Regulation of the costimulator B7, not class II major histocompatibility complex, restricts the ability of murine kidney tubule cells to stimulate CD4+ T cells

Pioglitazone modulates immune activation and ameliorates inflammation induced by injured renal tubular epithelial cells via PPARγ/miRNA‑124/STAT3 signaling

Acute kidney injury (AKI) is commonly a result of renal ischemia reperfusion injury (IRI), which produces clinical complications characterized by the rapid deterioration of renal function, leading to chronic kidney disease and increases the risk of morbidity and mortality. Currently, only supportive treatment is available. AKI, which is accompanied by immune activation and inflammation, is caused by proximal tubular injury. The present study investigated the role of tubular epithelial cells as drivers of inflammation in renal IRI and their potential function as antigen-presenting cells, as well as the molecular mechanisms by which peroxisome proliferator-activated receptor-γ (PPARγ) agonists [such as pioglitazone (Pio)] exert reno-protective action in renal IRI. A total of 50 Wistar male albino rats were divided into five groups: Sham + DMSO, Sham + Pio, IRI + DMSO, IRI + prophylactic preoperative (pre) Pio and IRI + postoperative Pio. The histopathological changes in renal tissue samples and the renal epithelial cell expression of CD86, miRNA-124, STAT3, pro-inflammatory cytokines, inducible nitric oxide synthase (iNOS) and Arginase-II were analyzed by immunohistochemistry, reverse transcription-quantitative PCR, western blotting and ELISA respectively. IRI was a potent inducer for CD86 immunoexpression. An ameliorative action of Pio was demonstrated via decreased CD86 immunoexpression, upregulation of miRNA-124, decreased STAT3 expression and beneficial anti-inflammatory effects. The tubular epithelium served a notable role in the inflammatory response in renal IRI. Pio exerted its anti-inflammatory effects via PPARγ/miRNA-124/STAT3 signaling.

Renal proximal tubular epithelial cells exert immunomodulatory function by driving inflammatory CD4+ T cell responses

In immune-mediated glomerular diseases like crescentic glomerulonephritis (cGN), inflammatory CD4⁺ T cells accumulate within the tubulointerstitial compartment in close contact to proximal and distal tubular epithelial cells and drive renal inflammation and tissue damage. However, whether renal epithelial cell populations play a role in the pathogenesis of cGN by modulating CD4⁺ T cell responses is less clear. In the present study, we aimed to investigate the potential of renal epithelial cells to function as antigen-presenting cells, thereby stimulating CD4⁺ T cell responses. Using a FACS-based protocol that allowed comparative analysis of cortical epithelial cell populations, we showed that particularly proximal tubular epithelial cells (PTECs) express molecules linked with antigen-presenting cell function, including major histocompatibility complex class II (MHCII), CD74, CD80, and CD86 in homeostasis and nephrotoxic nephritis, a murine model of cGN. Protein expression was visualized at the PTEC single cell level by imaging flow cytometry. Interestingly, we found inflammation-dependent regulation of epithelium-expressed CD74, CD80, and CD86, whereas MHCII expression was not altered. Antigen-specific stimulation of CD4⁺ T cells by PTECs in vitro supported CD4⁺ T cell survival and induced CD4⁺ T cell activation, proliferation, and inflammatory cytokine production. In patients with antineutrophil cytoplasmic antibody-associated glomerulonephritis, MHCII and CD74 were expressed by both proximal and distal tubules, whereas CD86 was predominantly expressed by proximal tubules. Thus, particularly PTECs have the potential to induce an inflammatory phenotype in CD4⁺ T cells in vitro, which might also play a role in the pathology of immune-mediated kidney disease.

Role of major histocompatibility complex class II expression by non-hematopoietic cells in autoimmune and inflammatory disorders: facts and fiction

It is well established that interactions between CD4(+) T cells and major histocompatibility complex class II (MHCII) positive antigen-presenting cells (APCs) of hematopoietic origin play key roles in both the maintenance of tolerance and the initiation and development of autoimmune and inflammatory disorders. In sharp contrast, despite nearly three decades of intensive research, the functional relevance of MHCII expression by non-hematopoietic tissue-resident cells has remained obscure. The widespread assumption that MHCII expression by non-hematopoietic APCs has an impact on autoimmune and inflammatory diseases has in most instances neither been confirmed nor excluded by indisputable in vivo data. Here we review and put into perspective conflicting in vitro and in vivo results on the putative impact of MHCII expression by non-hematopoietic APCs--in both target organs and secondary lymphoid tissues--on the initiation and development of representative autoimmune and inflammatory disorders. Emphasis will be placed on the lacunar status of our knowledge in this field. We also discuss new mouse models--developed on the basis of our understanding of the molecular mechanisms that regulate MHCII expression--that constitute valuable tools for filling the severe gaps in our knowledge on the functions of non-hematopoietic APCs in inflammatory conditions.

Limited costimulatory molecule expression on renal tubular epithelial cells impairs T cell activation

BACKGROUND/AIMS

MHC molecules are upregulated on renal proximal tubular epithelial cells (TEC) under inflammatory conditions. This allows TEC to act as 'non-professional' antigen-presenting cells (APC). The aim of this study was to compare the costimulatory molecule expression pattern and the T cell activation capacity between renal TEC and professional APC, e.g. bone marrow-derived dendritic cells (BM-DC).

