Localization of CD68+ and tartrate-resistant acid phosphatase (TRAP)+ cells in gouty tophus tissues. (a) Tophus tissue sections from patients with chronic gouty arthritis were processed for immunohistochemical staining using anti-CD68 antibody (brown). (b) Serial sections were stained for TRAP (red). (c, d) Electron microscopic findings of CD68+ cells. Scale bars in left panels of a and b = 500 μm; scale bars in right panels of a and b = 50 μm; scale bars in c and d = 5 μm.