Lack of correlation between the induction of donor class I and class II major histocompatibility complex antigens and graft rejection

The induction of donor major histocompatibility complex (MHC) antigens on nonrejected and rejected rat renal allografts was compared at various times after transplantation in two strain combinations, DA-to-PVG and LEW-to-DA. Graft rejection was prevented by preoperative donor-specific blood transfusion (DST). Quantitative absorption analysis and immunohistology were performed using monoclonal antibodies specific for donor class I and class II MHC antigens. A significant increase in the expression of donor MHC antigens, both class I and class II, was demonstrated on nonrejected as well as rejected kidneys after transplantation. A kinetic analysis showed that induction of donor class I antigens was accelerated on the nonrejected grafts, and by day 5 the nonrejected kidneys showed increased expression of class I antigen when compared with the rejected grafts (a 37- vs. a 25-fold increase in expression). Increased expression of donor class I antigens persisted on the nonrejected grafts and was still detectable on long-term-surviving kidneys, 50 days after transplantation. The magnitude of class II antigen induction was similar on both rejected and nonrejected grafts (8-fold by 5 days after transplantation). Immunohistology demonstrated that class I and class II antigens were induced on identical structures in the kidney in both situations. In particular the vessel endothelia, which do not express class II antigens in normal kidney, become strongly positive in both rejected and nonrejected grafts 5 days after transplantation. Although renal allograft rejection is completely suppressed in rats given a single donor-specific blood transfusion before transplantation, graft survival cannot be explained by the lack of induction of donor MHC antigens. Donor MHC antigens are induced on these nonrejected kidney grafts, and therefore they could act as target molecules for the effector cells that mediate graft destruction. Thus the induction of donor MHC antigens on tissue allografts should not be considered as indicative of a rejection response resulting in graft destruction.     

The effects of cyclosporine on the induction of donor class I and class II MHC antigens in heart and kidney allografts in the rat

We have previously reported 5-30-fold increases in the expression of class I and class II major histocompatibility complex (MHC) antigens in rejecting heart and kidney allografts in the DA-to-PVG rat strain combination. We examine here the effects of immunosuppression with cyclosporine on the induction of donor class I and class II MHC antigens in heart and kidney allografts in this strain combination. Immunohistological studies and quantitative absorption analyses using monoclonal antibodies and assay systems specific for donor class I and class II MHC antigens were used throughout. Heart allografts in cyclosporine-treated rats were examined on day 3,5,7,9,11, and 14 after transplantation, and kidney allografts in cyclosporine-treated rats were examined at day 7. In addition, untreated heart and kidney isografts were studied at days 1,3,5, and 7 after grafting. Immunohistological studies on frozen sections showed that cyclosporine-treated heart and kidney allografts showed no induction of class II MHC antigens, in contrast to untreated heart and kidney allografts. Class I MHC antigen induction did occur in spite of cyclosporine-therapy, but at levels lower than those seen in untreated allografts. Moreover, the pattern and degree of class I induction in the cyclosporine-treated allografts resembled very closely those seen in isografts, and so this induction was, in all probability, a consequence of the transplantation procedure rather than of specific immune responses. We also noted, in the cyclosporine-treated heart allografts, that all donor interstitial dendritic cells had disappeared and been replaced by recipient interstitial dendritic cells by the end of the second week after grafting. In addition, there was no reduction in the class II antigen content of kidney allografts treated for 7 days with cyclosporine. The absence of class II antigen induction in allografts where rejection is effectively suppressed with cyclosporine might be of clinical value in the differential diagnosis between rejection and cyclosporine toxicity in renal transplantation, and between active and inactive cellular infiltrates in heart transplantation.     

