These observations demonstrate that acute graft rejection in this model is associated with the expression of Th1 cytokines, IL-2, and IFN-gamma, whereas long-term survival is associated with predominant expression of Th2 cytokines, IL-4, and IL-10. The expression of IFN-gamma in long-surviving allografts in the absence of IL-2 provides evidence for altered activation of the Th1 response in this intrathymic immune modulation model.

SUMMARYWe have recently shown that T cells infiltrating cardiac allografts early in graft rejection use a limited T-cell receptor ( TCR) Vb repertoire. In this study we tested whether this limited repertoire of Vb genes is important for graft rejection. A cell line, AL2-L3, was established from LEW lymphocytes infiltrating ACI heart allografts 2 days after transplantation. This cell line is composed of CD4+ T cells that primarily recognize the class II RT1.B major histocompatibility complex (MHC) molecule expressed by the donor graft. This cell line precipitated acute rejection of donor hearts with a median survival time (MST ) of 10·5 days following adoptive transfer to sublethally irradiated LEW recipients. This rate of graft rejection was significantly (P<0·0007) accelerated when compared with a MST of 60 days for allografts in irradiated control recipients. The AL2-L3-mediated acceleration of graft rejection was donor specific as WF third-party heart allografts were rejected with a delayed tempo (MST=28·5 days). The Vb repertoire of this cell line was primarily restricted to the expression of Vb4, 15 and 19 genes. The nucleotide sequence analysis of the b-chain cDNAs from this cell line demonstrated that the restricted use of the V gene repertoire was not shared with the N, D and J regions. A wide variety of CDR3 loops and Jb genes were used in association with selected Vb genes. These data provide evidence for the role a restricted repertoire of Vb genes plays in cardiac allograft rejection in this model. The restricted usage of the Vb repertoire in an early T-cell response to allografts may provide the opportunity to therapeutically disrupt the rejection reaction by targeting selected T-cell populations for elimination at the time of organ transplantation.

Donor-recipient microchimerism has recently been suggested to play a critical role in the induction and maintenance of allograft tolerance. In this study we sought evidence for this hypothesis using the LEW-to-ACI cardiac allograft as a model system. Donor-specific tolerance to cardiac allografts was induced by intravenous or intraportal injection of graft recipients with donor peripheral blood, T cells, or B cells 7 days before transplantation. All the graft recipients injected with donor antigens accepted donor heart grafts indefinitely when compared with control recipients that rejected donor allografts in 12 days. Long-term graft survivors rejected third-party BN heart allografts in 14 days without an adverse effect on the survival of the first LEW heart allografts, demonstrating the specificity of the tolerance. Tissue lysates prepared from heart, kidney, liver, bone marrow, thymus, lymph nodes, and spleen of tolerant (>120 days) graft recipients were analyzed for the presence of donor DNA using LEW T cell receptor C beta gene-specific primers for polymerase chain reaction that detects donor DNA at > or = 1:10,000 dilution. Donor DNA was detected in 77% of tolerant graft recipients. Chimeric recipients showed variations in the levels and presence of donor DNA in different tissues. The status of donor microchimerism, with respect to its presence and tissue distribution, was dependent upon the donor cell type and route of injection used for the induction of tolerance. Intraportal injection of the graft recipients with donor peripheral blood resulted in the highest degree of chimerism, whereas intravenous injection with donor B cells did not induce detectable microchimerism in this group of recipients. These data clearly demonstrate that the presence of microchimerism is common following administration of donor cells, but that its presence is not an absolute requirement for the long-term survival of allografts.

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