Post-transplant repopulation of naïve and memory T cells in blood and lymphoid tissue after alemtuzumab-mediated depletion in heart-transplanted cynomolgus monkeys

Repopulation of memory T cells (Tmem) in allograft recipients after lymphodepletion is a major barrier to transplant tolerance induction. Ineffective depletion of naïve T cells (Tn) and Tmem may predispose to repopulation of Tmem after transplantation. Cynomolgus macaque monkeys given heart allografts were lymphodepleted using Alemtuzumab (Campath-1H; anti-CD52). Peripheral blood (PB) and lymph nodes (LN) were analyzed for CD95(-) (Tn) and CD95(+) cells (Tmem), one day, one month and up to three months after Alemtuzumab infusion. CD52 expression, susceptibility to Alemtuzumab cytotoxicity and pro-apoptotic caspase-3 were evaluated in Tn and Tmem. In vivo, Alemtuzumab induction profoundly depleted lymphocytes in PB (99% reduction) but exerted a lesser effect in LN (70% reduction), with similar depletion of Tn and Tmem subsets. After transplantation, Tmem comprised the majority of lymphocytes in PB and LN. In vitro, LN T cells were more resistant to Alemtuzumab-mediated cytotoxicity than PB lymphocytes. CD4(+) Tn and Tmem were equally susceptible to Alemtuzumab-mediated cytotoxicity, whereas CD8(+) Tn were more resistant than CD8(+) Tmem. However, no significant differences in CD52 expression between lymphocyte subsets in PB and LN were observed. Caspase-3 expression was higher in PB than LN T cells. CD4(+) and CD8(+) Tn expressed lower levels of Caspase-3 than Tmem, in both PB and LN. Thus, after Alemtuzumab infusion, residual Tn in secondary lymphoid tissue may predispose to rapid recovery of Tmem in allograft recipients.

Multiphoton intravital microscopy of the transplanted mouse kidney

Graft outcomes after kidney transplantation continue to be adversely affected by ischemia-reperfusion injury and rejection. High-resolution, real-time imaging of the transplanted kidney could shed valuable insights into these dynamic processes, but such methodology has not been established. Here we describe a technique for intravital imaging of the transplanted mouse kidney using multiphoton fluorescence microscopy. The technique enabled real-time, high-resolution imaging and quantitation of renal filtration, cell death, leukocyte adhesion and capillary blood flow after transplantation. Using this technique, we found that brief graft ischemia associated with the transplantation procedure led to a rapid decline in renal filtration accompanied by a significant increase in microvascular leakage and renal tubular epithelial cell death within the first 3 h after transplantation. No significant changes in leukocyte adhesion or capillary blood flow were observed during the same time period. This report establishes multiphoton fluorescence microscopy as a sensitive tool for simultaneously studying functional and structural perturbations that occur in the mouse kidney after transplantation and for investigating the migration of leukocytes to the graft.

Investigation of lymphocyte depletion and repopulation using alemtuzumab (Campath-1H) in cynomolgus monkeys

As the target CD52 molecule is expressed on erythrocytes of most nonhuman primate strains, using alemtuzumab in these species would cause massive hemolysis. Six cynomolgus monkeys of Indonesian origin, screened by agglutination assay for absence of CD52 on erythrocytes, were administered alemtuzumab in a cumulative dose to a maximum of 60 mg/kg. In two monkeys, mycophenolate mofetil (MMF) was added as maintenance therapy. Complete depletion of T and B lymphocytes (>99.5%) was achieved with 20 mg/kg alemtuzumab and was more profound than in monkeys treated with antithymocyte globulin (n = 5), as quantified by flow cytometry. Repopulation was suppressed by weekly injections of 10 mg/kg. Without MMF, repopulation of CD20(+)B cells and CD8(+)T cells was complete within 2 and 3 months, respectively, and repopulation of CD4(+)T cells was 67% after 1 year. MMF significantly delayed CD4(+)T-cell repopulation. Among repopulating CD4(+) and CD8(+) T cells, a phenotypic shift was observed from CD45RA(hi)CD62L(hi) naïve cells toward CD45RA(lo)CD62L(lo) effector memory cells. In lymph nodes, the depletion of naïve cells was more profound than of memory cells, which may have initiated a proliferation of memory cells. This model offers opportunities to investigate lymphocyte depletion/repopulation phenomena, as well as the efficacy of alemtuzumab in preclinical transplantation models.

Long-term controlled normoglycemia in diabetic non-human primates after transplantation with hCD46 transgenic porcine islets

Xenotransplantation of porcine islets into diabetic non-human primates is characterized by (i) an initial massive graft loss possibly due to the instant blood-mediated inflammatory reaction and (ii) the requirement of intensive, clinically unfriendly immunosuppressive therapy. We investigated whether the transgenic expression of a human complement-regulatory protein (hCD46) on porcine islets would improve the outcome of islet xenotransplantation in streptozotocin-induced diabetic Cynomolgus monkeys. Immunosuppression consisted of thymoglobulin, anti-CD154 mAb for costimulation blockade, and mycophenolate mofetil. Following the transplantation of islets from wild-type pigs (n = 2) or from 1,3-galactosyltransferase gene-knockout pigs (n = 2), islets survived for a maximum of only 46 days, as evidenced by return to hyperglycemia and the need for exogenous insulin therapy. The transplantation of islets from hCD46 pigs resulted in graft survival and insulin-independent normoglycemia in four of five monkeys for the 3 months follow-up of the experiment. One normalized recipient, selected at random, was followed for >12 months. Inhibition of complement activation by the expression of hCD46 on the pig islets did not substantially reduce the initial loss of islet mass, rather was effective in limiting antibody-mediated rejection. This resulted in a reduced need for immunosuppression to preserve a sufficient islet mass to maintain normoglycemia long-term.

