Antigens of varying size persist longer in subepithelial than in subendothelial immune deposits in murine glomeruli.

The kinetics of removal of immune deposits from the subendothelial and subepithelial areas of glomeruli were analyzed in mice. Radiolabeled, cationized Ag of different molecular size, including human serum albumin, bovine thyroglobulin, and human IgM, were used to form the immune deposits in mouse glomeruli with specific, purified rabbit antibodies to these proteins. The disappearance curves of the radiolabeled Ag from glomeruli consisted of two exponential components. The immune deposits and their location in glomeruli were identified by immunofluorescence and electron microscopy. The t1/2 of disappearance of immune deposits were assigned to subendothelial or subepithelial deposits on the basis of ultrastructural observations. The t1/2 of subendothelial immune deposits ranged from 0.6 to 1.9 days with the three different Ag-antibody systems. In contrast, the t1/2 of the subepithelial immune deposits ranged from 9.32 to 231 days. The cationized human serum albumin in subepithelial areas had the longest t1/2, and this was not altered by the endogenous immune response to the injected materials, as determined in studies with nude mice. The results constitute formal documentation of the prolonged t1/2 of an exogenous Ag in glomerular immune deposits. The described approach can serve to examine variables that alter this prolonged presence of subepithelial immune deposits in glomeruli.