Pathogenesis Of Crescentic Glomerulonephritis Research Articles

#2837 Novel therapeutic for crescentic glomerulonephritis through targeting CLDN1 in parietal epithelial cells

Abstract Background and Aims Crescentic glomerulonephritis (CrGN) is the final mode of kidney injury common to several immune-mediated kidney diseases. CrGN is characterized by extensive glomerular parietal epithelial cells (PECs) proliferation forming crescents. The destructive crescent is then progressively replaced by fibrosis. Currents therapies for CrGN do not directly target the deleterious response of resident kidney cells. In a pathological context, claudin-1 (CLDN1), a transmembrane protein involved in epithelial tight junctions, can be exposed outside the tight junctions and mediate pro-fibrotic pathways and extracellular matrix (ECM) remodelling. Lixudebart (formerly ALE.F02) is a first-in-class monoclonal antibody that specifically targets and blocks exposed CLDN1 in injured epithelial cells. A phase II clinical trial is under way for patients with antineutrophil cytoplasmic antibody-associated vasculitis (AAV) with rapidly progressive glomerulonephritis which induces kidney fibrosis (RENAL-F02, NCT06047171). CLDN1 is highly expressed by glomerular PECs. This study investigated the functional role of CLDN1 in CrGN and the potential benefit to target CLDN1 in CrGN. Method CLDN1 expression in renal tissues of CrGN patients was analyzed using kidney multicolor immunofluorescence staining and spatial transcriptomics. Correlation between CLDN1 expression and clinical endpoints (eGFR, proteinuria), disease biomarkers and crescent evolution were studied. A spatially resolved molecular roadmap from CLDN1+ crescentic glomeruli was conducted. Proof-of-concept studies using anti-CLDN1 mAb were performed in preclinical models of CrGN. Results In tissues (n = 150) of patients with AAV and IgAN, multicolor immunofluorescence revealed up-regulated CLDN1 expression by cellular and fibrocellular crescents. At the time of diagnostic kidney biopsy, glomerular CLDN-1 expression was correlated with podocyte loss (as measured with P57 staining) and fibronectin area. The extent of dual expression of CLDN1 and CD44 at the surface of active PECs was associated with poor renal outcome (eGFR < 30 ml/min) in AAV and IgAN patients with a median follow-up of 2.5 and 3.7 years respectively. Spatial transcriptomics analysis highlighted the association between CLDN1+ crescentic glomeruli and ECM genes. Treatment with anti-CLDN1 mAb reduced albuminuria, improved kidney function and decreased fibrosis biomarkers in nephrotoxic serum-induced CrGN in mice. Conclusion Our results suggest a functional role of CLDN1 in the pathogenesis of CrGN, providing preclinical proof-of-concept for anti-CLDN1 antibodies as a novel therapeutic approach in patients with CrGN.

Vasculitis and crescentic glomerulonephritis in a newly established congenic mouse strain derived from ANCA-associated vasculitis-prone SCG/Kj mice

Lupus nephritis (LN) is the secondary glomerulonephritis (GN) involved in systemic lupus erythematosus (SLE) and a typical immune complex-type GN. Antineutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV) is an autoimmune disease characterized by systemic vasculitis and pauci-immune-type crescentic glomerulonephritis (CrGN) with ANCA production. Human AAV causes death due to lung haemorrhage and end-stage renal disease, for which renal replacement therapies are necessary. The SLE/AAV overlap syndrome was recently reported in humans. The spontaneous crescentic glomerulonephritis-forming/Kinjoh (SCG/Kj) mouse is a unique model of human AAV showing production of myeloperoxidase (MPO)-ANCA. We previously discovered seven disease susceptibility quantitative trait loci (QTL) derived from SCG/Kj mice by linkage analysis. To investigate the individual functions of each QTL, and to identify AAV susceptibility genes, we introduced them into a B6/lpr background to establish SCG/Kj interval congenic mice (SICM). B6/lpr.C1scg mice, a type of SICM, exhibited the production of autoantibodies, including MPO-ANCA. The GN in B6/lpr.C1scg mice was not pauci-immune type: deposition of immunoglobulins and complement components was observed in nephritic glomeruli, similar to that in LN. The incidence of GN in female B6/lpr.C1scg mice was 100%. Granulocyte infiltration was also observed in the glomerular tuft and crescents. B6/lpr.C1scg mice also displayed vasculitis in multiple organs, most frequently the lung and kidney. Vasculitis was characterized by the infiltration of mononuclear cells to vascular walls followed by granulocyte infiltration, resembling human lupus vasculitis. The incidence of lung vasculitis was over 90% in male and female B6/lpr.C1scg mice. Blood MPO-ANCA levels were significantly associated with histopathological disease phenotypes. MPO deposition was observed in nephritic glomeruli, and granulocytes infiltrated into inflamed vessels and glomeruli. These observations suggest that the activation of granulocytes and local MPO release contribute to the pathogenesis of GN and vasculitis. As a monocongenic mouse, B6/lpr.C1scg mice show the association between murine chromosome 1 segment and autoimmunity. This strain can be used as a model of the SLE/AAV overlap syndrome, and will be useful for elucidating the mechanism of ANCA generation and the pathogenesis of CrGN and vasculitis, as well as in the search for genetic factors related to AAV.

