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Background: Donor leucocytes (DL) play an important role in rat liver transplant tolerance and their postoperative administration can convert rejection to tolerance. They appear to induce early activation, altered patterns of infiltration and death of recipient alloreactive T cells. The ability of immunosuppressive drugs to combine with DL administration was examined in a rat heart transplant model., Methods: Immediately after PVG to DA heterotopic heart transplantation, 6 x 10(7) spleen DL were injected. Cyclosporine A (CsA), 1.5 mg/kg/day, or methotrexate (MTX), 0.1 or 0.2 mg/kg/day, were given from day (d) 0 to d4 (early) or from d3 to d7 (delayed). Castanospermine (CAST) was administered from d0 to d7 at 100 or 300 mg/kg/day. In a separate experiment, transplanted hearts and recipient spleens were collected from treatment groups for analysis of infiltrate and cytokine mRNA expression., Results: Delayed treatment with CsA or early treatment with MTX but not CAST combined with DL to result in prolonged graft survival. Recipients treated with DL and delayed CsA had a reduced level of intra-graft interleukin (IL)-2, interferon (IFN)-gamma, IL-4, and IL-4R mRNA expression and reduced infiltrate compared to DL alone. Early MTX plus DL led to almost complete inhibition of all markers of inflammation during treatment followed by a rapid increase after cessation. In combination with DL, CsA was more effective than MTX for induction of donor-specific tolerance at the dose and administration regimens tested., Conclusions: Delayed CsA or early MTX combine with DL to prolong heart allograft survival. Early and extensive inhibition of rejection by MTX was less effective than delayed and partial inhibition of the response by CsA for induction of transplant tolerance.

Background: Some immunosuppressive drug therapies inhibit transplant tolerance in animal models, and we have shown that treatment of recipients with methylprednisolone, but not cyclosporine, inhibits spontaneous acceptance of liver transplants. This study investigates the effects of mycophenolate mofetil (MMF) on liver acceptance and rejection., Methods: Piebald Virol Glaxo rat livers were transplanted into Dark Agouti recipients, which spontaneously tolerate (TOL) the liver, or into Lewis recipients, which reject (REJ) the liver. MMF (40 mg/kg/day subcutaneously) was given for 5 days from days 0 to 4 (early) or from days 3 to 7 (late). In separate experiments, liver grafts were collected for assessment of infiltrate and of interleukin (IL)-2, IL-4, IL-10, and interferon-gamma mRNA expression., Results: TOL liver transplants had a median survival time (MST) of more than 100 days (n=6), and neither early nor late MMF treatment of TOL transplants reduced survival (MST 85 days, P=0.19 and 78 days, P=0.08, respectively). Liver failure in most of these animals was the result of biliary problems, not rejection. There were few consistent differences between treated and untreated TOL animals in infiltrate or liver cytokine expression, although there was a moderate reduction in T-cell infiltrate in MMF-treated TOL animals (P=0.003 on day 5 TOL). In contrast, REJ transplants had an MST of 13 days (n=10), and early MMF treatment led to five of six animals surviving more than 100 days (P=0.0002), whereas late treatment was much less effective, with one of six animals surviving more than 100 days. REJ livers had significantly more IL-4 mRNA expression and immunoglobulin G1 deposition in the graft than TOL livers, and this was inhibited by early, but not late, MMF treatment., Conclusions: MMF treatment inhibited rejection but not acceptance of liver allografts. Early administration was more effective in preventing rejection and demonstrated a more marked effect on IL-4 expression and alloantibody deposition than on graft T-cell infiltrate and expression of other cytokines.

