Chronic renal allograft rejection. Selective involvement of the glomerular endothelium in humoral immune reactivity and intravascular coagulation

To study immune reactive and thrombotic mechanisms involved in chronic renal allograft rejection, Lewis rat kidneys were transplanted into bilaterally nephrectomized Brown Norway recipients tolerant of LEW erythrocyte antigens. Such BN rats fail to produce anti class I MHC alloantibodies after insertion of a LEW kidney. The LEW renal allografts experience a transient rejection episode without proteinuria followed by the development of chronic rejection, clinically characterized by glomerular proteinuria in the presence of stable renal function. Immunohistological studies of such chronically rejected LEW renal allografts showed the occurrence of glomerular and interstitial infiltration of predominantly monocytes and T cells. CD4-positive T cells dominated over CD8-positive T cells in the chronically rejected LEW renal grafts. IgG deposition was found deposited throughout the renal vasculature--this in contrast to IgM, which was observed only in the glomerular vasculature. Glomerular antibodies were not directed to endothelial class II MHC antigens, and showed only weak complement fixation as demonstrated by C3 staining. Selective glomerular IgM deposition was associated with vascular (platelet-containing) thrombi, and focal and segmental fibrinoid necrosis. In contrast, acutely rejected LEW renal grafts in unmodified BN recipients showed IgM deposition as well as thrombus formation throughout the entire renal vasculature. The results demonstrate that the antibody response to endothelial--and, in particular, glomerular endothelial non-MHC antigens--may bring about chronic vascular renal allograft rejection. How the formation of glomerular thrombotic lesions may be assisted by endothelial reactivity to cytokines from local immune reactive cells is discussed.     

A chronic renal rejection model with a fully MHC-mismatched rat strain combination under immunosuppressive therapy

BackgroundThe Fischer-to-Lewis (LEW) rat model of kidney transplantation is a widely accepted and well-characterized model of chronic rejection. In contrast to transplantation in a clinical setting, however, the absence of treatment with immunosuppressants and only minor mismatch of major histocompatibility complexes (MHCs) are critical discrepancies. Here, we established a rat model of chronic rejection using fully MHC-mismatched strains in which kidney disease progresses even under immunosuppressive therapy.MethodsLEW (RT1^l) rats were used as donors and Brown Norway (BN, RT1ⁿ) rats as recipients. Intramuscular administration of 0.1 mg/kg of tacrolimus was initiated on the day of transplantation. Post-transplantation, this dose was maintained until Day 9, suspended until Day 28 and then resumed from Day 29. Renal function, histopathology, and levels of donor-specific antibody (DSA) and several biomarkers of renal injury were assessed.ResultsOn Day 91 post-transplantation, recipients received tacrolimus treatment with short-term suspension exhibited reduced renal function and changes in histology. Those were characteristics of chronic rejection including glomerulosclerosis, interstitial fibrosis, and tubular atrophy in human transplantation recipients. Urinary protein excretion increased in a linear fashion, and elevated levels of several biomarkers of renal injury and DSA were observed even under administration of an immunosuppressant.ConclusionsWe established an allograft rejection model with impaired renal function and typical histopathological changes of chronic rejection in fully MHC-mismatched rats by controlling administration of an immunosuppressant. These findings suggest that this model more accurately reflects transplantation in a clinical setting than existing models and enables the evaluation of therapeutic agents.     

Chronic allograft nephropathy in athymic nude rats after adoptive transfer of primed T lymphocytes

The impact of presensitized T lymphocytes on the development of chronic allograft nephropathy (CAN) was investigated in nude athymic LEW.RNU recipients of F344 renal allografts. The recipients (n = 8) were reconstituted with 5 x 10(7) T lymphocytes primed against donor skin grafts to induce graft rejection. LEW.RNU (n = 8) and euthymic LEW recipients (n = 6) which underwent no further intervention after transplantation served as control groups. Adoptive transfer of primed T cells induced CAN in LEW.RNU rats. Their kidney function decreased progressively. After 90 days a moderate glomerulopathy, tubular atrophy and interstitial fibrosis were observed, vascular changes were only mild or absent. Cellular infiltrates were predominated by CD4+ T cells and ED1+ macrophages. Deposition of tenascin and laminin was enhanced. Grafts of euthymic recipients displayed only mild signs of CAN according to the Banff criteria. These data implicate an important role for the cellular immune response in the development of CAN.     

