Use of recombinase activation gene-2 deficient mice to ascertain the role of cellular and humoral immune responses in the development of chronic rejection

Introduction: Given its multifactorial etiology, the relative contribution of anti-donor cellular and humoral immune responses in the pathogenesis of chronic rejection is as yet ambiguous. We hypothesized that alloreactive T and B cells play a seminal role in the development of this lesion. Methods: To address this hypothesis, RAG-2 −/− mice were used as donors and recipients in a well-established murine model of aortic transplantation. Grafts were transplanted across the following groups: Group I: C3H → C3H; Group II: Wild-type [WT] 129Sv (H-2 b ) → C3H (H-2 k ); Group III: C3H → WT 129Sv; Group IV: 129SvEv RAG-2 −/− → C3H; and Group V: C3H → 129SvEv RAG-2 −/− . Grafts were harvested at d40 to 146 post-transplantation for morphologic and immunohistochemical analyses and semi-quantitative RT-PCR was employed to evaluate the intragraft mRNA expression of various immune mediators. Mixed lymphocyte reaction and complement-mediated alloantibody cytotoxicity assays were performed to determine anti-donor proliferative and humoral responses, respectively. Results: Unlike that across the syngeneic combination (Group I), marked intimal thickening with corresponding luminal narrowing was observed in the majority of the aortic allografts (Groups II–IV). On the contrary, the morphology of C3H aortic allografts harvested from the majority of the RAG-2 −/− was remarkably preserved. Correspondingly, anti-donor proliferative and humoral immune responses were undetectable in C3H → RAG-2 −/− recipients as was the intragraft mRNA expression of the Th 1 and the Th 2 -type cytokines. Conclusions: Taken together, these data suggest that in this murine model of aortic allotransplantation, donor-specific cellular and humoral responses play a dominant role in the initiation and perpetuation of chronic rejection.