Molecular characterization of a major nephritogenic domain in the autoantigen of anti-tubular basement membrane disease

The role of the immune system in kidney disease

The immune system and the kidneys are closely linked. In health the kidneys contribute to immune homeostasis, while components of the immune system mediate many acute forms of renal disease and play a central role in progression of chronic kidney disease. A dysregulated immune system can have either direct or indirect renal effects. Direct immune-mediated kidney diseases are usually a consequence of autoantibodies directed against a constituent renal antigen, such as collagen IV in anti-glomerular basement membrane disease. Indirect immune-mediated renal disease often follows systemic autoimmunity with immune complex formation, but can also be due to uncontrolled activation of the complement pathways. Although the range of mechanisms of immune dysregulation leading to renal disease is broad, the pathways leading to injury are similar. Loss of immune homeostasis in renal disease results in perpetual immune cell recruitment and worsening damage to the kidney. Uncoordinated attempts at tissue repair, after immune-mediated disease or non-immune mediated injury, result in fibrosis of structures important for renal function, leading eventually to kidney failure. As renal disease often manifests clinically only when substantial damage has already occurred, new diagnostic methods and indeed treatments must be identified to inhibit further progression and promote appropriate tissue repair. Studying cases in which immune homeostasis is re-established may reveal new treatment possibilities.

Conditional abatement of tissue fibrosis using nucleoside analogs to selectively corrupt DNA replication in transgenic fibroblasts

Progressive tissue fibrosis can compromise epithelial function resulting in organ failure. Appreciating evidence suggests that fibroblasts provide fibrogenic collagens during such injury. We further tested this notion by attempting to reduce the physiologic consequences of organ fibrosis through the selective killing of fibroblasts at sites of injury. Here, we report the conditional reduction of tissue fibroblasts using the coding sequence for herpesvirus thymidine kinase (DeltaTK) put under the control of a cell-specific promoter from the gene encoding fibroblast-specific protein 1 (FSP1). Transgenic fibroblasts from mice carrying FSP1.DeltaTK minigenes expressed thymidine kinase concordantly with native FSP1 and, compared to transgenic epithelium, were selectively susceptible to the lethal effects of nucleoside analogs either in culture or during experimental renal fibrosis. The numbers of fibroblasts in fibrogenic kidney tissue were reduced on exposure to nucleoside analogs as was the degree of type I collagen deposition and the extent of fibrosis. Fibroblast reduction following the stress of DNA chain termination highlights the important contribution of cell division during fibrogenesis. Our findings convey a proof of principle regarding the importance of FSP1(+) fibroblasts in fibrosis as well as providing a new approach to treating the relentless scarification of tissue.

Revisiting tolerance induced by autoantigen in incomplete Freund's adjuvant

Injection of autoantigens in IFA has been one of the most effective ways of preventing experimental, T cell-mediated, autoimmune disease in mice. The mechanism that underlies this protection has, however, remained controversial, with clonal deletion, induction of suppressor cells or of type 2 immunity being implicated at one time or another. Using high resolution enzyme-linked immunospot (ELISPOT) analysis, we have revisited this paradigm. As models of autoimmunity against sequestered and readily accessible autoantigens, we studied experimental allergic encephalomyelitis, induced by myelin oligodendrocyte glycoprotein, proteolipid protein, myelin basic protein, and renal tubular Ag-induced interstitial nephritis. We showed that the injection of each of these Ags in IFA was immunogenic and CD4 memory cells producing IL-2, IL-4, and IL-5, but essentially no IFN-gamma. IgG1, but not IgG2a, autoantibodies were produced. The engaged T cells were not classic Th2 cells in that IL-4 and IL-5 were produced by different cells. The IFA-induced violation of self tolerance, including the deposition of specific autoantibodies in the respective target organs, occurred in the absence of detectable pathology. Exhaustion of the pool of naive precursor cells was shown to be one mechanism of the IFA-induced tolerance. In addition, while the IFA-primed T cells acted as suppressor cells, in that they adoptively transferred disease protection, they did not interfere with the emergence of a type 1 T cell response in the adoptive host. Both active and passive tolerance mechanisms, therefore, contribute to autoantigen:IFA-induced protection from autoimmune disease.

