A Comparison of Spontaneous Versus Induced Tolerance in an Experimental Model of Rat Hepatic Allograft Transplantation

Abstract

In some rodent haplotype combinations, spontaneous tolerance (ST) develops after orthotopic liver transplantation (OLT) without any immunosuppression [e.g., Lewis (Lew, RT1 1) into Wistar Furth (WF, RT1 a)] whereas in other combinations vigorous, progressive rejection rapidly leads to the death of the recipients. We (and others) have induced tolerance (IT) in a rejecting strain combination [Dark Agouti (DA, RT1 a) into Lew] by intrathymic inoculation of donor bone marrow cells and 1 cc of antilymphocyte serum (ALS) 7-14 days prior to OLT. We hypothesized that cellular immunity in the two groups of animals was similar. We first compared survival in each group of animals and found that there was no difference in the number of animals surviving >100 days (8/11 vs 16/17, ST vs IT, respectively, P = 0.11). Liver function studies were similar in these animals at 2 and 4 weeks after OLT and comparable to syngeneic Lew into Lew OLT animals, but significantly lower than in the rejecting DA into Lew combination treated with only ALS. Animals that were unresponsive to their allografts demonstrated donor-specific tolerance by the acceptance of donor strain ( n = 4, ST and IT) and rejection of third party ( n = 1 and n = 2, ST and IT groups, respectively) heterotopic heart allografts. One-way mixed lymphocyte cultures (MLC) of peripheral blood lymphocytes against donor and third party antigen were suppressed to donor and third party stimulators versus the MLC of unmanipulated animals. Naive host strain responder lymph node cells and purified T cells demonstrated strong proliferative responses to donor strain antigen in both the ST and IT animals. Peripheral blood lymphocytes expressing donor MHC class I molecules were not detectable by flow cytometry in the ST animals using the monoclonal antibody (mAb) I-1.69 which is directed against Lew MHC class I molecules. There was variable expression (023%) of donor MHC class I molecules on peripheral lymphocytes in IT animals using the mAb C3, directed against DA MHC class I molecules. In summary, animals unresponsive to their liver allografts demonstrate donor-specific tolerance and functionally intact cellular immunity in vivo by acceptance of donor strain and rejection of third party heart allografts. The MHC class II response is suppressed to donor and third party stimulators in vitro in both groups of animals. In conclusion, cellular immunity in rats after liver allografting in the Lew into WF spontaneously tolerant strain combination is similar to that after tolerance induced by intrathymic manipulation in the DA into Lew combination.