Immunohistochemical detection of blood vessels in NR (A and C) and in I (B and D) synovial biopsies. At the time of surgery, synovial biopsies coming from NR or I areas were macroscopically selected by as described in Materials and methods. Immunohistochemical staining of blood vessels (→) was performed using anti-von Willebrand factor antibody. Positive staining was detected as brown peroxidase reaction product. (A) and (B) global image of the section, (C) and (D) magnification (×100) of vessel lumens.