Chronic Histological Damage in Early Indication Biopsies Is an Independent Risk Factor for Late Renal Allograft Failure

The impact of early histological lesions of renal allografts on long‐term graft survival remains unclear. We included all renal allograft recipients transplanted at a single center from 1991 to 2001 (N = 1197). All indication biopsies performed within the first year after transplantation were rescored according to the current Banff classification. Mean follow‐up time was 14.8 ± 2.80 years. In multivariate Cox proportional hazards analysis, arteriolar hyalinosis and transplant glomerulopathy were independently associated with death‐censored graft survival, adjusted for baseline demographic covariates. Arteriolar hyalinosis correlated with interstitial fibrosis, tubular atrophy, mesangial matrix increase, vascular intimal thickening and glomerulosclerosis. Clustering of the patients according to these chronic lesions, reflecting the global burden of chronic injury, associated better with long‐term graft survival than each of the chronic lesions separately. Early chronic histological damage was an independent risk factor for late graft loss, irrespective whether a specific, progressive disease was diagnosed or not, while T cell‐mediated rejection did not. We conclude that individual chronic lesions like arteriolar hyalinosis, tubular atrophy, interstitial fibrosis, glomerulosclerosis, mesangial matrix increase and vascular intimal thickening cannot be seen as individual entities. The global burden of early chronic histological damage within the first year after transplantation importantly affects the fate of the allografts.     

Chronic allograft nephropathy in paediatric renal transplantation

Chronic allograft nephropathy (CAN) is now the leading cause of renal transplant loss in paediatric transplant recipients. Despite improvements in immunosuppression, which have significantly reduced the incidence of acute rejection, the rates of chronic kidney loss have remained unchanged in paediatric transplant patients over the last 20 years. Chronic allograft nephropathy is a pathological diagnosis of which the key features are tubular atrophy and interstitial fibrosis. More consistent definitions and grading of these through the Banff classification have allowed more rigorous study of the development of chronic allograft nephropathy along with further identification of specific lesions associated with the underlying aetiologies. While initially thought to be primarily due to immune injury, it is now evident that CAN is the end result of a variety of immune and non-immune injuries including ischaemia reperfusion injury, calcineurin inhibitor (CNI) toxicity and infections. Protocol biopsy studies have demonstrated rates of CAN development in children similar to those in adults with comparable underlying pathological processes. This review outlines the current knowledge of CAN within the context of paediatric renal transplantation.     

Histopathologic findings associated with a chronic, progressive decline in renal allograft function.

The relationship between specific histopathologic findings of chronic rejection (CR) and the clinical course of renal transplant recipients with a chronic progressive decline in allograft function (CPDAF) is unknown. We used one or two hinged regression lines, fitted by least-squares to serial creatinine clearances, to define the onset and clinical course of CPDAF. Biopsies (N = 100) from patients transplanted from 1978 to 1982 were studied retrospectively. Interstitial fibrosis, tubular atrophy, and fibrointimal arterial narrowing were more pronounced in biopsies obtained after, but not before the onset of CPDAF. Interstitial hemorrhage, an infrequent finding in acute vascular rejection, preceded the onset of CPDAF, but the more common histologic findings of acute cellular rejection did not. The severity of histologic features of CR (as reflected by a score combining fibrointimal arterial narrowing, interstitial fibrosis, tubular atrophy, glomerular sclerosis, glomerular mesangial expansion, and glomerular basement membrane reduplication) correlated with the duration of subsequent allograft survival (r = -0.65, P less than 0.001). Glomerular size increased after transplantation, but was not different in patients with or without CPDAF, suggesting that mechanisms related to compensatory hypertrophy did not play a major role in the pathogenesis of CR. In summary, the histologic findings of CR did not predict the onset of CPDAF, did not distinguish whether the pathogenesis was mediated by immune or nonimmune events, but did correlate with the duration of subsequent allograft survival.     