Protease-activated receptors in kidney disease progression.

Protease-activated receptors (PARs) are members of a well-known family of transmembrane G protein-coupled receptors (GPCRs). Four PARs have been identified to date, of which PAR1 and PAR2 are the most abundant receptors, and have been shown to be expressed in the kidney vascular and tubular cells. PAR signaling is mediated by an N-terminus tethered ligand that can be unmasked by serine protease cleavage. The receptors are activated by endogenous serine proteases, such as thrombin (acts on PARs 1, 3, and 4) and trypsin (PAR2). PARs can be involved in glomerular, microvascular, and inflammatory regulation of renal function in both normal and pathological conditions. As an example, it was shown that human glomerular epithelial and mesangial cells express PARs, and these receptors are involved in the pathogenesis of crescentic glomerulonephritis, glomerular fibrin deposition, and macrophage infiltration. Activation of these receptors in the kidney also modulates renal hemodynamics and glomerular filtration rate. Clinical studies further demonstrated that the concentration of urinary thrombin is associated with glomerulonephritis and type 2 diabetic nephropathy; thus, molecular and functional mechanisms of PARs activation can be directly involved in renal disease progression. We briefly discuss here the recent literature related to activation of PAR signaling in glomeruli and the kidney in general and provide some examples of PAR1 signaling in glomeruli podocytes.

Cutaneous vasculitis: Report of 117 cases

Proteinase-3 mRNA expressed by glomerular epithelial cells correlates with crescent formation in Wegener's granulomatosis.Wegener's granulomatosis (WG) is characterized by systemic vasculitis with crescentic glomerulonephritis (CGN) and circulating autoantibodies directed against neutrophil cytoplasmic antigens (ANCA). Proteinase 3 (PR-3), a neutral serine proteinase in neutrophils implicated in the growth control of myeloid cells, has been identified as the target antigen for ANCA in WG. Since the kidneys are frequently involved in WG, we studied the in situ expression of PR-3 by renal parenchymal cells.We assessed the expression of PR-3 in kidney biopsies of 15 patients with WG by immunohistochemistry (IHC) and in situ hybridization (ISH). Normal kidney tissue served as the control.We detected PR-3 mRNA and PR-3 protein in distal tubular epithelial cells (TECs) and glomerular epithelial cells (GECs) in normal kidney tissue and in CGN. Furthermore, a strong glomerular PR-3mRNA expression restricted to the site of cellular crescents was detected in patients with WG. The analysis of 144 glomeruli with cellular or sclerotic crescents revealed a positive correlation of glomerular PR-3mRNA expression with the percentage of cellular crescents per glomerulus. The capability of human TECs and GECs to synthesize PR-3 was confirmed by Northern blot and ISH on cultured cells.These data provide evidence that nonhematopoetic renal parenchymal cells express PR-3 and that glomerular expression of PR-3 is associated with crescent formation in WG. Our findings suggest that renal parenchymal cells may directly be involved in the pathogenesis of CGN in WG.

