Characteristics of albumin processing during renal passage in anti-Thy1 and anti-glomerular basement membrane glomerulonephritis

Recent studies have shown that glomerular-filtered albumin appears to be processed by two distinct cellular pathways. The major pathway, a high-capacity retrieval pathway, returns most of the filtered albumin to the blood supply intact. The albumin not taken up by the retrieval pathway is degraded by lysosomes during renal passage and excreted as fragments in urine. We studied the interplay of the albumin retrieval pathway and the degradation pathway in the disease models of anti-Thy1 nephritis, a model of mild proteinuria, and anti-glomerular basement membrane (anti-GBM) disease, a model of severe proteinuria. This is achieved by investigating the integrity of urinary albumin and its excretion rate. Total albumin excretion (intact plus fragments) did not change significantly in the rats with anti-Thy1 nephritis. However, it was established that intact albumin excretion had a strong positive correlation with increasing total-protein excretion, which showed that the degradation pathway was being predominantly affected in this disease. For the rats with anti-GBM disease, total protein excretion increased 26-fold compared with the control group, and intact albumin excretion increased 250-fold. The profound changes in albumin excretion in anti-GBM disease are consistent with inhibition primarily of the retrieval pathway.

Expression of macrophage migration inhibitory factor in human glomerulonephritis

BACKGROUND

We have recently demonstrated that macrophage migration inhibitory factor (MIF) plays a pathogenic role in experimental glomerulonephritis (GN). The aim of the current study was to investigate MIF expression in human GN.

METHODS

MIF expression was examined by in situ hybridization and immunohistochemistry staining in 65 biopsies from a variety of glomerulonephridities.

RESULTS

There is constitutive expression of MIF mRNA and protein in normal human kidney that is largely restricted to tubular epithelial cells and to some glomerular epithelial cells. There was little change in the pattern of MIF expression in nonproliferative forms of GN such as minimal change disease and membranous GN. However, there was a marked increase in both glomerular and tubular MIF expression in proliferative forms of GN, including focal segmental glomerulosclerosis (FGS), lupus nephritis, crescentic GN, and mesangiocapillary proliferative GN. The prominent macrophage and T-cell infiltrate in these diseases were largely restricted to areas with marked up-regulation of MIF expression, contributing to glomerular hypercellularity, glomerular focal segmental lesions, crescent formation, tubulitis, and granulomatous lesions. De novo MIF expression was evident in glomerular endothelial cells and mesangial cells in proliferative forms of GN. In addition, many infiltrating macrophages and T cells showed MIF mRNA and protein expression. Quantitative analysis found that increased glomerular and tubular MIF expression gave a highly significant correlation with macrophage and T-cell accumulation, the severity of histologic lesions, and the loss of creatinine clearance.

CONCLUSIONS

Renal MIF expression is markedly up-regulated in proliferative forms of human GN, and this correlates with leukocyte infiltration, histologic damage, and renal function impairment. These results suggest that MIF may be an important mediator of renal injury in progressive forms of human GN. Based on these findings, together with the known pathogenic role of MIF in experimental GN, we propose that MIF is an attractive therapeutic target in the treatment of progressive forms of GN.

Glomerular epithelial-myofibroblast transdifferentiation in the evolution of glomerular crescent formation

BACKGROUND

Glomerular cellular crescents consist of epithelial cells and macrophages, which can undergo an irreversible process of fibrous organization. However, the origin of the fibroblast-type cells that mediate this fibrous organization is unclear.

METHODS

This study examined glomerular epithelial- myofibroblast transdifferentiation (GEMT) in the formation and evolution of glomerular crescents in two distinct rat models of glomerulonephritis: 5/6 nephrectomy and antiglomerular basement membrane (GBM) disease.

RESULTS

Early in the course of both disease models, and prior to crescent formation, immunohistochemistry staining and in-situ hybridization demonstrated de novo expression of alpha-smooth-muscle actin (alpha-SMA), a marker of smooth muscle cells and myofibroblasts, by glomerular parietal epithelial cells (GPEC). The expression of alpha-SMA by GPEC was accompanied by a loss of E-cadherin staining, a marker of epithelial cells. At this early stage of GEMT, ultrastructural studies identified the presence of characteristic actin microfilaments and dense bodies within GPEC which retained a normal epithelial morphology with apical-basal polarity and microvilli. A late stage of transdifferentiation was seen in fibrocellular crescents. In this case, GPEC attached to intact segments of the capsular basement membrane contained large bundles of actin microfilaments throughout the cell, and this was accompanied by a loss of polarity, microvilli, and tight junctions. There was a significant correlation between the presence of alpha-SMA(+) GPEC and glomerular crescent formation. Cellular crescents contained small numbers of alpha-SMA(+) myofibroblasts. These cells become the dominant population in fibrocellular crescents, which was associated with marked local proliferation. Relatively few alpha-SMA(+) myofibroblasts remained in fibrotic/organizing crescents. Most cells within cellular and fibrocellular crescents expressed transforming growth factor-beta (TGF-beta) and basic fibroblast growth factor (FGF-2), suggesting that these growth factors may regulate this GEMT process during the evolution of glomerular crescents.

CONCLUSIONS

This study provides the first phenotypic and morphological evidence that glomerular epithelial-myofibroblast transdifferentiation participates in the formation and evolution of glomerular crescents.