Chronic renal allograft rejection: the significance of non-MHC alloantigens

We studied the role of polymorphic endothelial antigens other than MHC in antibody-mediated chronic renal allograft rejection in two models. In the first model, donor Lewis rat kidneys were transplanted into BN recipients that had been made tolerant for donor class I antigens at the B cell (antibody) level. In this setting Lewis kidney grafts were chronically rejected with stable renal function but increasing proteinuria (> 100 mg/24 h). Rejected graft tissue showed mononuclear cell infiltration and the presence of glomerular vasculonecrotic lesions with fibrinoid material, associated with IgG and IgM deposition, but with absent or weak C3 binding. Graft endothelium showed no expression of MHC class II antigens. Serum antibodies were not reactive with donor class I antigens, but did react with endothelial non-MHC alloantigens. In the second model, more direct information on the role of endothelial non-MHC alloantigens in renal allograft rejection was obtained by transplanting Lewis 1 N kidneys into unmodified BN recipients (MHC-matched transplants). Here, similar to the first model, the animals developed severe proteinuria with stable renal function. Histopathological examination showed mononuclear cell infiltration and deposition of IgM and IgG along the glomerular vasculature, but this time in the presence of strong C3 reactivity. However, glomerular vasculonecrotic lesions with intense fibrin deposition were not observed. The data showed that although clinically the two kidney transplantation models used gave similar chronic rejection phenomena, histopathologically some striking differences were observed in the glomeruli. The precise mechanisms effecting chronic rejection of the grafts is still a puzzle. However, immune reactivity against graft (endothelial) non-MHC antigens may play a significant role.     

Effects of portal venous administration with allogenic cells on renal allograft survival in the rat

The effects of administration of donor lymphocytes via portal vein (PV) on capacity of alloreactivity and renal allograft survival were investigated in comparison with those of intra-venous (IV) administration in the rats. Orthotopic renal transplantations were performed from Brown-Norway (BN, RT-In) to Lewis (LEW, RT-11) male rats. Donor lymphocytes were prepared from BN or third party DA(RT-1a) rat spleens and lymph nodes and injected via PV or IV to LEW rats on the day of transplantation (day 0). Untreated LEW hosts rejected BN grafts at 7.8 +/- 0.6 days (n = 10). IV administration of 1 x 10(8) BN cells to LEW rats caused a slight prolongation of BN graft survival to 10.4 +/- 3.1 days (n = 9, p less than 0.05), whereas PV inoculation of the same number of BN cells further prolonged graft survival to 28.9 +/- 9.2 days (n = 9, p less than 0.01). This effect was antigen specific; the administration of 1 x 10(8) third party DA cells via PV to LEW rats did not prolong survival of BN graft (MST = 7.4 +/- 0.8, n = 6). Serum from tolerant recipients had significant antigen specific suppressor effect (70.6%) on the MLR proliferative reaction of LEW responder cells toward donor BN cells, but not third party DA cells. Spleen cells from these recipients did not show any suppressive effect. These results demonstrate that PV administration of donor lymphoid cells to recipients results in rapidly inducible and long-lasting immunologic tolerance specific to donor alloantigen, and that this tolerance is mediated by serum factor induced in hosts, but not by suppressor cells.     