Role of amino acid transporter LAT2 in the activation of mTORC1 pathway and the pathogenesis of crescentic glomerulonephritis

Molecular mechanisms and signaling pathways leading to cellular proliferation and lesion formation in the crescentic glomerulonephritis (CGN) remain elusive. In the present study we have explored a potential role of the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway and amino acid transporter (LAT) in the pathogenesis of CGN. Immunohistochemistry and western blot analysis of glomeruli isolated from a rat model of CGN revealed that activation of mTORC1 preceded crescent formation in glomerular parietal epithelial cells (PECs) and podocytes. Daily treatment of rats with the mTOR inhibitor everolimus just after induction of CGN was not beneficial and instead led to increased cellular necrosis of PECs. However, daily treatment starting 7 days after the onset of CGN was beneficial and maintained intact glomeruli. Out of three forms of L-type neutral amino acid transporters (LAT1–LAT3) studied here, only LAT2 was found to be upregulated in the PECs and podocytes in advance of the crescent formation as well as in the crescent lesion itself. Cell culture study revealed that plasma membrane expression of LAT2 markedly stimulated mTORC1 signaling pathway, which was significantly abrogated by coexistence of LAT inhibitor. Finally, LAT inhibitor significantly abrogated development of crescent formation of CGN on day 7. Our data suggest that LAT2 may have a pivotal role in the pathogenesis of CGN by activating the mTORC1 pathway in the glomerular epithelial cells.

Improvement of rapidly progressive lupus nephritis associated MPO-ANCA with tacrolimus

A 43-year-old Japanese woman with systemic lupus erythematosus (SLE) developed rapidly progressive renal failure and nephritic syndrome with a high titer of myeloperoxidase-antineutrophil cytoplasmic antibody (MPO-ANCA). Methylprednisolone pulse therapy did not suppress the progression of renal failure. Intravenous cyclophosphamide pulse therapy and administration of azathioprine was abandoned due to adverse effects. Tacrolimus was employed as an alternative immunosuppressive therapy and was well tolerated, effectively preventing renal failure. Oral prednisolone dosage was successfully tapered without recurrence, along with decreasing titer of MPO-ANCA. Renal biopsy showed diffuse proliferative lupus nephritis (International Society of Nephrology/Renal Pathology Society class IV-G A/C) with crescent formation. These findings indicate that in addition to lupus nephritis, which usually results from deposition of circulating or locally formed immune complexes, MPO-ANCA may be involved in the pathogenesis of crescentic glomerulonephritis. Furthermore, we propose that tacrolimus is an effective immunosuppressant for MPO-ANCA-related renal crisis in diffuse proliferative lupus nephritis.

Inhibition of indoleamine 2, 3-dioxygenase-mediated tryptophan catabolism accelerates crescentic glomerulonephritis

Immunomodulatory enzyme indoleamine 2, 3-dioxygenase (IDO) is one of the initial and rate-limiting enzymes involved in the catabolism of the essential amino acid tryptophan. Via catalysing tryptophan degradation, IDO suppresses adaptive T cell-mediated immunity and plays an important role in various forms of immune tolerance. Its role in T helper type 1 (Th1)-directed, cell-mediated crescentic glomerulonephritis (GN) is still unclear. Therefore, we investigated the activity and role of IDO in crescentic GN using a model of nephrotoxic serum nephritis (NTN), and IDO activity was inhibited by 1-methyl-tryptophan (1-MT) in vivo. Our results showed that activity of IDO, as determined by high performance liquid chromatography analysis of the kynurenine/tryptophan ratio, was increased markedly in the serum and renal tissue of NTN mice, and immunohistochemistry revealed that expression of IDO was up-regulated significantly in glomeruli and renal tubular epithelial cells during NTN. Treatment with 1-MT resulted in significantly exacerbated kidney disease with increased glomerular crescent formation, accumulation of CD4(+)T cells and macrophages in renal tissue, and augmented renal injury compared with phosphate-buffered saline-treated NTN mice, which was associated with enhanced Th1 responses and intrarenal cellular proliferation. These findings suggest that the development of NTN was regulated negatively by increased IDO activity, and IDO might play an important role in the pathogenesis of crescentic GN.

133: Pegfilgastim Induces a Crescentic Glomerulonephritis

PEGFILGASTIM INDUCES A CRESCENTIC GLOMERULONEPHRITIS Jorge Lamarche, Alfredo Peguero, Craig Courville, AnaVelez, and Ala’a Farahat James A. Haley Veterans Hospital and the University of South Florida Tampa, FL USA Hodgkin’s Lymphoma (HL) and the Human Immunodeficiency Virus (HIV) have been associated with a variety of glomerulonephritic processes. The following scenario involves a 48 year old HIV male who developed rapid and progressive glomerulonephritis (RPGN) with a biopsy proven crescentic glomerulonephritis (CGN) within one week after he underwent the first chemotherapeutic cylcle to treat his recently diagnosed HL. Prior to the treatment of HL the patient was successfully treated with HAART and his renal function was normal with a GFR of 92 ml/min. Despite a normal renal function, the patient’s U/A demonstrated a new onset proteinuria and microscopic hematuria four months prior to the chemotherapy administration. The chemotherapy regimen included pegfilgastim, dexamethasone, dacarbazine, doxorubicin, and vinblastine. Glomerular macrophage colony-stimulating factor (GMCSF) has been demonstrated to be a mediator in the pathogenesis of CGN. Filgastim, an analogue of GM-CSF, has been associated with the new onset proteinuria and microscopic hematuria. After the patient received his chemotherapy, he developed leukocytosis, culture-negative fevers, and acute renal failure. This clinical case likely represents the excacerbation of a mild glomerulonephritis into a full blown CGN after pegfilgastim administration.

