Mesangioproliferative glomerulonephritis in Il12rb2 KO mice. A glomerulus from an 8-month-old WT mouse displays the tuft of capillaries with an open lumen filled by erythrocytes and supported by a delicate branching framework of mesangium (A, PAS staining). In contrast, a glomerulus from an age-matched Il12rb2 KO mouse shows mesangial enlargement caused by mesangial hypercellularity (blue-stained nucleus) and matrix increase (fuchsia-stained material) resulting in capillary compression and occlusion (B, PAS staining). Immunofluorescent staining shows diffuse mesangial immunoreactivity for IgG (C) and for C3 (D) along the glomerular capillary loops in an Il12rb2 KO mouse, as opposed to the negative staining of glomeruli from an age-matched WT mouse (insets in C and D, respectively). H&E staining of kidney sections from a 21-month-old Il12rb2 KO mouse revealed, in contrast with the normal glomerulus from an aged-matched WT mouse (E), an advanced sclerosing glomerulonephritis with crescent formation (arrows) and adhesion to Bowman capsule, associated with thickening of its parietal layer (F). Altered glomeruli compressed by lympho-plasmacytoid infiltrates are observed in a 26-month-old Il12rb2 KO mouse (H), but not in an age-matched WT mouse (G). Magnification: (A-F) × 1000; (G-H) × 630.