METHODS

Flow cytometry analysis was used to study the costimulatory molecule surface expression on TEC or BM-DC. Ovalbumin-specific CD4 and CD8 T cell activation induced by TEC or BM-DC was compared, in terms of T cell proliferation, cytokine production and CTL activity.

RESULTS

TEC did not constitutively express significant amounts of costimulatory molecules. Stimulation of TEC with IFN-beta or IFN-gamma, but not other tested cytokines, enhanced the expression of PD-L1, ICOS-L and CD40. Compared to BM-DC, TEC only induced suboptimal T cell activation. Blockade of PD-L1 on both APC strongly increased T cell activity. Furthermore, high PD-L1-expressing TEC were more resistant to the cytolysis by CTL.

CONCLUSION

The low costimulatory molecule expression may explain the suboptimal T cell activation by TEC. The IFN-upregulated negative costimulatory molecule PD-L1 on TEC may play a protective role to limit tissue injury during renal parenchymal immune responses.

PD-L1 is expressed by human renal tubular epithelial cells and suppresses T cell cytokine synthesis

T cell activation is affected by both stimulatory and inhibitory co-signaling. MHC class II-expressing renal tubular epithelial cells (TEC) can function as APC for T cells. To study the influence of inhibitory ligands on TEC-mediated T cell activation, we examined the expression of programmed death ligand-1 (PD-L1) on human TEC line HK-2 cells, as well as in normal and diseased kidney samples. RT-PCR, FACS, and immunocytochemistry showed that PD-L1 is constitutively expressed on HK-2 cells, and is dramatically upregulated by IFN-gamma. In situ hybridization and immunohistochemical staining revealed constitutive low expression of PD-L1 on proximal tubules at both mRNA and protein levels in normal kidneys, but much higher expression in kidneys with type IV lupus nephritis. In vitro, pretreatment of IFN-gamma-stimulated HK-2 cells with anti-PD-L1 significantly enhanced IL-2 secretion from cocultured, mitogen-activated Jurkat or human peripheral blood T cells. These results suggest that the PD-L1:PD-1 pathway negatively regulates T cell activation by TEC, and may play an inhibitory role in TEC-mediated immune activation and immunopathology in the kidney.

Autologous stem cells for functional myocardial repair

Recent experimental studies based on innovative hypothesis utilizing cell therapy for the damaged myocardium are recently becoming increasingly promising. The naturally occurring myocardial reparative process is apparently complex and relatively inefficient. It consists of up-regulation of progenitor cell release from the bone marrow after myocardial infarction, homing of these cells to the injured tissue, and differentiation of these progenitor cells into vascular cells and cardiomyocytes within the infarcted tissue. Accordingly, there are two main strategies to regenerate myocardium with autologous stem cells: (1) Extracting stem cells from the bone marrow and injecting these cells into the damaged area, (2) Increasing the efficiency of the naturally occurring reparative process by increasing the mobilization of bone marrow-derived stem cells after myocardial infarction. This review summarizes the growing field of autologous stem cell utilization over the past decade and outlines scientific and clinical hurdles that need to be overcome before this therapy can fully reach its clinical potential.

Normal human kidney HLA-DR-expressing renal microvascular endothelial cells: characterization, isolation, and regulation of MHC class II expression

Human, but not murine, renal peritubular and glomerular capillaries constitutively express class II major histocompatibility (MHC) proteins at high levels in normal human kidney. Expression of class II proteins on renal microvascular endothelial cells (RMEC) makes it available to circulating lymphocytes and imparts a surveillance capacity to RMEC for controlling inflammatory responses. In this report, the co-expression of HLA-DR and the endothelial marker CD31 are used to identify RMEC as a distinct population of cells within a standard renal biopsy using flow cytometry. A three-laser, multicolor flow cytometry analysis using Alexa dyes, developed for characterizing the expression of cell surface antigens, identifies RMEC as a population separate from HLA-DR-expressing leukocytes. HLA-DR RMEC co-express HLA-DP and HLA-DQ. RMEC also express the T cell costimulatory factor CD58 but not CD80, CD86, or CD40. On the basis of high HLA-DR expression, RMEC are isolated for culture using fluorescence-activated cell sorting and magnetic beads. Cultured RMEC require normal basal physiologic concentrations of gamma interferon (gammaIFN) to maintain HLA protein expression. This expression is regulated by CIITA, the MHC class II-specific transcription factor. Four tissue-specific promoters have been described for CIITA. In freshly isolated RMEC, RT-PCR and hybridization using specific oligonucleotide probes to CIITA promoter sequences identify only the statin-sensitive gammaIFN-induced promoter IV of CIITA. Therefore, the constitutive expression of HLA-DR on RMEC in normal human kidney is located in a position for immune surveillance, depends on basal physiologic concentrations of gammaIFN, and may be amenable to regulation with statins.

Costimulatory molecules CD80 and CD86 in human crescentic glomerulonephritis

BACKGROUND

CD80 and CD86, cell-surface molecules found only on antigen-presenting cells (APCs), are required for activation of CD4-postitve (CD4+) T cells by interaction with CD28/cytotoxic T-lymphocyte-associated antigen 4 on T cells. The roles of these molecules in human glomerulonephritis (GN) presently are unknown.

METHODS

Twelve cases of crescentic GN, thought to be a T helper cell-directed delayed-type hypersensitivity-like injury, and 10 controls with non-immunoglobulin A proliferative GN were used. Expression of CD80, CD86, CD4, CD14, CD68, HLA-DR, and intercellular adhesion molecule-1 was investigated in renal tissues using monoclonal antibodies and compared with clinical data at the time of renal biopsy.