Endoscopic gastric submucosal transplantation of islets (ENDO-STI): technique and initial results in diabetic pigs

The results of transplantation of human donor islets into the portal vein (PV) in patients with diabetes are encouraging. However, there are complications, for example, hemorrhage, thrombosis and an immediate loss of islets through the 'instant blood-mediated inflammatory reaction' (IBMIR). The gastric submucosal space (GSMS) offers potential advantages. Islets were isolated from adult pigs. Recipient pigs were made diabetic by streptozotocin. Donor islets were injected into the GSMS through a laparotomy (Group 1A, n = 4) or endoscopically (Group 1B, n = 8) or into the PV through a laparotomy (Group 2, n = 3). The pigs were followed for a maximum of 28 days. Monitoring of C-peptide in Group 1 indicated that there was minimal immediate loss of islets whereas in Group 2 there was considerable loss from IBMIR. In Group 1, there were significant reductions in mean blood glucose and mean exogenous insulin requirement between pretransplantation and 20 days posttransplantation. In Group 2, there was no significant reduction in either parameter. Insulin-positive cells were seen in the GSMS in Group 1, but not in the liver in Group 2. Endoscopic gastric submucosal transplantation of islets (ENDO-STI) offers a minimally invasive and quick approach to islet transplantation, avoids IBMIR and warrants further exploration.

Contribution of naïve and memory T-cell populations to the human alloimmune response

T-cell alloimmunity plays a dominant role in allograft rejection. The precise contribution of naïve and memory T cells to this response however remains unclear. To address this question, we established an ex vivo flow-cytometric assay that simultaneously measures proliferation, precursor frequency and effector molecule (IFNgamma, granzyme B/perforin) production of alloreactive T cells. By applying this assay to peripheral blood mononuclear cells from healthy volunteers, we demonstrate that the CD4+ and CD8+ populations mount similar proliferative responses and contain comparable frequencies of alloreactive precursors. Effector molecule expression, however, was significantly higher among CD8+ T cells. Analysis of sorted naïve and memory T cells showed that alloreactive precursors were equally present in both populations. The CD8+ effector and terminally differentiated effector memory subsets contained the highest proportion of granzyme B/perforin after allostimulation, suggesting that these cells present a significant threat to transplanted organs. Finally, we demonstrate that virus-specific lymphocytes contribute significantly to the alloresponse in certain responder-stimulator HLA combinations, underscoring the importance of T-cell cross-reactivity in alloimmunity. These results provide a quantitative assessment of the roles of naïve and memory T-cell subsets in the normal human alloimmune response and establish a platform for measuring T-cell alloreactivity pre- and posttransplantation.

Tertiary lymphoid tissues generate effector and memory T cells that lead to allograft rejection

Tertiary lymphoid tissues are lymph node-like cell aggregates that arise at sites of chronic inflammation. They have been observed in transplanted organs undergoing chronic rejection, but it is not known whether they contribute to the rejection process by supporting local activation of naïve lymphocytes. To answer this question, we established a murine transplantation model in which the donor skin contains tertiary lymphoid tissues due to transgenic expression of lymphotoxin-alpha(RIP-LT alpha), whereas the recipient lacks all secondary lymphoid organs and does not mount primary alloimmune responses. We demonstrate in this model that RIP-LT alpha allografts that harbor tertiary lymphoid tissues are rejected, while wild-type allografts that lack tertiary lymphoid tissues are accepted. Wild-type allografts transplanted at the same time as RIP-LT alpha skin or 60 days later were also rejected, suggesting that tertiary lymphoid tissues, similar to secondary lymphoid organs, generate both effector and memory immune responses. Consistent with this observation, naive T cells transferred to RIP-LT alpha skin allograft but not syngeneic graft recipients proliferated and differentiated into effector and memory T cells. These findings provide direct evidence that tertiary lymphoid structures perpetuate the rejection process by supporting naïve T-cell activation.

Acute cellular rejection with CD20-positive lymphoid clusters in kidney transplant patients following lymphocyte depletion

Lymphoid clusters (LC) containing CD20-positive B cells in kidney allografts undergoing acute cellular rejection (ACR) have been identified in small studies as a prognostic factor for glucocorticoid resistance and graft loss. Allograft biopsies obtained during the first episode of ACR in 120 recipients were evaluated for LC, immunostained with CD20 antibody, and correlated with conventional histopathologic criteria, response to treatment and outcome. LC were found in 71 (59%) of the 120 biopsies. All contained CD20 positive B cells that accounted for 5-90% of the LC leukocyte content. The incidence of LC was highest in the patients who had no lymphoid depletion or had been treated with Thymoglobulin preconditioning (79% vs. 75%, respectively) compared to 37% in patients pretreated with Campath (p = 0.0001). Banff 1a/1b ACR were more frequent in the LC-positive than the LC-negative group (96% vs. 80%, respectively; p = 0.0051). With a posttransplant follow-up of 953 +/- 430 days, no significant differences were detected between LC-postitive and LC-negative groups in time to ACR, steroid resistance, serum creatinine and graft loss. CD20+LC did not portend glucocorticoid resistance or worse short to medium term outcomes. CD20+LC may represent a heterogenous collection in which there may be a small still to be fully defined unfavorable subgroup.

Cutting edge: Secondary lymphoid organs are essential for maintaining the CD4, but not CD8, naive T cell pool

Despite declining thymic output with age, the peripheral naive T cell pool of an adult animal remains remarkably stable. Therefore, a central question in immunology is how the naive T cell pool is maintained. Here we show that the maintenance of the naive CD4, but not CD8, T cell population in the thymectomized adult mouse is dependent on the presence of secondary lymphoid tissues. This finding is explained by the inability of naive CD4 T cells to sustain normal levels of the survival molecule Bcl-2 or to undergo homeostatic proliferation in the absence of secondary lymphoid organs. Thus, naive CD4 T cells must traffic through secondary lymphoid organs to maintain a stable CD4 pool while naive CD8 T cells encounter their survival and proliferation signals outside the organized structures of secondary lymphoid tissues.