Role of antibody in rat renal allograft rejection. II. Failure to enhance renal allografts by sensitization to donor class I antigens presented by donor strain erythrocytes

BN rats were immunized with one or three doses of 1 X 10(8) highly purified LEW erythrocytes (LEW-E) yielding IgM antibody (IgM-BN rats) and IgG antibody (IgG-BN rats) to LEW class I antigens, respectively. LEW kidneys transplanted into IgM-BN rats elicited cytotoxic T cell responses and lymphocytotoxic antibody responses comparable to those elicited by LEW renal grafts in unmodified BN rats. However, LEW kidneys were rejected by IgM-BN hosts in a slightly delayed fashion compared with controls (mean rejection times (MRTs), 9.4 versus 7.1 days); delayed rejection was associated with the absence of anti-LEW IgG hemagglutinins from the recipients' blood and the absence of vasculonecrotic lesions from rejected renal grafts. LEW kidneys inserted into IgG-BN rats were rejected in a slightly accelerated fashion compared with controls (MRT, 6.6 days). Lymphocytotoxins developed in IgG-BN recipients of LEW kidneys in a fashion similar to that of controls, but cytotoxic T cell responses were delayed up to the 6th day after transplantation. These observations confirm our previous finding that cytotoxic T cells do not play a decisive role in acute rejection in this model. The association observed between delayed or accelerated rejection of LEW kidneys by BN rats sensitized with LEW-E and the absence or presence of anti-donor IgG hemagglutinins in the blood of these recipients after transplantation suggests an important role for IgG anti-donor class I antibodies in the rejection of LEW renal allografts by BN rats.     

Pathogenesis of chronic renal allograft dysfunction

The pathogenesis of chronic renal allograft dysfunction was reviewed. Chronic rejection/chronic renal allograft nephropathy is the most prevalent cause of renal graft loss after the first year post-transplant. Both immunologic and non-immunologic factors play key roles in the pathogenesis of chronic allograft nephropathy. Acute rejection episodes are the most prevalent risk factor for chronic rejection. Many risk factors for chronic allograft nephropathy have been identified, such as glomerular hyper-filtration, delayed graft function, repeated acute rejection, systemic hypertension and hyperlipidemia. However, the precise pathogenesis of chronic allograft nephropathy remains obscure. The differential diagnosis of immunologically mediated chronic rejection and chronic allograft dysfunction caused by non-immunologic factors is usually impossible using clinical parameters. The histopathologic findings of chronic allograft nephropathy are progressive interstitial fibrosis with tubular atrophy and thickening of vascular intima, and these findings are non-specific. Therefore, the term chronic allograft nephropathy may be clinically preferable to chronic rejection to describe the gradual decline in graft function. The most effective way to prevent chronic allograft dysfunction is to avoid any kind of graft damage via immunologic or non-immunologic pathway.     

Allochimeric therapy induces unique regulatory T cells that mitigate chronic rejection

Induction of tolerance to an allogeneic graft without the need for nonspecific immunosuppression is a major goal of transplantation therapy. We have shown that treatment with molecularly engineered, allochimeric [alpha(1h)(1/u)]-RT1.Aa class I MHC antigens bearing donor-type Wistar-Furth (WF, RT1.A(u)) or Lewis (LEW, RT1A(1)) amino acid substitutions for host-type ACI (RTI.A(a)) sequences in the alpha(1)-helical region induces donor-specific tolerance to cardiac allografts in rat recipients. The mechanisms involved in the establishment and maintenance of specific allograft tolerance are still not fully understood. It is now clear that acquisition of transplantation tolerance is an active, highly regulated, multistep process. According to the pool size model of allograft tolerance, the allograft outcome, rejection, or tolerance often depend on the balance between cytopathic and regulatory T cells (T-regs). This study examined mechanisms of chronic rejection (CR) development on a model of cardiac transplant tolerance after adoptive transfer of T-regs followed by allochimeric therapy. Generation of T-regs was demonstrated in vitro by MLR coculture and confirmed by adoptive transfer of T cells from primary recipients to secondary hosts. To confirm the true nature of regulatory cells, we performed a second transfer into tertiary recipients. Unlike T-regs from tolerant hosts, T cells from naive rats did not prolong graft survival. Histological evaluation of T-regs-transfected groups showed absence of visible CR. In contrast, T-regs generated in recipients after high-dose cyclosporine treatment failed to inhibit CR in transferred singeneic recipients. Allochimeric therapy triggers generation of unique regulatory lymphocytes that mitigate development of chronic rejection through regulation of anti-inflammatory mechanisms and down-regulation of alloantibody response.     