Up-regulation of macrophage migration inhibitory factor in acute renal allograft rejection in the rat

Recent studies have identified a key role for macrophage migration inhibitory factor (MIF) in a number of immune cell-mediated diseases. The current study investigated the potential role of MIF in acute allograft rejection. Lewis rats underwent bilateral nephrectomy and then received an orthotopic DA renal allograft or an orthotopic Lewis renal isograft. Groups of six animals were killed at day 1 or 5 after transplantation. No immunosuppression was used. Animals receiving a renal allograft exhibited severe rejection on day 5, as shown by high levels of serum creatinine, very low rates of creatinine clearance, and severe tubulitis with a dense macrophage and T cell infiltrate. In contrast, isografts had normal renal function on day 5 with no histological evidence of rejection. Northern blotting showed that renal MIF mRNA expression was unchanged at day 1, but was increased 3.5-fold on day 5. In situ hybridization showed a marked increase in MIF mRNA expression by tubular cells and MIF mRNA expression by many infiltrating mononuclear cells in day 5 allografts. Immunostaining confirmed an increase in tubular MIF protein expression, particularly in areas of severe tubular damage with prominent leucocytic infiltration. Double staining showed that many infiltrating macrophages and T cells expressed the MIF protein in day 5 allografts. There was only a minor increase in MIF expression in day 5 isografts, demonstrating that neither surgical injury nor stress cause significant up-regulation of MIF expression in allograft rejection. In conclusion, this study has demonstrated that local MIF production is specifically increased in acute renal allograft rejection. These results suggest that MIF may play an important role in the cellular immune response mediating acute allograft rejection.

Transforming growth factor-beta regulates tubular epithelial-myofibroblast transdifferentiation in vitro

BACKGROUND

We recently found evidence of tubular epithelial-myofibroblast transdifferentiation (TEMT) during the development of tubulointerstitial fibrosis in the rat remnant kidney. This study investigated the mechanisms that induce TEMT in vitro.

METHODS

The normal rat kidney tubular epithelial cell line (NRK52E) was cultured for six days on plastic or collagen type I-coated plates in the presence or absence of recombinant transforming growth factor-beta1 (TGF-beta1). Transdifferentiation of tubular cells into myofibroblasts was assessed by electron microscopy and by expression of alpha-smooth muscle actin (alpha-SMA) and E-cadherin.

RESULTS

NRK52E cells cultured on plastic or collagen-coated plates showed a classic cobblestone morphology. Culture in 1 ng/ml TGF-beta caused only very minor changes in morphology, but culture in 10 or 50 ng/ml TGF-beta1 caused profound changes. This involved hypertrophy, a loss of apical-basal polarity and microvilli, with cells becoming elongated and invasive, the formation of a new front-end back-end polarity, and the appearance of actin microfilaments and dense bodies. These morphological changes were accompanied by phenotypic changes. Double immunohistochemistry staining showed that the addition of TGF-beta1 to confluent cell cultures caused a loss of the epithelial marker E-cadherin and de novo expression of alpha-SMA. An intermediate stage in transdifferentiation could be seen with hypertrophic cells expressing both E-cadherin and alpha-SMA. De novo alpha-SMA expression was confirmed by Northern blotting, Western blotting, and flow cytometry. In particular, cells with a transformed morphology showed strong alpha-SMA immunostaining of characteristic microfilament structures along the cell axis. There was a dose-dependent increase in the percentage of cells expressing alpha-SMA with increasing concentrations of TGF-beta1, which was completely inhibited by the addition of a neutralizing anti-TGF-beta1 antibody. Compared with growth on plastic, cell culture on collagen-coated plates showed a threefold increase in the percentage of cells expressing alpha-SMA in response to TGF-beta1.

CONCLUSION

TGF-beta1 is a key mediator that regulates, in a dose-dependent fashion, transdifferentiation of tubular epithelial cells into alpha-SMA+ myofibroblasts. This transdifferentiation is markedly enhanced by growth on collagen type I. These findings have identified a novel pathway that may contribute to renal fibrosis associated with overexpression of TGF-beta1 within the diseased kidney.

Mechanisms of glomerular macrophage infiltration in lipid-induced renal injury

BACKGROUND

A number of studies have demonstrated an important role for macrophages (M phi) in lipid-induced glomerular injury; however, little is known of the mechanisms that facilitate M phi infiltration in this disease. This study examined the expression of M phi chemotactic molecules M phi migration inhibitory factor (MIF) and leukocyte adhesion molecules intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) during the induction of glomerular M phi infiltration in ExHC rats, a strain that is susceptible to lipid-induced glomerular injury.

METHODS

Groups of five ExHC rats were fed a high-cholesterol diet (HCD) containing 3% cholesterol, 0.6% sodium cholate, and 15% olive oil and were killed after three days or one, two, or six weeks. Control animals were killed on day 0 or after six weeks on a normal diet.

RESULTS

ExHC rats fed an HCD showed marked hypercholesterolemia in the absence of any increase in plasma triglyceride levels from day 3 and developed mild proteinuria and segmental glomerular lesions at week 6. Immunoperoxidase staining identified a significant increase in glomerular ED1+ M phi at week 1, which was further increased at week 6, when M phi-derived foam cells were seen in almost all glomeruli. Many of the infiltrating glomerular M phi expressed lymphocyte function-associated antigen-1 (LFA-1) and very late antigen-4 (VLA-4), which are ligands for ICAM-1 and VCAM-1, respectively. Coincident with the induction of hypercholesterolemia on day 3 and prior to significant M phi infiltration, combined in situ hybridization and immunohistochemistry staining demonstrated a marked up-regulation of M-CSF and MIF mRNA expression by glomerular mesangial cells and podocytes. There was also a significant increase in ICAM-1 and VCAM-1 mRNA expression by intrinsic glomerular cells, including endothelial cells, on day 3 of the HCD.

