Chronic glomerulonephritis characterized histologically by proliferation of mesangial cells, increase in the mesangial matrix, and a thickening of the glomerular capillary walls. The wall thickening is sometimes said to be a result of the interposition of mesangial cytoplasm or matrix between the basement membrane and the endothelium of the capillary wall. It is often divided into types I and II, and sometimes III. Pathogenesis is not well understood, but some types are thought to involve the immune system, with the complement system, in particular, being implicated.