TGF-β type II receptor deficiency prevents renal injury via decrease in ERK activity in crescentic glomerulonephritis

The role of transforming growth factor-beta (TGF-beta) receptor complex in the pathogenesis of crescentic glomerulonephritis (GN) is not clear. To test the hypothesis that TGF-beta signaling plays a crucial role in the development and progression of crescentic GN by inducing the activation of extracellular signal-regulated kinase (ERK) and expression of its target genes, anti-glomerular basement membrane (GBM) GN was induced in TGF-beta type II receptor (TGF-betaIIR) gene heterozygous (TGF-betaIIR(+/-)) C57BL/6J mice and wild-type animals. GN was initiated in preimmunized mice by administration of rabbit anti-mouse GBM serum. TGF-betaIIR deficiency was significantly associated with decreased renal damage at days 14, 21, and 28 after induction of GN: renal function impairment, proteinuria, proportion of crescents, glomerular accumulation of periodic acid-Schiff-positive material, relative cortical interstitial volume, as well as renal cortical phosphorylation of ERK and plasminogen activator inhibitor type I (PAI-1) and alpha2(I) collagen mRNA levels were significantly decreased in TGF-betaIIR(+/-) mice compared with wild-type animals. These results provide the first direct evidence that TGF-betaIIR deficiency protects against renal injury in crescentic GN, possibly by inhibiting the sustained activation of ERK and PAI-1 and alpha2(I) collagen gene expression. Thus, TGF-beta signaling appears to play an important role in the development and progression of crescentic GN by inducing the ERK activity, and PAI-1 and alpha2(I) mRNA expression.

Plasminogen Activator Inhibitor-1 in Chronic Kidney Disease

In 1984, Loskutoff et al. ([1][1]) purified plasminogen activator inhibitor-1 (PAI-1) from conditioned media of cultured endothelial cells. This 50-kd glycoprotein is the primary physiologic inhibitor of the serine proteases tissue-type and urokinase-type plasminogen activators (tPA and uPA,

Doxycycline decreases proteinuria in glomerulonephritis

Treatment options for crescentic glomerulonephritis include the use of steroids, cytotoxic therapy, and, in severe cases, intravenous immunoglobulins and plasmapheresis. Injury and lysis of capillary glomerular basement membrane, which is made up of type IV collagen, laminin, fibronectin, and proteoglycans, by serine proteinases and matrix metalloproteinases (MMPs) likely is an important participant in the pathogenesis of crescentic glomerulonephritis. Tetracycline derivatives inhibit not only the activity of MMPs, but also their production, and have been investigated for the treatment of disorders in which the MMP system becomes amplified, such as degenerative osteoarthritis, periodontitis, cancer, and abdominal aortic aneurysm. We report an interesting case of crescentic glomerulonephritis in a young man who was treated with cyclophosphamide and prednisone. The patient developed steroid-induced acne that was treated with long-term oral doxycycline therapy. During the period the patient was administered doxycycline, proteinuria decreased by 70% and recurred when doxycycline was stopped. To our knowledge, this is the first report of possible benefits of a metalloproteinase inhibitor (doxycycline) in glomerulonephritis in humans. Future studies are urgently required to explore the option of metalloproteinase inhibitors in the treatment of proliferative glomerulonephritis.

