Detection of membrane-bound and soluble MHC class I antigen from donor migrating cells following rat liver transplantation

Assessment of the immune response to dose of nerve allografts

Nerve allotransplantation provides a limitless source of nerve graft material for the reconstruction of large neural defects. It does require systemic immunosuppression or induction of immune unresponsiveness to prevent allograft rejection. It is unknown whether a greater volume of nerve graft material will increase the risk of rejection or the need for more intensive immunosuppression. This study assessed the relationship between the quantity of nerve tissue transplanted and the magnitude of the resulting immune response. Forty female (BALB/c) mice were randomly assigned to two groups that received either nerve isografts (BALB/c) or nerve allografts (C57BL/6). Each group was then subdivided into two groups that received either one or 10 sciatic nerve graft inlays. Histological and immunological assessments were performed at 10 days after engraftment. Histologic analysis demonstrated greater cellular infiltration in the allograft than the isograft groups but no appreciable difference in infiltration related to quantity of transplanted nerve tissue. In vitro assessments of the immune response using mixed lymphocyte assays and limiting dilution analysis similarly demonstrated a robust immune response to allografts but no effect on quantity of transplanted nerve tissue. These data suggest that larger peripheral nerve allografts may not be subject to increased risk for rejection.

Peak protein expression of IL-2 and IFN-gamma correlate with the peak rejection episode in a spontaneously tolerant model of rat liver transplantation

Spontaneous orthotopic liver transplant (OLT) tolerance occurs uniformly between the inbred rat strains of DA (MHC haplotype RT1(a)) into PVG (RT1(c)) despite a fully allogeneic barrier. Animals transplanted in this combination do, however, undergo a rejection episode which appears to be self-limiting. In order to clarify this further we under took in situ measurements of the cytokines IL-2, IFN-gamma and TNF-alpha prior to, during and post rejection episode. The cytokine protein product was examined via immunoblotting assays and mRNA levels by RT-PCR. Comparisons were also made for syngeneic transplant combinations over the same time period. Peak protein expression of IL-2 and, to a lesser extent, IFN-gamma, occurred during the rejection episode between days 10 and 14. IFN-gamma was still present in syngeneic OLT on day 10 but was only present in allogeneic OLT on day 14. IL-2 was only detectable in allogeneic OLT on days 10 and 14. Transient increases in TNF-alpha occurred in allogeneic and syngeneic OLT with TNF-alpha levels falling by the peak rejection episode. Immunoblotting also confirmed the ability of hepatocytes to produce each of the cytokines studied. mRNA levels, by contrast, were maximal at days 1 and 10 for IL-2 and day 3 for IFN-gamma in allogeneic OLT when compared with syngeneic and non-transplanted controls. Earlier increases in IL-2 and IFN-gamma mRNA and time of peak protein expression do not correlate in this model. We therefore conclude that the measurement of peak mRNA levels alone are not enough to evaluate the rejection process especially since it is the cytokine protein products which have potential biological activity.

Paradoxical early immune activation during acceptance of liver allografts compared with rejection of skin grafts in a rat model of transplantation

Liver allografts in many animal models are often spontaneously accepted across a complete histocompatibility barrier without requirement for immunosuppression. In contrast, skin allografts are usually rejected, even across minor histocompatibility barriers. To identify the mechanism of liver allograft acceptance we have compared skin rejection with liver acceptance in DA rat strain recipients of PVG donors, a major histocompatibility complex (MHC) class I plus II mismatch. In spite of the established role of draining lymph nodes (LN) in induction of rejection of skin allografts, there was much greater involvement of LN after liver than after skin transplantation. Few donor cells migrated to these organs from transplanted skin but many cells migrated from transplanted liver. There was also a paradoxical increase in interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) mRNA in LN and spleen of liver allograft recipients that greatly exceeded their expression in skin allograft recipients. For example, there were 2. 7+/-1.6x104 molecules of IFN-gamma per 106 molecules of beta-actin mRNA in the LN draining liver allografts 1 day after transplantation compared with 2.0+/-0.3x103 molecules/106 beta-actin in LN draining skin allografts and 8.1+/-1.8x102 molecules/106 beta-actin in LN draining skin isografts. Examination of the graft showed that infiltration and cytokine mRNA up-regulation occurred more slowly in the transplanted skin than in liver but progressed inexorably in skin grafts until rejection. These results show that liver acceptance is associated with a paradoxical marked early activation then subsequent decline of the immune response.

Kinetics of intragraft cytokine expression, cellular infiltration, and cell death in rejection of renal allografts compared with acceptance of liver allografts in a rat model: early activation and apoptosis is associated with liver graft acceptance

BACKGROUND

Liver transplants in the rat strain combination PVG-to-Dark Agouti are spontaneously tolerated, whereas kidney transplants in the same strain combination are rejected in 7-9 days.

METHODS

To identify organ-specific differences that might yield further information about the mechanism of tolerance induction in this strain combination, liver or kidney grafts, spleen, and draining lymph nodes were harvested at days 1, 3, 5, and 7, and examined by immunohistochemistry, terminal deoxynucleotide transferase-mediated dUTP nick end labeling assay, and reverse transcriptase-polymerase chain reaction for interferon-gamma, interleukin (IL)-2, IL-4, and IL-10.

