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Antigens of porcine lung were prepared by homogenization and ultrasonic treatment of lung tissue. The antigens were digested by collagenase and trypsin and chromatographed on Sephadex G 200. After immunization of rabbits with certain fractions of the chromatographed material, antibodies could be obtained in rabbits which fixed in vitro and in vivo in the glomerular mesangium of rats, hogs and the human, but not in the basement membrane of glomeruli of these species. Following intravenous injection into rats, the antibodies could be observed in the mesangial area without an apparent loss of antigenicity for 55 days. While 5 days after the application of 20 mg of the anti-mesangial IgG-preparation, there were no glomerular changes histologically demonstrable, after 55 days small amounts of rat-IgG could be demonstrated histochemically within the mesangium. Deposits of rat-complement (C3) could not be demonstrated with certainty. Severe morphological lesions were absent. Rats injected with the same doses of antibody and simultaneously immunized with rabbit-IgG showed a substantially greater deposit of autologous rat-IgG and rat-complement within the mesangial area after 55 days. By histological examination focal and segmental scleroses of the mesangium were determined. A significant pathological proteinuria did not occur. The present model constitutes a new possibility for studying the function of the glomerular mesangium.

A 10-month-old infant developed a steroid resistant nephrotic syndrome. The renal biopsy revealed diffuse mesangial sclerosis of the glomerula. The child died from interstitial pneumonia 3 months after onset of the renal symptoms. Post mortem, the glomerular changes were diffuse but prominent in certain segments of the glomeruli. The immunohistological examination showed granular deposits of IgM and C3 in the mesangium and in the subendothelial region of the basement membrane. These findings are compatible with the hypothesis that diffuseal sclerosis is caused by glomerular deposition of immune complexes.

The influence of autolysis on the immunhistological detectability and the immunological properties of tissue-bound basement membrane antibodies were investigated in the rat kidney. The immunhistological demonstration of antibodies was not affected up to 3 days post mortem. The disturbing autofluorescence of the autolytic tissue can be avoided by using peroxydase labeled antibodies. Basement-membrane antibodies that were eluted from the kidneys after an autolysis period of 2 days showed a homogenous linear deposition in kidney basement membrane after reinjection into normal rats. Their antibody properties were not affected.