RESULTS

CD80+ and CD86+ cells were observed significantly more in crescentic GN than in controls. CD86 was expressed in the glomerulus and interstitium, especially in the crescent, and adhesion to Bowman's capsule and periglomerular areas corresponding to these changes. Tubular epithelial cells showed no CD86 expression, but they expressed CD80, and some of them expressed HLA-DR. CD4, CD14, CD68, and CD86 showed similar distribution patterns. Positive correlations were found between CD86+ cells and CD4+, CD14+, and CD68+ cells. The number of interstitial CD86+ cells correlated with deterioration of renal function. Most CD86+ cells were monocyte/macrophages.

CONCLUSION

This study suggests that the costimulatory molecules CD80 and CD86 have different expressions in human crescentic GN, and CD86 is concerned with crescent formation and CD4+ T-cell accumulations. The majority of APCs are macrophages, and tubular cells also can act as APCs.

Autologous cell transplantation for the treatment of damaged myocardium

Autologous cell transplantation for the treatment of damaged myocardium after myocardial infarction is becoming an increasingly promising strategy. This form of treatment can be divided into 2 treatment strategies: The first uses differentiated cell types to replace the scarred tissue with living cells, while the second strategy uses stem cells in an attempt to regenerate myocardium. Over the past decade, multiple cell types have been used in animal studies, and clinical trials to determine the safety of injecting and engrafting skeletal myoblasts into damaged myocardium are presently being conducted. Animals studies focused on using stem cells to regenerate damaged myocardium have shown a naturally occurring reparative process that consists of up-regulation of progenitor cell release from the bone marrow after myocardial infarction, homing of these cells to the injured tissue, and differentiation of these progenitor cells into vascular cells and cardiac myocytes within the infarcted tissue. Unfortunately, this process occurs with great infrequency. Strategies to regenerate myocardium with stem cells either extract stem cells from the bone marrow and inject these cells into the damaged area or they attempt to increase the efficiency of the natural reparative process by increasing the mobilization of bone marrow-derived stem cells after myocardial infarction. This review summarizes the field of cell transplantation over the past decade, discusses areas of controversy, and proposes an outline of advancements that need to be made in both the clinical and scientific arenas for autologous cell transplantation to fully reach its clinical potential.

Cold ischemia augments allogeneic-mediated injury in rat kidney allografts

BACKGROUND

Some clinical studies demonstrate that kidney grafts with prolonged cold ischemia experience early acute rejection more often than those with minimal ischemia. The mechanism, however, is putative. Therefore, the aim of this study was to unravel the impact of ischemia on the immune response in rat kidney allografts compared with that in isografts.

METHODS

To induce ischemic injury, donor kidneys were preserved for 24 hours in 4 degrees C University of Wisconsin solution before transplantation. No immunosuppression was administered. The histomorphology according to the BANFF criteria for acute rejection and infiltrating cells were assessed at days 1, 2, 3, 4, 6, and 8 post-transplantation.

RESULTS

In allografts, exposure of the kidney to ischemia led to a significantly earlier onset of interstitial cell infiltration and tubulitis compared with nonischemic allografts. The BANFF score of interstitial cell infiltration was 1 +/- 0 vs. 0.25 +/- 0.29 at day 3 and 2 +/- 0 vs. 1.25 +/- 0.25 at day 4. In contrast, in isografts, the effect of ischemia on the histology was not significant. From day 6, the histologic differences between ischemic and nonischemic grafts disappeared. Ischemia led to a more intense expression of P-selectin (day 1), intercellular adhesion molecule-1 (ICAM-1; day 2), and major histocompatibility complex (MHC) class II on endothelium and proximal tubular cells (day 2) in both allografts and isografts. Concurrently with the up-regulated ICAM-1 and MHC expression, significantly more CD4(+) cells and macrophages infiltrated the ischemic allografts at days 2 and 3 and the ischemic isografts at day 4. Importantly, the influx of these cells after ischemia was significantly greater in allografts than in isografts.

CONCLUSIONS

Cold ischemia augments allogeneic-mediated cell infiltration in rat kidney allografts. The earlier onset of acute rejection in 24-hour cold preserved allografts may be prevented by better preservation or treatment using tailored immunosuppression.

Unusual expression of human lymphocyte antigen class II in normal renal microvascular endothelium

BACKGROUND

The human lymphocyte antigen (HLA) class II proteins (DR, DQ, and DP) and DM, a protein involved in loading antigenic peptide onto the class II molecules, have a coordinate regulation that facilitates antigen presentation to CD4+ T cells. CIITA is a specific transcription factor responsible for the coordinate regulation of these genes. DR expression in the kidney was described to be constitutive on renal microvascular endothelium in the early 1980s, but expression of other genes involved in class II antigen presentation (DQ, DP, DM, and CIITA) has not been characterized.

METHODS

Expression of the HLA class II proteins, DM, and CIITA in normal human kidney cortex was evaluated by immunofluorescence microscopy, Northern blots, and reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

The endothelium of glomerular and peritubular capillaries constitutively express DR, as indicated by colocalization of DR and CD31 antibodies. However, the endothelium of larger renal blood vessels is devoid of class II proteins. Capillaries that express DR do not have detectable DQ, DP, or DM by immunofluorescence. Northern blots identified DR, DP, and DM mRNAs but not DQ mRNA. CIITA was amplified by RT-PCR at a level that could account for the class II expressed by the microvascular endothelium.