Donor class I and class II major histocompatibility complex antigen expression following liver allografting in rejecting and nonrejecting rat strain combinations

Orthotopic liver allografts in the nonrejecting DA-to-PVG strain combination and in the DA-to-LEW strain combination were studied at various times after transplantation for donor class I and class II MHC expression using immunohistological techniques and quantitative analyses. DA-to-DA isografts were also studied. In the isografts, weak class I induction on hepatocytes and biliary epithelium was noted from day 5, and this persisted to day 15, the last time point examined. In DA-to-PVG allografts, class I induction also appeared on hepatocytes and biliary epithelium from day 5, but was more intense than in the isografts. Nevertheless, the induction was patchy within most grafts, and in some grafts was not prominent. Quantitative absorption analyses demonstrated that the maximum increase in donor class I expression was only 3-fold over the normal liver. In the strong DA-to-LEW combination, class I induction on hepatocytes seemed to appear earlier, beginning at day 3, and was more uniform and intense than in the DA-to-PVG model from day 5. In the isografts, there was no induction of class II antigens on hepatocytes or biliary epithelium at any stage, but from days 5 to 15 there was a marked increase in the number of isolated, class II-positive cells in the hepatic lobule, probably representing class II induction in the Kupffer cells of the isografts. In DA-to-PVG allografts, biliary epithelium became class II-positive from day 5, and this persisted to day 30, the last time point examined. Weak but definite class II induction was seen on some hepatocytes from day 5 through day 30. However, the majority of hepatocytes remained class II-negative. By day 30, there was virtually no donor class II staining the sinusoids, but isolated class II-positive cells of recipient type were seen, the pattern suggesting a replacement of the graft Kupffer cells by recipient Kupffer cells at this stage. By quantitative absorption analysis, donor class II expression in the grafts increased approximately 5-fold. In DA-to-LEW allografts, class II induction was not noticeably different from that seen in the DA-to-PVG model, except that induction of class II antigens on the Kupffer cells possibly appeared earlier in this strain combination.     

The effect of thymectomy on tolerance induction and cardiac allograft vasculopathy in a miniature swine heart/kidney transplantation model.

BACKGROUND: We have previously demonstrated that MHC class I disparate hearts transplanted into miniature swine treated with a short course of cyclosporine developed florid cardiac allograft vasculopathy (CAV) and were rejected within 55 days. However, when a donor-specific kidney is cotransplanted with the heart allograft, recipients become tolerant to donor antigen and accept both allografts long-term without the development of CAV. In the present study, we have investigated the role of the host thymus in the induction of tolerance and prevention of CAV in heart/kidney recipients. METHODS: Total thymectomies were performed in six animals (postoperative day [POD]-21), which on day 0 received either an isolated MHC class I disparate heart allograft (n=3) or combined class I disparate heart and kidney allografts (n=3), followed in both cases by a 12-day course of cyclosporine (POD 0-11). Graft survival and the development of CAV in these thymectomized recipients were compared to the same parameters in non-thymectomized, cyclosporine-treated recipients bearing either class I disparate heart allografts (n=5) or heart and kidney allografts (n=4). RESULTS: In the group of animals bearing isolated class I disparate heart allografts, the thymectomized recipients rejected their allografts earlier (POD 8, 22, 27) than the non-thymectomized recipients (POD 33,35,45,47,55). The donor hearts in both the thymectomized and non-thymectomized animals developed florid CAV. In the group of animals bearing combined class I disparate heart and kidney allografts, the nonthymectomized recipients accepted both donor organs long term with no evidence of CAV. In contrast, none of the thymectomized heart/kidney recipients survived >100 days, and they all developed the intimal proliferation of CAV. CONCLUSION: Thymic-dependent mechanisms are necessary for the induction of acquired tolerance and prevention of CAV in porcine heart/kidney recipients.     

