PATHOGENESIS.

Many manifestations are mediated by antibodies. The classic example is that of diffuse proliferative glomerulonephritis. Immune complexes, which consist of nuclear antigens (especially DNA) and high-affinity complement-fixing IgG (especially IgG1 and IgG3) and ANAs (especially antibodies to DNA), form in the circulation and are deposited in the glomerular basement membrane (GBM) or form in situ; histone may facilitate immune complex deposition. The complement system is then activated and chemotactic factors are generated. These factors induce the attraction and infiltration of leukocytes, which then phagocytose immune complexes and cause the release of mediators (such as activators of the clotting system), which further perpetuate the glomerular inflammation. With continuing immune complex deposition, chronic inflammation may ensue, ultimately leading to fibrinoid necrosis and scarring (crescents) and loss of renal function. In lupus membranous glomerulonephritis, similar mechanisms occur, although immune complex-containing, poorly complement-fixing IgG2 and IgG4 form primarily in situ on the GBM; there is no cellular infiltrate. The mechanism for the GBM protein leakage, which results in the nephrotic syndrome, is not clear. In lupus mesangial glomerulonephritis, mesangial cells (macrophage-like