How is in situ glomerulonephritis caused by immune complexes?

➢ Deposition of antibodies specific for fixed (intrinsic) or planted (from outside) antigens in the glomerulus is another major pathway of glomerular injury. ➢ Antigens expressed by podocytes have been implicated in membranous nephropathy. ➢ Antibodies also may react in situ with previously “planted” non glomerular antigens, which deposit and become concentrated in the kidney through interaction with various glomerular components. ➢ Planted antigens mainly derived from 1. breakdown of apoptotic cells, in patients with systemic lupus erythematosus; 2. bacterial products, such as endostreptosin, a protein expressed by group A streptococci; 3. large aggregated proteins [IgG], which tend to deposit in the mesangium. ➢Locally formed immune complexes may also grow in size through additional interactions with circulating free antibodies and antigens. ➢ Most of these planted antigens, as with circulating immune complexes deposited on the GBM, show a granular pattern of deposition by immunofluorescence microscopy