CONCLUSION

The renal microvascular endothelium constitutively expresses DR without the other class II proteins or DM. This discoordinate expression of HLA class II genes is unusual and may contribute to the kidney's ability to control CD4+ T-cell responses.

Growing kidneys

The number of kidney transplantations performed per year is restricted by the limited availability of donor organs. One possible solution to this shortage is the use of renal xenografts. However, the transplantation of xenografts is complicated by hyperacute and acute rejection. A second possible solution is to 'grow a kidney' from a transplanted renal anlage. It has been postulated that the host immune response might be attenuated after the transplantation of such an anlage (metanephros) instead of a developed kidney. Transplanted metanephroi become chimeric organs in that their blood supply originates, at least partly, from the host. It is possible to transplant a developing metanephros, without the use of immunosuppression, from one rat to another. Transplanted metanephroi grow, differentiate, become vascularized, and function in host rats. 'Growing kidneys' via the transplantation of metanephroi may hold promise as a novel therapeutic approach to the treatment of chronic renal failure.

Transplantation of metanephroi across the major histocompatibility complex in rats

To determine whether transplanted metanephroi grow, differentiate, and function in hosts that differ in major histocompatibility complex loci (RT1 loci in rats) from donors in a defined way, we implanted metanephroi from embryonic day (E) 15 PVG (RT1(c)) rat embryos into the omentum of nonimmunosupressed uninephrectomized PVG-RT1(avl) (host) rats. By 4 wk posttransplantation, metanephroi had grown and differentiated such that glomeruli, proximal and distal tubules, and collecting ducts had normal structure and ultrastructure. At 12 wk posttransplantation, weights of metanephroi were 54 +/- 8 mg. Inulin clearances were 0.9 +/- 0.3 microl. min(-1). 100 g rat wt(-1). In vitro, splenocytes from PVG rats stimulated the proliferation of cells originating from both PVG-RT1(avl) rats in which a transplant had been performed and PVG-RT1(avl) rats with no transplant. Full-thickness PVG-RT1(avl) skin engrafted normally on PVG-RT1(avl) rats in which PVG metanephroi had been previously implanted and metanephroi retained a normal appearance. In contrast, skin from PVG rats sloughed, and the tubular architecture of metanephroi was obliterated by a mononuclear cell infiltrate consistent with acute rejection. Here we show for the first time that functional chimeric kidneys develop from metanephroi transplanted across the MHC into nonimmunosupressed hosts and provide evidence that a state of peripheral immune tolerance secondary to T cell "ignorance" permits their survival.

Astrocytes and central nervous system endothelial cells do not express B7-1 (CD80) or B7-2 (CD86) immunoreactivity during experimental autoimmune encephalomyelitis

The identity of cell types within the central nervous system (CNS) capable of activating T lymphocytes is a fundamental issue in the understanding of multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). To become fully activated, a T cell must recognize its antigen and receive co-stimulation, the latter being optimally delivered via B7-1 and/or B7-2 molecules expressed by the antigen presenting cell (APC). There are conflicting reports regarding whether astrocytes or CNS endothelial cells (EC) can act as fully competent APCs. The present studies were performed to determine whether astrocytes or CNS EC express B7-1 or B7-2 immunoreactivity during EAE. No expression of B7-1 or B7-2 by either astrocytes or EC was detected during acute, remitting, relapsing or chronic EAE, whether EAE was induced by active immunization or cell transfer using five different myelin antigens. These results suggest that neither astrocytes nor CNS EC can deliver co-stimulatory signals via B7 molecules in the setting of murine EAE, rendering them incapable of acting as fully competent APCs.

Virulence and pathogenicity of Helicobacter pylori

Bacterial and host response factors play significant roles in the pathogenicity of H. pylori-related disease manifestations. The complete DNA sequences for two H. pylori strain genomes have been published. The differences in the sequences between these two unrelated strains may enable clinicians to identify rapidly other conserved and potentially virulent genes and products. Whether these two DNA sequences are sufficient representation of the H. pylori genetic heterogeneity is unknown. The host immune response and the cascade of events that occurs with H. pylori infection are being clarified rapidly. Understanding the role of this gastric bacterium in apoptosis and cellular proliferation would enable clinicians to understand its relationship to ulcerogenesis and gastric malignancy. Piecing together many observations related to H. pylori would result in understanding the interaction of H. pylori factors and host responses that lead to the variety of disease manifestations associated with this chronic infection. The development of animal models with H. pylori and other Helicobacter species has set the stage in which in vitro observations can be tested in the in vivo model.

An epithelial cell line that can stimulate alloproliferation of resting CD4+ T cells, but not after IFN-gamma stimulation

It has previously been shown that IFN-gamma-induced up-regulation of HLA class II on the surface of epithelial cells is not sufficient to induce proliferation of allospecific CD4+ T cells in vitro. To further investigate this phenomenon, a human epithelial bladder carcinoma, T24, was induced to constitutively express HLA class II without IFN-gamma stimulation, by permanent transfection with the full-length class II transactivator (CIITA) gene. Proliferation of allospecific T cells to transfected and wild-type cells with and without prior activation with saturating levels of IFN-gamma for 4 days was examined. IFN-gamma-activated T24 did not induce any response from CD4+ T cells. However, T24.CIITA induced significant levels of alloproliferation, which could be abrogated by pretreatment of T24.CIITA with a mAb to LFA-3. Prestimulation of T24. CIITA with saturating levels of IFN-gamma for 4 days also prevented allospecific CD4+ T cell proliferation. These findings suggest that epithelial cells may be intrinsically able to process and present alloantigen and provide adequate costimulation. We propose that IFN-gamma has a secondary, as yet unidentified, effect that acts to negatively regulate this response, at least in some epithelial cells.