Gene expression analysis in human renal allograft biopsy samples using high-density oligoarray technology

BACKGROUND

High-density oligoarray technology is a novel method for screening the expression of thousands of genes in a small tissue sample. Oligoarray analysis of genes expressed during human renal allograft rejection has not been reported previously.

METHODS

Seven human renal allograft biopsies with histologic evidence of acute cellular rejection and three renal allograft biopsies without evidence of rejection (control) were analyzed for the expression of 6800 human genes using high-density oligoarrays (GeneChip, Affymetrix, Santa Clara, CA). Quantitative expression of gene transcripts was determined and a comparison analysis between acute rejection and control biopsy samples was performed. Up-regulation of a specific gene transcript during acute rejection was considered to be significant if transcript abundance increased fourfold or more relative to control biopsy samples.

RESULTS

Comparison analysis revealed that between 32 and 219 gene transcripts are up-regulated (>fourfold) during acute rejection. Of these transcripts, only four (human monokine induced by interferon-gamma, T-cell receptor active beta-chain protein, interleukin-2 stimulated phosphoprotein, and RING4 (a transporter involved in antigen presentation)) were consistently up-regulated in each acute rejection sample relative to at least two of three control biopsy samples. Six other genes were up-regulated in six of seven acute rejection samples. These were interferon-stimulated growth factor-3, complement factor 3, nicotinamide N-methyltransferase, macrophage inflammatory protein-3beta, myeloid differentiation protein, and CD18. Only two gene transcripts were down-regulated in five of seven acute rejection samples. Significant up-regulation of cytotoxic T-cell effector molecules, previously reported as markers of acute renal rejection in humans, was not detected.

CONCLUSIONS

High-density oligoarray technology is useful for screening gene expression in transplanted tissues undergoing acute rejection. Because this method does not rely on a priori knowledge of which genes are involved in acute rejection, it is likely to yield novel insights into the mechanisms and diagnosis of rejection.

Failure to induce neonatal tolerance in mice that lack both IL-4 and IL-13 but not in those that lack IL-4 alone

Current evidence suggests that neonatal tolerance to a foreign Ag is the consequence of IL-4-mediated Th2 immunity rather than the thymic deletion of Ag-specific T cells. Here, we addressed the role of IL-4 in neonatal tolerance by testing whether tolerance to a minor histocompatibility Ag can be induced in newborn mice that lack IL-4 (IL-4(-/-)). We found that IL-4 does not play a dominant role in the induction of neonatal tolerance as newborn female IL-4(-/-) mice could be readily tolerized to the H-Y male Ag. In contrast, mice that lack both IL-4 and IL-13 (IL-4(-/-)/IL-13(-/-)) were resistant to the induction of neonatal tolerance, and their splenocytes produced exaggerated amounts of IFN-gamma on rechallenge with the same Ag encountered during the neonatal period. These findings argue against the view that IL-4 alone is critical for the induction of neonatal tolerance and suggest that the combined actions of both IL-4 and IL-13 are essential for this process.

The dual role of IL-2 in the generation and maintenance of CD8+ memory T cells

The mechanisms responsible for the generation and maintenance of T cell memory are unclear. In this study, we tested the role of IL-2 in allospecific CD8+ T cell memory by analyzing the long-term survival, phenotype, and functional characteristics of IL-2-replete (IL-2+/+) and IL-2-deficient (IL-2-/-) CD8+ TCR-transgenic lymphocytes in an adoptive transfer model. We found that IL-2 is not essential for the in vivo generation, maintenance, or recall response of CD8+ memory T cells. However, IL-2 increased the size of the CD8+ memory pool if present at the time of initial T cell activation but reduced the size of the pool if present during memory maintenance by inhibiting the proliferation of CD8+ memory T cells. Thus, IL-2-based vaccine strategies or immunosuppressive regimens that target IL-2 should take into account the divergent roles of IL-2 in CD8+ T cell immunity.

Alloantigen-driven T cell death mediated by Fas ligand and tumor necrosis factor-alpha is not essential for the induction of allograft acceptance

BACKGROUND

Fas ligand (FasL)-Fas and tumor necrosis factor alpha (TNFalpha)-tumor necrosis factor receptor (TNFR) interactions regulate immune responses and contribute to self-tolerance by mediating antigen-driven T cell apoptosis. It is not known whether FasL and TNFalpha, expressed by the recipient's lymphoid or nonlymphoid cells, are essential for the apoptosis of alloreactive T lymphocytes and the induction of allograft acceptance.

METHODS

We compared the survival of fully allogeneic vascularized cardiac allografts between wild-type (wt) and FasL-mutant (gld) recipient mice. In addition, we studied cardiac allograft survival in gld mice injected with TNFalpha-neutralizing antibody. Allograft acceptance (graft survival >100 days) was induced by treating the recipients with CTLA4Ig, a recombinant fusion protein that blocks B7-CD28 T cell costimulation. In vivo alloantigen-driven apoptosis of mature CD4+ and CD8+ T lymphocytes was analyzed in mice repeatedly stimulated with allogeneic splenocytes.

RESULTS

We found that CTLA4Ig induces 100% long-term acceptance of cardiac allografts in wt and gld mice. Similarly, CTLA4Ig induced 100% allograft acceptance in gld recipients injected with TNFalpha-neutralizing antibody. In vivo alloantigen-driven apoptosis of mature CD4+ and CD8+ T cells was significantly reduced in gld mice and in wt mice treated with anti-TNFalpha antibody. However, neutralizing TNFalpha activity in gld mice failed to abrogate alloantigen-driven T cell apoptosis.

CONCLUSIONS

These data indicate that: (1) FasL and TNFalpha expression are not obligatory for the induction of long-term allograft acceptance by CTLA4Ig and (2) FasL- and TNFalpha-independent death pathways contribute to alloantigen-driven T cell apoptosis.

