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Figure 1: Immunohistological staining cyclooxygenase 2 (COX 2) and ED1 in HRHF distal radiocarpal articular cartilage, synovium and ligaments of longitudinally sections of paraffin embedded bones. ED1 detects a 90 kDa lysosomal membrane glycoprotein in osteoclasts, phagocytic macrophages and their progenitors. (a)–(f) COX 2 staining was visualized using DAB intensified with cobalt (black signal); light hematoxylin and eosin ((h) and (e)) staining was used as a counterstain. (a) No COX 2 immunostaining was observed in distal radial articular cartilage and synovium of a normal control (NC). (b) Higher-power image of same section as shown in (a). (c) COX2+ cells are present in the articular cartilage and synovium of a 12-week high-repetition high-force (HRHF) rat’s distal radius. (d) Higher-power image of same section as shown in (c). (e) COX2+ cells are present in the distal radial articular cartilage and radiocarpal ligament of a 12 week HRHF rat. (f) Higher-power image of same section as shown in (e). (g)–(i) Several COX2+ cells are present in the radiocarpal synovium of an HRHF 12 rat (red cells). (g) Same section double labeled for ED1 (green cells, (h)). (i) Merged photo. Arrow indicates a group of COX2+/ED1+ double labeled cells. (j) ED1+ cells (brown DAB signal) were absent in distal radius articular cartilage of an NC rat. Section is lightly counterstained with hematoxylin. (k) Mononucleated ED1+ cells (arrows, presumably osteoclast progenitor cells) were observed in the subchondral bone of the distal radius of an HRHF rat. (l) ED1+ cells were also present in HRHF carpal bones. Scale bars = 50 μm. b: bone, c: articular cartilage, lig: ligament, s: synovium.