Allergens and irritants transcriptionally upregulate CD80 gene expression in human keratinocytes

The human CD80 costimulatory molecule is an important signal between professional antigen-presenting cells and T helper cells. The immunobiology of CD80 expression by keratinocytes, especially during allergic and irritant contact dermatitis, however, is less well understood. CD80 cell surface expression and gene transcription by keratinocytes was increased when keratinocytes were exposed to certain allergens (chemicals that induce inflammation via hapten-specific T cells) and irritants (chemicals that are toxic to epidermal cells). Therefore, the human CD80 promoter was cloned and luciferase reporter constructs containing various promoter fragments were engineered. Promoter mapping of these CD80 constructs in transiently transfected keratinocytes showed that a construct containing the proximal 231 bp immediately upstream of the transcription start site of the CD80 promoter was most active in keratinocytes and was inducible to a level ranging from 2- to 10-fold higher in keratinocytes treated with certain allergens and irritants, compared with untreated keratinocytes. This pattern of promoter fragment activity in keratinocytes is identical to that found in professional antigen-presenting cells. This is the first demonstration that the CD80 promoter is active in keratinocytes and that this activity is further increased in keratinocytes treated with certain allergens and irritants. These data suggest that allergens and irritants may, in part, break peripheral tolerance by their direct effects on keratinocyte costimulatory molecule expression, thereby facilitating interactions with epidermotropic T helper cells via the CD80-CD28 or CTLA-4 pathways.

Characterization of an HLA-A3 restricted human kidney specific T cell clone

BACKGROUND

The tissue specificity of a cytolytic T lymphocyte is determined by the MHC class I bound peptide it recognizes. We have developed an allorestricted human CTL clone, DBS 1.5, that recognizes an epitope found on HLA-A3+ kidney epithelial cells but not on HLA identical B-lymphoblastoid cells. The peptide recognized by this clone has been isolated from HPLC separated, acid eluted peptides from purified HLA class I molecules from HLA-A3+ kidney tissue. This peptide shares no sequence homology with any known protein.

METHODS

To confirm the tissue specificity of the HLA-A3 restricted clone and the peptide it recognizes we have transfected the gene for HLA-A3 into a number of tumor cell lines both human and murine not expressing this antigen. The resulting transfected lines, confirmed by immunofluorescent staining, were used as targets to determine if expression of HLA-A3 alone was sufficient to allow recognition and lysis by the HLA-A3 restricted T cell clone.

RESULTS

The HLA-A3 restricted T cell clone recognized HLA-A3 when expressed on human kidney epithelial cells and to a lesser extent on human lung epithelium and human epidermal cells. Of the tumor lines transfected with HLA-A3 only the human kidney tumor cell line was lysed at a level equal to the original kidney epithelial cell used to develop the clone.

CONCLUSION

These results confirm that this allorestricted human CTL clone is tissue specific recognizing a peptide found in human epithelial tissue that must be presented in the context of HLA-A3 for recognition.

Hypothesis: is renal allograft rejection initiated by the response to injury sustained during the transplant process?

Allograft rejection can be caused by numerous factors such as damage to the donor kidney during surgical removal or implantation, injury sustained during the transport process between the donor and recipient, and suboptimal allograft perfusion during the intra- and post-operative period. In cadaveric allografts, damage can occur during cold storage, during the transit stage between donor and recipient, and hemodynamic instability due to the initial damage that caused its removal from the donor (such as brain death or trauma). We hypothesize that rejection requires recognition of this injury in addition to recognition of alloantigens. If indeed injury proves to be one factor in acute rejection episodes, then therapeutic efforts can be made to reduce injury during the transplantation process.

IFN-gamma and LPS differentially modulate class II MHC and B7-1 expression on murine renal tubular epithelial cells

BACKGROUND

We have investigated inducible class II major histocompatibility complex (MHC) and B7 expression on primary murine renal tubular epithelial cells, called F1K cells, and examined their role in activating nephritogenic T cells derived from kidneys of animals with autoimmune glomerulonephritis.

METHODS

Class II MHC, class II transactivator, and costimulatory molecule expression were evaluated in untreated and cytokine-treated F1K cells by Northern hybridization and flow cytometry. Cell-surface B7-1 expression was evaluated in vitro by immunoprecipitation and in vivo by immunohistochemistry. T-cell activation studies were then performed to assess the functional significance of B7-1 expression on F1K cells.

RESULTS

Coincubation of F1K cells with interferon (IFN)-gamma and lipopolysaccharide (LPS) significantly decreased IFN-gamma-induced class II MHC expression, by both fluorescence-activated cell sorting and Northern analyses. LPS-mediated inhibition of class II MHC in this setting was effected through a decrease in class II transactivator mRNA levels in treated F1K cells. By contrast, IFN-gamma and LPS coincubation induced B7-1 but not B7-2 expression in F1K cells, as detected by Northern analysis, flow cytometry, and immunoprecipitation. In addition, renal tubular staining for B7-1 was apparent in kidneys isolated from IFN-gamma+LPS-treated recipient mice, as well as mice with autoimmune glomerulonephritis. Further studies evaluated the interaction of F1K cells and MR1.3, a nephritogenic CD4+ Th2 clone derived from kidneys of animals with autoimmune glomerulonephritis. Cytokine production assays revealed that F1K cells activated MR1.3 cells if they were pretreated with both IFN-gamma and LPS 48 hours prior to exposure to nephritogenic T cells.

