Bone damage caused by oncostatin M (OSM) in combination with either IL-1 or tumour necrosis factor alpha (TNF-α) in murine joints. Adenovirus vectors overexpressing murine OSM, IL-1 or TNF-α were injected intra-articularly into the right knee joints of mice at 5 × 106 plaque-forming units [pfu]/vector/joint. The left knee joints were injected with the empty control vector. All joints received a total of 1 × 107 pfu/joint, and all animals were sacrificed at day 7 following administration. Sections (5 μm) were stained with H&E. (a) Control, (b) OSM, (c) IL-1, (d) TNF-α, (e), (f) OSM + IL-1, and (g), (h) OSM + TNF-α. The joints showed a moderate (b–d) to severe (e–h) synovial hyperplasia and an infiltration of inflammatory cells. Marked synovial hyperplasia with angiogenesis was also seen with bone erosions (arrows) and bone fractures, with evidence of synovial invasion (e and g). b, bone; bm, bone marrow; f, bone fracture; m, muscle; s, synovial cells; v, blood vessel. (a)–(e), (g) Bar = 50 μm; (f), (h) bar = 20 μm.