Localisation of citrullinated proteins in synovial membranes. (a) Immunostaining of citrullinated proteins by the anti-modified citrulline kit was mainly confined to the subsynovium. (b) No staining was visible on the control. (c) Staining produced by the anti-α-enolase antibody on an adjacent section was much stronger, and included the subsynovial cells which also stained for citrullinated antigens. Original magnification × 20 in all cases.