Distribution of renal lesions in idiopathic systemic vasculitis: A three-dimensional analysis of 87 glomeruli

EGF-Receptor-Dependent TLR7 Signaling in Macrophages Promotes Glomerular Injury in Crescentic Glomerulonephritis

Glomerulonephritis (GN) is a group of inflammatory diseases and an important cause of morbidity and mortality worldwide. The initiation of the inflammatory process is quite different for each type of GN; however, each GN is characterized commonly and variably by acute inflammation with neutrophils and macrophages and crescent formation, leading to glomerular death. Toll-like receptor (TLR) 7 is a sensor for self-RNA and implicated in the pathogenesis of human and murine GN. Here, we show that TLR7 exacerbates glomerular injury in nephrotoxic serum nephritis (NTN), a murine model of severe crescentic GN. TLR7-/- mice were resistant to NTN, although TLR7-/- mice manifested comparable immune-complex deposition to wild-type mice without significant defects in humoral immunity, suggesting that endogenous TLR7 ligands accelerate glomerular injury. TLR7 was expressed exclusively in macrophages in glomeruli in GN but not in glomerular resident cells or neutrophils. Furthermore, we discovered that epidermal growth factor receptor (EGFR), a receptor-type tyrosine kinase, is essential for TLR7 signaling in macrophages. Mechanistically, EGFR physically interacted with TLR7 upon TLR7 stimulation, and EGFR inhibitor completely blocked the phosphorylation of TLR7 tyrosine residue(s). EGFR inhibitor attenuated glomerular damage in wild-type mice, and no additional glomerular protective effects by EGFR inhibitor were observed in TLR7-/- mice. Finally, mice lacking EGFR in macrophages were resistant to NTN. This study clearly demonstrated that EGFR-dependent TLR7 signaling in macrophages is essential for glomerular injury in crescentic GN.

Urinary podocyte mRNA is a potent biomarker of anti-neutrophil cytoplasmic antibody-associated glomerulonephritis

BACKGROUND

Anti-neutrophil cytoplasmic antibody-associated glomerulonephritis (ANCA-GN) is a critical kidney disease that sometimes results in an unfavorable renal outcome. Cellular crescent formation is a hallmark of ANCA-GN and is associated with renal prognosis, response to treatment, and it was reportedly associated with podocyte detachment. Because there is a need to explore non-invasive biomarkers for the evaluation of ANCA-GN activity, we tested whether urinary podocyte mRNA might be a potent non-invasive biomarker.

METHODS

We measured two different types of urinary podocyte mRNA, including podocin mRNA in relation to urine creatinine concentration (U-PodCR) and urinary podocin mRNA in relation to nephrin mRNA (U-PNR), which were reportedly associated with the activity of various glomerular diseases.

RESULTS

In ANCA-GN patients (n = 19), we discovered that U-PodCR was positively correlated with the percent of crescent formation until 50% crescent was reached because of podocyte depletion; U-PNR was correlated with the percent of crescent formation in all patients. Furthermore, patients with high levels of urinary podocyte mRNA exhibited a favorable renal outcome compared with the outcomes of patients with low levels of urinary podocyte mRNA. The levels of urinary podocyte mRNA were correlated with the rate of improvement in estimated glomerular filtration rate.

CONCLUSIONS

U-PodCR, U-PNR or a combination of these parameters might serve as a non-invasive potential biomarker in patients with ANCA-GN to predict the percent of crescent formation and renal prognosis.

Comparative Changes Noted in Renal Biopsies on Light Microscopy of ANCA Positive Vs ANCA Negative Serology

OBJECTIVES

Pauci-immune glomerulonephritis is the commonest cause of rapidly progressive glomerulonephritis (RPGN) which is associated with increased mortality and morbidity. More than 90% of these patients have serological presence of either antineutrophil cytoplasmic antibodies (ANCA), of cytoplamic (C) or perinuclear (P) type. "Immunofluoresence studies" exhibiting minimal or no fluorescence is diagnostic in all such cases. The present study aims to study the differences between renal biopsies of serologically ANCA negative versus ANCA positive individuals.

MATERIALS AND METHODS

One hundred and twenty renal biopsies (of clinically suspected cases of systemic vasculitis) were sub-divided sub-divided under the heading of serologically ANCA positive and serologically ANCA negative; and scoring them by means of a semi-quantitative scoring system devised at the beginning of the study to identify statistically significant, specific light microscopic features in the sub-components of renal biopsy.

RESULTS

Fifteen parameters were found to be statistically significantly (p-value <0.05) in ANCA positive serological cases. These were glomerular capillary loop infiltration by neutrophils, cellular crescents, fibro-cellular crescents, glomerular fibrinoid necrosis, glomerular sclerosis, peri-glomerular infiltration, interstitial oedema, interstitial eosinophils, tubular atrophy, tubular necrosis, tubulitis, arterial hyalinization, arterial necrosis, arterial vessel wall polymorpho nuclear infiltrate and myointimal hypertrophy.

