Mechanisms of tissue deposition of immune complexes.

Immune deposits in renal glomeruli can arise by deposition of circulating immune complexes or by local formation of antigen-antibody complexes. Circulating immune complexes tend to form deposits in the mesangial and subendothelial areas and their size limits their passage through the lamina densa of the glomerular basement membrane. In local immune complex formation endogenous or planted molecules serve as antigens. Subepithelial immune deposits arise mainly by local formation of immune deposits. Charge-charge interactions contribute to planting of antigens in glomeruli or to initial binding of immune complexes to glomeruli. Precipitating antigen-antibody systems are required for retention of immune deposits in glomeruli.