Induction of autologous immune complex nephritis in rats by heterologous anti-kidney mitochondrial antiserum: A preliminary report

Production of heterologous IgG antibody against Heymann nephritis antigen by injections of immune complexes

Heterologous IgG antibody (ab) can be produced against Heymann nephritis (HN) antigen (ag) in rabbits by administering it in Freund's complete adjuvant. The developing abs reacted at high titre with rat kidney brush border (BB) regions of the renal proximal tubules in an indirect fluorescence ab test. A single IV injection of the heterologous ab into a susceptible strain of rat resulted in the localization of IgG ab to glomerular fixed ags, producing immune complex glomerular nephritis. The injected ab also reacted with the BB region of the renal proximal tubules. The aim of this experiment was to find out whether heterologous IgG ab against the HN ag can also be produced in recipient rabbits by injecting immune complexes (ICs) composed of a rat kidney tubular preparation [rat kidney fraction 3 (rKF3)] and donor rabbit-derived rabbit anti-rKF3 IgG ab. We found that anti-rKF3 IgG ab--against the BB region of the renal proximal tubules--could be induced in rabbits injected with ICs, and the resulting ab was able to initiate passive HN in rats. This was the first time a pathogenic IgG ab was produced against HN ag in rabbits without the use of adjuvant. Ab responses in recipient rabbits were achieved by ab information transfer. Recipient rabbits injected with the IC produced the same class of immunoglobulin with the same specificity against the target ag rKF3, as was present in the innoculum, namely rabbit anti-rKF3 IgG ab.

Presence of immunoglobulin M antibodies around the glomerular capillaries and in the mesangium of normal and passive Heymann nephritis rats

Summary Diffuse distribution of small, faintly staining, beaded deposits of rat immunoglobulin M (IgM) around the glomerular capillary blood vessels, and a more intensely staining larger deposition in the mesangium, were observed on the kidney sections of normal rats. As glomerular-fixed nephritogenic antigens are known to be present on the epithelial aspect of the glomerular basement membrane (GBM), especially at the soles of foot processes and at the slit pores, it was assumed that the IgM antibodies were directed against these antigens. Investigation by immunofluorescent antibody double-staining techniques of rat kidney sections obtained from normal and rabbit anti-FX1A-injected rats stained for the nephritogenic antigen showed that a number of antigenic sites in the glomeruli and in the mesangium shared antibody hits by heterologous rabbit IgG and autologous rat IgM antibodies. Most sites in the glomeruli stained specifically for rat IgM or rabbit IgG, but preferentially for the latter. The intensely fluorescent mesangial deposits stained mainly for rat IgM, indicating that at these sites the antigenic material was virtually saturated, while areas at the entry to the mesangial space also stained for rabbit IgG, indicating that at these locations free nephritogenic epitopes were still available for reaction with the anti-FX1A antibody. Western blot analysis have shown that the rabbit anti-rat FX1A IgG and the rat anti-rat KF3 IgM antibodies are directed against the same renal tubular-derived antigen with a molecular weight of 70,000. These experimental findings collectively demonstrate that the heterologous IgG and autologous IgM antibodies are directed against the same nephritogenic antigen, which is found in the glomeruli, the mesangium and the proximal convoluted tubules. Thus, the IgM autoantibody has a possible physiological role but, in addition, there is evidence of active immunophagocytic events, manifested in a rapid and continuous entrapment and expulsion of macromolecules after their processing by the mesangial cells of normal and passive Heymann nephritis rats.