CONCLUSION

The presence of above parameters in a renal biopsy report of a patient (in absence of facilities of autoimmune serology and immunofluoresence) can alert both nephrologist and nephropathologist to keep a possibility of renal symptoms arising out of systemic vasculitis.

Antineutrophil Cytoplasmic Autoantibody–Negative Pauci-immune Crescentic Glomerulonephritis

Pauci-immune crescentic glomerulonephritis (CrGN) is one of the most common causes of rapidly progressive glomerulonephritis. The majority of patients with pauci-immune CrGN had circulating antineutrophil cytoplasmic autoantibody (ANCA). However, patients with ANCA-negative pauci-immune CrGN were not investigated fully. This study aimed to analyze the characteristics of this subgroup of patients. Patients whose pauci-immune CrGN was diagnosed from 1997 to 2006 in one center were studied retrospectively. The criteria of pauci-immune was defined as "the intensity of glomerular immunoglobulins staining by direct immunofluorescence assay in renal sections was negative to 1+ staining on a scale of 0 to 4+." Clinical and pathologic characteristics were compared between patients with and without ANCA. Among the 85 patients with pauci-immune CrGN, 28 (32.9%) were ANCA negative. Compared with the 57 ANCA-positive patients, the ANCA-negative patients were much younger (39.7 +/- 17.0 versus 57.6 +/- 14.0 yr; P < 0.001). The level of urinary protein and the prevalence of nephrotic syndrome were significantly higher in ANCA-negative patients than that in ANCA-positive patients (P < 0.01 and P < 0.001, respectively). However, the prevalence of extrarenal involvement was significantly lower in ANCA-negative patients than that in ANCA-positive patients. The renal survival was poorer in ANCA-negative patients than that in ANCA-positive ones (P < 0.05). ANCA-negative pauci-immune CrGN was not rare and might represent an independent disease entity from ANCA-positive vasculitis.

Genetic linkage of albuminuria and renal injury in Dahl salt-sensitive rats on a high-salt diet: comparison with spontaneously hypertensive rats

Our aim was to study the effects of high-salt diet on the genetics of albuminuria and renal injury in the Dahl salt-sensitive (SS) rat. We compared SS with salt-resistant spontaneously hypertensive rats (SHR) and with genetically related salt-sensitive stroke-prone SHR (SHRSP). Moreover, we performed genome-wide linkage analysis to identify quantitative trait loci (QTL) contributing to salt-induced renal injury in an F2population derived from SS and SHR ( n = 230). In response to high-salt diet SS and SHRSP developed a striking increase in systolic blood pressure, urinary albumin excretion (UAE), and renal damage indices compared with SHR. Both SHRSP and SS developed severe glomerulosclerosis, whereas microangiopathy, tubulointerstitial fibrosis, and inflammation were more pronounced in SHRSP. We detected two QTL with significant linkage to UAE on rat chromosomes (RNO) 6 and 19. Comparison with the recently identified salt-independent UAE QTL in young animals revealed that the UAE QTL on RNO6 is unique to high-salt conditions, whereas RNO19 plays a significant role during both low- and high-salt conditions. Some F2animals demonstrated severe microangiopathy and tubulointerstitial injury, which exceeded the degree observed in the parental SS strain. Three loci demonstrated suggestive linkage to these phenotypes on RNO3, RNO5, and RNO20, whereas no linkage to glomerular damage was found. Further analyses at these loci indicated that the severity of renal injury was attributable to the SHR allele. Our data suggest that the SHR genetic background confers greater susceptibility for the development of microangiopathy and tubulointerstitial injury in salt-sensitive hypertension than the SS background.

Clinicopathologic predictors of death and ESRD in patients with pauci-immune necrotizing glomerulonephritis

BACKGROUND

Pauci-immune necrotizing glomerulonephritis (PING) occurs in various settings and has a very variable prognosis. We investigated whether clinicopathologic findings at the time of renal biopsy may predict major disease outcomes.

METHODS

We evaluated 72 consecutive patients with biopsy-documented PING. Kaplan-Meier curves and Cox models assessed event rates and risk factors for death, end-stage renal disease (ESRD), and death or new ESRD (after the renal biopsy).

RESULTS

During a follow-up of 305 person-years, 11 patients died, 13 patients developed ESRD, and 16 patients died or developed new ESRD. Among patients first seen within 3 months of renal biopsy (incident cases), the 5-year mortality rate was 20%, whereas the death or new ESRD rate was 34%. In univariate analyses, older age, lower creatinine clearance, erythrocyte sedimentation rate, and percentages of abnormal glomeruli, glomeruli with fibrous crescents, and glomeruli with global sclerosis were significant predictors of mortality, whereas antineutrophil cytoplasmic autoantibodies with cytoplasmic staining conferred borderline protection. For ESRD, significant predictors included a greater creatinine level, lower hematocrit, interstitial fibrosis, tubular necrosis, greater C-reactive protein level, and percentages of abnormal glomeruli, glomeruli with extracapillary proliferation, cellular crescents, and global glomerulosclerosis. For death or new ESRD, predictors were fairly similar. Adjusting for baseline creatinine level, the risk for ESRD increased 1.78-fold (95% confidence interval [CI], 1.23 to 2.58) per each 10% increase in global sclerosis and 1.47-fold (95% CI, 1.05 to 2.07) per each 10% increase in glomeruli with cellular crescents.