Increased expression of MHC class II antigens in rejecting canine lung allografts

Expression of major histocompatibility complex class II antigens was investigated in the normal lungs and in lung allografts of mongrel dogs after single-lung transplantation. Cryostat sections were stained with an indirect immunoperoxidase technique that used B1F6 and 7.5.10.1 as anti-MHC class II monoclonal antibodies. In the normal lungs and native lungs of the recipient dogs after single-lung transplantation, only some cells of lymphoid tissue and macrophages/dendritic cells were MHC class II-positive. During acute rejection, increased infiltration with MHC class II-positive cells in perivascular, peribronchial, and interstitial areas and intraalveolar spaces was found in lung allografts. In addition, expression of MHC class II antigens was induced on the bronchial epithelium and vascular endothelium. Induced expression of MHC class II antigens on the bronchial epithelium and vascular endothelium in rejecting lung allografts was found as early as two days after single-lung transplantation. The intensity of MHC class II antigen expression on bronchial epithelium and vascular endothelium in graft lungs increased with the progression of rejection response and directly correlated with the bronchoalveolar lavage fluid (BALF) levels of biochemical markers, as tumor necrosis factor alpha, gamma-interferon (IFN-gamma), interleukin 2 (IL-2) and soluble interleukin 2 receptor (SIL-2R). Abnormal expression of MHC class II antigens on bronchial epithelium and vascular endothelium and abnormal elevation of BALF levels of the cytokines in lung allografts could be prevented by cyclosporine (CsA) treatment. Our results suggested that MHC class II antigen expression could be induced on the bronchial epithelium and vascular endothelium of canine lung allografts during acute rejection. This abnormal expression of MHC class II antigens on bronchial epithelium and vascular endothelium of graft lungs may serve as a specific index for diagnosis of lung allograft rejection when infection as an inducing factor can be excluded. Furthermore, bronchial epithelium and vascular endothelium of lung allografts have become MHC class II-positive, and are likely to be the targets for low-grade rejection, resulting in the development of bronchiolitis obliterans and occlusive vascular disease in lung allografts.     

IgM and IgG alloantibody responses to MHC class I and II following rat renal allograft rejection. Effects of transplantectomy and posttransplantation blood transfusion.

Renal allograft rejection in rats and humans is a potent inducer of alloantibody to donor major histocompatibility complex antigens. Alloantibody in such presensitized recipients can cause hyperacute rejection of subsequent renal allografts. In order to characterize alloantibody production in rats presensitized by renal graft rejection, ACI (RT1a) kidneys were transplanted into untreated fully allogeneic PVG (RT1c) recipients and allowed to reject while one native kidney remained in situ for host survival. Serum samples collected at weekly intervals were analyzed by flow cytometry for IgM and IgG antibody binding to ACI lymphoid target cells. The specificity of alloantibody responses was assessed by (1) differential binding to congenic rat strain target cells expressing only donor class I (PVG.R1) versus both donor class I and II (PVG.1A) antigens, (2) differential binding to unseparated donor lymphoid target cells versus lymphoid target cells depleted of class II MHC antigen-expressing cells, and (3) specific blocking of monoclonal antibodies to donor class I (R2/10P, R2/15S) or class II (F17.23.2) epitopes. Alloantibody responses to both donor class I and II MHC antigens were detected. The initial IgM response to donor class I MHC antigens peaked at the time of rejection, followed by a steady decline to relatively low levels by 4 weeks posttransplantation. The IgM response to donor class II MHC antigens was found to be cyclical with apparent peaks at day 7 and 5-6 weeks. The IgG response to donor class I and class II MHC antigens reached maximum by 5-6 weeks before slowly decreasing. IgM and IgG alloantibody specific for class I and class II MHC antigens could be detected through 19 weeks posttransplantation. The effects on circulating alloantibody of two manipulations, posttransplantation donor specific blood transfusion and allograft removal, were examined in this model. The alloantibody responses to class I MHC antigens were not affected by giving DSBT weekly beginning at day 14 after transplantation. However, posttransplantation DSBT eliminated the second peak of IgM alloantibody to class II MHC antigens seen approximately 5-6 weeks posttransplantation and also decreased circulating IgG specific for class II antigens. Transplantectomy at day 5-7 days after transplantation had no apparent effect on circulating IgM or IgG alloantibody through 7 weeks posttransplantation. These data indicate that in a fully allogeneic rat renal allograft model alloantibody responses are elicited to both class I and II MHC donor antigens, but that the kinetics and regulation of the responses to class I differ from those to class II alloantigens.(ABSTRACT TRUNCATED AT 400 WORDS)     

Successful induction of long-term specific tolerance to fully allogeneic renal allografts in miniature swine.

