Ultrastructure of matriceal changes in chronic phase of Masugi nephritis by quick-freezing and deep-etching method.

The three-dimensional ultrastructure of glomerular sclerosis in the chronic phase of Masugi nephritis was investigated using a quick-freezing and deep-etching method. Newly formed mesangial matrix, which was increased in the axial portions, was composed of fine fibrillar networks similar to those in the lamina densa of the basement membrane. These fibrils were 10-20 nm in diameter and directly attached to the cell membranes of mesangial cells, endothelial cells and podocytes by connecting fibrils. Moreover, thicker fibrils with diameters of 20-30 nm were present in the networks and were connected with cross-bridges. A newly formed matrix of fine fibrillar networks was also seen in the areas of mesangial interposition in the glomerular capillary wall. The border between the matrix and lamina densa was unclear. The fibrils organizing the networks of lamina densa of the glomerular loop were thickened, with some decoration. Connecting fibrils were disrupted in the areas of endothelial detachment. It is suggested that prolonged tissue injury with endothelial detachment might induce mesangial sclerosis composed of fine fibrillar networks. The increase in density of the networks seemingly interfere with the contractile function of mesangial cells, which is followed by alteration of mesangial flow.