Furthermore, the ideal animal model, which duplicates as well as controls for this immunologic heterogeneity, is lacking. To try to simulate differences in HLA matching, immunosuppression regiments and cytomegalovirus infection, heterotopic heart transplantation was performed in two separate, complete MHC mismatch, rat strain combinations (WF-LEW, BN-LEW) requiring chronic immunosuppression and employing four separate immunosuppression/infection protocols. Animals were followed for 6 months, killed, and rejection and vascular changes were scored blinded to the group. The mean vascular and acute rejection scores were not significantly different between treatment regiments for either specific strain combination. There was a trend for the subtherapeutic groups to have higher vascular scores. Overall, there were no significant differences in vascular scores between the WF-LEW and BN-LEW groups (1.25+/-0.18 vs. 1.13+/-0.20, P=NS). Similar numbers of WF-LEW and BN-LEW exhibited cellular infiltration and necrosis of the allograft, but the intensity of the response (rejection score) was more severe in the WF-LEW combination (4.54+/-0.22 vs. 3.92+/-0.21, P=0.052) when limiting the analysis to those with myocyte necrosis. There was no significant correlation between acute rejection and vascular lesion severity in the WF-LEW combination (r=0.22, P=NS) but a high correlation between these parameters in the BN-LEW combination (r=0.74, P<0.0001). These data suggest that, although acute rejection and chronic rejection are related, MHC matching may influence their interdependence. These data also may explain why the clinical association between acute and chronic rejection is difficult to demonstrate.