Dissociation of immune complexes in tissue sections by excess of antigen

Immune complexes (IC) present in the glomeruli of rabbits with chronic serum sickness (CSS) and in patients with systemic lupus erythematosus (SLE), idiopathic membranous nephropathy (IMN), and acute poststreptococcal glomerulonephritis (PSGN) were analyzed by incubation with antigenic preparations. The efficacy of these preparations to dissolve IC was assayed by comparison of results of direct immunofluorescence tests performed with the kidney tissues before and after incubation with antigenic preparations. The FITC-conjugated antisera used in these tests were specific for IgG, C3, and-in the case of CSS-for the eliciting antigen, bovine serum albumin (BSA). During the acute proteinuric phase of CSS in rabbits, incubation of tissue sections with BSA alone led to complete dissolution of IC. In many rabbits with late phase proteinuria, however, tissues had to be incubated with both BSA and aggregated fraction II of rabbit serum. In all biopsy specimens from patients with IMN, and in some specimens from patients with PSGN and SLE, aggregated fraction II of human serum resulted in complete or incomplete dissolution of IC. On the other hand, incubation of tissues with excess DNA in SLE or with streptococcal antigens PSGN did not lead to dissolution of IC. These studies suggest significant participation of antibodies to aggregated immunoglobulins (i.e., rheumatoid factors or rheumatoid-like factors) in IC found in the above-mentioned diseases. Other antigen -antibody systems, however, may also contribute to the deposits in the glomerulonephritides studied.