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

Mathematical model of renal interstitial fibrosis

Lupus nephritis (LN) is an autoimmune disease that occurs when autoantibodies complex with self-antigen and form immune complexes that accumulate in the glomeruli. These immune complexes initiate an inflammatory response resulting in glomerular injury. LN often concomitantly affects the tubulointerstitial compartment of the kidney, leading first to interstitial inflammation and subsequently to interstitial fibrosis and atrophy of the renal tubules if not appropriately treated. Presently the only way to assess interstitial inflammation and fibrosis is through kidney biopsy, which is invasive and cannot be repeated frequently. Hence, monitoring of disease progression and response to therapy is suboptimal. In this paper we describe a mathematical model of the progress from tubulointerstitial inflammation to fibrosis. We demonstrate how the model can be used to monitor treatments for interstitial fibrosis in LN with drugs currently being developed or used for nonrenal fibrosis.

How does proteinuria cause progressive renal damage?

The possibility that proteinuria may accelerate kidney disease progression to end-stage renal failure has received support from the results of increasing numbers of experimental and clinical studies. Evidence indicating that this process occurs through multiple pathways, including induction of tubular chemokine expression and complement activation that lead to inflammatory cell infiltration in the interstitium and sustained fibrogenesis, is reviewed. Macrophages are prominent in the interstitial inflammatory infiltrate. This cell type mediates progression of renal injury to the extent that macrophage numbers in renal biopsy predict renal survival in patients with chronic renal disease. Chemoattractants and adhesive molecules for inflammatory cells are upregulated by excess ultrafiltered protein load of proximal tubular cells via activation of NF-kappaB-dependent and NF-kappaB-independent pathways. This mechanism is a potential target for therapeutic approaches, as shown by beneficial effects of manipulations with inhibitory molecules of NF-kappaB activation or of chemokine receptors in experimental studies. Targeting complement synthesis or activation in proximal tubule might offer novel therapeutic opportunities. Finally, proximal tubular cell receptors for uptake of plasma proteins that are under investigation may provide activation signals on excess tubular protein handling.

Renal albumin absorption in physiology and pathology

Albumin is the most abundant plasmaprotein serving multiple functions as a carrier of metabolites, hormones, vitamins, and drugs, as an acid/base buffer, as antioxidant and by supporting the oncotic pressure and volume of the blood. The presence of albumin in urine is considered to be the result of the balance between glomerular filtration and tubular reabsorption. Albuminuria has been accepted as an independent risk factor and a marker for renal as well as cardiovascular disease, and during the past decade, evidence has suggested that albumin itself may cause progression of renal disease. Thus, the reduction of proteinuria and, in particular, albuminuria has become a target in itself to prevent deterioration of renal function. Studies have shown albumin and its ligands to induce expression of inflammatory and fibrogenic mediators, and it has been hypothesized that increased filtration of albumin causes excessive tubular reabsorption, resulting in inflammation and fibrosis, resulting in the loss of renal function. In addition, it is known that tubular dysfunction in itself may cause albuminuria owing to decreased reabsorption of filtered albumin, and, recently, it has been suggested that significant amounts of albumin fragments are excreted in the urine as a result of tubular degradation. Thus, although both tubular and glomerular dysfunction influences renal handling of albumin, it appears that tubular reabsorption plays a central role in mediating the effects of albumin on renal function. The present paper will review the mechanisms for tubular albumin uptake and the possible implications for the development of renal disease.

Early proinflammatory activation of renal tubular cells by normal and pathologic IgG

BACKGROUND/AIMS

To verify whether human IgG induces proinflammatory activation of human proximal tubular epithelial cells (PTEC) independent of the metabolic overload of protein reabsorption.

METHODS

Cultured PTEC were incubated with normal IgG, IgG from systemic lupus erythematosus (SLE) patients, albumin or transferrin. IL-6 secretion and extracellular regulated kinase (ERK) activation (dual-phosphorylated ERK) were measured by ELISA and by Western blotting of PTEC extracts, respectively; renal biopsy specimens from patients with IgG and non-IgG proteinuria were analyzed by immunohistochemistry and in situ hybridization to detect ERK-P and IL-6.