RESULTS

Renal allograft rejection was associated with the progressive development of an intense mononuclear cell infiltrate. Markers of lymphocyte activation and cytokine up-regulation appeared from day 3, and many apoptotic parenchymal cells were noted on days 5-7, at the peak of rejection. Conversely, liver allograft tolerance was associated with more rapid infiltration by activated T cells and earlier increases in cytokine expression, but with a more limited degree of cellular infiltration. Concurrent with the early activation, high levels of apoptosis were found in areas of leukocyte infiltrate, paralleling the disappearance of activated T cells from the graft between days 3 and 5.

CONCLUSIONS

Apoptosis of infiltrating leukocytes in liver allografts may represent an important process in the induction of spontaneous liver transplant tolerance and may underlie the abortive nature of the effector response observed within tolerated livers. In contrast, activated cells in renal allografts in the same strain combination survive and proliferate, express high levels of cytokines, and are efficient in bringing about graft destruction.

Tolerance to rat liver allografts: IV. Acceptance depends on the quantity of donor tissue and on donor leukocytes

Liver allografts in some rat strains are often spontaneously accepted across a complete major histocompatibility barrier without the requirement for immunosuppression while other nonliver allografts are rejected. In previous studies, we have shown that spontaneous acceptance is dependent on liver passenger leukocytes. Depletion of passenger leukocytes by donor irradiation allows rejection, with DA recipients of irradiated PVG livers having a median survival time (MST) of 16 days. Here we show that, in this model, spontaneous acceptance is reconstituted by intravenous injection of donor leukocytes. Intravenous injection of 3-5x10(7) PVG liver leukocytes significantly prolonged DA survival time (MST=96 days, P=0.026), as did 5x10(7) spleen leukocytes (MST>100 days, P=0.002). Deletion of T cells from the reconstituting inoculum reduced survival time (MST=78 days, P=0.039), whereas deletion of B cells or monocytes/macrophages had no effect on survival time. In contrast, PVG hearts are regularly rejected by DA recipients, and PVG liver or spleen leukocytes, even at doses of greater than 3x10(8) cells/recipient, were unable to induce heart acceptance. To investigate the possibility that acceptance of the irradiated liver but not the heart might be due to the large mass of the liver, two kidneys and two hearts of PVG origin were transplanted to each DA recipient together with 1.5x10(8) PVG leukocytes. These organs survived for greater than 200 days, thereby showing that a large mass of donor tissue, in association with donor leukocytes, leads to acceptance of organs that are rejected if transplanted singly. It appears likely that spontaneous liver transplant tolerance is a high-dose or activation-associated immune phenomenon.

Novel immunosuppressive proteins purified from the serum of liver-retransplanted rats

Liver grafts between certain rat strain combinations, such as DA (RT1a)-into-PVG (RT1c), are accepted without the use of immunosuppressive agents. To explore the nature and role of serum proteins in liver-induced immunosuppression, we have developed a retransplantation model of rat liver grafting. In this procedure, orthotopic liver transplantation (OLT) is carried out in the DA-into-PVG combination; two days later the DA liver is removed and a new PVG liver implanted into the same recipient (re-OLT). Serum from re-OLT rats was immunosuppressive when tested in mixed lymphocyte reactions (MLR). Three novel proteins were detected in re-OLT serum by SDS-PAGE, with sizes of 180 kD, 87 kD, and 10 kD. The N-terminal sequences of these were distinct and did not match protein sequences in the computer databases, although there was some homology between the 10 kD sequence and the beta-chain of rat hemoglobin. Purified 87 kD and 10 kD proteins were immunosuppressive in MLR; in both cases suppression was dose-dependent and nonstimulator-specific. Production of the 180 kD and 87 kD molecules required the presence of the recipient spleen. We conclude that re-OLT serum contains novel immunosuppressive proteins, which may be products of immune recognition and associated with the immediate termination of graft rejection.

Isolation of a 40 kDa immunoinhibitory protein induced by rat liver transplantation

In certain combinations of donor and recipient rat strains, such as DA (RT1a) donors into PVG (RT1c) recipients, rejection after orthotopic liver transplantation (OLT) is overcome without immunosuppressive drugs, although other organs transplanted between these combinations are promptly rejected. The mechanisms involved in achieving drug-free liver allograft tolerance still remain poorly understood. In the present study, OLT (DA into PVG) serum from various postoperative times was analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis and two unique proteins of 40 kDa and 37 kDa were found to be in large concentrations in 60 day post-OLT serum. These proteins could only be detected at specific times after OLT in the DA into PVG combination and could not be detected in the serum of syngenically transplanted animals (DA into DA) and (PVG into PVG), rejector combinations (DA into LEW) requiring immunosuppressive treatment or induced by other organ transplants. When these proteins were purified and sequenced they were found to have an identical N-terminal sequence which is not listed in sequence databases. Mixed lymphocyte assays revealed that only the 40 kDa protein has a immunosuppressive capability which additionally appears to be donor specific. The 40 kDa protein will aid further in the understanding of how drug-free tolerance is attained in certain liver allografts and may also act as a marker of when treatment with conventional immunosuppressive drugs can be stopped in clinical OLT providing a homologue of the molecule can be found. This possibility appears likely as case reports already exist of patients who have successfully been able to cease treatment with such drugs.