CONCLUSION

These results suggest that hypercholesterolemia can induce a classic proinflammatory response within the kidney glomerulus, involving production of well-described M phi chemotactic and adhesion molecules, which results in M phi recruitment and the development of glomerular injury.

IL-1 up-regulates osteopontin expression in experimental crescentic glomerulonephritis in the rat

Osteopontin (OPN) is a macrophage chemotactic and adhesion molecule that acts to promote macrophage infiltration in rat anti-glomerular basement membrane (GBM) glomerulonephritis. The present study investigated the role of interleukin-1 (IL-1) in the up-regulation of renal OPN expression in this disease model. Accelerated anti-GBM glomerulonephritis was induced in groups of six rats. Animals were treated by a constant infusion of the IL-1 receptor antagonist or saline (control) over days -1 to 14 (induction phase) or days 7 to 21 (established disease). In normal rat kidney, OPN was expressed in a few tubules (<5%) and absent from glomeruli. During the development of rat anti-GBM disease (days 7 to 21), there was substantial up-regulation of OPN mRNA and protein expression in glomeruli (>5 cells per glomerular cross-section) and tubular epithelial cells (50-75% OPN-positive). Up-regulation of OPN expression was associated with macrophage accumulation within the kidney, severe proteinuria, loss of renal function, and severe histological damage including glomerular crescentic formation and tubulointerstitial fibrosis. In contrast, IL-1 receptor antagonist treatment of either the induction phase of disease or established disease significantly reduced OPN mRNA and protein expression in glomeruli (/75-85%, P < 0.001) and tubules (/45-60%, P < 0.001). The reduction in OPN expression was associated with significant inhibition of macrophage accumulation and progressive renal injury. In vitro, the addition of IL-1 to the normal rat tubular epithelial cell line NRK52E up-regulated OPN mRNA and protein levels, an effect that was dose-dependent and inhibited by the addition of IL-1 receptor antagonist, thus demonstrating that IL-1 can act directly to up-regulate renal OPN expression. In conclusion, this study provides in vivo and in vitro evidence that IL-1 up-regulates OPN expression in experimental kidney disease and support for the argument that inhibition of OPN expression is one mechanism by which IL-1 receptor antagonist treatment suppresses macrophage-mediated renal injury.

Macrophage migration inhibitory factor expression in human renal allograft rejection

BACKGROUND

Macrophage migration inhibitory factor (MIF) plays a pivotal role in immune-mediated diseases. Despite the long-standing association of MIF with the delayed-type hypersensitivity response, the potential role of MIF in allograft rejection is unknown.

METHODS

MIF expression was assessed by in situ hybridization and immunohistochemistry staining in 62 biopsies of human renal allograft rejection and in normal human kidney.

RESULTS

MIF mRNA and protein is constitutively expressed in normal kidney, being largely restricted to tubular epithelial cells, some glomerular epithelial cells, and vascular smooth muscle cells. In both acute and chronic renal allograft rejection, there was marked up-regulation of MIF mRNA and protein expression by intrinsic kidney cells such as tubular epithelial cells and vascular endothelial and smooth muscle cells. There was also MIF expression by infiltrating macrophages and T cells. Of note, macrophage and T cell infiltrates were largely restricted to areas with marked up-regulation of MIF expression, potentially contributing to the development of severe tubulitis and intimal or transmural arteritis. Quantitative analysis found that increased MIF expression in allograft rejection gave a highly significant correlation with macrophage and T cell accumulation in both the glomerulus and interstitium (P<0.001). In addition, the number of MIF+ tubules and interstitial MIF+ cells correlated significantly with the severity of allograft rejection (P<0.01), and the loss of renal function (P<0.01). In contrast, no up-regulation of renal MIF expression and no leukocyte accumulation was seen in allograft biopsies without evidence of rejection.

CONCLUSIONS

This is the first study to demonstrate that local MIF expression is up-regulated during allograft rejection. The association between up-regulation of MIF expression, macrophage and T cell infiltration and the severity of renal allograft rejection suggests that MIF may be an important mediator in the process of allograft rejection.

Tubular epithelial-myofibroblast transdifferentiation in progressive tubulointerstitial fibrosis in 5/6 nephrectomized rats

BACKGROUND

Tubulointerstitial fibrosis is the final common pathway to end-stage renal failure. The present study investigated the potential role of tubular epithelial cells (TEC) in progressive fibrosis in the rat remnant kidney model.

METHODS

Rats underwent 5/6 nephrectomy or a sham operation (control), and groups of six animals were killed at weeks 1, 3, 5, 9, 13, 17 and 21.

RESULTS

Immunohistochemistry staining and in situ hybridization at week 3 after nephrectomy demonstrated de novo expression of alpha-smooth muscle actin (alpha-SMA)--a marker of smooth muscle cells and myofibroblasts--by TEC that was invariably associated with disruption of the tubular basement membrane (TBM). This phenotypic evidence of tubular epithelial-myofibroblast transdifferentiation was supported by ultrastructural studies identifying the presence of characteristic actin microfilaments and dense bodies within TEC with a transformed morphology. In the late stage of this apparent tubular epithelial-myofibroblast transdifferentiation, TEC lost apical-basal polarity and tight junctions, became elongated, detached from the TBM, separated from neighboring cells and appeared to migrate into the peritubular interstitium through the damaged basement membrane. Indeed, focal peritubular accumulation of alpha-SMA+ myofibroblasts and local tubulointerstitial fibrosis was closely associated with alpha-SMA+ tubules, suggesting a tubular epithelial origin for some of these cells. Quantitative analysis found a significant correlation between the number of alpha-SMA+ TEC and the accumulation of interstitial alpha-SMA+ myofibroblasts and the severity of tubulointerstitial fibrosis (both P < 0.001).

