Interleukin (IL) 12 is known to play a major role in the induction of T helper type 1 immune responses. Recently, it was reported that the IL-12 expression may be important in the development of immunological renal damage in rats with crescentic glomerulonephritis [1] or in the increase of glomerular permeability to albumin in patients with minimal-change nephrotic syndrome [2].

To investigate the role of IL-12 in human IgA nephropathy, we examined 50 patients (25 men and 25 women; age range 17-71, mean+/-SD 32.5+/-14.1 years) who underwent renal biopsy at the 2nd Department of Internal Medicine of the Hiroshima University School of Medicine in Japan. The diagnosis of IgA nephropathy was based on clinical, light microscopic, electron microscopic, and immunofluorescence findings. The histological damage was classified as mild, moderate, or severe based on seven items examined by microscopy, according to our previously reported method [3]. As controls, we used renal biopsy specimens from 17 patients (5 men and 12 women; age range 16-41, mean+/-SD 24.9+/-6.9 years) with minimal-change disease and mild urinary findings. Biopsy specimens fixed in formalin and embedded in paraffin were immunostained for IL-12 as follows. The sections were deparaffinized using xylene and alcohol, and the antigen was unmasked by incubation in 0.01% trypsin diluted with 0.06 M phosphate-buffered saline (pH 7.2) for 20 min at 37 deg C. Then the sections were incubated overnight at 4 deg C in a moist chamber with the primary antibody (polyclonal antihuman IL-12; Santa Cruz Biotechnology, Santa Cruz, Calif., USA). After washing with phosphate-buffered saline (pH 7.6) for 30 min, the sections were reacted with rabbit IgG using an avidin-biotin-peroxidase complex kit (Vector Laboratories, Burlingame, Calif., USA), and the products were visualized by applying diaminobenzidine.