Immunologic 'ignorance' of vascularized organ transplants in the absence of secondary lymphoid tissue

Secondary lymphoid organs (the spleen, lymph nodes and mucosal lymphoid tissues) provide the proper environment for antigen-presenting cells to interact with and activate naive T and B lymphocytes. Although it is generally accepted that secondary lymphoid organs are essential for initiating immune responses to microbial antigens and to skin allografts, the prevailing view has been that the immune response to primarily vascularized organ transplants such as hearts and kidneys does not require the presence of secondary lymphoid tissue. The assumption has been that the immune response to such organs is initiated in the graft itself when recipient lymphocytes encounter foreign histocompatibility antigens presented by the graft's endothelial cells. In contrast to this view, we show here that cardiac allografts are accepted indefinitely in recipient mice that lack secondary lymphoid tissue, indicating that the alloimmune response to a vascularized organ transplant cannot be initiated in the graft itself. Moreover, we demonstrate that the permanent acceptance of these grafts is not due to tolerance but is because of immunologic 'ignorance'.

The alloimmune response and effector mechanisms of allograft rejection

Allograft rejection is the consequence of the recipient's alloimmune response to nonself antigens expressed by donor tissues. Allospecific T lymphocytes are activated by donor peptides which are presented in the context of major histocompatibility complex molecules by either donor or recipient antigen presenting cells. Antigen presenting cells also provide essential costimulatory signals which are required for T cell proliferation and differentiation into either helper or effector lymphocytes. Effector mechanisms of allograft rejection include those mediated by cytotoxic T lymphocytes, macrophages, natural killer cells, and B lymphocytes. Importantly, alloimmune responses are controlled by regulatory molecules which include membrane receptors and cytokines. Novel insights into the interactions between antigen presenting cells and T lymphocytes, and further understanding of how alloimmune responses are regulated, will help in developing effective antirejection and tolerance-inducing strategies.

The role of cytokines, CTLA-4 and costimulation in transplant tolerance and rejection

T cell costimulation and cytokine production play an important role in generating the alloimmune responses that lead to allograft rejection. Recent data, however, provide evidence that costimulatory molecules, such as B7-1 and B7-2, and T cell activating cytokines, such as IFN-gamma and IL-2, also trigger negative feedback mechanisms in T lymphocytes which limit alloimmune responses. These feedback mechanisms are essential for the induction of long-term allograft acceptance and, in certain situations, transplantation tolerance.

The role of the common cytokine receptor gamma-chain in regulating IL-2-dependent, activation-induced CD8+ T cell death

IL-2-dependent, activation-induced T cell death (AICD) plays an important role in peripheral tolerance. Using CD8+ TCR-transgenic lymphocytes (2C), we investigated the mechanisms by which IL-2 prepares CD8+ T cells for AICD. We found that both Fas and TNFR death pathways mediate the AICD of 2C cells. Neutralizing IL-2, IL-2R alpha, or IL-2R beta inhibited AICD. In contrast, blocking the common cytokine receptor gamma-chain (gamma c) prevented Bcl-2 induction and augmented AICD. IL-2 up-regulated Fas ligand (FasL) and down-regulated gamma c expression on activated 2C cells in vitro and in vivo. Adult IL-2 gene-knockout mice displayed exaggerated gamma c expression on their CD8+, but not on their CD4+, T cells. IL-4, IL-7, and IL-15, which do not promote AICD, did not influence FasL or gamma c expression. These data provide evidence that IL-2 prepares CD8+ T lymphocytes for AICD by at least two mechanisms: 1) by up-regulating a pro-apoptotic molecule, FasL, and 2) by down-regulating a survival molecule, gamma c.

Increased susceptibility to immunologically mediated glomerulonephritis in IFN-gamma-deficient mice

It is postulated that IFN-gamma confers susceptibility to immunologically mediated tissue injury. To test this hypothesis, we compared the intensity of accelerated anti-glomerular basement membrane glomerulonephritis between wild-type (IFN-gamma+/+) and IFN-gamma gene knockout (IFN-gamma-/-) mice. This disease model is initiated by binding of heterologous (sheep) anti-glomerular basement membrane Abs to the glomeruli of mice preimmunized with sheep IgG. The secondary cellular and humoral immune responses to the planted Ag then lead to albuminuria and glomerular pathology. We found that IFN-gamma-/- mice or IFN-gamma+/+ mice injected with IFN-gamma-neutralizing Ab develop worse albuminuria and glomerular pathology than IFN-gamma+/+ mice. The humoral response to sheep IgG (serum mouse anti-sheep IgG titers and intraglomerular mouse IgG deposits) was comparable in the IFN-gamma+/+ and IFN-gamma-/- groups. In contrast, IFN-gamma-/- mice mounted a stronger cellular immune response (cutaneous delayed-type hypersensitivity reaction) to sheep IgG than IFN-gamma+/+ mice. These findings provide evidence that endogenous IFN-gamma has a protective role in immunologically mediated glomerulonephritis initiated by foreign Ags.

Regulation of alloantigen-mediated T-cell proliferation by endogenous interferon-gamma: implications for long-term allograft acceptance

BACKGROUND

Recent data suggest that interferon (IFN)-gamma is not an essential mediator of acute rejection but, instead, is critical for the induction of long-term allograft acceptance. The in vivo mechanisms by which endogenous IFN-gamma regulates the alloimmune response and thus facilitates the induction of long-term allograft survival are not known.

METHODS

We examined long-term cardiac and skin allograft survival, alloantigen-induced T-cell proliferation, and alloantigen-induced T-cell apoptosis in wild-type (IFN-gamma+/+) and IFN-gamma gene-knockout (IFN-gamma-/-) mice treated with either B7-CD28 T-cell costimulation blockade alone or B7-CD28 T-cell costimulation blockade combined with donor splenocyte transfusion.