Production of a new model of slowly progressive Heymann nephritis

A slowly progressive autoimmune kidney disease was induced in Sprague Dawley rats by subcutaneous injection of a chemically modified kidney antigen (rKF3), incorporated into Alum and Distemper complex vaccine, followed by subcutaneous injections of an aqueous preparation of the same antigen. Pathogenic autoantibodies developed, which reacted with fixed glomerular nephritogenic antigen. Subsequently, immunopathological events lead to chronic progressive immune complex glomerulonephritis and proteinuria. The slowly developing disease was morphologically and functionally similar to Heymann nephritis (HN). The damage observed in the kidneys of experimental animals at 8 weeks and at the end of the experiment was examined by direct fluorescent antibody test, histology and electron microscopy. The changes were similar to the typical lesions found in HN rat kidneys, but less severe. Animals became proteinuric from 17 weeks onward (instead of the usual 4-8 weeks). By the end of the experiment, at 8 months, 100% of the rats were proteinuric. This new experimental model of autoimmune kidney disease, which is not complicated by intraperitoneal deposition and retention of Freund's complete adjuvant and renal tubular antigens, allowed us to investigate the pathogenesis of the disease processes from a different aspect, and promises to be a useful and improved model for the investigation of future treatment options.

The organ distribution of gp-330 (Heymann antigen) and gp-90 in the mouse and the rat

The Heymann antigen (gp-330) and an antigen with lower molecular weight (gp-90) are major constituents of the brush border of the renal proximal tubules in the rat and the mouse. The Heymann antigen can also be found at discrete sites in the glomerular visceral epithelium of the rat, but not of the mouse. Gp-90 is present diffusely along the glomerular capillary wall of rat and mouse. The Heymann antigen is probably the target antigen for membranous glomerulonephritis in the rat, while in the mouse, where this form of glomerulonephritis can also be induced, gp-90 seems to be the antigen involved. We have separated the antibody populations against these two antigens by preparing eluates from kidneys of rats and livers of mice that had been injected with an antiserum against pronase-digested mouse renal tubular antigens. Using these purified antibodies we have examined by indirect immunofluorescence the distribution of the two antigens on normal mouse and rat tissues. The expression of the Heymann antigen is limited to the epithelia of several organs, while gp-90 has a more widespread distribution in many cells of different origin and function in both the mouse and the rat.

Membranous glomerulonephritis in the mouse

Glomerulonephritis was induced in C57. B110 mice by a single injection of rabbit IgG against homologous, pronase-digested, renal tubular antigens. The heterologous phase was characterized by a transient increase of glomerular permeability with fixation of rabbit IgG to the capillary walls, in a linear or fine-granular pattern, and to the brush borders of the proximal tubuli. The autologous phase was marked by the immune response to the injected protein, during which subepithelial immune deposits, consisting of mouse IgG1, rabbit IgG, and mouse C3 developed. Small amounts were still present at 1 year after the injection of antiserum. The antibody response of the mice correlated with the development and resolution of the deposits. None of the mice developed a nephrotic syndrome. Control mice treated with normal rabbit IgG did not show immune deposits in their kidneys at any stage despite a comparable antibody response to rabbit IgG. Immunoelectronmicroscopy showed that the rabbit antibodies fixed directly to an antigen in the cell membrane of the glomerular visceral epithelium. It seems, therefore, likely that in situ formation of subepithelial immune complexes occurred in the autologous phase by fixation of mouse immunoglobulins to rabbit IgG already present in the glomerular wall.

Chronic nephritis induced by antibodies reacting with glomerular-bound immune complexes

The pathogenesis of chronic membranous glomerulonephritis induced in rats by passive immunization with heterologous antibodies to rat renal tubular epithelial (RTE) antigens was investigated. This model is designated as "passive Heymann nephritis" (PHN) in order to contrast it with classical Heymann nephritis induced by active immunization with homologous RTE in adjuvant. A single i.v. injection of heterologous (rabbit) antibody to RTE evoked chronic proteinuria after a latent period of one to three days. The onset of proteinuria was accompanied by the granular deposition of rabbit IgG and rat beta1C globulin along the glomerular capillary wall. Renal isografts developed PHN only when transplanted within the first three days following injection of the heterologous anti-RTE antibodies. The data suggest that the heterologous antibodies form immune complexes with RTE antigens preexisting in the circulation, and these complexes subsequently deposit in the glomerular capillary walls. Chronic proteinuria is then perpetuated by a host reaction to the foreign protein in the deposits (i.e., rabbit IgG), in a fashion analogous to that seen in the autologus phase of nephrotoxic serum nephritis. These studies indicate that continued glomerular deposition of preformed circulating immune complexes may not always be a requisite for the perpetuation of glomerular injury in immune complex disease.