CONCLUSIONS

These studies are the first description of a differential regulation of class II MHC and B7-1 expression in renal tubular epithelial cells mediated by IFN-gamma and LPS. Such findings indicate that discrete proinflammatory stimuli could potentiate antigen-presenting capabilities of renal tubular epithelial cells in vivo and further suggest a direct role of such nonprofessional antigen-presenting cells in modulating renal immune responses.

Polarized expression and function of the costimulatory molecule CD58 on human intestinal epithelial cells

BACKGROUND & AIMS

Intestinal epithelial cells (IECs) can process foreign protein antigens and display antigenic peptides to CD4(+) T lymphocytes via HLA class II molecules. The purpose of this study was to determine the nature of the second, or costimulatory, signal provided by IECs.

METHODS

We investigated surface expression of the costimulatory molecules CD58 (LFA-3), CD80 (B7-1), and CD86 (B7-2) by using flow cytometry, confocal microscopy, and vectorial biotinylation. Antibodies specific for CD58, CD80, and CD86 were used in blocking experiments to assess the role of these molecules in providing a costimulatory signal to CD4(+) T cells by IECs.

RESULTS

CD58, but not CD80 or CD86, was observed to be expressed constitutively on both native IECs and in the IEC lines T84 and HT-29. The surface expression of CD58 was highly polarized and restricted to the basolateral surface of the cell. Antibodies against CD58, but not CD80 or CD86, inhibited the stimulation of CD4(+) T-cell proliferation mediated by IECs.

CONCLUSIONS

CD58 is expressed by polarized IECs in a topologically restricted manner at the region of T-cell contact and can function as a costimulatory molecule in HLA class II-mediated antigen presentation.

The study of self-tolerance using murine haemoglobin as a model self antigen

T cell tolerance to self proteins involves both thymic and peripheral mechanisms. We have used allotypic differences in murine haemoglobin (Hb) to study the development of tolerance to the abundantly expressed self-protein. In Hb beta s/H-2k mice, the response to Hb beta d is directed against Hb beta d (64-76) presented by I-Ek molecules. Using T cell hybridomas and clones specific for this epitope, we have demonstrated that Hb(64-76)/I-Ek complexes and present on antigen-presenting cells in all lymphoid organs including dendritic cells, B cells and macrophages. In the thymus, the presence of these complexes results in negative selection of transgenic T cells with high levels of Hb(64-76)/I-Ek-specific receptor. However, cells with intermediate levels of specific receptor escape negative selection and can be found in the periphery. Under normal circumstances these cells remain tolerant, but can be activated by mechanisms which increase the number of Hb(64-76)/I-Ek complexes.

Cross-presentation of self antigens to CD8+ T cells: the balance between tolerance and autoimmunity

Upon encounter with foreign antigen, tissue-associated antigen-presenting cells (APCs) migrate to draining lymph nodes to prime specific T cells. Using the transgenic RIP-mOVA model, we recently demonstrated that self antigens derived from peripheral tissues are constitutively transported to draining lymph nodes, and can be presented in association with MHC class I molecules by a bone marrow-derived APC population. This form of class I-restricted presentation of exogenous antigen has been referred to as cross-presentation and can induce activation and proliferation of antigen-specific CD8+ T cells. In the absence of CD4+ T cell help, activation of CD8+ T cells is inefficient, and cross-presentation leads to peripheral deletion of autoreactive CD8+ T cells, acting as a mechanism to maintain self-tolerance. If CD4+ T cell help is available, CD8+ T cell responses to self antigens can be rendered immunogenic, leading to autoreactive responses. Whether autoimmunity results from such responses also depends on the tissue location of the antigen. In RIP-mOVA mice, which express the model antigen mOVA (a membrane-bound form of ovalbumin) in the pancreatic beta cells and kidney proximal tubules, OVA-specific CD8+ T cells, activated by cross-presentation, infiltrated the pancreas and caused B cell destruction. Interestingly, however, these cells did not infiltrate the kidney, suggesting that proximal tubular cells are to some extent protected from immune destruction. Analysis of the role of antigen concentration indicates that high doses were required for efficient cross-presentation, suggesting that this pathway is directed towards immune responses to high-dose antigens, such as may be present during viral infection.

Transplantation of developing metanephroi into adult rats

BACKGROUND

Transplantation of developing metanephroi into adult hosts has been proposed as a means to augment host renal function.

METHODS

We implanted whole metanephroi from embryonic day 15 (E15) rats subcapsularly in kidneys or into the omentum of non-immunosupressed adult rat hosts. At the time of implantation, some host rats underwent unilateral nephrectomy (UNX) or unilateral nephrectomy and partial contralateral renal infarction (1 1/2 NX). E15 metanephroi contained only metanephric blastema, segments of ureteric bud, and primitive nephrons with no glomeruli.