Identification of two alternatively spliced forms of human tubulointerstitial nephritis antigen (TIN-Ag)

Tubulointerstitial nephritis antigen (TIN-Ag) is a recently described basement membrane glycoprotein reactive with autoantibodies in some forms of immunologically mediated human tubulointerstitial nephritis. This report presents the complete cDNA and predicted amino acid sequences of two human TIN-Ag mRNA species referred to as TIN1 and TIN2. Translation through the open reading frames of these clones indicates the presence of a signal peptide and putative pre-propeptide. TIN1 additionally contains a characteristic laminin-like epidermal growth factor (EGF) motif and significant homology within the carboxy terminus with the cysteine proteinase family of enzymes. The EGF motif bears important similarities in the positions of cysteines with two motifs in the propeptide of von Willebrand factor. The EGF motif and part of the region that is homologous with the cysteine proteinase family are removed from the TIN2 cDNA. However, the rest of the sequence is identical in these two forms, indicating an alternatively spliced TIN-Ag mRNA product. Both forms contain putative calcium-binding sites. Secondary structure predictions strongly suggest differences between TIN1 and TIN2 leading to the hypothesis that these two forms of TIN-Ag may exhibit differences in their function. Expression studies with appropriate probes demonstrate expression mainly in the kidney and in the intestinal epithelium and lack of expression in other tissues. In the kidney, both TIN1 and TIN2 transcripts are detected, however, TIN1 appears to be the predominant form.

The solution structure of the N-terminal domain of alpha2-macroglobulin receptor-associated protein

The three-dimensional structure of the N-terminal domain (residues 18-112) of alpha2-macroglobulin receptor-associated protein (RAP) has been determined by NMR spectroscopy. The structure consists of three helices composed of residues 23-34, 39-65, and 73-88. The three helices are arranged in an up-down-up antiparallel topology. The C-terminal 20 residues were shown not to be in a well defined conformation. A structural model for the binding of RAP to the family of low-density lipoprotein receptors is proposed. It defines a role in binding for both the unordered C terminus and the structural scaffold of the core structure. Pathogenic epitopes for the rat disease Heymann nephritis, an experimental model of human membranous glomerulonephritis, have been identified in RAP and in the large endocytic receptor gp330/megalin. Here we provide the three-dimensional structure of the pathogenic epitope in RAP. The amino acid residues known to form the epitope are in a helix-loop-helix conformation, and from the structure it is possible to rationalize the published results obtained from studies of fragments of the N-terminal domain.

Induction of passive Heymann nephritis with antibodies specific for a synthetic peptide derived from the receptor-associated protein

Passive Heymann nephritis (pHN) is an experimental rat model for human membranous glomerulopathy. In pHN, the formation of subepithelial immune deposits (ID) involves as antigenic targets the membrane glycoprotein gp330/megalin and the 44-kD receptor-associated protein (RAP). A single binding site for ID- inducing antibodies (Abs) was previously mapped to the 86 NH2-terminal amino acids of RAP (RAP1-86). To further narrow this epitope, Abs eluted from the glomeruli were immunoblotted on membranes that were loaded with overlapping synthetic peptides representing the amino acid sequence of RAP (SPOTs system). Two adjacent Ab-binding domains with the sequences PVRLAF, (amino acids 39-44) and HSD-LKIQE (amino acids 46-53), which were separated by a single L residue at amino acid 45, were detected. Rabbit Abs raised against synthetic peptides containing these domains individually (P31-44 and P46-53) failed to procedure glomerular IDs. By contrast, Abs raised against a larger composite peptide (P31-53) induced IDs within 3d that were firmly cross linked to the glomerular basement membrane. These data suggest that Ab binding in vivo depends on the conformation of the antigenic target sequence that is preserved in the synthetic peptide P31-53, which covers the entire Ab-binding domain of RAP but not in its subdomains, P31-44 and P46-53. Collectively, these results locate the sole ID-inducing epitope of RAP to amino acids 39-53.