RESULTS

We found that IFN-gamma is essential for long-term allograft survival induced by treating mice with either B7-CD28 T-cell costimulation blockade alone or B7-CD28 T-cell costimulation blockade combined with donor splenocyte transfusion. Alloantigen-induced T-cell proliferation in vivo was significantly greater in IFN-gamma-/- mice than in IFN-gamma+/+ mice, and T-cell costimulation blockade abrogated alloantigen-induced T-cell proliferation in wild-type mice but failed to do so in mice that lack IFN-gamma. In contrast, alloantigen-induced T lymphocyte apoptosis in vivo did not differ between IFN-gamma+/+ and IFN-gamma-/- mice, and T-cell costimulation blockade enhanced alloantigen-induced T-cell apoptosis in both mouse strains.

CONCLUSIONS

These data suggest that endogenous IFN-gamma facilitates the induction of long-term allograft survival by limiting the proliferation of alloactivated T lymphocytes. The data also suggest that B7-CD28 T-cell costimulation blockade exerts immunosuppressive actions by inhibiting the proliferation of activated T lymphocytes and by promoting their apoptosis.

Interferon-gamma is necessary for initiating the acute rejection of major histocompatibility complex class II-disparate skin allografts

BACKGROUND

Although interferon (IFN)gamma has immunostimulatory functions, it is not essential for the acute rejection of fully allogeneic grafts in mice. It is not known whether IFNgamma plays a critical role in the acute rejection of MHC class I- or MHC class II-disparate allografts.

METHODS

We studied the survival of skin allografts transplanted from fully allogeneic (BALB/c), MHC class I-disparate (bml), or MHC class II-disparate (bm12) donors to C57BL/6 wild-type (IFNgamma+/+) and IFNgamma gene-knockout (IFNgamma-/-) recipients. We also investigated the in vitro responses of IFNgamma+/+ and IFNgamma-/- T cells to MHC class II-disparate splenocytes.

RESULTS

We found that IFNgamma-/- recipients reject BALB/c and bml skin grafts at the same rate as IFNgamma+/+ mice but are not capable of rejecting bm12 skin. Despite the inability of IFNgamma-/- mice to reject bm12 skin grafts, IFNgamma-/- T cells displayed vigorous proliferation and cytotoxic responses when stimulated with bm12 splenocytes in vitro. Furthermore, priming IFNgamma-/- recipients with bm12 splenocytes enabled these mice to reject bm12 skin grafts at a normal rate and to mount a cutaneous delayed-type hypersensitivity response to the bm12 antigen.

CONCLUSION

The data demonstrate that IFNgamma is not necessary for generating effector mechanisms associated with acute transplant rejection but that it is required for initiating alloimmune responses to MHC class II-disparate skin grafts.

Breakdown of self-tolerance and the pathogenesis of autoimmunity

Autoimmunity results from a breakdown of physiological mechanisms responsible for maintaining tolerance to self-antigens. These mechanisms are traditionally divided into central and peripheral. T or B lymphocytes that bind to self-antigens with high avidity are deleted or rendered unresponsive during their ontogeny in generative lymphoid organs such as the thymus and the bone marrow (central tolerance). However, this elimination process is incomplete, and regulatory mechanisms that keep mature autoreactive lymphocytes in check are necessary for preventing autoimmunity (peripheral tolerance). Peripheral tolerance mechanisms include passive or activation-induced T and B cell apoptosis, anergy, ignorance, and perhaps suppression of autoreactivity by regulatory lymphocytes. Observations in humans and experimental animals with defined genetic mutations provide examples of autoimmune disorders arising from failure to maintain peripheral tolerance to self. However, multiple factors are necessary for the induction of autoimmunity. For example, bacterial and viral infections may precipitate autoimmune disease in genetically susceptible individuals by exposing autoreactive T cells to cross-reactive peptides (molecular mimicry) or by enhancing lymphocyte stimulation.

Impaired alloantigen-mediated T cell apoptosis and failure to induce long-term allograft survival in IL-2-deficient mice

We examined whether IL-2 regulates alloimmune responses by studying allograft survival in wild-type (IL-2+/+) and IL-2 gene-knockout (IL-2-/-) mice. The acute rejection of vascularized, cardiac allografts and the generation of allospecific CTLs were not impaired in the absence of IL-2. In contrast, blocking the B7-CD28 T cell costimulation pathway with CTLA4Ig induced long-term allograft survival (> 100 days) in IL-2+/+ recipients but failed to do so in IL-2-/- mice or in wild-type mice that had been treated with IL-2-neutralizing Ab around the time of transplantation. Allografts rejected by IL-2-/- recipients exhibited extensive mononuclear cell infiltrates despite CTLA4Ig administration. In vivo allostimulation in the absence of IL-2 led to exaggerated T lymphocyte proliferation and impaired apoptosis of activated T cells in untreated and CTLA4Ig-treated mice. These findings indicate that endogenous IL-2 is required for the induction of long-term allograft survival, and that IL-2 regulates alloimmune responses by preparing activated T lymphocytes for alloantigen-induced apoptosis.

IFN-gamma is critical for long-term allograft survival induced by blocking the CD28 and CD40 ligand T cell costimulation pathways

It is postulated that IFN-gamma production hinders long-term acceptance of transplanted organs. To test this hypothesis, we compared survival of skin and heart allografts in wild-type (IFN-gamma+/+) mice to that in IFN-gamma gene knockout (IFN-gamma-/-) mice. We found that perioperative blockade of the CD28 and/or CD40 ligand T cell costimulation pathways induces long-term skin and heart allograft survival in IFN-gamma+/+ recipients but fails to do so in IFN-gamma-/- mice or in wild-type mice treated with IFN-gamma-neutralizing Ab at the time of transplantation. In vitro studies showed that endogenously produced IFN-gamma down-regulates T cell proliferation and CTL generation in MLCs. These actions of IFN-gamma were not mediated by TNF-alpha production or Fas-Fas ligand interactions. In vivo studies revealed exaggerated expansion and, subsequently, impaired deletion of superantigen-reactive T lymphocytes in IFN-gamma-/- mice injected with staphylococcal enterotoxin B. Taken together, our findings indicate that IFN-gamma does not hinder but instead facilitates induction of long-term allograft survival possibly by limiting expansion of activated T cells.

