3-nitrotyrosine (3NT) is regarded as some kind of a „footprint“ of NO generation. Immunohistochemical analysis was performed on 9 specimens of human synovium (3 rheumatoid arthritis, 4 osteoarthritis (OA), 1 juvenile idiopathic arthritis, and 1 inflamed Baker’s cyst derived from a joint of a patient with villonodular synovitis). Serial sections were stained with monoclonal antibody 60-E3 to 3NT, and with antibodies to CD31, CD68, and CD14 reacting to endothelial cells, macrophages and monocytes, respectively. The majority of specimens demonstrated a pattern of strong 3NT staining localized to endothelial cells accompanied by weak immunostaining of tissues closely surrounding the 3NT-positive endothelia (7 of the 9 specimens, including all of the specimens derived from osteoarthritic joints). We observed strong 3NT immunostaining of synovial stroma in only 2 specimens of inflamed synovia, those collected from the Baker’s cyst secondary to villonodular synovitis and a knee joint with rheumatoid arthritis. We conclude that in human synovial tissue, tyrosine is primarily nitrated in endothelial cells. 3NT-positive staining of endothelial cells in OA synovia suggests that activation of endothelial cells occurs even in apparently non-inflammatory OA synovial tissue.

        Key words: nitric oxide, nitrotyrosine, synovium, osteoarthritis, immunohistochemistry