CONCLUSIONS

This study provides phenotypic and morphological evidence to support the hypothesis that TEC are pro-fibrogenitor cells capable of tubular epithelial-myofibroblast transdifferentiation in progressive renal fibrosis. In addition, we postulate that disruption of the TBM, which facilitates epithelial cell contact with the interstitial matrix, promotes this process of transdifferentiation.

Local macrophage and myofibroblast proliferation in progressive renal injury in the rat remnant kidney

BACKGROUND

We have recently shown that blockade of angiotensin II activity inhibits local macrophage and myofibroblast proliferation in progressive non-immune renal injury in the rat remnant kidney. However, it is not known whether this local proliferation contributes to macrophage and myofibroblast accumulation and the development of renal injury. Therefore, we examined this issue in a detailed time-course study of the rat remnant kidney.

METHODS

Groups of five rats were killed 4, 8,12 or 16 weeks after 5/6 subtotal nephrectomy (STNx) or a sham operation. Macrophage and myofibroblast proliferation was assessed by two-colour immunostaining for ED1+ macrophages or alpha-smooth muscle actin (alpha-SMA)-positive myofibroblasts with the proliferating cell nuclear antigen (PCNA) or bromodeoxyuridine.

RESULTS

All parameters of renal function and histology remained normal in the sham-operated controls, and no macrophage or myofibroblast accumulation was evident. In contrast, prominent macrophage accumulation developed in both the glomerulus and tubulointerstitium in STNx animals, peaking at week 12. Many ED1+ macrophages showed PCNA expression, accounting for 19-34% of the total macrophage population. There was a highly significant correlation between proliferating macrophages and total macrophage accumulation in the glomerulus (r = 0.82, P < 0.0001) and tubulointerstitium (r = 0.70, P < 0.001). Macrophage proliferation was largely restricted to focal areas of renal damage, such as glomerular segmental lesions and severe tubulointerstitial damage. Also, the subpopulation of proliferating macrophages gave a highly significant correlation with loss of renal function, proteinuria, and glomerular and tubulointerstitial lesions. In addition, many alpha-SMA myofibroblasts were evident within expanded mesangial areas and the tubulointerstitium following STNx. Interestingly, active lesions contained many large alpha-SMA+ cells double-stained for PCNA, accounting for 24-29% of total myofibroblasts. There was a highly significant correlation between the number of proliferating myofibroblasts and total myofibroblast accumulation during the evolution of this disease, and both populations correlated with progressive renal injury.

CONCLUSIONS

This study has shown that local proliferation is an important mechanism in both macrophage and myofibroblast accumulation during the development of renal injury in the rat remnant kidney. In addition, local macrophage proliferation is postulated as a mechanism for amplifying kidney damage in nonimmune renal injury.

Local macrophage proliferation in human glomerulonephritis

BACKGROUND

Local macrophage proliferation has been described in several animal models of glomerulonephritis (GN), but its significance in human disease is unknown.

METHODS

Double immunostaining for CD68 and the proliferating cell nuclear antigen (PCNA) was used to identify macrophage proliferation in 84 biopsies from a variety of glomerulonephridities.

RESULTS

A small resident population of glomerular and interstitial CD68+ macrophages was identified in normal human kidney, of which only 1 to 2% showed evidence of proliferation on the basis of PCNA expression. A mild macrophage infiltrate, with only occasional proliferating macrophages, was seen in the less aggressive forms of GN (minimal change disease, non-IgA mesangioproliferative GN and IgA nephropathy). This was in sharp contrast to the more aggressive forms of disease (lupus class IV, vasculitis-associated GN, crescentic GN and mesangiocapillary proliferative GN), in which the prominent macrophage infiltrates contained many proliferating macrophages, accounting for 28 to 47% of the total macrophage population. Macrophage proliferation was largely restricted to areas of severe tissue damage (glomerular segmental proliferative lesions, crescents and foci of tubulointerstitial damage), suggesting that local proliferation is a mechanism for amplifying macrophage-mediated injury. Glomerular and interstitial macrophage proliferation gave a significant correlation with loss of renal function (P < 0.0001) and histologic lesions (P < 0.0001), but not with proteinuria. Interstitial T-cell proliferation also gave a significant correlation with loss of renal function and histologic damage, even though proliferation within the T-cell population was much lower than in the macrophage population.

CONCLUSIONS

This study demonstrates that macrophage proliferation is a feature of the more aggressive forms of human GN. Local proliferation may be an important mechanism for amplifying macrophage-mediated renal injury. In addition, the degree of local macrophage proliferation may be a useful diagnostic and prognostic indicator for human GN.

