Cellular architecture of the synovium in the tendon sheath of horses : An immunohistochemical and scanning electron microscopic study

The intimal lining cells of the synovium in joints have been studied morphologically and histochemically and shown to consist of macrophagic cells (type A) and fibroblast-like cells (type B). It is believed that the structure of the synovium in the tendon sheath is similar to that in the joint, but there have been only a few morphological studies of the tendon sheath. The present study revealed the cellular architecture of synovium in the tendon sheath of horses by histochemistry and scanning electron microscopy (SEM). Like the joint, the inner surface of the tendon sheath was covered with a cell-rich intimal layer. Acid phosphatase-positive A cells accumulated in the mesotendon but few in other regions. B cells were selectively immunolabeled with protein gene product (PGP) 9.5 antiserum and distributed in the entire length of the synovial intima in the tendon sheath. The synovial intima consisted of a surface layer rich in the processes of B cells and a deep layer containing cell bodies of B cells. Using SEM, B cells could be classified into two types according to the morphology of their processes. B cells of dendritic type were located mainly in the joint-side of the tendon sheath and extended branched processes to form a meshwork on the intimal surface. B cells of flat type were located in the skin-side of the tendon sheath and in the mesotendon. Their membranous processes extended in a horizontal direction and covered the intimal surface, resembling epithelium. It appears likely that the morphology and distribution of synovial intimal cells are influenced by various factors, such as the nature of the underlying tissues and the magnitude of mechanical stress

Increased concentrations of protein gene product 9.5 in the synovial fluid from horses with osteoarthritis

Our previous study established protein gene product 9.5 (PGP 9.5), a ubiquitin C-terminal hydrolase, as a specific cytochemical marker of synovial lining cells (type B synoviocytes) in the horse joint. The present study aimed to detect PGP 9.5 in the synovial fluid and shows that PGP 9.5 is a valuable marker of osteoarthritis in the horse. Immunohistochemical staining confirmed rich and consistent localization of PGP 9.5 immunoreactivity in the cytoplasm of synovial lining cells in the normal horse joint. Western blot analysis of synovial fluid from normal joints could detect a significant band corresponding to that contained in the brain and synovial membrane extracts. When 60 synovial fluid samples from normal and abnormal joints were assayed with an enzyme-linked immunosorbent assay (ELISA) system, the concentration of PGP 9.5 tended to be elevated in osteochondrosis dissecance, inflammatory arthropathy and intra-articular fracture, among which a statistically significant elevation was recognizable between the intra-articular fracture and the control. Thus, this study demonstrated the possibility that PGP 9.5, derived from synovial lining cells, may be a new biochemical marker for arthritic disorders of the horse