DIVALENCY OF THE MONOCLONAL-ANTIBODY 5-1-6 IS REQUIRED FOR INDUCTION OF PROTEINURIA IN RATS

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 ne phritogenic dose. The total kidney binding of I-125-Fab fragment was 2 09.5 +/- 34.3 mug/2 kidneys. This exceeded that obtained by injection of 3 mg MoAb 5-1-6 IgG1 (58.9 +/- 12.5 mug/2 kidneys at 1 h) and was s imilar to that obtained following injection of 3 mg F(ab')2 fragment ( 235.3 +/- 16.9 mug/2 kidneys). Immunofluorescence (IF) showed a linear pattern along the glomerular capillary wall at 1 h after the administ ration 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 glomer uli, whereas granules were densely localized in Fab-injected rat glome ruli. Complement-depleted rats injected with 3 mg of MoAb 5-1-6 IgG1 d eveloped proteinuria with the same time course as non-depleted rats. T his observation, together with the ability of F(ab')2 to induce protei nuria, indicates that proteinuria induced by MoAb 5-1-6 is complement- independent. This study suggests that MoAb 5-1-6-induced proteinuria i s initiated by cross-linking of the epitopes by divalent MoAb 5-1-6 an d is independent of complement activity.