Stem cell factor and crescentic glomerulonephritis

Background: Numerous cells and cytokines have been implicated in the pathogenesis of crescentic glomerulonephritis (CGN). Recently, there has been growing awareness of the role of mast cells and their growth factor, stem cell factor (SCF), in the process of tissue inflammation and fibrosis. Methods: In this study, renal biopsy specimens from 28 patients with a histopathologic diagnosis of CGN were evaluated immunohistochemically for the presence of mast cells, SCF, and its receptor (c-kit). In addition, CD34+ hematopoietic cells, monocytes (CD68+ cells), and myofibroblasts (α-smooth muscle actin-positive [α-SMA+] cells) were counted. Renal biopsy specimens from cadaveric kidney donors and kidneys removed for hypernephroma (n = 6) served as controls. Point counting of positive immunostaining for SCF, α-SMA, and collagens III and IV was undertaken. Glomerular and interstitial fibrosis (IF) scores were determined. Results: Patients who developed progressive chronic kidney failure showed a significant increase in percentage of crescents, number of interstitial c-kit+ cells, and glomerular CD68+ cells compared with those with a favorable outcome. Analysis showed a significant elevation of tryptase+ mast cells in the interstitium of renal biopsy specimens of patients with CGN compared with controls. SCF and c-kit+ cells were found in glomeruli and interstitium, with occasional immunostaining of the crescent with SCF. Both glomerular and interstitial SCF immunostaining was significantly higher in biopsy specimens of patients compared with controls. Glomerular and interstitial SCF showed a significant positive correlation with 24-hour urinary protein level. There were a few CD34+ cells in both glomeruli and interstitium, but their numbers did not differ between patients and controls. Colocalization of CD34+ and c-kit+ was seen in some rounded interstitial and spindle-shaped cells. Number of interstitial mast cells proved to be a strong predictor of IF. Glomerular SCF correlated negatively with creatinine clearance and positively with glomerular CD68+ cells. Interstitial immunostainable SCF correlated positively with interstitial CD68+ cells and interstitial collagen III. On double antigen labeling, SCF was shown in the vicinity of α-SMA+ cells. Conclusion: These results show the potential involvement of mast cells and their growth factor SCF/c-kit in CGN.

Mast cells and tubulointerstitial fibrosis in patients with ANCA-associated glomerulonephritis.

To elucidate the role of mast cells (MCs) in the pathogenesis of crescentic glomerulonephritis, we investigated the immunohistochemical localization of MCs in the kidney and the correlation between MC localization and tubulointerstitial lesions in biopsy specimens and serum stem cell factor (SCF) levels in patients with antineutrophil cytoplasmic autoantibody (ANCA)-associated glomerulonephritis. Thirteen patients with ANCA-associated glomerulonephritis were enrolled in this study. Clinical parameters, such as serum creatinine and urinary protein excretion, were obtained from each patient at the time of biopsy. Paraffin-embedded sections were used for immunohistochemical staining, using the labelled streptavidin bio-tin (LSAB) method. Monoclonal antibodies to human tryptase, alpha-smooth-muscle actin, and CD68 were used as primary antibodies. Ten cortical interstitial fields were randomly selected at an original magnification of x400 and assessed using a computer-assisted color image analyzer. Tubulointerstitial fibrosis was assessed as the percentage of the area stained with Masson trichrome in ten cortical interstitial fields. The measurement of serum SCF levels was performed by using an enzyme-linked immunoassay. In all of the control subjects, a few tryptase-positive MCs were observed in the glomeruli and interstitium. In contrast, sparse MCs were observed in the interstitium, but not in the glomeruli of diseased kidneys. The number of interstitial MCs in the tubulointerstitial lesions was positively correlated with the degree of interstitial fibrosis. Moreover, a significant positive correlation was observed between the number of interstitial MCs and the serum SCF concentration (r = 0.85; P = 0.001). Our findings suggest that MC infiltration induced by SCF in interstitial tissues seems to be associated with tubulointerstitial fibrosis in human ANCA-associated glomerulonephritis.

Up-regulation of extracellular matrix proteoglycans and collagen type I in human crescentic glomerulonephritis

The pathogenesis of crescentic glomerulonephritis (CGN) involves cellular migration and proliferation in the urinary space, frequently followed by fibrous organization. Extracellular matrix proteoglycans (PGs) may regulate these events via effects on cellular migration, interactions with growth factors, including transforming growth factor-beta (TGF-beta), and control of collagen fibrillogenesis. The expression of PG in human CGN is unknown. Renal tissues from 18 patients with CGN were examined immunohistochemically for versican, decorin, biglycan and collagen type I, and were compared with morphologically normal tissues from six tumor nephrectomies. Synthesis of decorin, biglycan, and procollagen type I mRNAs was evaluated by in situ hybridization. Versican was strongly expressed in cellular crescents and periglomerular areas, whereas decorin and biglycan accumulated in collagen type I-enriched regions, including fibrocellular and fibrous crescents, and interstitial fibrosis. PG and collagen type I accumulation colocalized with myofibroblasts in crescents, periglomerular areas, and interstitium. The temporal and spatial patterns of expression demonstrated in this study provide evidence to support pathogenic roles for PG in the evolution of CGN. Based on known biological properties of this molecule, versican may facilitate migration of cells in developing crescents. Decorin and biglycan may contribute to progression of CGN, perhaps via interactions with collagen type I in the remodeled extracellular matrix.