Differential diagnosis between acute rejection and infection after lung transplantation in rats]

Infiltration of mononuclear cell subpopulations was analyzed immunohistochemically in acute lung allograft rejection (BN/LEW) and mycoplasma pulmonis bronchopneumonia in inbred rats. In lung allograft rejection, marked infiltration of activated macrophages, moderate infiltration of helper and suppressor T lymphocytes, and slight or moderate infiltration of B lymphocytes were observed around bronchioles and vessels, as a thick layer of cells like concentric circles, forming a dense cuff. In acute and chronic mycoplasma infection, focal inflammatory reactions were observed with various degrees of infiltration of mononuclear cell subpopulations around bronchioles and vessels, ranging from very mild to severe infiltration, even in the same section or even around the same bronchiole. This difference in the infiltration pattern between the focal, unequal and dappled infiltration in lung infection and the homogeneous and even cuff infiltration in acute rejection may be useful in differential diagnosis between acute rejection and infection following lung transplantation.     

Immunomodulation for intestinal transplantation by allograft irradiation, adjunct donor bone marrow infusion, or both

BACKGROUND: The passenger leukocytes in the intestine have a lineage profile that predisposes to graft-versus-host disease (GVHD) in some animal models and have inferior tolerogenic qualities compared with the leukocytes in the liver, other solid organs, and bone marrow. Elimination by ex vivo irradiation of mature lymphoid elements from the bowel allografts is known to eliminate the GVHD risk. We hypothesized that infusion of donor bone marrow cells (BMC) in recipients of irradiated intestine would improve tolerogenesis without increasing the risk of GVHD. METHODS: Orthotopic small intestine transplantation was performed with the GVHD-prone Lewis (LEW)-to-Brown Norway (BN) combination and the reverse GVHD-resistant BN-to-LEW model under a short course of tacrolimus treatment (1 mg/kg/day, days 0-13, 20, 27). Grafts were irradiated ex vivo, using a 137Cs source. In selected experimental groups, donor BMC (2.5 x 10(8)) were infused on the day of small intestine transplantation. RESULTS: The unmodified LEW intestine remained intact, whether transplanted alone or with adjunct donor BMC infusion, but all of the BN recipients died of GVHD after approximately 2 months. Intestinal graft irradiation (10 Gy) effectively prevented the GVHD and prolonged survival to 92.5 days, but all of the BN recipients died with chronic rejection of the LEW grafts, which was prevented by infusion of adjunct donor BMC without causing GVHD. In the GVHD-resistant reverse strain direction (BN-->LEW), all intestinal recipients treated for 27 days with tacrolimus survived > or =150 days without regard for graft irradiation or adjunct BMC, but chronic rejection was severe in the irradiated intestine, moderate in the unaltered graft, and least in the irradiated intestine transplanted with adjunct BMC. Mild arteritis in the 150 day allografts of both strain combinations (i.e., LEW--> BN and BN-->LEW) may have been irradiation associated, but this was prevented when weekly doses of tacrolimus were continued for the duration of the experiment rather than being stopped at 27 days. CONCLUSIONS: Recipients are protected from GVHD by irradiating intestinal allografts, but the resulting leukocyte depletion leads to chronic rejection of the transplanted bowel. The chronic rejection is prevented with adjunct donor BMC without causing GVHD. Although application of the strategy may be limited by the possibility of radiation injury, the results are consistent with the paradigm that we have proposed to explain organ-induced graft acceptance, tolerance, and chronic rejection.     

PG490-88, a new immunosuppressant, effectively prevents acute and chronic rejection in rat renal allografts

PG490-88 is a semisynthetic derivative of the novel compound PG490 (triptolide) purified from a Chinese herb. It has been shown to prolong acute allograft survival in multiple experimental organ transplant models. However, the effect of PG490-88 on prevention of acute and chronic renal allograft rejection has not been determined. Kidneys of ACI or F344 rats were transplanted into bilaterally nephrectomized LEW recipients as the acute or chronic allograft rejection models, respectively. Treatment of LEW recipients with PG490-88 significantly prolonged ACI kidney graft survival in a dose-dependent manner when compared with the untreated allograft controls. LEW recipients of F344 kidney grafts who received PG490-88 for 90 days with a brief course of low-dose FK506 showed normal serum creatinine levels and markedly reduced histological changes of chronic rejection at day 90 after transplantation. These results suggest that PG490-88 significantly prolongs kidney allograft survival in an acute rejection model and prevents chronic allograft rejection in rats.     