Heterogeneous T cell receptor V beta gene repertoire in murine interstitial nephritis

Anti-tubular basement membrane disease (alpha TBM) produces T cell-mediated interstitial nephritis in SJL/J mice following immunization with heterologous renal tubular antigen. Initial mononuclear infiltrates appear in vivo after six to eight weeks, with subsequent progression to renal fibrosis and endstage kidney disease. Cultured lymph node derived nephritogenic T cells from these mice react to a small epitopic region of the 3M-1 target antigen and share a common amino acid motif in their V beta CDR3 regions. We now have used RT-PCR to further characterize the renal expression of T cell receptor (TcR) V beta gene repertoires during the course of this disease. Individual kidneys with focal mononuclear infiltrates characteristic of early alpha TBM disease express up to three different TcR V beta genes; however, the same V beta genes are not found in all kidneys at the same early stage of injury. DNA sequencing of the V beta RT-PCR products reveals a heterogeneous population of VDJ recombinations and deduced CDR3 amino acid sequences. Our studies do not support TcR V beta region gene restriction in histologically-detectable alpha TBM disease, but are more consistent with a dynamic, organ-specific autoimmune disease, directed at multiple autoantigenic epitopes.

Identification of a cDNA encoding tubulointerstitial nephritis antigen

Tubulointerstitial nephritis antigen (TIN-ag) is a 58-kDa basement membrane glycoprotein that is recognized by human autoantibodies in certain forms of tubulointerstitial nephritis. To further characterize this macromolecule and isolate cDNAs encoding TIN-ag, amino acid sequences from tryptic peptides were used to design and synthesize primers in order to amplify a probe for screening a rabbit kidney cortex cDNA library. A cDNA encoding TIN-ag was cloned and sequenced. The predicted amino acid sequence deduced from this cDNA includes the chemically determined sequences of peptides derived from TIN-ag, supporting its authenticity. The predicted amino acid sequence also shows that the carboxyl-terminal region of the molecule exhibits a 30% homology with human preprocathepsin B, a member of the cysteine proteinase family of proteins. A domain in the amino-terminal region of TIN-ag contains an epidermal growth factor-like motif that shares homology with laminin A and S chains, alpha 1 chain of type I collagen, von Willebrand's factor, and mucin, suggesting structural and perhaps functional similarities among these molecules. Immunoprecipitation of in vitro generated recombinant protein using a TIN-ag-specific monoclonal antibody (A8), confirms the identity of the isolated TIN-ag cDNA. In this report the cDNA and predicted amino acid sequences of TIN-ag are presented. Knowledge of the primary structure of TIN-ag will facilitate our understanding of the molecular structure of this novel basement membrane component and may provide clues toward understanding its functional role.

T cells reactive to an inducible heat shock protein induce disease in toxin-induced interstitial nephritis

T cells reactive against immunodominant regions of inducible heat shock proteins (HSPs) have been identified in the chronic inflammatory lesions of several experimental autoimmune diseases. Since HSPs are known to be induced by a number of renal tubular epithelial cell toxins associated with chronic interstitial nephritis, we investigated the relevance of HSP expression and T cell reactivity to HSP70 in a model of progressive inflammatory interstitial nephritis. Chronic administration of cadmium chloride (CdCl2) to SJL/J mice induces HSP70 expression in renal tubular cells 4-5 wk before the development of interstitial mononuclear cell infiltrates. CdCl2 also induces HSP70 expression in cultured tubular epithelial cells from SJL/J mice. CD4+, TCR-alpha/beta+ T cell lines specific for an immunodominant HSP peptide are cytotoxic to heat stressed or CdCl2-treated renal tubular cells. Such HSP-reactive T cells mediate an inflammatory interstitial nephritis after adoptive transfer to CdCl2-treated mice at a time when immunoreactive HSP70 is detectable in the kidneys, but before the development of interstitial mononuclear cell infiltrates. T cells isolated from the nephritic kidneys of mice treated with CdCl2 for 13 wk are also cytotoxic to heat shocked or cadmium-treated tubular cells. These kidney-derived T cells additionally induced interstitial nephritis after passive transfer, indicating their pathogenic significance. Our studies strongly support a role for HSP-reactive T cells in CdCl2-induced interstitial nephritis and suggest that the induction of HSPs in the kidney by a multitude of "non-immune" events may initiate or facilitate inflammatory damage by HSP-reactive lymphocytes.