Major histocompatibility complex class II matching is of overwhelming importance for achieving tolerance to kidney transplants (KTX) in miniature swine. When class II antigens are matched, long-term specific tolerance across complete MHC class I antigen barriers can uniformly be induced by a 12-day perioperative course of cyclosporine. This same regimen is ineffective in fully MHC-mismatched combinations. We hypothesized that initial induction of tolerance to kidney donor class II antigens by bone marrow transplantation might allow tolerance to be induced to a subsequent fully allogeneic KTX in combination with CsA therapy. We report here the results of such fully allogeneic KTX performed in 4 recipients of prior single-haplotype class II-mismatched BMT. All animals received KTX from donors class II matched to the BMT donor and received a 12-day course of intravenous CsA (10 mg/kg/day). All four animals have maintained normal serum creatinine values (less than 2.0 mg/dl) for greater than 200 days posttransplant. Specific hyporesponsiveness to both BMT and KTX donor-type MHC antigens was found in mixed lymphocyte culture and cell-mediated lympholysis assays. Compared with third-party grafts, significantly prolonged survival of BMT donor-specific (P = 0.031) and KTX donor-specific (P = 0.031) skin grafts was observed. These results demonstrate that induction of tolerance to class II antigens by BMT allows a short course of CsA to induce specific tolerance to fully allogeneic renal allografts.     

Induction of tolerance to heart transplants by simultaneous cotransplantation of donor kidneys may depend on a radiation-sensitive renal-cell population

BACKGROUND: To determine the mechanism by which cotransplantation of a donor kidney and heart allograft induces tolerance to both organs in miniature swine, we examined the renal elements responsible for tolerance induction. METHODS: Recipients received 12 days of cyclosporine, and transplants were performed across a major histocompatibility complex (MHC) class I mismatch. Group 1 animals received heart transplants (n=5); group 2 animals received heart and kidney allografts with no other manipulation (n=4); group 3 animals received heart transplants and donor-specific renal parenchymal cells (n=4); group 4 animals received heart and kidney allografts from lethally irradiated donors (n=7); group 5 animals received irradiated hearts and nonirradiated kidneys (n=2); group 6 animals received nonirradiated hearts and peripheral blood leukocytes from swine MHC matched to recipients and becoming tolerant to donor antigen (n=2); group 7 animals received nonirradiated hearts and donor-specific peripheral blood monocyte cells (PBMC) (n=2). RESULTS: Animals in group 1 developed vasculopathy and fulminant rejection by day 55. Animals in group 2 never developed vascular lesions. Parenchymal kidney cell infusion (group 3) did not prolong cardiac survival. Animals in group 4 developed arteriopathy by postoperative day (POD) 28. Group 5 recipients accepted allografts without vascular lesions. Adoptive transfer of leukocytes from tolerant swine (group 6) prolonged cardiac graft survival as much as 123 days, whereas donor PBMC infusion (group 7) did not affect cardiac survival or development of arteriopathy. CONCLUSIONS: Radiosensitive elements in kidney allograft may be responsible for tolerance induction and prevention of chronic vascular lesions in recipients of simultaneous heart and kidney allografts.     

