Microphotographs of representative knee joints of meniscectomized rabbits. Partial meniscectomy was performed on the rabbit knee to induce osteoarthritis-like morphology. Representative histologic sections of synovial membrane in (a) an untreated knee joint (normal) or (b) a meniscectomized knee joint were stained with H&E. Hyperplasia of synovial cells, fibrosis, and inflammatory cell infiltration was observed in the meniscectomized knee. Synovial membrane in (c) a normal knee joint or (b) a meniscectomized knee joint were immunostained with the anti-FGF8 antibody KM1334. Sections were reacted with horseradish peroxidase-labeled anti-mouse IgG, developed using diaminobenzidine (brown) and counter stained with hematoxylin (blue). Very weak staining of FGF8 was observed in a few synovial cells, but not in other tissues in normal knee joints. (d) Many of the proliferated synovial cells (arrows) in meniscectomized knee joints showed positive reaction to FGF8. Positive staining of FGF8 was also observed in fibroblasts (arrowheads). (e) Normal and (f) meniscectomized articular cartilage was stained with safranin O. Reduction of safranin-O staining (red) and clusters of chondrocyte were observed in meniscectomized articular cartilage. Scale bar = 20 μm.