RESULTS

Normal and SLE IgG, but not albumin or transferrin, induced an early significant increase in IL-6 secretion by PTECs. Also ERK activation was found after 1-hour incubation of PTEC with IgG, but not with control medium and albumin-treated PTEC. Activated ERK and IL-6 were found to colocalize in tubular cells in the kidney specimens of patients with IgG proteinuria only.

CONCLUSION

IgG-dependent early activation of ERK and increased IL-6 secretion in PTEC suggest that IgG filtered during nonselective proteinuria may play a specific role in tubulointerstitial disease. Such a role could be particularly relevant in diseases associated with abnormal IgG pool compositions, such as SLE. Preliminary results on human renal biopsy specimens suggest that our in vitro observations may also be relevant in vivo.

alpha(v)beta(6) Integrin expression in diseased and transplanted kidneys

BACKGROUND

Integrins have been implicated in the pathogenesis of a diverse range of kidney diseases. Herein, we provide the first detailed description of an epithelial restricted integrin, alpha(v)beta(6), in kidney biopsies from patients suffering acute and chronic renal diseases and after transplantation.

METHODS

Immunoperoxidase staining for beta(6) was performed on 267 selected biopsy specimens from native (N= 126) and transplanted kidneys (N= 141) and scored semiquantitatively. The site of beta(6) expression in tubules was determined using haematoxylin counterstaining and by colocalization with Tamm-Horsfall protein. Comparisons were made between subcategories of diseases of native kidneys and between "service" and "protocol" biopsies of transplanted kidneys.

RESULTS

beta(6), when present, is largely confined to the distal tubules and collecting ducts, colocated with Tamm-Horsfall protein. When sparsely present, it was often restricted to the tubular segment associated with the juxtaglomerular apparatus. It was found in tubular cells shed into the urine. beta(6) was not expressed in thin membrane nephropathy, or in nonproliferative forms of glomerulonephritis, with the exception of focal and segmental glomerulosclerosis (FSGS). It was diffusely expressed where there was glomerular necrosis or thrombosis and in most forms of acute or chronic tubulointerstitial disease. beta(6) was diffusely up-regulated in allografts biopsied for delayed function, in almost all kidneys that have clinical or subclinical rejection episodes and was prominent in chronic allograft nephropathy.

CONCLUSION

beta(6) integrin is not normally expressed in adult native or transplanted kidneys but is commonly up-regulated in the distal tubule in disease. Our descriptive study suggests that it is a molecule worthy of further study.

Fas activation induces renal tubular epithelial cell beta 8 integrin expression and function in the absence of apoptosis

Cell fate following Fas (CD95) ligand or agonistic anti-Fas antibody stimulation is determined by multiple factors, including Fas expression level, microdomain localization, and modulating cytokines. Highly expressed Fas clusters and activates a canonical apoptosis signaling pathway. In less susceptible cells, Fas transduces apoptosis-independent signals, which are not well defined, but have been linked to inflammation, angiogenesis, and fibrosis. To identify apoptosis-independent Fas pathways, cultured renal tubular epithelial cells were stimulated with agonistic anti-Fas antibodies under conditions that did not cause cell death. Analysis of filter cDNA microarrays revealed beta(8) integrin subunit mRNA induction in Fas-stimulated cells. beta(8) integrin mRNA expression increased within 3-6 h of Fas ligation due to enhanced mRNA stabilization, and mRNA increases were sustained for 48-72 h. Expression of plasma membrane beta(8) integrin, as well as its heterodimer partner alpha(v), was increased by Fas activation with a similar kinetic pattern. Fas-induced alpha(v)beta(8) expression correlated with increased migration to vitronectin, the ligand for alpha(v)beta(8). Results from studies with function-blocking antibodies against other alpha(v)beta integrins or suppression of beta(8) integrin expression by RNA interference demonstrated that induced beta(8) integrin expression mediated Fas-stimulated migration. We conclude that alpha(v)beta(8) integrin induction defines an unexpected role for Fas in cell migration, rather than as a cell death receptor.

