Light microscopic characterization of the fibroblast‐like synovial intimal cell (synoviocyte)

Abstract

Objective. To reassess synovial intimal cell populations by light microscopy. Methods. Non‐inflamed, rheumatoid and osteoarthritic synovia were analyzed as tissue sections and cytospin preparations by a series of combined immunohistochemical and cytochemical staining techniques. Results. Two populations of intimal cells were identified. The first carried macrophage markers. The second showed high uridine diphosphoglucose dehydrogenase (UDPGD) activity, minimal cytoplasmic CD68, absent non‐specific esterase (NSE) activity, and absent leukocyte and endothelial antigens. The majority of these cells showed a high content of prolyl hydroxylase. Conclusion. Combined cytochemical staining for NSE and UDPGD activity allows effective separation of intimal cell populations. We suggest that the cells of high UDPGD activity are the fibroblast‐like or type B synovial intimal cells defined by electron microscopy. High UDPGD activity probably reflects a preferential ability to synthesize glycosaminoglycans, including hyaluronan.