Glomerulonephritis

In the majority of patients with immune complex-mediated glomerulonephritis, the cause is unknown; i.e. the nature of the antigen involved is not determined. Antigen derived from viruses, bacteria, parasites, drugs and from the host may be involved. The reasons for the development of anti-GBM antibody are not known; viral or solvent damage to alveolar capillary basement membrane, rendering it antigenic, has been suggested as a possible cause.

Proliferative glomerulonephritis

Proliferative changes occur in many immune complex-mediated nephritides and also in anti-GBM nephritis. There are the following subtypes.

Diffuse proliferative glomerulonephritis

All the glomeruli are similarly affected. Immunofluorescence shows granular deposits of immunoglobulin and C3. This type of glomerulonephritis, presenting as an acute nephritis, is commonly seen after a streptococcal infection (see below). Immune complexes are seen as electron-dense deposits on electron microscopy.

Focal segmental glomerulonephritis

Only some of the glomeruli here show proliferative changes whilst others are normal; hence the term 'focal'. The affected glomeruli show segmental involvement of the tufts; i.e. changes are present in one or more parts of the glomerulus.

This condition may occur as a primary renal disease, but it is also seen in SLE, subacute infective endocarditis, with infected atrioventricular shunts (shunt nephritis), and in disorders with IgA deposits (e.g. Henoch-Schönlein purpura and IgA nephropathy). A severe focal necrotizing form is seen in microscopic polyangiitis and Wegener's granulomatosis. Special subtypes (IgA nephropathy and focal glomerulosclerosis) are discussed below.

Proliferative glomerulonephritis with crescent formation (rapidly progressive glomerulonephritis; RPGN) or crescentic glomerulonephritis

The term 'crescent' is applied to an aggregate of macrophages and epithelial cells in Bowman's space. Crescents are associated with severe damage to the glomerular tuft and are seen in occasional glomeruli in several types of glomerulonephritis. However, if most glomeruli show crescents the glomerulonephritis is usually placed in this subtype, as clinical progression to renal failure is rapid.

This condition is seen in both immune complex- and anti-GBM antibody-mediated nephritis. It particularly occurs in microscopic polyangiitis, Wegener's granulomatosis and Goodpasture's syndrome.