Phenotypic changes and cell cycle activation in early tubulointerstitial injury of rat adriamycin nephrosis

Tubular response, including phenotypic changes against a variety of injuries, is an initial event that promotes tubulointerstitial injuries. Using the progressive kidney disease model of rat adriamycin (ADR) nephrosis, the present study focused on the cell cycle activation and phenotypic changes that occur in the tubuli in early tubulointerstitial injury in ADR nephrosis. At 12 weeks, experimental animals developed overt nephrosis with tubulointerstitial injury, which correlated well with the degree of proteinuria and incidence of glomerulosclerosis. Initial pathology of the tubuli showed a slight dilatation of tubuli, which tended to occur in individual nephrons. Immunohistochemistry demonstrated that vimentin-positive tubuli and osteopontin (OPN)-positive tubuli were associated mostly with proliferating cell nuclear antigen expression. Protein levels of OPN in the renal cortex were correlated with the level of proteinuria by western blotting. Vimentin- and OPN-expressing tubuli were tightly associated with a peritubular influx of alpha-smooth muscle actin (SMA)-positive cells or ED-1-positive cells. In addition, we found thrombomodulin+/ TUNEL+ (dUTP-biotin nick-end labeling) peritubular endothelial cells and ED-1+/alpha-SMA+ cells at an early stage among interstitial inflammatory cells. These results suggest that cell cycle activation in tubular cells forms the background for the phenotypic tubular changes that are involved in chronic tubulointerstitial injury in ADR nephrosis.

C5b-9 and adhesion molecules in human idiopathic membranous nephropathy

BACKGROUND

Cellular immune responses and C5b-9 seem to play an important role in the pathogenesis and progression of idiopathic membranous nephropathy (IMN). The aim of the study was to investigate the role of C5b-9 and adhesion molecules in the pathogenesis of the disease.

METHODS

The clinical and pathological data of 35 patients with biopsy-proven IMN were correlated with immunohistochemical findings using monoclonal antibodies against T lymphocytes, monocytes/macrophages (MM), HLA-DR antigens, C5b-9, and adhesion molecules such as alpha3beta1, LFA-1beta, and ICAM-1.

RESULTS

In the glomeruli, C5b-9 deposits showed a significant correlation with the intensity of IgG and C3 deposition. The stage of the disease had a significant negative relationship with the glomerular alpha3beta1 expression. In the tubulointerstitium (TIN), the number of HLA-DR(+) cells was highly correlated with the numbers of total T lymphocytes, MM, and LFA-1beta(+) cells, as well as with the percentage of tubules with C5b-9 deposits. The extent of ICAM-1 expression in the TIN was significantly correlated with the numbers of interstitial MM, HLA-DR(+), and LFA-1beta(+) cells, as well as with the extent of tubular C5b-9 deposition. The severity of tubular atrophy and interstitial fibrosis had a relationship with the numbers of total T lymphocytes, MM, HLA-DR(+), and LFA-1beta(+) cells and with the extent of tubular C5b-9 deposition and ICAM-1 expression in the TIN. Serum creatinine (Scr) was highly correlated with the numbers of interstitial total T lymphocytes, MM, HLA-DR(+), and LFA-1beta(+) cells. Moreover, Scr had a significant relationship with the severity of tubular atrophy and interstitial fibrosis, as well as with the extent of tubular C5b-9 deposition and ICAM-1 expression in the TIN. Proteinuria was significantly correlated with the extent of tubular alpha3beta1 expression.

CONCLUSIONS

In IMN, C5b-9 formation may be secondary to IgG and C3 deposition. Proteinuria may contribute to the TIN damage by altering the expression of alpha3beta1 integrins in tubular cells. De novo ICAM-1 and C5b-9 expression within the TIN as well as the activated interstitial cells may be important factors leading to renal damage and renal function impairment.