Immunoregulation and TGF-beta 1. Suppression of a nephritogenic murine T cell clone

Transforming growth factor beta (TGF-beta) has been clearly linked in several model systems to the development of pathologic extracellular matrix deposition in the glomerulus and interstitium. TGF-beta additionally exerts multiple immunomodulatory effects on T and B lymphocytes, including growth inhibition. Such pleiotropic effects make it difficult to predict how TGF-beta might directionally affect the expression of T cell mediated kidney disease. We have examined the effects of TGF-beta 1 on the activity of effector T cells in a model of autoimmune interstitial nephritis. M52.26 is an antigen-specific, nephritogenic, cytotoxic T cell clone. TGF-beta 1 mediates a concentration-dependent inhibition of M52.26-directed cytotoxicity of tubular epithelial cells in culture, and also of M52.26-mediated transfer of interstitial nephritis to syngeneic recipients. The loss of these functional activities is associated with distinct changes in cytokine gene expression in M52.26. These cytokine alterations consist of a loss of IFN-gamma and perforin expression, and an up-regulation of TGF-beta expression, which is likely relevant to the observed effector T cell inactivation.

Inhibition of murine nephritogenic effector T cells by a clone-specific suppressor factor

We have used a murine model of organ-specific autoimmunity to characterize therapeutic modalities capable of down-regulating the cellular limb of the autoimmune response. Murine interstitial nephritis is an autoimmune disease mediated by tubular antigen-specific CD8+ nephritogenic effector T cells which are delayed-type hypersensitivity (DTH) reactive and cytotoxic to renal epithelial cells. Previous studies have demonstrated that disease can be suppressed with experimentally induced populations of T cells (Ts1 and Ts2 cells) obtained after injection of tubular antigen-coupled splenocytes into syngeneic mice. As the target of Ts2 is the CD8+ effector T cell, we have evaluated its effects on nephritogenic effector T cell clones isolated from diseased animals. Our studies demonstrate that soluble proteins expressed by Ts2 cells (TsF2) specifically abrogate the DTH, cytotoxic, and nephritogenic potential of M52 cells, although T cell receptor and IL-2 receptor expression are unchanged in these unresponsive M52 clones. TsF2-induced inhibition is dependent on new mRNA and protein synthesis. In a cytotoxic clone, M52.26, exposure to TsF2 induces expression of TGF-beta 1 which is, in turn, required for inhibition of cytotoxicity and nephritogenicity. Our studies are consistent with TGF-beta 1 behaving, at least in some T cells, as a nonspecific final effector of clone-specific suppression.

Molecular analysis of the helper T cell response in murine interstitial nephritis. T cells recognizing an immunodominant epitope use multiple T cell receptor V beta genes with similarities across CDR3

Anti-tubular basement membrane disease (alpha TBM disease) produces T cell-mediated interstitial nephritis in SJL mice after immunization with renal tubular antigen. Initial mononuclear infiltrates appear in vivo after several weeks, with the subsequent progression to renal fibrosis and end stage renal disease over many months. We have analyzed the fine specificity of the autoreactive helper T cell repertoire in alpha TBM disease through the isolation and characterization of a panel of CD4+ Th1 clones harvested after 1-2 wk from animals immunized to produce disease. All clones capable of mediating alpha TBM disease are directed towards a 14-residue immunodominant epitope (STMSAEVPEAASEA) contained within the target antigen, 3M-1. Evaluation of the T cell receptor (TCR) V beta repertoire used by these autoreactive T cells reveals the use of several V beta genes, but with some preference for V beta 14. Sequencing across the putative CDR3 region of the TCR beta chains suggests that common amino acids at the V beta(N)D beta junction and the D beta(N)J beta junction may contribute to the specific ability of these cells to recognize the immunodominant epitope.

The target antigen of anti-tubular basement membrane antibody-mediated interstitial nephritis

Our previous studies showed that 54 kD and 48 kD tubular basement membrane (TBM) proteins were the major form of the target antigen involved in anti-TBM antibody-mediated tubulo-interstitial nephritis in humans. In those studies, we isolated the 54 kD glycoprotein (named gp54) from collagenase-digested bovine TBM. NH2-terminal amino acid sequencing indicated that gp54 represented a newly defined glycoprotein. In this study, we further characterized the target antigen, using mouse monoclonal antibodies to gp54 and polyclonal anti-gp54 peptide antibody. Two monoclonal antibodies (H79 and H80) were established, and they reacted, by immunofluorescence, predominantly with the proximal TBM of humans, rabbits, and Wistar, Sprague-Dawley, and Brown-Norway rats, but not with that of Lewis rats. They were also fixed by blotting intensely to the 54 kD component and weakly to the 48 kD component of collagenase-digested human TBM. In vivo transfer of H79 to Wistar rats showed extensive linear binding of mouse IgG to the TBM and the basal membrane of the small intestine; however, no pathologic changes were seen by light microscopy. The anti-gp54 peptide antibody reacted with both the 54 kD and 48 kD TBM components of human TBM. mRNA was prepared from rabbit kidneys, and fractionated to enrich mRNA encoding the 54 kD and 48 kD peptides. On in vitro translation experiments with the mRNA fraction, the 54 kD and 48 kD peptides were immunoprecipitated with anti-gp54 antibodies. These findings indicate that the 54 kD and 48 kD components are encoded with different mRNA, but that they share the same antigenic epitope.(ABSTRACT TRUNCATED AT 250 WORDS)

