[Immunohistochemical localization of various components of the basal membrane and interstitial collagen in diabetic nephropathy].

We analyzed the composition of the extracellular matrix in the glomeruli from 31 cases with different degrees of diabetic nephropathy by immunohistochemical means. While the enlarged mesangial matrix in diffuse glomerulosclerosis showed an increased staining reaction for the basement membrane components collagen IV and V, laminin and fibronectin, the staining pattern of the basement membrane associated heparan sulfate proteoglycan (HSPG) was markedly reduced. Early, small nodular lesions in diabetic glomeruli were similarly positive for most of the basement membrane (BM)-components, while HSPG remained absent. With an increase in the diameter of the noduli, however, the staining reaction for the BM-components diminished, while interstitial collagens V and III were present in these noduli in substantial amounts. Our findings provide evidence that the changes in the glomerular matrix in diabetic nephropathy may be divided into distinct and progressing stages of lesions. The reduced amount of HSPG even in slight, early lesions may represent the morphological correlate to the impaired filter function of the glomerular BM, while the occurrence of interstitial collagens within the glomeruli in late nodular stages may be regarded as the result of an altered pattern of expression of the mesangial cells.