Divalency of the monoclonal antibody 5-1-6 is required for induction of proteinuria in rats

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Abstract
SUMMARY: A single i.v. injection of 3 mg of the F(ab')2 fragment of MoAb 5-1-6 into rats induced immediate proteinuria (128.1 ± 80.7 mg/24 h on day 1) which lasted 1–2 days. In contrast, rats administered 10 mg of the corresponding Fab fragment did not develop abnormal proteinuria even though an equivalent dose of the intact MoAb 5-1-6 far exceeded the nephritogenic dose. The total kidney binding of 125I-Fab fragment was 209.5 ± 34.3 μg/2 kidneys. This exceeded that obtained by injection of 3 mg MoAb 5-1-6 IgG1 (58.9 ± 12.5 μg/2 kidneys at 1 h)and was similar to that obtained following injection of 3 mg F(ab')2 fragment (235.3 ± 16.9 μg/2 kidneys). Immunofluorescence (IF) showed a linear pattern along the glomerular capillary wall at I h after the administration of MoAb 5-1-6 IgG1. F(ab')2 or Fab fragment. On day 5, fine to coarse granules were observed scattered in F(ab')2 injected rat glomeruli. whereas granules were densely localized in Fab-injected rat glomeruli. Complement-depleted rats injected with 3 mg of MoAb 5-1-6 IgG 1 developed proteinuria with the same time course as non-depleted rats. This observation, together with the ability of F(ab')2 to induce proteinuria. indicates that proteinuria induced by MoAb 5-1-6 is complement-independent. This study suggests that MoAb 5-1-6-induced proteinuria is initiated by cross-linking of the epitopes by divalent MoAb 5-1-6 and is independent of complement activity.