DEMONSTRATION OF CYTOKERATIN IN ENDOTHELIAL CELLS OF THE SYNOVIAL MICROVASCULATURE IN SITU AND IN VITRO

We have used a panel of anti-cytokeratin antibodies and immunofluorescencemicroscopy to examine synovial tissue from a variety of largeand small joints in patients with various rheumatic conditions,including RA, OA, AS, pigmented villonodular synovitis (PVNS)and tenosynovitis (TS). In every case we regularly found bloodvessels with endothelia which express cytokeratin. Positivestaining was obtained with a guinea pig anti-keratin antibody,with monoclonal antibody 8.13 and with a monoclonal antibodyspecific for keratin 18. Staining of endothelial cells was confirmedby double labelling with antibodies to cytokeratin and factorVIII/von Willebrand factor. We also detected a polypeptide correspondingto cytokeratin 18 (MW 45 000) by Western blotting of synovialtissue. In addition we have isolated pure populations of synovialendothelial cells in culture and demonstrate an extensive cytokeratinintermediate filament network which co-localizes with vimentinfilaments. An understanding of the role of the cytokeratin 18network in synovial endothelium may be important for our understandingof endothelial changes in synovial disease. KEY WORDS: Cytokeratin 18, Endothelium, Synovium, Rheumatoid arthritis