Quantitative studies of monoclonal antibody 5-1-6-induced proteinuric state in rats

Abstract

SUMMARY Murine monoclonal antibody (MoAb) 5-1-6 was already reported to bind to epithelial cell fool processes and to cause proteinuria in rats. In vivo kinetics of the injected MoAb 5-1-6, relationship between the quantity of kidney-binding antibody and proteinuria. and changes in the amount of antigenic molecule recognized by this MoAb in the proteinuric state were studied. The amount of total kidney-binding antibody (TK Ab) as determined I h after a 2 mg administration was 50.8 ± 10.4 μg/2 kidneys, and TKAb declined to 1.9 ± 0.4 at day 15. The minimum dose of MoAb required to induce proteinuria was 125 μg as the injected dose. This dose corresponded to 12-8 μg of TKAb at I h and 0.34 μg of TKAb at day 5. The amount of MoAb 5-1 -6 binding to isolated normal glomeruli was also shown to exceed 147-7 μg/76000 glomeruli, indicating proteinuria to be induced provided more than 8.7% (= 12.8/147.7) of the critical epitopes is specifically occupied by MoAb. The total amount of MoAb 5-1-6 bound to glomeruli in vivo and in vitro was assayed with [125I]-labelled anti-mouse IgG. The amount of [125I] anti-mouse IgG bound to glomeruli was 6.93 ± 0.45 μg/10 000 glomeruli from rat 5 days after this MoAb injection and 26.58 ± 0.66 μg/10000 control glomeruli, indicating the decrease in the number of MoAb 5-1-6-rccognizcd antigen molecules in glomeruli isolated from the rat in proteinuric state induced by this MoAb. Thus, the MoAb 5-1-6-recognized molecule itself may principally function to regulate the permeability of the glomerular capillary wall and the decrease of the molecule may lead to proteinuria.