IL-4 is an endogenous inhibitor of neutrophil influx and subsequent pathology in acute antibody-mediated inflammation

IL-4 is an immunoregulatory cytokine that has in vitro and in vivo anti-inflammatory actions. In this study we investigated whether endogenously produced IL-4 modulates inflammatory processes that occur after Abs bind to target tissue by comparing the severity of glomerulonephritis induced by heterologous anti-glomerular basement membrane Abs in wild-type (IL-4+/+) mice to that of glomerulonephritis induced in homozygous IL-4 gene knockout (IL-4-/-) mice. Two hours after Ab injection, IL-4-/- mice had significantly higher intrarenal intercellular adhesion molecule-1 mRNA expression and intraglomerular neutrophil accumulation than the IL-4+/+ group. Treatment of IL-4-/- mice with recombinant murine IL-4 at the time of disease induction reduced intercellular adhesion molecule-1 expression and neutrophil influx to levels observed in IL-4+/+ kidneys. Four days after Ab administration, untreated IL-4-/- mice developed significantly greater urinary protein excretion, intracapillary fibrinogen deposits, and glomerular hypercellularity than IL-4+/+ mice. These results demonstrate that endogenous IL-4 suppresses neutrophil influx and limits tissue damage in Ab-induced glomerulonephritis, suggesting that IL-4 is an important regulator of acute inflammatory processes.

Differential regulation of expression of the MHC class II molecules RT1.B and RT1.D on rat B lymphocytes: effects of interleukin-4, interleukin-13 and interferon-gamma

Susceptibility to induction of both T helper 1- (Th1) and Th2-mediated autoimmunity is multifactorial and involves genetic linkage to the major histocompatibility complex (MHC) class II haplotype. Brown Norway (BN) rats exposed to mercuric chloride develop a Th2-dependent systemic autoimmunity, whereas Lewis rats, which are highly susceptible to Th1-mediated autoimmunity, develop immune suppression after mercuric chloride exposure. Exposure to mercuric chloride is known to enhance B-lymphocyte expression of the MHC class II molecule RT1.B, predominantly in BN rats. We demonstrate that, in contrast, expression of RT1.D was unmodified on these B cells, whereas both RT1.B and RT1.D were up-regulated on epithelial cells. Regulation of B-cell MHC class II isotype expression was further studied in vitro, using BN rat lymph node (LN) cells. Interleukin-4 (IL-4) strongly enhanced B-cell expression of RT1.B (2.8-fold), whereas RT1.D expression was only slightly, although significantly, modified (1.2-fold). B cells from Lewis rats showed a similar IL-4-induced enhancement of RT1.B expression (2.5-fold), whereas, in contrast, RT1.D expression was unmodified. Exposure of LN cells from BN rats to interferon-gamma induced a moderate increase of B-cell MHC class II expression, predominantly of RT1.B. Strong and rapid enhancement of B-cell RT1.D expression was observed after stimulation by phorbol 12-myristate 13-acetate and ionomycin. Rat IL-13 did not modify B-cell MHC class II expression; however, it induced typical morphological changes in peritoneal macrophages. These experiments demonstrate isotype-specific and strain-dependent regulation of MHC class II expression on rat B lymphocytes, which may be of pathophysiological relevance for the strain-dependent susceptibility for Th1- or Th2-mediated autoimmunity.

Expression of recombinant rat interleukin-13 (IL-13) and generation of a neutralizing rat IL-13 antiserum

Using baculoviral and bacterial systems, we expressed biologically active recombinant rat IL-13 and generated neutralizing rat IL-13 antiserum. Recombinant rat IL-13 produced by baculovirus-infected insect cells stimulated proliferation of TF-1 premyeloid cell line and induced expression of 15-lipoxygenase mRNA in human peripheral blood monocytes. Antiserum generated by immunizing a rabbit with recombinant bacterial rat IL-13 specifically inhibited TF-1 proliferation induced by baculoviral rat IL-13 but did not neutralize human IL-13 mitogenic activity. Western blotting with anti-rat IL-13 serum revealed a approximately 12 kD protein band in supernatants of insect cells infected with recombinant baculovirus carrying the rat IL-13 cDNA. The availability of recombinant rat IL-13 and rat IL-13 antibodies should facilitate studying the role of IL-13 in rat models of human inflammatory disorders.

Blocking the CD28-B7 T cell costimulation pathway induces long term cardiac allograft acceptance in the absence of IL-4

Blocking the CD28-B7 T lymphocyte costimulatory pathway with the recombinant protein CTLA4Ig induces long term allograft survival in rodents. It has been suggested that this results from selective activation of the Th2 immune pathway. To test this hypothesis, we compared vascularized cardiac allograft survival in wild-type (IL-4 +/+) and homozygous IL-4 gene-knockout (IL-4 -/-) mice. We report in this study that long term survival (>100 days) of fully allogeneic grafts can be induced readily in IL-4 -/- recipients treated with a short course of CTLA4Ig. We also demonstrate that IL-4 -/- mice are deficient in Th2-type cytokine expression following in vitro or in vivo allostimulation. These results suggest that IL-4 production and subsequent generation of a Th2-type immune response are not obligatory for CTLA4Ig-induced long term acceptance of vascularized allografts.

Blocking the CD28-B7 T cell costimulation pathway induces long term cardiac allograft acceptance in the absence of IL-4

Blocking the CD28-B7 T lymphocyte costimulatory pathway with the recombinant protein CTLA4Ig induces long term allograft survival in rodents. It has been suggested that this results from selective activation of the Th2 immune pathway. To test this hypothesis, we compared vascularized cardiac allograft survival in wild-type (IL-4 +/+) and homozygous IL-4 gene-knockout (IL-4 -/-) mice. We report in this study that long term survival (>100 days) of fully allogeneic grafts can be induced readily in IL-4 -/- recipients treated with a short course of CTLA4Ig. We also demonstrate that IL-4 -/- mice are deficient in Th2-type cytokine expression following in vitro or in vivo allostimulation. These results suggest that IL-4 production and subsequent generation of a Th2-type immune response are not obligatory for CTLA4Ig-induced long term acceptance of vascularized allografts.