CONCLUSION

Global glomerulosclerosis and crescents in a renal biopsy are strong predictors of the long-term outcome of PING.

Determinants of outcome in ANCA-associated glomerulonephritis: a prospective clinico-histopathological analysis of 96 patients

BACKGROUND

The predictive value of clinical and renal histological features for renal outcome in patients with anti-neutrophil cytoplasmic autoantibody (ANCA)-associated glomerulonephritis was investigated in a prospective analysis of 96 patients with ANCA-associated vasculitis, and moderate renal involvement (creatinine <500 micromol/L).

METHODS

The extent of 39 histological features in 96 biopsies (performed at entry in a clinical trial) was scored by two independent observers, according to a standardized protocol. Age, gender, diagnosis, glomerular filtration rate at entry (GFR0), ANCA-specificity, proteinuria, and treatment of these 96 patients were also taken into account. Treatment was standardized and started after the biopsy was performed. End-points included renal function at 18 months (GFR18), GFR18 corrected for GFR0 (CORGFR18), and the occurrence of relapse or death.

RESULTS

Parameters that most strongly correlated with GFR18 were GFR0 (r = 0.67), interstitial fibrosis (r = -0.45), glomerulosclerosis (r = -0.37), and tubular atrophy (r = -0.36). Parameters that most strongly correlated with CORGFR18 were segmental (r = 0.45) and cellular (r = 0.30) crescents, and fibrinoid necrosis (r = 0.46). None of the clinical and histological features predicted the occurrence of relapse or death. By applying a stepwise linear multiple regression analysis, we designed a formula for the estimation of renal function at 18 months: GFR18 (mL/min) = 17 + 0.71 x GFR0 (mL/min) + 0.34 x fibrinoid necrosis (%) + 0.33 x segmental crescents (%), (r2 = 0.60; standard deviation = 19 mL/min). Our results were independent of diagnosis, ANCA-specificity, and treatment limb.

CONCLUSIONS

These data suggest that in ANCA-associated glomerulonephritis, GFR0 and predominantly chronic renal lesions are potent predictors of GFR18. Active lesions are associated with renal function recovery and may be reversible. The formula for the estimation of GFR18 shows that a combination of GFR0 and renal histology is a better predictor for GFR18 than GFR0 only.

Long-term renal injury in ANCA-associated vasculitis: an analysis of 31 patients with follow-up biopsies

BACKGROUND

We reported previously that in renal disease in relation to antineutrophil cytoplasm auto-antibodies (ANCA)-associated vasculitis, renal outcome correlates better with the percentage of normal glomeruli than with separate active lesions. This may imply that glomeruli, once affected by necrotizing and crescentic lesions, are irreversibly damaged. We quantified and evaluated the course of renal lesions in the present study.

METHODS

We retrospectively analysed 31 patients with renal disease in relation to ANCA-associated vasculitis, all treated with immunosuppressive drugs. In all patients, a renal biopsy was performed at diagnosis. A follow-up biopsy was performed in all patients on the indication of a suspected renal relapse, after a mean interval of 31 months.

RESULTS

The mean percentage of normal glomeruli in the renal biopsy did not change over time (29% in the initial and 30% in the follow-up biopsy). The mean percentage of glomeruli with crescents, however, significantly decreased from 57 to 30% (P<0.001). The percentage of glomerulosclerosis significantly increased from 12 to 39% (P<0.001). The data were independent of diagnosis, gender, age, time interval between the biopsies, and treatment.

CONCLUSIONS

This is the first study to quantify glomerular changes between two time points in patients with renal vasculitis. Our results suggest that, on average, no new glomeruli are recruited into the active disease process. The sum of the percentage of crescentic and sclerotic glomeruli in the initial biopsies is larger than the percentage of sclerotic glomeruli in the follow-up biopsies. Thus, therapy seems not only to prevent normal glomeruli from being recruited into the active disease process for a certain time, but seems also to allow part of the active lesions to revert into a normal phenotype, although another part of the active lesions will be transformed to a chronic phenotype.

Colocalization of ANCA-antigens and fibrinoid necrosis in ANCA-associated vasculitis

A variety of antineutrophil cytoplasmic auto-antibodies (ANCAs) are known to be associated with small vessel vasculitides such as Wegener's granulomatosis and microscopic polyangiitis. To visualize colocalization patterns of the fibrinoid necrotic lesions and ANCA-antigens more accurately, we have developed a double staining technique in which an immunohistochemical staining is followed by a histological staining. Instead of using sequential biopsy slides of histologically and immunohistochemically stained sections, which may lead to an underestimation of the number and size of the lesions, our technique permits the visualization of the colocalized patterns of fibrinoid necrosis with an ANCA-antigen in a single slide. The double staining procedure is presented in this Technical Note.