Proteinase-3 mRNA expressed by glomerular epithelial cells correlates with crescent formation in Wegener's granulomatosis

Wegener's granulomatosis (WG) is characterized by systemic vasculitis with crescentic glomerulonephritis (CGN) and circulating autoantibodies directed against neutrophil cytoplasmic antigens (ANCA). Proteinase 3 (PR-3), a neutral serine proteinase in neutrophils implicated in the growth control of myeloid cells, has been identified as the target antigen for ANCA in WG. Since the kidneys are frequently involved in WG, we studied the in situ expression of PR-3 by renal parenchymal cells. We assessed the expression of PR-3 in kidney biopsies of 15 patients with WG by immunohistochemistry (IHC) and in situ hybridization (ISH). Normal kidney tissue served as the control. We detected PR-3 mRNA and PR-3 protein in distal tubular epithelial cells (TECs) and glomerular epithelial cells (GECs) in normal kidney tissue and in CGN. Furthermore, a strong glomerular PR-3mRNA expression restricted to the site of cellular crescents was detected in patients with WG. The analysis of 144 glomeruli with cellular or sclerotic crescents revealed a positive correlation of glomerular PR-3mRNA expression with the percentage of cellular crescents per glomerulus. The capability of human TECs and GECs to synthesize PR-3 was confirmed by Northern blot and ISH on cultured cells. These data provide evidence that nonhematopoetic renal parenchymal cells express PR-3 and that glomerular expression of PR-3 is associated with crescent formation in WG. Our findings suggest that renal parenchymal cells may directly be involved in the pathogenesis of CGN in WG.

Renal Expression of lnterleukin-2 Receptor mRNA in Patients with Crescentic Glomerulonephritis

We studied paraffin sections of renal biopsies from 7 patients with crescentic glomerulonephritis (CGN) by in situ hybridisation, to detect sites of interleukin-2 receptor (IL-2R) mRNA expression. Frozen sections from a further patient with CGN were studied by immunohistochemistry with a monoclonal antibody to CD25, to detect IL-2R protein. Positive control sections were taken from biopsies of acute cellular renal transplant rejection and negative controls from biopsies of membranous glomerulonephritis. No autoradiographic signal was detected in negative controls. IL-2R mRNA expression was seen in rejected transplants and in sections from 4 to 7 patients with CGN. Expression was seen in cortical interstitial cells, renal tubular epithelial cells, cells within glomerular crescents and in one glomerulus at the margin of Bowman's capsule. Tubular cell expression of IL-2R protein was confirmed by immunohistochemistry. We have confirmed that IL-2R mRNA expression occurs locally within the kidneys in CGN and have identified expression in tubular epithelial cells. The results suggest that local activation of immunocompetent cells occurs in the kidney and may be of significance in the pathogenesis of CGN.

Intrarenal localization of interleukin-1β mRNA in crescentic glomerulonephritis

Il-1 beta is a potent proinflammatory peptide, and induces expression of other cytokines which are involved in the immune response. Kidney biopsies from nine patients with crescentic GN were studied by in-situ hybridization to determine the site of expression of Il-1 beta mRNA. Biopsies from nine patients with nonproliferative renal disease were studied as negative controls, and tonsillar tissue was studied as a positive control. An Il-1 beta cDNA probe was 32P-labelled by random primers and hybridized to paraffin-embedded tissue sections after de-waxing. Il-1 beta mRNA was expressed in tonsil, but not in negative controls. Positive mRNA expression was seen in four of the nine crescentic biopsies. This was observed in interstitial cells with morphological characteristics of macrophages adjacent to tubular cells, in cells within the glomerular tuft, and in tubular epithelial cells. Il-1 beta mRNA is expressed in renal tissue in crescentic GN. Tubular and interstitial expression of Il-1 beta mRNA appears of equal prominence to glomerular expression. Intrarenal cytokine synthesis may be involved in the pathogenesis of crescentic glomerulonephritis.