The role of indirect recognition of MHC class I and II allopeptides in a fully mismatched miniature swine model of lung transplantation.

UNLABELLED: Considerable evidence suggests that indirect recognition of MHC allopeptides plays an important role in solid-organ rejection. Here, we examine whether immunization with class I or class II allopeptides accelerates rejection in a fully MHC-mismatched lung transplant model in miniature swine.
METHODS: Recipients were immunized with either donor-derived class I or class II peptides. Sensitization to the peptides was confirmed by DTH testing and in vitro proliferation assays. Nonimmunized control (n = 6), class I peptide-immunized (n = 3), and class II peptide-immunized (n = 3) swine were transplanted with fully mismatched lungs using only a 12-day course of tacrolimus.
RESULTS: One control animal rejected its graft on postoperative day 103, while the others maintained their grafts for over 1 year. In the class I peptide-immunized group, two recipients rejected their grafts (days 14 and 52). The third animal has not rejected the graft (day 120, experiment is ongoing). In contrast, in the class II-peptide immunized group, only one animal rejected its graft on day 52, while the others maintained their grafts over 1 year. Both anti-donor IgM and IgG antibodies were detectable in all acute rejectors, although no alloantibody was detectable in long-term acceptors. Regardless of the fate of the graft, all animals have maintained their proliferative responses to the peptides. However, only acceptors maintained donor-specific hyporesponsiveness in cell-mediated lymphocytotoxity and mixed lymphocyte reaction assays.
CONCLUSIONS: Pretransplant sensitization of lung allograft recipients to donor allopeptides accelerates graft rejection. This appears particularly true for class I-derived allopeptides, suggesting that class II molecules may be less antigenic when presented indirectly.