Altered distribution of class I and class II MHC antigens during acute pancreas allograft rejection in the rat

The expression of MHC class I and class II antigens was investigated in a model of acute pancreas allograft rejection in the rat. Pancreaticoduodenal and duct-ligated DA(RT1a)-to-LEW(RT1(1] and LEW(RT1(1]-to-LEW.1U(RT1u) pancreas grafts were compared with normal organs and with LEW(RT1(1] isografts at daily intervals from day 1 to day 10 after transplantation. The results show profound changes of MHC antigen distribution in allografts during the process of rejection. Exocrine acinar cells, being class-I-antigen-negative in the normal pancreas, strongly express these antigens during rejection. Class II antigens, normally not found in pancreatic endothelia or parenchymal cells, appear in duct epithelia, acinar cells, and endothelia of big vessels. Endocrine islet cells and smooth muscle cells stay Ia-negative throughout the rejection process. Focal class I reactivity is also observed in acinar cells of pancreaticoduodenal isografts; but class II antigens are neither seen in parenchymal cells nor in endothelia of any isograft. Thus, in the rat pancreas allograft model, the induction of class II antigens is an early phenomenon characteristic of an ongoing immune response, and it provides a valuable new diagnostic criterion. Antibodies reactive exclusively with donor-haplotype antigens demonstrate an increase in donor-derived class I and class II antigen-positive interstitial cells in addition to parenchymal antigenic changes. A possible effect of the antigenic alteration described on the course of the rejection process is discussed.     

Different patterns of donor MHC antigen induction in rat kidney allografts following active and passive enhancement

We compare the expression of donor class I and class II major histocompatibility complex antigens in DA kidney grafts transplanted to PVG recipients treated by different protocols of donor-specific immunosuppression. MHC expression was evaluated using donor-specific antibodies and assays by immunohistology and quantitative absorption analysis. PVG recipients were either untreated or treated by (A) twice-weekly intravenous injections of 0.5 ml DA blood for 12 weeks; (B) 0.5 ml DA blood intravenously at 7 days pregraft; (C) as for (B), but with the addition or oral cyclosporine at 10 mg/kg/day from the day of grafting; and (D) passive enhancement with DA anti-PVG serum. Grafts were assessed at 3, 5, and 7 days after transplantation. In untreated controls at day 3, there is a periarteriolar leukocyte infiltrate, weak or absent class II induction, but strong class I induction. Class II induction in untreated controls is maximal at day 5. We confirm that active enhancement by blood transfusion, even using the intensive protocol of twice-weekly transfusions for 3 months, results in accelerated leukocyte infiltration and accelerated donor class I and class II MHC induction. At day 3, there is an intense, diffuse leukocyte infiltration and maximal class II induction. Cyclosporine treatment of blood-transfused recipients reduced the leukocyte infiltration and MHC induction to levels seen in untreated controls--i.e., the accelerated MHC induction caused by the transfusion was partially reversible by cyclosporine. In passively enhanced recipients, leukocyte infiltration and class I MHC induction were similar to untreated controls. However, class II induction was much delayed, not being evident until day 7.     

The Indirect Alloresponse Impairs the Induction but Not Maintenance of Tolerance to MHC Class I-Disparate Allografts

We studied the effects of indirect allorecognition on the induction and maintenance phases of tolerance in miniature swine cotransplanted with heart and kidney allografts. MHC class I-mismatched heart and kidney grafts were cotransplanted in recipients receiving CyA for 12 days. Recipients were unimmunized or immunized with a set of donor-derived or control third-party MHC class I peptides either 21 days prior to transplantation or over 100 days after transplantation. T-cell proliferation, delayed type hypersensitivity reaction (DTH) and antibody production were assessed. All animals injected with donor MHC class I peptides developed potent indirect alloresponses specific to the immunizing peptides. While untreated recipients developed stable tolerance, all animals preimmunized with donor allopeptides rejected kidney–heart transplants acutely. In contrast, when peptide immunization was delayed until over 100 days after kidney–heart transplantation, no effects were observed on graft function or in vitro measures of alloimmunity. Donor peptide immunization prevented tolerance when administered to recipients pre transplantation but did not abrogate tolerance when administered to long-term survivors post transplantation. This suggests that the presence of T cells activated via indirect allorecognition represent a barrier to the induction but not the maintenance of tolerance.     

