[Secondary nephrotic syndrome due to collagen disease and vasculitis]

The most frequent and representative nephrotic syndrome associated with collagen disease is encountered in patients suffering from lupus nephritis. Lupus nephritis is a glomerulonephritis, which discloses various localizations of immune complexes in the endothelium, mesangium and subepithelium. In addition, vasculitides complicated by nephrotic syndrome also show the deposition of immune complexes in their glomeruli, such as Henoch-Schönlein nephritis and cryoglobulinemic nephritis. The pathogenetic mechanisms of these nephrotic syndromes are explained as follows. The depositions of immune complexes in glomeruli causes proteinuria through a variety of mechanisms. Namely, subendothelial and mesangial immune deposits give capillary and mesangial injuries as well as inflammation that are mediated through activation of complements and cytokines, and subsequently leads to nephrotic-range proteinuria and impairment of renal function. On the other hand, subepithelial and intramembranous deposits disrupt the regulated arrangement of epithelial cells and slit diaphragms, and then disturb the slit diaphragms. The eventual dysfunction of slit diaphragms accordingly progresses to massive proteinuria even without capillary injury. Therefore, nephrotic syndrome associated with collagen disease or vasculitis is usually observed in lupus nephritis or vasculitis related to immune complex depositions, but is not observed in non-immune complex glomerulopathy or vasculopathy.