PATHOLOGY OF TUBULOINTERSTITIAL DAMAGE IN GLOMERULONEPHRITIS WITH PROTEINURIA

Abstract

The thesis investigates two important pathogenetic mechanisms of tubulointerstitial damage (TID): 1) proteinase-antiproteinase balance in the renal tubules and 2) complement dependant renal tubular damage. We also studied the associated changes of the tubular glycoconjugates, the glycoproteins of the tubular basement membrane (TBM) and interstitium, and cortical type I interstitial cells (ICs) in TIO. The degree of damage occurring in TID was quantified by morphometric techniques. Renal tissues from suitable cases, comprising 10 controls and 45 patients with various primary and secondary glomerulonephritides were studied for all the above parameters to obtain an integrated understanding of the changes in TID. This work was based on electron microscopy and immunohistochemistry, with double labelling when required. The patients were divided into two groups: one with tubulointerstitial lesions (TlLs) (30 cases), and the other without (15 cases). Proteinase inhibitors, α-1-antitrypsin and α-1-antichymotrypsin showed a significant antiproteinase response in the proximal tubules in both disease groups, indicating that they were subjected to proteolytic attack. This response correlated with proteinuria and occurred in the tubules which showed protein reabsorption. There was consistent deposition of C3d, C5 to C9 and terminal complement complex (TCC) neoantigens in the same locations in the segments of the TBM, especially in the disease group with TlLs, and was statistically significant. Complements of the classical pathway were rarely deposited, implying that in-situ activation via the alternate pathway leads to the deposition of TCC, and damage to the basal domain of the tubules. TCC neoantigens have been shown to deposit on the membranous structures (MS) in the TBM. The insertion of TCC on MS could lead to membrane lysis and release of proteolytic enzymes in the TBM. Circular profiles of lytic damage in the TBM around damaged and distorted MS on electron microscopy support this. There was a significant correlation between the MS, lytic areas and TCC deposits which can lead to tubular epithelial cell detachment and necrosis. There was significant inverse correlation of the TBM thickness with the creatinine clearance. Both disease groups showed increased deposition of collagen type IV and laminin, which contributed to the thickening of the TBM. Lectin histochemistry showed significant loss of basal sialic acid in the distal tubules in TlLs, indicating basal damage to the tubular epithelial cells. This segment also showed maximum damage on morphometry, and is therefore the best predictor of glomerular filtration rate (GFR). WGA, PNA and PHA-L lectins staining of the casts showed significant excretion of (D-glcNAC) 2, NeuNAc; β-D-gal(1-3)-D-galNAc and oligosaccharides in the disease group with TILs. The urinary estimation of these carbohydrate moieties can serve as markers of renal tubular damage. In TID the interstitium showed concurrent increase in collagens types I and III, along with fibronectin. The cortical type I ICs showed significant increase in lipid droplets (LDs) per IC in the disease group. The LDs showed polarity towards the intertubular capillary (ITC) lumen and were close to them. It is possible that in TID there is compression of the ITCs, and the type I ICs may then attempt to cause vasodilatation through the increased production of antihypertensive hormones, which they are known to produce.