Amount of antibody is critical for immune complex displacement by charge competition from both rabbit glomeruli and anionic beads.

The purpose of this study was to determine the feasibility of displacing cationized bovine serum albumin (CBSA) immune complexes from glomeruli by charge competition. An in vitro model identified protamine as an effective agent for displacing 125I-CBSA from anionic beads (dextran sulfate-coated Sepharose 4B). Anti-CBSA serum prevented displacement of 125I-CBSA from anionic beads in a dose-dependent fashion. When 125I-CBSA was injected intravenously into rabbits 98% of 125I-CBSA disappeared from blood within 5 min, at which time CBSA was visualized by immunofluorescence in glomerular capillary walls but not in liver, muscle, skin, spleen or lung. By 24 h 90% of 125I-CBSA had disappeared from glomeruli. In contrast, injection of anti-CBSA antibody caused persistence of 125I-CBSA in kidney (particularly along glomerular capillary walls) for more than 7 days (detected by counting 125I in kidney, by radionuclide imaging and by immunofluorescence). Protamine administration (50 mg intravenously daily for 6 days) caused significant reduction of 125I-CBSA trapped in kidney only if the amount of anti-CBSA injected was small. Protamine did not significantly displace 125I-CBSA from glomeruli if the anti-CBSA dose was larger. Therefore both in vivo and in vitro displacement of 125I-CBSA by protamine depended upon the amount of antibody. We conclude that although charge dependent displacement of immune complexes from glomeruli is probably feasible using protamine this approach would only work in the presence of small amounts of antibody.