Immunologic determinants of susceptibility to experimental glomerulonephritis: role of cellular immunity

To identify the immunologic mechanisms that influence susceptibility to GN, we compared the severity of accelerated anti-glomerular basement membrane (GBM) nephritis between Lewis (LEW) and Brown Norway (BN) rats and analyzed differences in their immune responses to the nephritogenic immunoglobulin. Lewis (LEW) rats preimmunized with sheep IgG developed proliferative GN with marked proteinuria [peak protein excretion (mean +/- SEM) = 85.3 +/- 15.3 mg/24 hr; normal = 6.4 +/- 0.8 mg/24 hr] after receiving a subnephritogenic dose of sheep anti-rat GBM antiserum. Identically treated Brown Norway (BN) rats, on the other hand, had minimal renal pathology and minimal proteinuria (peak protein excretion = 22.6 +/- 3.1 mg/24 hr; normal = 13.0 +/- 0.6 mg/24 hr). Serum titers of rat anti-sheep IgG isotypes and intraglomerular binding of sheep IgG, rat IgG, and rat complement (C3) were comparable in both strains. In contrast, only LEW rats developed a strong cellular immune response to sheep IgG represented by intrarenal T lymphocyte (OX19+) and monocyte (ED1+) accumulation [LEW vs. BN (mean +/- SEM): OX19+ = 0.60 +/- 0.10 vs. 0.14 +/- 0.01 cells/glomerulus, control = 0.02 +/- 0.01; ED1+ = 4.0 +/- 0.4 vs. 1.0 +/- 0.2 cells/glom., control = 0.8 +/- 0.3] and a significant cutaneous delayed-type hypersensitivity (DTH) reaction [LEW versus BN (mean +/- SEM): delta ear thickness = 0.22 +/- 0.02 vs. 0.05 +/- 0.03 mm; control = 0.04 +/- 0.02 mm]. Upon rechallenge with sheep IgG in vitro, LEW splenocytes expressed a T helper 1 (Th1) cytokine pattern (IFN gamma and IL-2 mRNA, but little IL-4 mRNA) which is associated with delayed-type hypersensitivity reactions. BN splenocytes, on the other hand, expressed IL-4 in addition to IL-2 and IFN gamma mRNA that is consistent with an undifferentiated (Th0) cytokine profile. These studies suggest that humoral immunity to heterologous immunoglobulin planted in the kidney is not sufficient for full expression of accelerated anti-GBM nephritis, and that additional cellular immune mechanisms are required. We conclude that susceptibility to accelerated anti-GBM nephritis is strongly influenced by the host's propensity to mount a Th1-type response and DTH reaction to the disease-inciting immunoglobulin.

Acute rejection of vascularized heart allografts in the absence of IFNgamma

It is generally assumed that IFNgamma plays a central role in acute allograft rejection. To test this hypothesis, we transplanted fully allogeneic (MHC class I and II incompatible) C3H/HeJ (H2k) murine hearts to IFNgamma-/- (IFNgamma gene-knockout) and IFNgamma+/+ BALB/c (H2d) mice. The phenotype of IFNgamma-/- mice was confirmed by demonstrating absent IFNgamma protein production by Con A stimulated IFNgamma-/- splenocytes. Both IFNgamma-/- and IFNgamma+/+ strains rejected transplanted hearts acutely: graft survival (mean +/- SD) was 5.2+/-0.4 and 6.0+/-0.0 days, respectively. Histologic examination revealed similar patterns of acute cellular rejection in both mouse groups. IFNgamma mRNA was present in hearts rejected by IFNgamma+/+ mice but was absent in those rejected by IFNgamma-/- mice. IL-2, IL-4, IL-10, and TNFalpha mRNA expression, on the other hand, was similar in grafts rejected by either strain. We also observed that hapten-induced delayed-type hypersensitivity (DTH) response was significantly reduced but not absent in IFNgamma-/- mice. Our results demonstrate that IFNgamma is not required for acute cellular rejection of fully allogeneic murine hearts. We propose that non-DTH mechanisms of allograft destruction could be enhanced in the absence of IFNgamma and thus lead to robust acute rejection.

Atheroembolic renal disease

Atheroembolic renal disease is an important and often underdiagnosed cause of renal insufficiency in the elderly. Renal damage results from embolization of cholesterol crystals from atherosclerotic plaques in large vessels such as the abdominal aorta to small arteries of the kidney. The typical patient is a white man older than 60 years who has an insidious increase in serum creatinine levels after an arteriographic procedure or vascular surgery. Renal outcome ranges from partial recovery of kidney function to end stage renal disease requiring replacement therapy. Tissue injury from cholesterol crystal embolization is not restricted to the kidneys but also involves the skin, muscles, abdominal organs, and central nervous system resulting in significant morbidity and mortality. Accurate diagnosis is often made by performing a skin, muscle, or renal biopsy. Although effective therapy is lacking, heightened awareness of atheroembolic renal disease is necessary for prompt diagnosis and institution of supportive care.