Distribution of alphavbeta3, alphavbeta5 integrins and the integrin associated protein--IAP (CD47) in human glomerular diseases

The alphav integrins present on the membrane of numerous cells, mediate attachment to matrix proteins, cell proliferation, migration and survival. We studied the expression of alphav integrinis and CD47 (a beta3 chain integrin associated protein) in various forms of glomerulonephritis (GN) characterized by mesangial proliferation and/or increased mesangial matrix. In normal glomeruli, epithelial cells expressed alphavbeta3, alphavbeta5 and CD47; endothelial cells expressed alpha5beta1 and CD47; mesangial cells expressed alphavbeta5, CD47, and to a less extent alphavbeta3. In acute post infectious GN (APIGN), membrano-proliferative GN (MPGN) and diabetic nephropathy(DN), we observed that the beta3 chain, normally expressed by mesangial cells, was not detectable in the mesangium while its expression by epithelial cells was not modified. Parallel to the disappearance of alphavbeta3, the CD47 expression was decreased on the mesangial cells in MPGN, APIGN and DN. The expression of alphavbeta5 was clearly increased on podocytes and on proliferating mesangial cells in APIGN. By contrast, the mesangial expression of alphavbeta was normal or decreased in DN. The alpha5 chain of integrin, absent on normal mesangial cell, was expressed on proliferating mesangial cells in MPGN and APIGN. Thus, we observed modifications of alphavbeta3 and alphavbeta5 expression during human GN. The modulations of alphavbeta3 and alphavbeta5 expression differed according to the different glomerular cell types and were not parallel in glomerular cells: alphavbeta3 was decreased (and alphavbeta5 unchanged) on proliferating mesangial cells and alphavbeta5 was increased (and alphavbeta3 unchanged) in podocytes. This may reflect the existence of two distinct regulatory pathways.

Integrin expression and IgA nephropathy: in vitro modulation by IgA with altered glycosylation and macromolecular IgA

BACKGROUND

Signal transduction by mesangial cell (MC) integrins regulates cell growth and survival, extracellular matrix production, and organization. The aim of the study was to investigate human MC integrin modulation by differently glycosylated IgA and macromolecular IgA, which are thought to play a pathogenetic role in IgA nephropathy (IgAN).

METHODS

MCs were incubated with purified human polymeric IgA, heat-aggregated IgA, IgA glycoforms generated by enzymatic hydrolysis of saccharide residues and serum fractions from IgAN patients, and controls isolated by lectin affinity and containing IgA with peculiar glycan patterns. Integrins were quantitated by flow cytometry.

RESULTS

Cultured MCs highly expressed alphavbeta3 and some alpha3beta1; alphavbeta3 was up-regulated by matrix components (P < 0.02). In vitro desialylated and degalactosylated polymeric human IgA enhanced alphavbeta3 expression on cultured MCs (P < 0.001). Serum IgA glycoforms isolated from IgAN patients with high exposure of internal sugars, GalNAc, Neu5Ac2,6GalNAc, and Man enhanced alphav expression on cultured MCs more than healthy controls. CONCLUSIONS.: These data support the hypothesis that IgA glycation plays a role in modulating the cell-matrix interaction, and that this mechanism can be operating in IgAN.

Factors influencing the course and the response to treatment in primary focal segmental glomerulosclerosis

BACKGROUND

The clinical course of primary focal segmental glomerulosclerosis (FSGS) varies and there is considerable controversy as to which factors are of importance in determining prognosis or response to therapy. The aim of this study was to identify clinical, pathological or immunohistochemical features at biopsy that could identify patients with progressive disease who might benefit from treatment, and predict long-term outcome.