RESULTS

Four to six weeks post-implantation, metanephroi from E15 rats had enlarged, become vascularized, and had formed mature tubules and glomeruli. Ureters of metanephroi transplanted into the omentum were anastomosed to hosts' ureters that remained after UNX. Four weeks following ureteroureterostomy, the contralateral kidney was removed. Inulin clearances of seven metanephroi implanted into UNX hosts averaged 0.11 +/- 0.02 microliters/min/100 g (2.42 +/- 0.70 microliters/min/g kidney wt) and the creatinine clearances averaged 0.65 +/- 0.18 microliters/min/100 g. Metanephroi weighed 71 +/- 15 mg (approximately 4% of the contralateral native kidney). The transplanted metanephroi were vascularized by arteries originating from the omentum. Both weights of transplanted metanephroi (145 +/- 24 mg) and inulin clearances of transplanted metanephroi (30.1 +/- 8.7 microliters/min/g kidney weight) were significantly increased in rats that underwent 1 1/2 NX compared to UNX. In contrast, transplantation of developed kidneys resulted in rejection.

CONCLUSIONS

Our findings establish that functional chimeric kidneys develop from metanephroi transplanted in adult hosts.

Discoordinate Surface Expression of IFN-γ-Induced HLA Class II Proteins in Nonprofessional Antigen-Presenting Cells with Absence of DM and Class II Colocalization

We compared HLA class II expression in a human melanoma line (a nonprofessional APC), induced by IFN-γ or by stable transfection with CIITA, with constitutive class II expression in an EBV-transformed B lymphoblastoid cell line (a professional APC) from the same donor. IFN-γ-induced and CIITA-transfected melanoma cells expressed DR, DP, and DQ at levels similar to those expressed by the professional APC; however, DP and DQ proteins and DM-dependent DR epitopes were delayed in appearing on the cell surface when induced by IFN-γ. The delay in cell surface expression of some IFN-γ-induced class II epitopes was observed even though Northern blots demonstrated class II and DM genes to be coordinately transcribed and their mRNA levels to be equivalent to that in B lymphoblastoid cells. Confocal microscopy suggests that discoordinate cell surface expression of class II results from different intracellular trafficking for IFN-γ-induced class II proteins in the melanoma line compared with that in professional APCs. Specifically, although DR and DM proteins were present 2 days after IFN-γ induction, colocalization of DR and DM proteins intracellularly was not apparent in cells at any time after induction. Failure of DR and DM proteins to colocalize suggests that IFN-γ-induced cells lack an intracellular MIIC-like compartment. The absence of a compartment containing DR and DM to facilitate interaction between the two proteins may account for the delayed surface expression of class II epitopes whose formation requires both class II and DM.

Expression of B7-1 and B7-2 costimulatory molecules by human gastric epithelial cells: potential role in CD4+ T cell activation during Helicobacter pylori infection

Human gastric mucosal epithelial cells display class II MHC, the expression of which is increased during Helicobacter pylori infection. These observations suggest that the gastric epithelium may participate as antigen-presenting cells (APC) during local immune responses. The increase in class II MHC expression occurs in parallel with an elevation in gastric CD4+ T cell numbers within and adjacent to the epithelium. Since the expression of either B7-1 (CD80) or B7-2 (CD86) on APC is required for the activation of T cells, it was important to establish human gastric epithelial cells expressed those surface ligands. The expression of B7-1 and B7-2 was detected on human gastric epithelial cell lines and freshly isolated epithelial cells from gastric biopsies with specific antibodies. B7-2 expression was higher than B7-1 at both protein and transcript levels and was increased after crosslinking class II MHC molecules on IFNgamma-treated epithelial cells and in cells pretreated with the combination of IFNgamma and H. pylori. Similarly, B7-2 expression was higher on gastric epithelial cells from H. pylori-infected tissues compared with those from uninfected specimens. To determine the function of these molecules on gastric epithelial cells, antibodies to B7-1 and B7-2 were shown to reduce the ability of the cells to stimulate alloreactive CD4+ T cells. These observations are the first to demonstrate that B7-1 and B7-2 are expressed on mucosal epithelial cells in situ. Thus, the expression of B7-1 and B7-2 by epithelial cells may allow them to act as APC in regulating local responses such as those that occur during infection with H. pylori.

Anomalous expression of costimulatory molecules B7-1, B7-2 and CD28 in primary biliary cirrhosis

BACKGROUND

T lymphocytes require two important signals for efficient activation: 1) recognition of antigens bound to self major histocompatibility complex antigens, and 2) simultaneous stimulation via so-called costimulatory molecules. Interaction of the costimulatory B7 molecules on antigen presenting cells with CD28 on T lymphocytes appears to be particularly important, as it modifies secretion of cytokines, especially interleukin 2. In primary biliary cirrhosis biliary epithelial cells aberrantly express major histocompatibility complex class II antigens and may function as antigen presenting cells.

METHODS

We studied expression of HLA-DR, B7-1, B7-2 and CD28 on cryostat liver sections in 16 patients with primary biliary cirrhosis, three patients each with autoimmune hepatitis and primary sclerosing cholangitis and nine patients with chronic viral hepatitis (five hepatitis B, four hepatitis C) using mouse monoclonal antibodies in an indirect immunoperoxidase technique.

RESULTS

In advanced primary biliary cirrhosis, HLA-DR was found on 57% of bile ducts, B7-2 on 5% of bile ducts, and B7-1 could not be detected on any bile duct. Neither B7-1 nor B7-2 was seen on bile ducts in the four patients with early primary biliary cirrhosis. HLA-DR+ bile ducts also lacked expression of B7 molecules in autoimmune hepatitis. In contrast, HLA-DR, B7-1 and B7-2 were expressed simultaneously on professional antigen presenting cells such as macrophages in epitheloid granulomas.

