Expression pattern of angiopoietin-1 (Ang-1) in synovial tissues. The arrows denote the lining cell layer, the double arrowhead denotes subsynovial macrophages and the single arrowhead denotes vascular endothelium. The immunohistochemistry was performed with a goat antihuman Ang-1 polyclonal antibody from Santa Cruz Biotechnology (Santa Cruz, CA, USA). (a) Synovial tissue from a patient with rheumatoid arthritis showing positive staining for Ang-1. (b) Positive staining in osteoarthritis synovial tissue. (c) Ang-1 staining is absent in normal synovial tissue. (a), (b) and (c) Original magnification × 226. (d) Immunohistochemistry of synovial tissues from normal (NL) subjects (n = 5) and those with rheumatoid arthritis (RA) (n = 9) and osteoarthritis (OA) (n = 8). The bars represent mean ± SE. (e) Ang-1 mRNA levels in synovial tissue (ST) and RA fibroblasts (Fib) were quantified using real-time reverse transcription-PCR and normalized to glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Bars represent the mean ± SE (n = 3). Lining, synovial tissue lining cell layer; Mac, subsynovial macrophages; Endo, vascular endothelium. *P < 0.05.