METHODS

The clinical and pathological findings of 33 adult patients with primary FSGS were retrospectively analysed in order to identify features at biopsy that could be predictive of outcome or response to treatment. For this purpose an immunohistochemical study was also performed, using monoclonal antibodies against intracellular adhesion molecules-1, C5b-9, alpha 3 beta 1 integrin, alpha-smooth-muscle actin (SMA), and TGF-beta1.

RESULTS

At biopsy 17 patients (51%) were nephrotic and 16 (49%) non-nephrotic. Of the nephrotic patients, 11 were treated and six received only symptomatic therapy. Initial treatment with prednisolone (Pred) for 6-12 months (average 9 months) resulted in remission in 64% of nephrotic patients. To those with partial or no response, cyclosporin (CsA) or cyclophosphamide was given. At the end of follow-up (mean 57 months) three nephrotic patients (28%) were in complete remission, six (54%) in partial remission, and two (18%) did not respond to the treatment. In the seven treated non-nephrotic patients, Pred induced a complete remission in two (28%), a partial remission in three (44%), while two patients (28%) did not respond. Plasma creatinine remained stable in nephrotic patients who responded and it almost doubled in non-responders. Plasma creatinine also remained unchanged in treated non-nephrotic patients who responded to Pred, while two non-responders reached end-stage renal disease (ESRD). In contrast, 50% of untreated nephrotic patients and 67% of untreated non-nephrotic patients progressed to ESRD. Multivariate analysis showed only age and plasma creatinine at biopsy to have an independent predictive value for renal survival in nephrotic patients. This analysis also demonstrated that only the severity of interstitial fibrosis predicted the response to the treatment. In addition, the tubulointerstitial but not the glomerular expression of C5b-9, alpha 3 beta 1 integrin, alpha-SMA, and TGF-beta1 was significantly more extensive in non-responders and correlated with renal function at biopsy. However, only tubulointerstitial expression of TGF-beta1 independently correlated with the degree of renal function impairment at biopsy, but none of the above markers independently predicted renal survival or response to therapy.

CONCLUSIONS

Nephrotic patients with FSGS may benefit from a more prolonged course of Pred. Nephrotic patients responding to treatment have a significantly better renal survival than non-responders. Age and plasma creatinine at biopsy are independent risk factors leading to ESRD. The severity of tubulointerstitial fibrosis is predictive of response to therapy.

Integrins in kidney development, function, and disease

Integrins are heterodimeric cell surface receptors that mediate heterophilic cell-cell interactions and interactions between cells and the extracellular matrix (Hynes RO. Cell 69: 11-25, 1991). As such, they are involved in morphogenetic processes during development, as well as in the maintenance of normal tissue architecture in fully developed organs. Integrins are now recognized to be a large family of receptors, and several different integrins have been demonstrated as being expressed in the developing and adult kidney (Korhonen M, Ylkanne J, Laitinen L, and Virtanen I. Development 122: 3537-3547, 1996; Rahilly MA and Fleming S. J Pathol 167: 327-334, 1992). This review will summarize present knowledge about integrin expression in the developing, normal, and diseased kidney and attempt to provide a hypothetical framework for understanding integrin function in the urogenital system. Since the last time this area was reviewed (Hamerski DA and Santoro S. Curr Opin Nephrol Hypertens 8: 9-14, 1999), there have been significant publications on the roles of integrins in kidney development and disease. At present, there are many more questions than answers, and integrins present an area where many novel and exciting findings will emerge in the coming years.

Nitric oxide mediates cyclosporine-induced apoptosis in cultured renal cells

BACKGROUND

The clinical use of cyclosporine (CsA) is limited by its nephrotoxicity. Apoptosis, perhaps instigated by increased nitric oxide synthase (NOS) activity, may play a role in such toxicity.

METHODS

Human mesangial cells, human tubular cells, human umbilical vein endothelial cells, or murine endothelial cells were cultured with CsA at final concentrations of 0 to 1000 ng/mL for 4 to 24 hours. As inhibitors of apoptosis, 0.01 mol/L L-nitromethylarginine (L-NAME) or 1 microg/mL cycloheximide (CHX) was added, whereas 0.01 mol/L sodium nitroprusside (as a nitric oxide donor) was used as a positive control. Apoptosis was assessed by using TUNEL method and by DNA fragmentation by electrophoresis. In addition, NOS enzymatic activity, Northern blots for inducible NOS (iNOS) mRNA, and immunohistochemically demonstrable iNOS protein were evaluated.