Reversal of established rat crescentic glomerulonephritis by blockade of macrophage migration inhibitory factor (MIF): potential role of MIF in regulating glucocorticoid production

Macrophage migration inhibitory factor (MIF) is a potent pro-inflammatory cytokine that also counter-regulates glucocorticoid action. We investigated whether immunoneutralization of MIF could reverse established experimental crescentic glomerulonephritis and if this treatment could modulate endogenous glucocorticoid levels. Accelerated anti-GBM glomerulonephritis was induced in six littermate pairs of rats. Once crescentic disease was established on day 7, one animal in each pair was given a daily injection of neutralizing anti-MIF antibody (Ab) or irrelevant isotype control Ab for 14 days and then killed on day 21. In addition, a group of 6 animals was killed on day 7 of disease without any treatment. Animals receiving the control Ab exhibited a rapidly progressive glomerulonephritis with severe renal injury (proteinuria), loss of renal function (creatinine clearance), anemia, and marked histologic damage (including glomerular crescent formation), compared with animals killed on day 7 without treatment. In contrast, anti-MIF Ab treatment partially reversed the disease by restoring normal renal function and reducing histological damage compared with untreated animals killed on day 7 (p < 0.05). Interestingly, anti-MIF Ab treatment also prevented severe anemia (p < 0.05). Reversal of disease was associated with a significant reduction in leukocyte infiltration and activation and renal interleukin-1 (IL-1) production. Importantly, anti-MIF Ab treatment caused a significant increase in endogenous serum corticosterone levels, which correlated with the reversal of disease parameters. In conclusion, this study has demonstrated that blocking MIF activity can partially reverse established crescentic glomerulonephritis and suggests that MIF operates by both enhancing the cellular immune response and suppressing the endogenous anti-inflammatory glucocorticoid response.

Interleukin-10 differentially modulates MHC class II expression by mesangial cells and macrophages in vitro and in vivo

Inhibition of major histocompatibility complex (MHC) class II expression by macrophages is the primary mechanism by which interleukin-10 (IL-10) exerts immune suppression. Little, however, is known of the effects of IL-10 on other types of cells which can be induced to express MHC class II during an inflammatory response. We therefore studied the effects of IL-10 treatment on the expression of MHC class II molecules in a rat model of immunologically induced glomerulonephritis. MHC class II mRNA levels in whole kidney were increased in saline-treated (control) animals with glomerulonephritis (2.6-fold increase versus normal, P = 0.028) and this was partially inhibited by treatment with IL-10 (P = NS). Double immunostaining of tissue sections was used to compare MHC class II expression by infiltrating macrophages and resident glomerular cells. IL-10 treatment reduced the proportion of glomerular macrophages which expressed detectable MHC class II (70% reduction, P = 0.03). In contrast, IL-10 treatment was associated with an increase in the number of resident glomerular cells expressing MHC class II, particularly within mesangial areas. Therefore, the effects of IL-10 on macrophages and mesangial cells were compared in vitro. IL-10 reduced constitutive MHC class II mRNA and cell surface expression by peritoneal macrophages. In contrast, IFN-gamma-stimulated mesangial cells (1097 cell line) cultured with IL-10 for 24 hr showed increased MHC class II mRNA (26% increase) and surface expression (72% increase in percentage MHC II+ by flow cytometry, P = 0.04) as compared with cells stimulated with IFN-gamma alone. IL-10 also directly up-regulated expression of ICAM-1 by 1997 cells. In conclusion, IL-10 was found to have contrasting effects on the production and cell surface expression of MHC class II molecules by mesengial cells and by macrophages, both in vitro and in vivo. The implications of these findings for IL-10-mediated immunosuppression are discussed.

Immunoregulatory activity in adult rat testicular interstitial fluid: roles of interleukin-1 and transforming growth factor beta

Studies on the effect of rat testicular interstitial fluid (IF) on T-cell function have reported both stimulatory and inhibitory actions. Specific cytokines produced within the testis, particularly interleukin-1 (IL-1) and transforming growth factor beta (TGFbeta), may contribute to these apparently conflicting observations. In proliferation assays employing lectin- or antibody-activated thymocytes or mature T cells in vitro, adult rat testicular IF stimulated T-cell activation and/or proliferation at low assay doses and was inhibitory at higher doses. The stimulatory activity was blocked by recombinant IL-1 receptor antagonist. The inhibitory activity was not affected by a polyspecific TGFbeta antiserum. The biological characteristics of the inhibitor were distinct from those of a similar, but considerably less potent, activity in platelet-depleted serum. These data demonstrate that rat testicular IF contains biologically significant concentrations of IL-1 but has a predominantly inhibitory action on T-cell responses. The factor predominantly responsible for this inhibitory activity displays a relatively large apparent molecular weight, is protease sensitive and partially heat labile, but does not appear to be one of the known mammalian TGFbeta isoforms.

Rat mesangial cells express macrophage migration inhibitory factor in vitro and in vivo

Mesangial cells are thought to promote glomerular macrophage accumulation in glomerulonephritis. This may occur through the production of macrophage migration inhibitory factor (MIF), a molecule known to regulate macrophage accumulation at sites of inflammation. To study this, glomerular MIF expression and macrophage accumulation were examined in rat anti-Thy-1 disease, a model of mesangioproliferative nephritis. In situ hybridization and immunohistochemistry showed that MIF is expressed by some podocytes in normal rat glomeruli. De novo MIF expression by glomerular endothelium was seen on day 1 of anti-Thy-1 disease. On day 6, glomerular MIF mRNA and protein expression were prominent in segmental proliferative lesions, which was also the location of most infiltrating macrophages. Double-staining identified de novo MIF mRNA and protein expression by proliferating mesangial cells within these lesions. Cytokine regulation of mesangial cell MIF expression was examined in vitro. Northern blotting showed that cultured rat mesangial cells express a single 0.6-kb species of MIF mRNA, and Western blotting detected a single protein band of 12.5 kD. Six-hour stimulation of mesangial cells with interferon-gamma or platelet-derived growth factor significantly increased MIF mRNA levels. However, the addition of recombinant MIF to mesangial cells did not affect mesangial cell proliferation or constitutive transforming growth factor-beta mRNA expression, nor did MIF induce monocyte chemoattractant protein-1 mRNA expression. In conclusion, this is the first study to demonstrate that mesangial cells can produce MIF in vivo and in vitro. It is postulated that mesangial cell MIF production in response to injury acts to promote macrophage accumulation within segmental proliferative lesions in rat anti-Thy-1 nephritis.

