Immunohistochemical staining of FSTL1 in the STs and articular cartilage from control trauma patients and OA patients. (A-B) The STs from control trauma patients. The synovial cells of the lining and sublining with little or weak FSTL1 immunostaining are shown. (C-H) The STs from OA patients. The synovial cells of the lining and sublining with positive FSTL1 immunostaining are shown. (I-L) The articular cartilage from control trauma patients (I-J) and OA patients (K-L). The chondrocytes with little or weak FSTL1 immunostaining are shown. The STs (C and D; E and F; G and H) were collected from three different OA patients. The STs (G and H) and articular cartilage (K and L) were collected from the same OA patients. All tissue samples were counterstained with hematoxylin. (A, C, E, G, I and K) Original magnification, ×100. (B, D, F, H, J and L) Original magnification, ×400. The negative controls stained with polyclonal goat IgG (original magnification, ×100) are shown in the insets (A, C, E, G, I and K). Arrows indicate the capillary endothelial cells in the STs from control trauma patients (B) and OA patients (D, F and H). Representative images from one of three separate experiments with similar results are shown. FSTL1, follistatin-like protein 1; IgG, immunoglobulin G; OA, osteoarthritis; ST, synovial tissue.