RESULTS

Within 12 to 24 hours, CsA significantly increased the fraction (8 to 35%) of apoptotic cells in each cell line, according to the dose. Fragmentation of DNA confirmed apoptosis. L-NAME and CHX inhibited the phenomenon, whereas sodium nitroprusside enhanced it. Each cell line significantly increased NOS activity in response to CsA, an effect blunted by L-NAME and CHX. Neither inhibitor modified the increased iNOS mRNA expression elicited by CsA. Positive staining for both iNOS and p53 proteins was observed in all cell lines incubated with CsA that were inhibited by CHX; L-NAME inhibited only p53 staining.

CONCLUSIONS

CsA induces apoptosis in various renal cell lines, and this effect is mediated by the induction of iNOS via p53. These effects may contribute to the acellular fibrosis characteristic of late CsA nephrotoxicity.

Activation of mitogenic pathways by albumin in kidney proximal tubule epithelial cells: implications for the pathophysiology of proteinuric states

Albumin is filtered into the proximal tubule in large quantities in nephrotic states. It has been proposed that this protein may have a toxic effect on tubular epithelial cells and may be responsible for the initiation of interstitial inflammation and scarring. The mitogenic effect of recombinant human albumin in wild-type opossum kidney cells and in similar cells transfected with a dominant negative p85 subunit (deltap85) of phopshatidylinositide 3-kinase (PI 3-kinase) has been studied. This study demonstrates that recombinant human albumin stimulates proliferation of opossum kidney cells in culture. This effect is mediated via PI 3-kinase, and is inhibited by wortmannin and deltap85 expression. Albumin stimulates PI 3-kinase activity in opossum kidney cells as determined by three different experimental procedures. Recombinant albumin also stimulates pp70(s6) kinase activity in a kinase cascade downstream of PI 3-kinase. Activity of pp70(s6) kinase is essential for albumin-induced proliferation of opossum kidney cells. It is proposed that this mitogenic pathway may have a critical role in proximal tubular homeostasis and pathophysiology of proteinuric states.

Role of tubule epithelial cells in the pathogenesis of tubulointerstitial fibrosis induced by glomerular disease

Tubulointerstitial fibrosis is a final common pathway for progressive renal injury in most 'inflammatory' and 'non-inflammatory' glomerulopathies. Indeed, the level of tubulointerstitial fibrosis correlates closely with the degree of chronic renal dysfunction in these settings. An emerging body of evidence suggests that tubule epithelial cells are dynamic players in the pathogenesis of tubulointerstitial fibrosis. Here we briefly review the potential mechanisms of tubule cell activation in patients with glomerular disease. These mechanisms include: (a) direct involvement of glomerular and tubulointerstitial compartments by the primary disease; (b) secondary activation of tubule epithelial cells by glomerulus-derived cytokines; (c) perturbation of tubule epithelial cell function by plasma proteins and associated moieties filtered in excess through injured glomeruli; (d) tubulointerstitial ischaemia downstream to glomerular injury; and (e) hyperfunction of remnant tubules. Activated tubule epithelial cells are, in turn, a rich source of cytokines, chemokines and other mediators that promote leukocyte recruitment, cytotoxicity and fibrogenesis, thereby establishing a 'vicious cycle' of tubulointerstitial injury. The further delineation of the role played by the tubule epithelial cell in the pathogenesis of tubulointerstitial fibrosis may suggest novel approaches for the treatment of progressive renal diseases.