Immune modulation of biologic systems in renal somatic cells

The various theories discussed here suggest that somatic renal cells are susceptible to biologic modulation by the immune system independent of an inflammatory effect. (1) The mode of repression of type IV collagen synthesis by novel, soluble antigen-binding proteins, the down-regulation of class II MHC expression with interruption of antigen presentation to epithelia after selective gene regulation by antibody, and the diverse interactions of antibody with renal glomerular cells producing functional disturbances in endocytosis and permselectivity; (2) modification of surface-antigen composition; (3) alteration of matrix deposition, remodeling and composition; (4) biophysical perturbation of cytoskeletal and cell membrane components; (5) and lastly, alterations in cell adhesion through cell-surface alterations, all lend testimony to the richness of the signal transduction pathways in somatic cells. Although the preceding examples represent only a small fraction of those which may take place within the glomerular and tubular microenvironments, these paradigms may nevertheless serve as new models upon which one can consider the multitude of potential communications between disparate biologic systems that connect in complex organisms.

The inflammatory function of renal glomerular mesangial cells and their interaction with the cellular immune system

The autoimmune nature of chronic progredient glomerular diseases has been well established. Like in other chronic inflammatory diseases, the active role of organ-borne cells has become increasingly apparent--both for the inflammatory process and for the initiation and perpetuation of the immune reaction. In most forms of glomerulonephritis, intrinsic glomerular mesangial cells are likely candidates to come into intimate contact with immune cells such as monocytes or lymphocytes. On the basis of cell culture studies we would like to integrate the current knowledge available about the responsiveness of mesangial cells to inflammatory agents and the resulting secretory capacity and, moreover, their possible role in sustaining chronic inflammatory injury and autoimmune reactions through a direct interaction with lymphocytes. Apart from being responsive to physiological stimuli such as angiotensin II, glomerular mesangial cells are predominantly activated by agents related to inflammation. This includes exogenous substances such as the components of gram-negative bacteria and an array of highly potent immunological stimuli like antigen-antibody complexes, activated complement, or various cytokines. The transformation of resting mesangial cells to proliferating cells with an accompanying expansion of their secretory profile and responsiveness is due to mediators like platelet-derived growth factor, transforming growth factor, and others. Numerous low-molecular-weight substances (O2-, H2O2, NO, platelet-activating factor, eicosanoids), proteins (proteinases, matrix components, interleukins 1 and 6, colony-stimulating factors, growth factors), and cell-surface molecules released or expressed by mesangial cells participate in the inflammatory process. Among these products interleukin 1 and/or 6, class II major histocompatibility antigen and integrins also support an interaction with the cellular immune system. It has been well documented that mesangial cells induced in vitro by recombinant T-cell lymphokines, such as interferon-gamma, do express MHC II and ICAM-1 and could function as antigen-presenting cells. However, and perhaps more interestingly, our own recent experiments with cocultures of syngeneic mouse lymphocytes and mesangial cells have demonstrated that T-cells are directly activated by cultured mesangial cells, thus resembling a mesangial cell-specific autoimmune reaction. In parallel to clinical studies searching for a mesangial autoantigen these experiments might help to elucidate the mechanisms of initiation and perpetuation of mesangial cell-dependent autoimmune glomerulonephritis.