A functional role for osteopontin in experimental crescentic glomerulonephritis in the rat

This study examined whether osteopontin (OPN), a molecule with monocyte chemotactic and adhesive activity, participates in macrophage-mediated renal disease, Accelerated anti-glomerular basement membrane glomerulonephritis was induced in groups of six rats. Animals were treated with a neutralizing anti-OPN or an irrelevant control antibody over days 0-7 (induction phase) or days 7-14 (established disease). Administration of the control antibody had no effect on the severity of the disease. In contrast, anti-OPN treatment significantly reduced glomerular injury (urinary protein excretion) and prevented a loss of renal function (creatinine clearance) during the induction of disease. This was accompanied by a significant reduction in renal macrophage and T-cell accumulation, T-cell activation, and histological injury (glomerular hypercellularity, segmental lesions, crescents, and tubulointerstitial lesions). An important finding was that anti-OPN treatment of established crescentic glomerulonephritis led to a significant reduction in glomerular injury and recovery of renal function in association with inhibition of macrophage and T-cell accumulation, T-cell activation, and histological damage. Anti-OPN treatment significantly inhibited the upregulation of OPN and its ligand CD44 but demonstrated no effect on upregulation of intercellular adhesion molecule-1 (ICAM-1) expression in the kidney. Interestingly, anti-OPN treatment significantly reduced skin swelling and leukocyte infiltration in the delayed type hypersensitivity response. However, anti-OPN treatment had no effect on the humoral immune response. In summary, this study has demonstrated that OPN plays a functional role in macrophage and T-cell accumulation and renal damage in both the induction and progression of a rat model of crescentic glomerulonephritis. Thus, OPN may be of pathological importance in human glomerulonephritis and in cell-mediated immune diseases generally.

De novo glomerular osteopontin expression in rat crescentic glomerulonephritis

Osteopontin (OPN) is a secreted acidic glycoprotein that has potent monocyte chemoattractant and adhesive properties. Up-regulation of tubular OPN expression is thought to promote interstitial macrophage infiltration in experimental nephritis; however, the role of OPN in glomerular lesions, particularly crescent formation, is unknown. The present study used Northern blotting, in situ hybridization and immunohistochemistry to examine OPN expression in a rat model of accelerated anti-GBM glomerulonephritis. Osteopontin mRNA and protein is expressed by some parietal epithelial cells, thick ascending limbs of Henle and medullary tubules and collecting ducts in normal rat kidney. De novo OPN mRNA and protein expression was evident in glomerular visceral and parietal epithelial cells in anti-GBM glomerulonephritis. Glomerular OPN expression preceded and correlated with macrophage infiltration in the development of hypercellularity, focal and segmental lesions and, notably, crescent formation. There was marked up-regulation of OPN expression by tubular epithelial cells that also preceded and correlated with interstitial macrophage (r = 0.93, P < 0.001) and T-cell infiltration (r = 0.85, P < 0.001). Both glomerular and tubular OPN expression correlated significantly with proteinuria (P < 0.001) and a reduction in creatinine clearance (P < 0.01). In addition, double immunohistochemistry showed co-expression of osteopontin and one of its ligands, CD44, in intrinsic renal cells. CD44 and OPN expression by parietal epithelial cells was evident in crescent formation, while virtually all OPN-positive tubules expressed CD44. Infiltrating macrophages and T-cells were CD44-positive, but only a small proportion of T-cells and few macrophages showed OPN expression. Interestingly, strong OPN mRNA and protein expression was seen in macrophage multinucleated giant cells. In summary, this study suggests that OPN promotes macrophage and T-cell infiltration in the development of renal lesions in rat anti-GBM glomerulonephritis, including glomerular crescent and multinucleated giant cell formation.

Local macrophage proliferation in the pathogenesis of glomerular crescent formation in rat anti-glomerular basement membrane (GBM) glomerulonephritis

Glomerular crescent formation is a feature of aggressive forms of glomerulonephritis. The conventional view of crescent formation within Bowman's space involves proliferation of parietal epithelial cells and the recruitment of blood monocytes. However, the potential role of local macrophage proliferation in this process has not been investigated. The current study examines macrophage proliferation within Bowman's space on the basis of expression of the proliferating cell nuclear antigen (PCNA) in a rat model of crescentic glomerulonephritis (accelerated anti-GBM disease). ED1+ macrophages accounted for 42% of cells within early cellular crescents, and 38% of these crescent macrophages were proliferating on the basis of PCNA expression. Macrophages became the dominant cell population in advanced cellular and fibrocellular crescents (64-71%), and there was a significant increase in the level of macrophage proliferation, with 62% and 67% of ED1+ macrophages expressing the PCNA, respectively. This high level of macrophage proliferation was confirmed by incorporation of bromodeoxyuridine and the presence of mitotic figures within crescents. Indeed, macrophages accounted for 73% of all proliferating cells within advanced and fibrocellular crescents. Macrophage proliferation within Bowman's space was a local event, as shown by a lack of proliferating monocytes in the circulation, the presence of mitotic figures within crescents and a reciprocal relationship between the numbers of ED1+ PCNA+ cells within Bowman's space compared with that in the capillary tuft during the progression from early to advanced and fibrocellular crescents. In conclusion, this study has changed the conventional view of the pathogenesis of crescent formation in glomerulonephritis with the demonstration of substantial local macrophage proliferation within Bowman's space. It is proposed that local proliferation is a major mechanism of macrophage accumulation within crescents and plays an important role in the progression of epithelial-dominated early cellular crescents to macrophage-dominated advanced and fibrocellular cellular crescents.