Expression of MHC class I-related Chain B (MICB) molecules on renal transplant biopsies

BACKGROUND: MICA and MICB (MHC class I-related chain A and B) are polymorphic genes that encode molecules related to MHC class I and are expressed on epithelial cells in response to stress. Incompatible donor MIC antigens can stimulate antibody production in transplant recipients. This study was designed to determine MICB expression in kidney pretransplant and any subsequent changes in expression following transplantation and to correlate changes with inflammatory markers and clinical events. METHODS: Paired renal biopsies obtained from living donor (n=10) and cadaveric allografts (n=50) before and 7 days posttransplant were stained for MICB, leukocytic infiltration, and HLA class II antigens. RESULTS: Variable tubular MICB expression was evident in donor biopsies [high 6/60 (10%), low/negative 13/60 (22%), intermediate 41/60 (68%)]. Following transplantation, MICB was up-regulated on renal tubules of 17/60 (28%) biopsies and was associated with MHC class II antigen induction (P=0.02) and leukocyte infiltration (P=0.01). Acute tubular necrosis leading to delayed graft function (DGF) and acute rejection (AR) cause cellular stress within the transplanted kidney. We found a strong association between up-regulation of MICB and cellular stress, 15/17 biopsies with up-regulated MICB expression had AR and/or DGF (P=0.003). CONCLUSIONS: This is the first study demonstrating variable levels of MICB expression in kidneys before transplantation and induction of MICB expression following renal transplantation. MICB expression is associated with HLA class II antigen induction, leukocytic infiltration of the graft and cellular stress in the transplanted kidney. Expression of MICB could contribute significantly to the alloimmune response in mismatched donors and recipients.     

MHC class II presenting cells are necessary for the induction of intrathymic tolerance.

OBJECTIVE: This study determined the form of cellular donor MHC alloantigen necessary for the induction of intrathymic tolerance. BACKGROUND: The authors have achieved indefinite donor-specific tolerance, to a fully MHC-disparate rat heterotopic cardiac allograft, after the pretransplant intrathymic injection of unfractionated donor splenocytes and a single injection of rabbit anti-rat lymphocyte serum (ALS), without subsequent immunosuppression. METHODS: Male 4-12-week-old Buffalo (RT1b) rats underwent an intrathymic injection of either fractionated Lewis (RT1(1)) red blood cells (purified by Ficoll gradient) or T lymphocytes (purified by nylon wool column and plastic adherence), both of which express only MHC class I alloantigens, or B lymphocytes, macrophages, and dendritic cells (purified by plastic adherence) which express both MHC class I and class II alloantigens. At the completion of alloantigen injection the Buffalo recipient rats were given 1 ml of ALS intraperitoneally. Twenty-one days later a heterotopic Lewis heart was transplanted. RESULTS: The intrathymic injection of the fractions of Lewis MHC class I and class II expressing B lymphocytes, macrophages, and dendritic cells induced a donor-specific tolerance that resulted in indefinite Lewis cardiac allograft survival (MST > 125 days) in all recipients without further immunosuppression, whereas groups receiving MHC class I expressing red blood cell or T lymphocyte injections plus ALS rejected Lewis cardiac allografts with a MST of 7.3 and 16.5 days, respectively, thus indicating that the MHC class II expressing cell is necessary for the induction of intrathymic tolerance. Buffalo recipients with a long-term surviving Lewis cardiac allograft, after Lewis MHC class II expressing cells were still able to reject a third-party heterotopic ACI (RT1a) cardiac allograft in normal time (MST = 7.0 days), but did not reject a second Lewis cardiac allograft (MST > 100 days). Additionally, the intrathymic injection of MHC class II expressing cells resulted in decreased interleukin-2 (IL-2) production and an 80% decrease in in vitro donor-specific cell mediated cytotoxicity, whereas the cytolytic response to a third party was unaltered. CONCLUSION: Donor MHC class II, and not class I, expressing cells are the cells in donor splenocytes, injected intrathymically, responsible for the development of donor-specific allograft tolerance.     