Chronic allograft nephropathy

Chronic allograft nephropathy (CAN) is the leading cause of renal allograft loss in paediatric renal transplant recipients. CAN is the result of immunological and nonimmunological injury, including acute rejection episodes, hypoperfusion, ischaemia reperfusion, calcineurin toxicity, infection and recurrent disease. The development of CAN is often insidious and may be preceded by subclinical rejection in a well-functioning allograft. Classification of CAN is histological using the Banff classification of renal allograft pathology with classic findings of interstitial fibrosis, tubular atrophy, glomerulosclerosis, fibrointimal hyperplasia and arteriolar hyalinosis. Although improvement in immunosuppression has led to greater 1-year graft survival rates, chronic graft loss remains relatively unchanged and opportunistic infectious complications remain a problem. Protocol biopsy monitoring is not current practice in paediatric transplantation for CAN monitoring but may have a place if new treatment options become available. Newer immunosuppression regimens, closer monitoring of the renal allograft and management of subclinical rejection may lead to reduced immune injury leading to CAN in the paediatric population but must be weighed against the risk of increased immunosuppression and calcineurin inhibitor nephrotoxicity.     

Effects of everolimus on cellular and humoral immune processes leading to chronic allograft nephropathy in a rat model with sensitized recipients

BACKGROUND: Chronic allograft nephropathy (CAN) remains the most common cause of late graft loss especially in sensitized patients. The aim of this study is to evaluate the therapeutic effect of everolimus on cellular and humoral mechanisms of chronic allograft damage in a rat model with sensitized recipients. METHODS: F344 kidneys were transplanted to LEW.RNU rats. The athymic recipients were reconstituted with 3.5 x 10(7) or 5 x 10(7) presensitized CD4+T-lymphocytes. In the treatment group, everolimus was introduced five weeks posttransplantation. Rats were monitored for peripheral blood lymphocytes, renal function, histological changes in the graft, and the development of donor-specific alloantibodies. RESULTS: Rats developed cell dose-dependent renal failure. Increased urinary albumin excretion and glomerulopathy were frequently accompanied by the development of donor-specific major histocompatibility complex (MHC) alloantibodies. In the everolimus group, five of six animals survived for 20 weeks with stable serum creatinine and displayed neither acute cellular rejection nor CAN. Prolonged survival was accompanied with significantly reduced tubulointerstitial cell infiltrate in the graft. Increased urinary albumin excretion was present in all, acute tubular necrosis in five of six, and glomerular sclerosis in two grafts. MHC alloantibodies were found in four of six animals. CONCLUSION: The used rat model offers the opportunity to study the influence of everolimus on the interaction of humoral and cellular mechanisms involved in chronic renal damage. Everolimus leads to a prolongation of allograft survival, reduced cell infiltrate in the graft, and prevents tubular atrophy and interstitial fibrosis. The development of alloantibodies and albuminuria was not prevented. These data suggest that although cellular rejection is clearly suppressed, humoral mechanisms of CAN cannot be completely controlled by everolimus treatment in the sensitized rat model.     

