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 prolinein collagen and other proteins with collagen-like amino acid sequences.This study aims to assess the production and tissue distribution of thisenzyme in normal and diseased synovia from patients with various jointdiseases, on the basis that it is a putative marker of collagen-producingcells and, therefore, in this context, of fibroblasts. Sections from fivenormal, 10 osteoarthritic (OA) and 26 rheumatoid arthritic (RA) synoviawere labelled with a mouse monoclonal antibody to proline-4-hydroxylase.The enzyme was found to be expressed by a proportion of synovial intimalcells and by fibroblasts in the underlying connective tissue in normal, OAand RA synovia. Labelling was more pronounced in OA and RA cases. Theintimal cells labelling positively showed type B synoviocyte morphology,which was confirmed by subsequent double immunolabelling with 5B5 andantibody against type IV collagen using immunocytochemistry andimmunoelectron microscopy.