Induction of Cardiac Allograft Tolerance Across a Full MHC Barrier in Miniature Swine by Donor Kidney Cotransplantation

We have previously shown that tolerance of kidney allografts across a full major histocompatibility complex (MHC) barrier can be induced in miniature swine by a 12‐day course of high‐dose tacrolimus. However, that treatment did not prolong survival of heart allografts across the same barrier. We have now tested the effect of cotransplanting an allogeneic heart and kidney from the same MHC‐mismatched donor using the same treatment regimen. Heart allografts (n = 3) or heart plus kidney allografts (n = 5) were transplanted into MHC‐mismatched recipients treated with high‐dose tacrolimus for 12 days. As expected, all isolated heart allografts rejected by postoperative day 40. In contrast, heart and kidney allografts survived for >200 days with no evidence of rejection on serial cardiac biopsies. Heart/kidney recipients lost donor‐specific responsiveness in cell‐mediated lympholysis and mixed‐lymphocyte reaction assays, were free of alloantibody and exhibited prolonged survival of donor, but not third‐party skin grafts. Late (>100 days) removal of the kidney allografts did not cause acute rejection of the heart allografts (n = 2) and did not abrogate donor‐specific unresponsiveness in vitro. While kidney‐induced cardiac allograft tolerance (KICAT) has previously been demonstrated across a Class I disparity, these data demonstrate that this phenomenon can also be observed across the more clinically relevant full MHC mismatch. Elucidating the renal element(s) responsible for KICAT could provide mechanistic information relevant to the induction of tolerance in recipients of isolated heart allografts as well as other tolerance‐resistant organs.     

Immunohistological observations of rat fetal pancreas allografts transplanted into unmodified and cyclosporine-treated recipients

Administration of CsA (15 mg/kg/day) prolonged the survival of DA (RT1a) rat fetal pancreas transplanted to the renal subcapular site of both PVG (RT1c) and Lewis (RT1(1] recipients. Sections of fetal pancreas examined 40 days after transplantation into allogeneic CsA-treated recipients showed growth and development of the fetal pancreas tissue, and the presence of numerous insulin-containing islets. CsA treatment prevented the induction of MHC antigen within allografts. Whereas at day 4, both rejecting and CsA treated grafts showed donor class I MHC expression on duct epithelium and islet cells, only rejecting grafts displayed class I MHC induction on acinar cells. Rejecting grafts showed strong induction of class II MHC antigen expression on duct epithelium from day 4 onward but this was completely prevented by CsA treatment. Islet cells in both rejecting and CsA treated allografts remained class II-negative throughout. CsA also resulted in a reduction in the day 6 cellular infiltrate of allografts (median area leukocyte infiltrate reduced from 43% to 10%) with a marked decrease in the number of MRC OX-8-positive cells. These results show a favorable effect of CsA on rat fetal pancreas allografts with a reduction in MHC antigen expression within the graft and prolonged survival of insulin-rich endocrine tissue.     

The role of class I and class II MHC antigens in the rejection of vascularized heart allografts in mice

We have examined the role of entire major histocompatibility complex (MHC) disparity, individual class II or class I alloantigens in the rejection of vascularized heart allografts. Our results demonstrate that entire MHC, as well as both class II and class I disparities, may induce acute heart graft rejection or severe and irreversible heart muscle destruction. However, in 1 of 2 combinations differing at class II and 1 of 5 differing at class I, hearts have shown a good function greater than 100 days postgrafting. Furthermore, each donor-recipient combination has demonstrated a unique pattern of heart allograft function as well as a degree of heart muscle damage. In conclusion, these data suggest that the rejection process depends upon multiple factors such as the immune-response-gene-regulated immunoresponsiveness of the recipient as well as the expression of alloantigens on heart grafts during the induction and effector phases of the immune response.     