Anti-inflammatory lymphokine mRNA expression in antibody-induced glomerulonephritis

T-helper subset 2 (Th2) lymphocytes produce interleukin 4 (IL-4) and IL-10, which exert anti-inflammatory actions on monocytes and macrophages. Th1 lymphocytes, on the other hand, secrete interferon-gamma (IFN gamma) which promotes tissue inflammation. The functional dichotomy between TH1 and Th2 lymphocyte subsets suggests that these cells play a regulatory role in inflammatory disease. The participation of Th subpopulations and their lymphokine products in experimental glomerulonephritis (GN) has not been previously evaluated. In this study, we examined renal expression of Th1 and Th2-type lymphokines in the first 48 hours of passive anti-glomerular basement membrane (anti-GBM) GN in the rate. Using the reverse transcriptase-polymerase chain reaction (RT-PCR) method, apparent increase in expression of both TH1-type (IL-2 and IFN gamma) and Th2-type (IL-4 and IL-10) lymphokine mRNA was observed in glomerular-enriched renal tissue obtained from nephritic rats. Induction of monocyte-derived IL-1 alpha and IL-1 receptor antagonist (IL-1RA) mRNA expression was also detected shorted after initiation of GN. Evidence for influx of mononuclear cells including T lymphocytes into the kidney was noted during the same time period as cytokine mRNA expression. Utilizing a monoclonal anti-rat IL-4 antibody, we also detected interleukin 4-producing cells in the renal cortex 24 hours following induction of GN. these experiments demonstrate for the first time anti-inflammatory lymphokine (IL-4 and IL-10) mRNA expression and IL-4 protein production in the kidney during antibody-mediated GN. WE hypothesize that Th lymphocyte subsets modulate glomerular inflammation by producing lymphokines with opposing actions.

Lipoxygenase products in normal and diseased glomeruli

Figure 4 is a schematic summary of current evidence implicating products of the 15-lipoxygenase pathway of arachidonic acid metabolism, principally 15-S-HETE and LXA4, as endogenous antagonists for the proinflammatory actions of leukotrienes. Here, we have presented evidence for the pathophysiologic relevance of leukotrienes in glomerular immune injury and the emerging data on the multifaceted counterinflammatory actions of 15-lipoxygenase products as they relate specifically to the renal glomerulus. Clearly, these concepts are of a broader nature and would be expected to pertain to inflammatory reactions in general, be they in the glomerulus, the renal interstitium, or in extrarenal sites. The extent to which these early observations can be exploited to design strategies for the control of self-destructive inflammatory reactions in the kidney and elsewhere will be determined by future studies. Imaginative design of molecular tools for the manipulation of these enzyme systems in vivo, however, represents a potentially fruitful area of research towards the attainment of a highly worthwhile goal: the cure of glomerulonephritis.

Induction of 15-lipoxygenase by interleukin-13 in human blood monocytes

15-Lipoxygenase (15-LO) catalyzes hydroperoxidation of fatty acids, a reaction of potential relevance to inflammation, membrane remodeling, and atherosclerosis. In human leukocytes, 15-lipoxygenation of arachidonic acid produces 15-(S)-hydroxyeicosatetraenoic acid and lipoxin A4, which suppress white cell chemotaxis, adherence, and activation, and antagonize proinflammatory leukotrienes. Interleukin (IL)-13, produced by T-helper subset 2 (TH-2) lymphocytes, specifically and potently induced 15-LO gene expression and enzyme activity in human monocytes. Among other TH-2 lymphokines, this induction of 15-LO is shared by IL-4 but not by IL-10. Interferon-gamma, a product of TH-1 lymphocytes, blocked IL-13-mediated induction of 15-LO. The induction of the anti-inflammatory 15-LO pathway by IL-13 reveals a new facet of IL-13 biology that supports its role as a cytokine with potential to down-regulate inflammatory pathways. The contrasting effects of interferon-gamma and IL-13 on 15-LO induction demonstrate mechanisms by which T-lymphocyte subsets may modulate macrophage/monocyte function in inflammation or atherosclerosis.

Co-regulated expression of glomerular 12/15-lipoxygenase and interleukin-4 mRNAs in rat nephrotoxic nephritis

Arachidonate 12- and 15-lipoxygenase (LO) products are generated in experimental glomerulonephritis. 15-S-HETE (a 15-LO product) and lipoxins (interaction products between 5-LO and either 12-LO or 15-LO) counteract the proinflammatory actions of leukotrienes. IL-4 has been shown to up-regulate 15-LO gene expression in human leukocytes. Based on homology with human 15-LO, we cloned a 0.76 kbp fragment of a rat LO cDNA from leukocytes stimulated by interleukin-4 (IL-4). The deduced amino acid sequence shows 71.0% and 60.1% homology to human 15-LO and 12-LO, respectively, and 100% homology to a recently cloned "leukocyte type" rat 12-lipoxygenase enzyme, which possesses significant 15-lipoxygenase activity (heretofore referred to as "12/15-LO"). A deletion mutant was utilized to generate internal standard cRNA in quantitative PCR assays. Glomerular 12/15-LO mRNA increased significantly over controls 24 and 48 hours after NTS injection, then decreased at 72 hours. RNA from NTS glomeruli contained higher levels of 12/15-LO mRNA than that from unstimulated peripheral leukocytes, suggesting that 12/15-LO transcription is up-regulated locally in native and/or infiltrating glomerular cells. Glomerular IL-4 mRNA increased markedly 16 hours post-NTS, and was then reduced, suggesting a potential role for T cell-derived IL-4 in directing the expression of 12/15-LO during glomerulonephritis. This represents the first demonstration of tandem regulated in vivo gene expression for a lymphokine (IL-4) and a lipoxygenase, both of which promote counter-inflammatory influences in immune complex-mediated injury.

Cloning of rat interleukin-13 (IL-13) cDNA and analysis of IL-13 gene expression in experimental glomerulonephritis

Using a reverse transcriptase-polymerase chain reaction method, a cDNA for the complete coding region and part of the 5'-untranslated region of rat IL-13 was cloned from rat renal cortex RNA following the induction of anti-glomerular basement membrane antibody-induced glomerulonephritis. The coding region of IL-13 cDNA displays 74% and 87% sequence identity with the coding regions of human and mouse IL-13 cDNA, respectively. The deduced amino acid sequence of rat IL-13 reveals 63% and 79% homology with the human and mouse proteins, respectively. Using the rat IL-13 cDNA as a molecular probe, increased production of IL-13 mRNA in renal and splenic tissue is demonstrated in the first 48 hours of antibody-induced glomerulonephritis in the rat. The data suggest a role for IL-13 in the inflammatory response in vivo.