Tubular antigen-binding proteins repress transcription of type IV collagen in the autoimmune target epithelium of experimental interstitial nephritis

We have been studying immune interactions with somatic cells using a tubular antigen-binding protein (ThF) secreted by helper T lymphocytes harvested from mice that have an autoimmune form of interstitial nephritis called anti-tubular basement membrane disease. This ThF, although characterized originally because of its ability to induce effector T cells, additionally recognizes the nephritogenic 3M-1 antigen expressed by its target renal tubular epithelium. We believe these proteins, in general, may modulate directly some homeostatic functions in organ-derived cells, and now report that our ThF represses specifically the cellular transcription and secretion of basement membrane type IV collagen in tubular epithelium. These in vitro findings of reduced levels of mRNA encoding type IV collagen correlate well with in situ hybridization studies performed on kidneys expressing early autoimmune lesions, and predict a progressive drop in the expression of type IV collagen in the interstitium. Such a novel and unexpected repression of transcription of type IV collagen might easily impart or facilitate permanent change in the infrastructure of kidney architecture during autoimmune injury and, perhaps, contributes to the process of tubular atrophy attendant to prolonged renal inflammation.

Biosynthetic and proliferative characteristics of tubulointerstitial fibroblasts probed with paracrine cytokines

Fibroblasts in parenchymal organs potentially contribute extracellular matrix to local fibrogenic processes. This contribution, in some circumstances, may be initiated by cytokines disseminated from inflammatory lesions. Different populations of fibroblasts, however, might respond distinctively to this cytokine bath depending on the microenvironment in which they reside. We have begun to explore this issue using syngeneic, low-passage fibroblasts cultured in serum-free media that were derived originally from the dermis (DFBs) and from tubulointerstitium (TFBs) of the kidney. Our findings indicate that, while fibroblasts from each compartment appear similar at the ultrastructural level, there are a variety of functional differences which distinguish their proliferative response, and their collagen secretory response (types I, III, IV, and V) following challenge with various doses of immune-relevant cytokines (TGF beta, EGF, IL-1, IL-2 and gamma IFN) in culture. DFBs, for example, express more surface EGF receptors than do TFBs, and, as a consequence, exhibit a more robust proliferative response to EGF in serum-free media. Unstimulated DFBs also secrete more collagen types I and III than TFBs, while unstimulated TFBs secrete more types IV and V. The expression of these collagens in TFBs was confirmed by Northern blot hybridization. When these sets of fibroblasts were further stimulated by cytokines, some of the cytokines not only differentially effect the secretion of various species of collagens within the same group of cells, but also between cells from populations which are anatomically distinct. DFBs, furthermore, at mid-level doses of cytokine, demonstrated a general trend towards less secretion of all types of collagen (particularly for TGF beta, EGF, and IL-2), while TFBs seemed less repressive. In TFBs the cytokine-induced responses for collagen types I and III tended to be discordant, and for types I and IV EGF inhibited, while TGF beta stimulated the secretory process. These findings speak collectively for the presence of a functional heterogeneity among organ-based populations of syngeneic fibroblasts in normal tissues.

Isolation and characterization of cDNA from renal tubular epithelium encoding murine Rantes

We have been interested in identifying proinflammatory molecules which might play a role in attracting monocytes and T cells to the kidney. Some of the new intercrines are potential candidates. In this report we have isolated cDNA encoding murine Rantes (MuRantes) from renal tubular epithelium (MCT cells). MuRantes is a 91 amino acid member of the -C-C- or intercrine beta subgroup of the Scy superfamily. The amino acid sequence for mature MuRantes was deduced from its coding cDNA and was found to be 90% homologous to its mature human counterpart (HuRantes). MCT epithelium expresses a single mRNA transcript for MuRantes of approximately 1100 bp. The MuRantes protein could be detected in cell lysates of MCT epithelium by western blotting and in the cytoplasm of MCT cells by immunofluorescence using a polyclonal antibody generated against HuRantes fusion protein. A search protocol using MuRantes-specific primers and cDNA amplification revealed that mRNAs for MuRantes are expressed additionally in syngeneic mesangial cells (MMC cells), whole kidney, liver, and spleen, as well as in nephritogenic antigen-specific CD4+ helper and CD8+ effector T cells. cDNA amplification studies also demonstrated a significant elevation in mRNA transcripts encoding MuRantes in response to the stimulation of MCT epithelium with TNF alpha and IL-1 alpha in culture, but not with TGF beta, gamma IFN, or IL-6. Our findings indicate that proximal tubular epithelium is an authentic source of MuRantes, and that transcripts encoding MuRantes are responsive to the modulating influence of paracrine factors having a known role in the development of parenchymal injury.