CONCLUSION

HLA-DR+ biliary epithelial cells in primary biliary cirrhosis insufficiently co-express B7-1 or B7-2 molecules. Therefore, they must either use different costimulatory molecules, or otherwise are deficient in lymphocyte activation. Since recognition of antigen in the absence of B7-CD28 interaction may lead to anergy of lymphocytes, this might contribute to the impaired cytokine secretion found in primary biliary cirrhosis.

Tubulointerstitial responses in the progression of glomerular diseases: albuminuria modulates alpha v beta 5 integrin

Proteinuria represents one of the most unfavorable prognostic factors in the progression of nephropathies. Several lines of evidence support a role for proteinuria per se in the development of interstitial fibrosis, albeit the molecular mechanisms are still unknown. We investigated the potential role of integrins expressed on tubular cells in regulating the synthesis and organization of interstitial matrix or as mediators of tubulointerstitial damage in conditions mimicking the nephrotic milieu. Under basal conditions, cultured tubular cells highly expressed alpha 3 beta 1 and, at focal contacts, alpha v beta 3. In contrast, alpha v beta 5 was weakly and diffusely distributed all over the plasma membrane. Cultures on a variety of matrix substrates (fibronectin, laminin, collagen types I and IV, vitronectin, von Willebrand factor, fibrinogen) did not induce any phenotypic change in integrin expression by tubular cells. Conversely, the addition of albumin resulted in a highly increased membrane expression of beta 5, which was organized in typical focal contacts and was related to the dose of albumin added. Immunofluorescence, flow cytometry, immunoprecipitation and RT-PCR experiments argue for a complex mechanism that includes increased post-transcriptionally regulated protein synthesis, accelerated conversion of precursors to mature forms, and increased surface delivery to discrete adhesive structures. Up-regulation of the beta 5 chain in tubular cells was confirmed in 9 out of 11 kidney biopsies from proteinuric glomerulonephritides including membranous and focal sclerosing glomerulonephritis, while it was not expressed in nonproteinuric kidneys including five biopsy specimens. This is the first report indicating that proteinuria up-regulates the surface expression and distribution of a specific integrin chain on tubular cells. These observations suggest the participation of integrins in a hitherto unexplored mechanism of tubulo-interstitial responses to glomerular injury.

Dominance of tissue-restricted cytotoxic T lymphocytes in the response to allogeneic renal epithelial cell lines

Our current knowledge of cytotoxic T lymphocytes (CTL) is largely derived from studies of effector populations generated in allogeneic mixed leukocyte cultures (MLC) and assayed for lytic activity to lymphoid cell (LC) targets. We herein report that the CTL response to allogeneic renal epithelial cell lines (REC) is dominated by effectors that efficiently lyse REC targets but show little cross-reactivity with LC targets. In contrast, CTL generated against allogeneic spleen cell stimulators (ie., in MLC) lysed REC and LC targets at comparable levels. Lytic activity in both types of cultures was mediated by CD8+TCRalpha/beta+ cells directed to classical H2 class I alloantigens. Anti-REC effectors cross-reacted with fibroblast and macrophage targets but not with targets commonly used to detect alloreactive CTL, such as lipopolysaccharide- or Con A-stimulated lymphoblasts or lymphoid tumor lines, whereas MLC-elicited effectors efficiently lysed all targets. CTL clones propagated from anti-REC cultures exhibited the same allospecificity and tissue specificity as bulk anti-REC effectors. Individual CTL clones were highly heterogeneous in their capacity to recognize the same class I alloantigen expressed on cells derived from different tissues. These data demonstrate that the cellular environment in which CD8 precursors encounter class I alloantigens can have a profound effect on the cell-type specificity of CTL populations. An important implication of these data is that conventional assays of CTL lytic activity may fail to reveal a significant component of the host response to allogeneic tissues.

MHC antigens in interferon gamma (IFN gamma) receptor deficient mice: IFN gamma-dependent up-regulation of MHC class II in renal tubules

MHC class II gene products in parenchymal cells, such as tubular epithelial cells in kidney, may play a role in the regulation of autoimmune reactions. Expression of MHC class II in renal tubular cells is normally very low, but it increases considerably under various pathologic conditions. The predominant role of IFN gamma in up-regulation of MHC class II expression has been demonstrated repeatedly. We tested the existence of alternative pathways of MHC class II regulation using IFN gamma receptor-deficient (IFN gamma R-/-) mice. Mutant and wild type mice received 50 micrograms bacterial endotoxin (LPS) i.p. Four days later the kidneys were removed for immunofluorescence examination. In agreement with published results LPS provoked an increase of immunoreactivity for MHC class I and MHC class II in proximal tubules of wild type mice. While MHC class I up-regulation was strictly IFN gamma receptor-dependent, up-regulation of MHC II was still evident in mutant mice, although less than in wild type mice. Since injection of IFN gamma induced proximal tubular MHC class II expression in wild type mice but not in IFN gamma R-/- mice, an alternative signaling pathway for IFN gamma does not seem to exist. Thus, up-regulation of MHC class II expression in renal tubules does not necessarily require IFN gamma. The markedly patchy pattern of immunofluorescence in IFN gamma R-/- mice suggests that induction of MHC class II after LPS injection may represent renal injury due to shock.