[Structure and antigenicity of the glomerular basement membrane]

The glomerular basement membrane is a complex extracellular matrix formed of various molecules which build a supramolecular network. The major structural components are collagen IV, laminin, heparan sulfate proteoglycan, and nidogen/entactin. Cross-reacting antibodies against laminin, nidogen, and collagen IV may occur after several infectious diseases. They are however of doubtful pathogenetic significance. The pathogenetic relevant autoantibodies in Goodpasture's syndrome and rapidly progressive glomerulonephritis with linear immunofluorescence pattern are directed against epitopes which are located on the collagenase resistant C-terminal globule NC1 of collagen IV. The human NC1 globule appears as a hexamer which dissociates into monomers and dimers under various experimental conditions. Dissociation is paralleled by a significant increase in available epitopes. Immunisation with the dissociated NC1 globule initiates a pulmo-renal syndrome in rabbits similar to the human Goodpasture's syndrome. In hereditary nephritis one of the alpha-chains which form the triple-helix of collagen IV seems to be altered within the NC1 region. This may possibly explain the typical morphologic findings in this disease as well as the reduced binding of antiglomerular basement membrane antibodies to basement membranes of kidneys in Alport's syndrome.