Ultrastructural localisation of CD44 in the rat lung in experimental Goodpasture's syndrome

Although CD44 is known to be involved in a wide array of cell to cell and cell to matrix interactions, its role in immune-mediated disease is not well understood. Therefore, using immunogold electron microscopy we have determined the precise localisation of CD44 in the rat lung in experimental Goodpasture's (GP) syndrome, a model of immune-mediated pulmonary disease. In normal rat lung CD44 was present on the surface of alveolar macrophages but was not detectable on endothelium. In GP syndrome there was strong CD44 expression on all infiltrating inflammatory leucocytes, both adherent to endothelium and within the alveolar spaces and interstitium. However the most striking finding was the progressively strong antibody staining for CD44 on pulmonary endothelium of alveolar capillaries and larger vessels over the 21 days of GP syndrome. In situ hybridisation confirmed that the endothelial CD44 staining was due to local protein synthesis. All epithelial cell surfaces, including bronchial epithelium and type I and II alveolar epithelial cells, were negative in normal rat lung and GP syndrome. De novo CD44 expression by endothelial cells during the progression of GP syndrome may contribute to leucocyte recruitment and cell-mediated lung injury.

Macrophage apoptosis in rat crescentic glomerulonephritis

The fate of macrophages at the site of inflammation is unknown. We investigated this question in a macrophage-mediated model of crescentic glomerulonephritis in which macrophage accumulation is relatively stable despite the presence of high levels of local macrophage proliferation. Accelerated anti-glomerular basement membrane glomerulonephritis was induced in groups of six rats that were killed on day 1, 7, 14, or 21. Macrophage apoptosis was demonstrated in kidney sections by three methods: in situ terminal deoxyribonucleotide transferase (TdT)-mediated dUTP nick end labeling (TUNEL) combined with ED1 antibody immunostaining of macrophages, ED1 immunostaining combined with classical nuclear morphology, and electron microscopy. Substantial macrophage apoptosis became evident on day 14 of the disease, following the appearance of high levels of macrophage proliferation. The parallel relationship between proliferation and apoptosis is the likely explanation for the stabilization of macrophage numbers within the inflamed kidney. A striking feature was that macrophage proliferation and apoptosis was largely restricted to areas of focal damage, such as in the development of glomerular crescents. Increasing levels of macrophage proliferation and apoptosis were evident as crescents developed from a cellular to a fibrocellular phenotype, with a dramatic reduction in both of these processes in the progression to a fibrotic phenotype, suggesting an important role for macrophage apoptosis in the resolution of fibrocellular crescents to an acellular fibrotic structure. In conclusion, this study has identified apoptosis as an important mechanism counterbalancing local proliferation in the regulation of macrophage accumulation at sites of inflammation. Indeed, apoptosis may be a central regulator of the progression and resolution of macrophage-mediated tissue injury.

Role of interleukin-1 in mesangial cell proliferation and matrix deposition in experimental mesangioproliferative nephritis

We examined the functional role of interleukin (IL)-1 in mesangial cell proliferation during rat anti-Thy-1 nephritis by blocking its action with IL-1 receptor antagonist (IL-1ra). Anti-Thy-1 nephritis was induced by intravenous injection of 5 mg/kg OX-7 IgG (day 0) into inbred Wistar rats. Groups of animals (n = 9) were implanted with a micro-osmotic pump on day -1, which delivered 25 micrograms/hour human recombinant IL-1ra or saline continuously until the rats were killed at day 6, the peak of mesangial cell proliferation. Immunostaining showed that IL-1 was expressed by mesangial cells during disease. IL-1ra treatment did not affect the mild, but significant, proteinuria seen after OX-7 injection. Compared with saline treatment, IL-1ra treatment reduced mesangial cell proliferation (decreases 24% P < 0.05), glomerular hypercellularity (decreases 29%; P < 0.05), and glomerular macrophage accumulation (decreases 20%; P < 0.05). However, IL-1ra treatment had no effect on glomerular IL-1 beta mRNA expression and caused only a small reduction in the high levels of glomerular expression of platelet-derived growth factor-beta protein (decreases 6%; P < 0.05). IL-1ra caused a modest reduction in the marked up-regulation of glomerular transforming growth factor-beta 1 mRNA expression on day 6 (decreases 26%; P < 0.05), although urinary excretion of this factor was unaffected. Interestingly, IL-1ra treatment had relatively little effect upon glomerular deposition of laminin, fibronectin, and collagen type IV seen in this acute disease. In conclusion, this study has 1) demonstrated that IL-1 is expressed by mesangial cells in vivo, 2) demonstrated that IL-1 is a mesangial cell growth factor in experimental mesangioproliferative nephritis, and 3) suggests that IL-1 has little or no fibrogenic activity in mesangial matrix deposition.

Intrinsic renal cells are the major source of interleukin-1 beta synthesis in normal and diseased rat kidney

BACKGROUND

A number of studies have demonstrated a pathological role for interleukin-1 (IL-1) in experimental models of glomerulonephritis, but the cellular pattern of renal IL-1 production remains poorly characterized. The aim of this study, therefore, was to identify the cell types expressing IL-1 in normal and diseased rat kidney.

METHODS

Renal IL-1 beta expression was examined in normal rats and during a 21-day time course of rat accelerated anti-GBM glomerulonephritis by northern blotting, in situ hybridization and double immunohistochemistry.