Background: Orthotopic liver transplants in many animal models are spontaneously accepted without requiring immunosuppression. Liver transplant acceptance is associated with early immune activation, and immunosuppressive drugs such as methylprednisolone inhibit acceptance. We investigated whether cyclosporine (CsA) inhibits rat liver transplant acceptance. We also examined the effects of CsA on infiltration and cytokine gene expression., Methods: Orthotopic liver transplantation was performed in the PVG donor to Dark Agouti recipient rat strain combination, which accepts the graft (tolerance; TOL), and in the PVG-to-Lewis combination, which rejects the graft in 9 to 16 days (rejection; REJ). CsA (1.5 mg/kg per day subcutaneously) was given to recipients for 5 days, starting from the day of transplantation to day 4 or from day 3 to day 7. In a separate experiment, transplanted livers were collected at days 1, 3, 5, and 7 after transplantation and examined for infiltration by immunohistochemistry and for expression of interleukin (IL)-2, IL-4, IL-10, and interferon-gamma mRNA by quantitative reverse transcriptase-polymerase chain reaction., Results: Both early and delayed treatment with CsA significantly increased survival in the REJ strain combination, with a median survival time of 81 days and more than 100 days, respectively, compared with 13 days in the untreated group. Neither treatment affected survival of TOL animals, and all TOL groups had a median survival time of more than 100 days. Delayed treatment did not reduce survival; more animals survived for greater than 100 days after delayed treatment, although this did not reach significance ( P=0.08). T-cell infiltrate was inhibited in CsA-treated TOL animals compared with untreated animals at all times after treatment, whereas CD25 cells were only inhibited on day 3. CsA treatment of TOL grafts markedly reduced expression of IL-2, IL-4, and interferon-gamma compared with untreated recipients., Conclusions: CsA did not significantly inhibit liver transplant acceptance and allowed some activation of T cells and CD25 expression but almost completely inhibited IL-2 and IL-4, which are required for survival of activated T cells.

Summary In many animal models transplanted livers are not rejected, even when there is a complete MHC mismatch between the donor and recipient and the recipient is not immunosuppressed. This distinguishes liver transplants from other organs, such as kidneys and hearts, which are rapidly rejected in mismatched individuals. Acceptance of transplanted livers in a rat model is not due to the absence of an immune response to the liver and there is a rapid, abortive response that is ultimately exhausted. Donor leucocytes transferred with the liver appear to be responsible for both liver acceptance and the abortive activation of the recipient’s T cells. The immune mechanism of liver transplant acceptance appears to be due to ‘death by neglect’ in which T cells are activated to express IL-2 and IFN-γ mRNA in the recipient lymphoid tissues, but not at adequate levels within the graft. Subsequently the activated T cells die leading to specific clonal deletion of liver donor-reactive T cells. These findings have important implications for liver transplant patients as immunosuppressive drugs that are given to prevent rejection can also interfere with this form of tolerance. In addition, it might be possible to modify the immunosuppressive drug treatment of transplant patients to promote the process of death by neglect of recipient alloreactive T cells. [ABSTRACT FROM AUTHOR]

Most approaches to transplant tolerance involve treatment of the recipient to prevent rejection. This study investigates donor treatment with IL-4 for its effect on subsequent rat liver allograft survival. Rat orthotopic liver transplants were performed in rejecting (PVC donor to Lewis recipient) or spontaneously tolerant (PVG to DA) strain combinations. Donors were untreated or injected intraperitoneally with IL-4 (30,000 U/day) for 5 days. Tissue infiltrates and gene expression were examined by immunohistochemistry and real-time quantitative PCR. IL-4 induced a marked leukocyte infiltrate in donor livers prior to transplant. Macrophages comprised the major population, although 13 cells, T cells and natural killer (NK) cells also increased. lL-4-induced liver macrophages had an alternatively activated phenotype with increased expression of mannose receptor but not inducible nitric oxide synthase (NOS2). lL-4 also induced lDO and IFN-gamma expression by NK cells. Donor IL-4-treatment converted rejection to acceptance in the majority of Lewis recipients (median survival time >96 days) and did not prevent acceptance in DA recipients. Acceptance in Lewis recipients was associated with increased donor cell migration to recipient spleens and increased splenic lL-2. IFN-gamma and IDO expression 24 h after transplantation. Donor IL-4-treatment increased leukocytes in the donor liver including potentially immuno-suppressive populations of alternatively activated macrophages and IDO-expressing NK cells. Donor treatment led to long-term acceptance of most livers in association with early immune activation in recipient lymphoid tissues. [ABSTRACT FROM AUTHOR]