Effector mechanisms in organ-specific autoimmunity. I. Characterization of a CD8+ T cell line that mediates murine interstitial nephritis

To further investigate mechanisms of cell-mediated tissue destruction in an organ-specific autoimmune disease, we have established and characterized a nephritogenic CD8+ T cell line. This target antigen-specific effector T cell line, M52, was derived from bulk populations of CD8+ T cells isolated from susceptible animals immunized to produce anti-tubular basement membrane (alpha TBM) disease. Our studies show that M52 retains the phenotypic and functional characteristics of nephritogenic T cells induced in vivo. M52 mediates antigen-specific delayed-type hypersensitivity (DTH) responses to the target antigen 3M-1, it is cytotoxic to 3M-1-expressing renal tubular epithelial cells in vitro, and it adoptively transfers interstitial nephritis to naive syngeneic recipients. Clonal analysis of these nephritogenic CD8+ T cells reveals distinct functional phenotypes within the M52 cell line. We have isolated a cytotoxic CD8+ clone, M52.26, which is not DTH-reactive to 3M-1, and multiple DTH-reactive clones which mediate less efficient cytotoxicity to 3M-1-expressing target cells. Cytofluorographic analysis of four randomly selected clones reveals alpha beta T cell receptor expression. Further characterization of these functionally distinct CD8+ T cell clones will help to define their respective roles in mediating tubular epithelial cell injury and the inflammatory lesion of autoimmune interstitial nephritis.

Analysis of the cDNA sequence encoding MHC-A beta in tubular epithelium from mouse kidney

Class II gene products of the major histocompatibility complex (MHC) are not expressed usually in abundance on normal epithelium. The cell surface visibility of such proteins for the immune system is thought to be limited protectively in order to minimize inflammation consequent to the recognition of self-antigens in parenchymal structures by T lymphocytes. In the current experiments we investigated whether the previously recognized sparseness of A beta on the surface of tubular epithelial cells might be accounted for by a protein coding difference deduced from the primary structure of its transcript compared with sequence from lymphoid cells that normally express A beta in generous amounts. We demonstrate, however, using clones obtained from a cDNA library prepared from tubular epithelium harvested from H-2s (A beta/alpha+; E beta/alpha-) mice susceptible to autoimmune interstitial nephritis, that the nucleotide sequence encoding the class II A beta chain in cells from both compartments is essentially identical. Our findings suggest that there is no primary structural aberrancy in the coding region of parenchymal A beta that would contribute to its low expression. The protective tolerance afforded by reduced numbers of class II molecules in normal tissues is, therefore, more likely the result of repressive regulatory processes.

Expression of homeobox genes in a proximal tubular cell line derived from adult mice

We have been studying the expression of several homeobox genes in cultures of proximal tubular epithelium (MCT cells) harvested from adult mus musculus. Hox genes 2.1, 2.3, and 3.3, in particular, are all expressed at low levels in resting MCT cells. The expression of Hox 2.1 and 3.3 were not influenced by mitogenic (epidermal growth factor: EGF, and platelet-derived growth factor: PDGF) nor by hypertrophogenic cytokines (angiotensin II: Ang II) in serum-free media. Transcripts for Hox 2.3, however, were elevated in MCT cells by Ang II. EGF, and serum treatment, as early as 30 minutes after their addition, whereas no change, or slight reductions were observed with transforming growth factor beta (TGF beta), PDGF, and gamma-interferon (gamma IFN). Hox 2.3 was also super-induced by serum, in the presence of cycloheximide, in cells rested previously in serum-free media, suggesting that new protein synthesis was not required for expressive augmentation. The induction of Hox 2.3, moreover, was not specific for tubular epithelium, since the gene could be activated in tubulointerstitial fibroblasts after treatment with EGF. These experiments collectively represent a first report regarding the characterization of transcripts encoding homeoboxes in adult cells derived from renal tissue. The putative DNA-binding properties of homeobox proteins in general, the prompt and rapid induction of Hox 2.3 by morphogenic cytokines in tubulointerstitial cells, and the observed effect of cycloheximide on this gene, all indicate that Hox 2.3 might have a role in the general activation of mature somatic cells, as an immediate early event. probably in the capacity of a nuclear trans-acting factor.