Epitope-specific induction of mesangial lesions with proteinuria by a MoAb against mesangial cell surface antigen

A MoAb 1-22-3 (IgG3) was produced in mice immunized with rat glomeruli. A blotting study indicated the antigen molecule recognized by this MoAb has a molecular weight of about 25 kD, which is the same as that of the Thy 1.1 molecule. This MoAb is capable of inducing the morphological changes similar to those induced by anti-thymocyte serum or the anti-Thy 1.1 MoAb, ER4 and massive proteinuria in rats by a single i.v. injection. Proteinuria started immediately after MoAb 1-22-3 injection and peaked on day 5. Reaction products were detected by immunoelectron microscopy in vitro on the limited mesangial cell surface facing endothelial cells and in vivo in partially lysed mesangial cells 30 min after injection. Unlike the proteinuria-inducing MoAb ER4, reactivity of MoAb 1-22-3 was detected neither on endothelial cells, epithelial cells, nor along the glomerular basement membrane in vivo and in vitro. There is a difference in reactivity toward guinea-pig and rabbit materials between MoAb 1-22-3 and the commercial anti-Thy 1.1 MoAb (OX7). The antigenic determinant of MoAb 1-22-3 is concluded to be a new epitope and only the binding of MoAb 1-22-3 to this epitope proved to lead to an abnormal increase of glomerular capillary wall permeability.