[Collagen type III glomerulopathy: a morphologic study].

Objective: To study the morphologic changes of collagen type III glomerulopathy and to investigate the possible cellular origin for collagen III production.

Methods: Light microscopy, immunofluorescent staining, immunohistochemistry (for collagen I, III and IV and alpha-SMA) and electron microscopy studies on 3 renal biopsy cases of collagen type III glomerulopathy were performed.

Results: Two cases presented with nephrotic syndrome, one of which was associated with systemic hypertension. The third case showed renal impairment and renal hypertension. None had any known family history of renal diseases. Light microscopy showed diffuse thickened glomerular basement membrane and expanded mesangium with deposition of weakly PAS-positive homogeneous material not associated with mesangial cell proliferation. Electron microscopy revealed massive collagen fiber deposits in the subendothelial spaces and mesangium. The mesangial cells also contained bundles of microfilaments in the subplasmalemmal regions. Immunohistochemically, the diffuse positivity for type III collagen corresponded to the homogeneous material seen under light microscopy. The staining for type I and IV collagens was negative. Alpha-SMA was expressed in many mesangial cells.

Conclusions: The diagnosis of collagen type III glomerulopathy can be made on the basis of detailed morphologic examination and ancillary investigations. It is possible that activated mesangial cells may be the cellular origin of collagen III.