AN IMMUNOCYTOCHEMICAL STUDY OF THE DISTRIBUTION OF PROLINE-4-HYDROXYLASE IN NORMAL, OSTEOARTHRITIC AND RHEUMATOID ARTHRITIC SYNOVIUM AT BOTH THE LIGHT AND ELECTRON-MICROSCOPIC LEVEL

The monoclonal antibody 5B5 reacts with the beta subunit of proline-4- hydroxylase, the enzyme which catalyses the formation of 4-hydroxyl pr oline in collagen and other proteins with collagen-like amino acid seq uences. This study aims to assess the production and tissue distributi on of this enzyme in normal and diseased synovia from patients with va rious joint diseases, on the basis that it is a putative marker of col lagen-producing cells and, therefore, in this context, of fibroblasts. Sections from five normal, 10 osteoarthritic (OA) and 26 rheumatoid a rthritic (RA) synovia were labelled with a mouse monoclonal antibody t o proline-4-hydroxylase. The enzyme was found to be expressed by a pro portion of synovial intimal cells and by fibroblasts in the underlying connective tissue in normal, OA and RA synovia. Labelling was more pr onounced in OA and RA cases. The intimal cells labelling positively sh owed type B synoviocyte morphology, which was confirmed by subsequent double immunolabelling with 5B5 and antibody against type IV collagen using immunocytochemistry and immunoelectron microscopy.