RESULTS

Interleukin-1 beta mRNA expression was readily detectable in normal rat kidney by northern blot analysis and in situ hybridization. Immunohistochemistry staining demonstrated constitutive IL-1 beta expression by glomerular endothelial cells and cortical tubular epithelial cells. There was a marked increase in whole kidney IL-1 beta mRNA in rat anti-GBM glomerulonephritis. Glomerular IL-1 beta immunostaining was upregulated, being expressed by podocytes, mesangial cells and infiltrating macrophages, and was particularly prominent within glomerular crescents. Double staining with the ED1 antibody showed IL-1 beta expression in up to 13% of glomerular macrophages, whereas 48% of macrophages within crescents stained for IL-1 beta. However, the most marked increase in IL-1 beta expression was seen in cortical tubular epithelial cells, particularly in areas of tubular damage. In situ hybridization confirmed that tubular IL-1 beta staining was due to local cytokine synthesis rather than protein absorption.

CONCLUSIONS

This study has identified constitutive IL-1 beta expression by glomerular endothelium and tubular epithelial cells in normal rat kidney. In addition, the marked upregulation of IL-1 beta expression by intrinsic glomerular cells and tubules in rat anti-GBM disease suggests an important role for these cells in IL-1 dependent crescent formation and tubulointerstitial injury.

Effect of interleukin-10 treatment on crescentic glomerulonephritis in rats

This study examined the utility of interleukin-10 (IL-10), a cytokine with potent anti-macrophage and anti-Th1 activity, in the treatment of experimental anti-glomerular basement membrane (GBM) nephritis in the rat. Accelerated anti-GBM disease was induced in Sprague-Dawley rats by immunization with rabbit IgG, followed five days later by an i.v. injection of anti-GBM serum. Groups of four rats received daily s.c. injections of recombinant mouse IL-10 (500, 10 or 0.2 microgram/kg/day) or saline (control) from the time of anti-GBM serum administration until being killed on day 14. IL-10 treatment suppressed the skin DTH response as measured by skin thickness (44 to 62% decrease vs. control, p < 0.05). Compared to saline controls, IL-10 treatment had no beneficial effect on renal function, proteinuria or histological damage (including crescent formation) at any dose examined. A detailed analysis of high dose IL-10 (500 micrograms/kg/day) and saline treated animals was undertaken. Saline controls had marked glomerular macrophage accumulation and proliferation, which was augmented by IL-10 treatment (46 to 99% increases and 44 to 143% increases, respectively; p < 0.05). Immunohistochemical staining found no difference in the state of macrophage activation between the groups, as determined by the percentage of macrophages expressing IL-1 beta protein. Northern blot analysis of whole kidney RNA demonstrated an 830% increase in IL-1 beta mRNA expression in saline controls compared to normal rat kidney. High dose IL-10 treatment reduced IL-1 beta mRNA levels by 60% compared to controls (P < 0.05), but did not significantly reduce glomerular IL-1 beta protein expression. IL-10 treatment increased serum levels of rat anti-rabbit IgG, induced a rat anti-mouse IL-10 response and augmented glomerular deposition of rat C3. In conclusion, IL-10 was not an effective treatment for rat crescentic anti-GBM glomerulonephritis. This may have been due to the failure of IL-10 to achieve a sufficient reduction in IL-1 beta expression and macrophage participation in disease, or promotion of the Th2 immune response.

Interleukin-10 is a mesangial cell growth factor in vitro and in vivo

Macrophages are involved in the pathogenesis of mesangioproliferative glomerulonephritis. As macrophages are known to produce interleukin-10 (IL-10), we investigated the effect of recombinant murine IL-10 (rIL-10) on mesangial cell growth. In vitro studies were performed using the rat 1097 mesangial cell line. These cells exhibited a dose-dependent proliferative response to rIL-10 (23% to 70% increases at 80 ng/mL; p < 0.01), as assessed by both 3H-thymidine uptake and cell count. This effect was inhibited by preincubation of rIL-10 with a neutralizing anti-IL-10 antibody. When added to cultures of growth-arrested 1097 cells, IL-10 induced dose-dependent proliferation that paralleled the effects of platelet-derived growth factor. Incubation with a neutralizing anti-IL-10 Ab for 48 hours reduced 3H-thymidine uptake (median, 27% decreases; range, 2% to 56% decreases) versus a control Ab; p < 0.05). Rat mesangial cells were also shown to express IL-10 mRNA and protein, as determined by Northern blotting and immunostaining, thereby suggesting a role for IL-10 in autocrine mesangial cell growth. To examine the effects of IL-10 in vivo, inbred male Sprague-Dawley rats were given subcutaneous rIL-10 (0.5 mg/kg) for 3 (n = 6), 7 (n = 3), or 14 days (n = 4), or vehicle control, then killed. IL-10 administration induced a transient reduction in creatinine clearance of 35% at Day 3 (p < 0.01). Following IL-10 administration, an increase in glomerular cellularity was seen, which was maximal at Day 3 (82.7 +/- 5.9 nuclei/glomerular cross section versus control 64.6 +/- 4.6, 28% increases; p < 0.001) and maintained at Day 14 (23% increases; p < 0.01). Immuno-histochemical staining for proliferating cell nuclear antigen demonstrated an increased number of proliferating cells per glomerular cross section at day 3 (48% increases versus controls; p < 0.05). Staining for alpha-smooth-muscle actin showed significant labeling only in the glomeruli of IL-10-treated animals; double-labeling with an anti-proliferating cell nuclear antigen Ab demonstrated that some of these mesangial cells were proliferating. Collectively, these results suggest that IL-10 is a growth factor for rat mesangial cells both in vitro and in vivo.