T-cell receptor expression in C57BL/6 mice that reject or are rendered tolerant to bm1 cardiac grafts

To study the molecular immunologic features of allograft rejection and tolerance induction by intrathymic pretreatment we developed a murine model of cardiac transplantation. In this model the transplant recipient was the C57BL/6 mouse with its major histocompatibility phenotype H-2b. Donors of cells for intrathymic pretreatment and of hearts for grafting were mice of the bm1 mutation. The bm1 mutation involves substitution of three amino acids in one of the alpha helixes of the class I H-2Kb molecule. Because of the discrete molecular configuration of the transplant antigen we hypothesized that there would be limited heterogeneity of receptor expression on C57BL/6 T cells responding to bm1 cardiac grafts and that intrathymic pretreatment would alter the T-cell repertoire of graft recipients by causing elimination of T cells responsible for graft rejection. Mice were given 0.3 ml of antilymphocyte serum intraperitoneally and had intrathymic injection of 25 x 10(6) bm1 splenocytes 12 to 21 days before transplantation with a bm1 cardiac graft. Flow cytometric analysis of lymph node and spleen cells was used to study the V beta T-cell repertoire of graft recipients. Cells were stained with monoclonal antibodies to CD3 and 13 V beta regions (n = 5, each group) of T cells in naive, sensitized, and tolerant animals. Untreated C57BL/6 mice (n = 9) rejected bm1 cardiac grafts a mean of 20.4 days after transplantation. Twelve mice pretreated with antilymphocyte serum and intrathymic bm1 cells had permanent graft survival (> 100 days, p < 0.0001). Animals treated with antilymphocyte serum alone (n = 5) or pretreated animals undergoing third-party BALB/c grafts (n = 4) rejected grafts in the normal time frame. There was significant alteration of percentage receptor expression of V beta 5.1, 7, 12, 13, and 17a in sensitized and tolerant mice. Of interest, V beta 7 expression was increased in the sensitized mice (3.8% to 8.3%,p = 0.005) and was virtually eliminated in tolerant mice (p = 0.005). In conclusion, these data suggest that V beta 7 is a critical receptor in the C57BL/6 response to subcutaneous bm1 cardiac grafts. Pretreatment of graft recipients with one dose of antilymphocyte serum and intrathymic bm1 cells appears to produce permanent tolerance to bm1 grafts with elimination of T cells expressing receptor chain V beta 7.