Expression of class II major histocompatibility complex antigens by bronchial epithelium in rat lung allografts

Variations in expression of class II major histocompatibility complex antigens on bronchial epithelial cells and vascular endothelium were investigated in normal rat lungs and allografted lungs during acute rejection and after cyclosporine (CsA) treatment. BN (RT1n) left lungs were transplanted into LEW (RT1l) recipients. Lungs were excised during acute rejection in untreated rats on postoperative days 1 through 5, and after CsA treatment (25 mg/kg on days 2 and 3) on days 5 and 100. Cryostat sections were examined for class II antigen expression with an immunoperoxidase technique, using various monoclonal antibodies. In the normal lung, class II antigens were not expressed by epithelial or endothelial cells. In the allografts, induction of class II antigens closely correlated with the rejection process: on day 2, the ciliated bronchial epithelium was locally positive; it became uniformly positive with increasing cellular peribronchial infiltration on days 3 and 4. CsA treatment prevented class II antigen expression to a certain extent, leaving the bronchial epithelium weakly positive at 100 days. Endothelial cells were invariably negative for class II antigens in all allografted lungs. The class II antigens expressed on the bronchial epithelial cells were of graft origin, except for recipient-type class II molecules found on the ciliated surface in CsA-treated animals. We conclude that expression of class II antigens by bronchial epithelium is the result of a bronchus-directed rejection process, and hypothesize that such a rejection process may have caused bronchiolitis obliterans in several of the patients with combined heart-lung transplants. Important is the observation that class II molecules can be present on the membranes of cells that do not themselves produce these antigens.     

Altered intragraft immune responses and improved renal function in MHC class II-deficient mouse kidney allografts

BACKGROUND: During renal allograft rejection, expression of MHC class II antigens is up-regulated on the parenchymal cells of the kidney. This up-regulation of MHC class II proteins may stimulate the intragraft alloimmune response by promoting their recognition by recipient CD4+ T cells. In previous studies, absence of donor MHC class II antigens did not affect skin graft survival, but resulted in prolonged survival of cardiac allografts. METHODS: To further explore the role of MHC class II antigens in kidney graft rejection, we performed vascularized kidney transplants using donor kidneys from A(beta)b-deficient mice that lack MHC class II expression. RESULTS: At 4 weeks after transplant, GFR was substantially depressed in control allografts (2.18+/-0.46 ml/min/kg) compared to nonrejecting isografts (7.98+/-1.62 ml/min/kg; P<0.01), but significantly higher in class II- allografts (4.38+/-0.60 ml/min/kg; P<0.05). Despite the improvement in renal function, class II- allograft demonstrated histologic features of acute rejection, not unlike control allografts. However, morphometric analysis at 1 week after transplantation demonstrated significantly fewer CD4+ T cells infiltrating class II- allografts (12.8+/-1.2 cells/mm2) compared to controls (25.5+/-2.6 cells/mm2; P=0.0007). Finally, the intragraft profile of cytokines was altered in class II- allografts, with significantly reduced expression of Th2 cytokine mRNA compared to controls. CONCLUSIONS: These results support a role of MHC class II antigens in the kidney regulating immune cells within the graft. Further, effector pathways triggered by class II antigens promote renal injury during rejection.     

Expression of donor class I major histocompatibility antigens on the vascular endothelium of mouse skin allografts

The expression of a class I MHC antigen on the vascular endothelium of mouse skin allografts was assessed by in vivo uptake of radiolabeled monoclonal anti-class-I antibody in the grafts after i.v. injection into the recipients. Endothelial localization of the bound antibodies was demonstrated via double-labeling immunofluorescence microscopy using factor-VIII-related antigen as a marker for endothelial cells. Treatment of recipients with cyclosporine was accompanied by low levels of class I antigen expression in the grafts, and similarly low levels were measured in grafts carried by nude recipients in the complete absence of rejection. Withdrawal of immunosuppressive therapy was followed by an increased class I antigen expression in the donor skin. An increase was also observed in skin grafts undergoing first-set rejection. We conclude that the expression of class I antigens on the capillary endothelium of mouse skin allografts in vivo is variable and is under influence of the immune status of the recipient.