Growth factor-dependent activation of alphavbeta3 integrin in normal epithelial cells: implications for tumor invasion

Integrin activation is a multifaceted phenomenon leading to increased affinity and avidity for matrix ligands. To investigate whether cytokines produced during stromal infiltration of carcinoma cells activate nonfunctional epithelial integrins, a cellular system of human thyroid clones derived from normal glands (HTU-5) and papillary carcinomas (HTU-34) was employed. In HTU-5 cells, alphavbeta3 integrin was diffused all over the membrane, disconnected from the cytoskeleton, and unable to mediate adhesion. Conversely, in HTU-34 cells, alphavbeta3 was clustered at focal contacts (FCs) and mediated firm attachment and spreading. alphavbeta3 recruitment at FCs and ligand-binding activity, essentially identical to those of HTU-34, occurred in HTU-5 cells upon treatment with hepatocyte growth factor/scatter factor (HGF/SF). The HTU-34 clone secreted HGF/SF and its receptor was constitutively tyrosine phosphorylated suggesting an autocrine loop responsible for alphavbeta3 activated state. Antibody-mediated inhibition of HGF/SF function in HTU-34 cells disrupted alphavbeta3 enrichment at FCs and impaired adhesion. Accordingly, activation of alphavbeta3 in normal cells was produced by HTU-34 conditioned medium on the basis of its content of HGF/SF. These results provide the first example of a growth factor-driven integrin activation mechanism in normal epithelial cells and uncover the importance of cytokine-based autocrine loops for the physiological control of integrin activation.

Adhesion molecules and urinary tumor necrosis factor-alpha in idiopathic membranous glomerulonephritis

Adhesion molecules are required in several physiological processes, but their altered function/expression is associated with the pathogenesis of inflammatory diseases. In the present study on idiopathic membranous glomerulonephritis (MGN) the expression of adhesion molecules (ICAM-1, VCAM-1, PECAM-1, E-selectin, LFA-1, Mac-1) was analyzed in different cellular compartments of the kidney using an indirect immunoperoxidase technique and monoclonal antibodies. Relationships between the expression of these molecules and the clinical and morphological activity of the disease and the urinary excretion of tumor necrosis factor alpha (TNF-alpha) were studied in 20 patients. The results were compared with the findings in ten normal kidneys and urinary TNF-alpha in 17 healthy subjects. The expression of adhesion molecules in glomeruli and tubules was unchanged apart from a diminished expression of VCAM-1 (P = 0.014) in glomerular parietal epithelial cells and PECAM-1 in glomerular endothelial cells (P < 0.01). Interstitial peritubular capillaries expressed significantly (P = 0.009) more E-selectin compared with the controls. The interstitial compartment had a highly increased number of cells expressing ICAM-1 in MGN (32.4 +/- 4.6 cells/high power field) compared with the controls (9.4 +/- 1.2; P < 0.001). Also, cells expressing VCAM-1 (10.2 +/- 1.6 vs. 2.8 +/- 1.9; P = 0.005). PECAM-1 (25.9 +/- 5.3 vs. 7.4 +/- 2.1; P = 0.006), and LFA-1 (20.4 +/- 3.6 vs. 8.3 +/- 1.5; P = 0.041) were increased in the interstitium. Proteinuria correlated particularly with the expression of E-selectin in peritubular capillaries (r = 0.63, P = 0.004). The number of LFA-1 expressing inflammatory cells in the interstitium correlated with peritubular capillary E-selectin (r = 0.8, P < 0.001) and interstitial ICAM-1 (r = 0.61, P = 0.009) expression, but histological alterations did not correlate with the expression of adhesion molecules. Tumor necrosis factor-alpha excretion was significantly increased in MGN (41 +/- 8 pg/mg creatinine) compared with the controls (13 +/- 2; P = 0.001), and in particular, it correlated with the interstitial expression of LFA-1 (r = 0.71, P = 0.002). This study suggests that active MGN leads not only to proteinuria but also to increased urinary TNF-alpha excretion. These may serve as triggers for the up-regulation of adhesion molecules in the peritubular capillaries and interstitial cells thus enhancing the development of the interstitial injury.