Immunohistochemical detection of FSTL1 in synovial tissues. (A-D) Trauma control synovial tissues with normal synovium. Synovial cells with little or weak FSTL1 immunostaining are shown. (E-H) RA synovial tissues. Hyperplastic synovial lining and sublining cells with positive FSTL1 immunostaining are shown. All tissues were counterstained with hematoxylin. (A, C, E and G) Original magnification, ×100. (B, D, F and H) Original magnification, ×400. The negative controls were stained with polyclonal goat IgG (original magnification, ×100) and are shown in the insets (A-D). Arrows indicate capillary endothelial cells from trauma control with normal synovial tissues (B) and RA synovial tissues (F and H). FSTL1, follistatin-like protein 1; RA, rheumatoid arthritis; IgG, immunoglobulin G.