Development of donor-specific immunoregulatory T-cells after local CTLA4Ig gene transfer to pancreatic allograft

BACKGROUND: CTLA4Ig gene transfer directly to graft tissue might have the potential to avoid the need for systemic immunosuppression. In our previous studies of bio-breeding (BB) rats, local adenovirus-mediated CTLA4Ig gene transfer protected the pancreas from autoimmune and alloimmune responses. This study investigated the potency of local CD28/B7 costimulatory blockade for induction of donor-specific tolerance and further examined the existing mechanisms. METHODS: Brown Norway (BN; RT1)-pancreaticoduodenal grafts transfected with Ad.CTLA4Ig via intraarterial ex vivo perfusion were transplanted into streptozotocin-induced diabetic Lewis (LEW; RT1) rats. RESULTS: Ad.CTLA4Ig transduced grafts combined with a short course of FK506 resulted in indefinitely prolonged survival (>156 days vs. 19.5 days with FK506 alone). CTLA4Ig was predominantly expressed in grafts on day 4. The expression was gradually diminished and was only slightly detectable at day >100. The proliferative responses against BN antigen were remarkably enhanced among recipients with rejected grafts, but the T-cells from tolerant recipients (>100 days) showed poor cytotoxic responses. On adoptive transfer assay, the splenic T-cells of tolerant recipients were able to suppress the rejection of BN, but not third-party Wistar Furth (WF; RT1) hearts in irradiated (480 cGy) LEW recipients. The percentage of CD4CD25 splenic T-cells was significantly increased in tolerant recipients (13.53 +/- 4.06% vs. 6.06 +/- 0.56% in naive rats). CONCLUSION: CTLA4Ig gene transfer to the pancreaticoduodenal allograft combined with a short course of FK506 induces donor-specific tolerance. The mechanism of maintaining tolerance could be explained by development of splenic T suppressor cells.     

The pathobiology of chronic allograft nephropathy: immune-mediated damage and accelerated aging

Chronic allograft nephropathy includes chronic calcineurin nephrotoxicity, recurrent and de novo glomerulonephritis and a group of disorders with graft dysfunction of unknown etiology designated chronic rejection. Review of risk factors of the latter category show that the chronic rejection lesions emerge in organs that have undergone injury. Despite the relevance of nonalloantigen-dependent progression factors in the tissue injury, alloantigen-dependent factors predominate in the pathogenesis. Lately, B cell responses have received increasing interest in transplant rejection and include responses against both major histocompatibility complex (MHC) and tissue-specific antigens, mainly on the endothelium and in the glomeruli. These humoral responses are thought to be involved in the development of vascular and glomerular lesions. Furthermore, at the tissue level, markers of senescence are found in the tubular epithelium contributing to the lesions of tubular atrophy and interstitial fibrosis.     

Chronic rejection: insights from a novel immunosuppressive-free model of kidney transplantation

The use of immunosuppressive drugs in models of chronic rejection may limit their usefulness for mechanistic studies. We have developed a new minor histocompatibility-mismatched rat kidney transplant model without the need for immunosuppression. Kidneys from LEW (RT1(l)) donors were transplanted to congenic WF.1L (RT1(l)) recipients and compared with the reversed strain combination and isogenic controls. Urinary protein excretion was measured serially in all recipients; kidneys were harvested 90, 120, and 180 d after transplantation for morphologic analysis and cytokine gene expression. In vitro lymphocytic reactivity and cytokine analysis of mixed lymphocyte reaction (MLR) culture supernatants by ELISA was also carried out. LEW into WF.1L kidney grafts developed proteinuria starting 120 d after transplantation and were associated with morphologic changes of focal segmental glomerulosclerosis together with interstitial cell infiltrates, upregulated gene expression of IL-1beta, IL-2, and TNF-alpha/-beta, as well as IL-2, IFN-gamma, and TNF-alpha production by lymphocytes in MLR culture supernatants. WF.1L kidneys transplanted into LEW recipients did not develop chronic rejection and had upregulation of Th2 cytokines, both within the allograft and in MLR supernatant of recipient lymphocytes cultured with WF.1L cells. Furthermore, these lymphocytes produced both Th1 and Th2 cytokines when cultured with WF cells, unlike lymphocytes from the LEW isografts, which produced Th1 cytokines when challenged with WF cells. These studies show that indirect allorecognition can cause strain-dependent chronic rejection associated with Th1-like cytokine production, whereas production of Th2 cytokines is associated with protection from the development of chronic rejection.