Immunohistochemical detection of microsomal epoxide hydrolase in human synovial tissue

Microsomal epoxide hydrolase catalyses the hydrolysis of epoxides to water- soluble trans-dihydrodiols. We studied the expression of the hydrolase in s ynovial tissue samples from patients with osteoarthritis (n=20), rheumatoid arthritis (n=36), ankylosing spondylitis (n=10) or psoriatic arthritis (n= 15) by use of immunohistochemistry with videodensitometric quantification o f staining. Strong immunostaining for microsomal epoxide hydrolase was dete cted in tunica media of synovial blood vessels and moderate staining in syn ovial lining cells. Experiments with antibodies against CD68 and CLA sugges ted that both type A (macrophage-like) and type B lining cells (fibroblast- like synoviocytes) express the hydrolase. In addition, some of the subsynov ial fibroblast-like cells, histiocytes and monocytes were intensively stain ed for microsomal epoxide hydrolase. In general, there were no major differ ences in the intensity of immunostaining for the hydrolase between the diag nostic groups. The enzyme may be involved in local hydrolysis of epoxide me tabolites of endo- and xenobiotics in synovial tissue.