title: Expression of the activation antigen CD97 and its ligand CD55 in rheumatoid synovial tissue.
abstract: OBJECTIVE
  Fibroblast-like synoviocytes (FLS) express decay-accelerating factor (CD55) at high levels. Recently, it was found that CD55 is a specific cellular ligand for the 7-span transmembrane receptor CD97. The objective of this study was to define the expression of this receptor-ligand pair in synovial tissue (ST) to provide more insight into the interaction between FLS and surrounding cells.
  
  
  METHODS
  Antibodies against CD97 and CD55 were used for immunohistologic analysis of synovial biopsy specimens from 16 patients with rheumatoid arthritis (RA) and 15 patients with osteoarthritis (OA). In addition, an enzyme-linked immunosorbent assay system was used to determine the expression of soluble CD97 (sCD97) in synovial fluid (SF) from 30 patients with RA, 13 with OA, and 10 with reactive arthritis (ReA).
  
  
  RESULTS
  In both RA and OA ST sections, strong expression of CD55 was confirmed on FLS in the intimal lining layer, where it was also found that all macrophages expressed CD97. The percentage of macrophages that expressed CD97 was lower in the synovial sublining (P = 0.005). The mean levels of sCD97 in SF were significantly higher in RA patients than in patients with OA or ReA (P < 0.0001).
  
  
  CONCLUSIONS
  These results suggest that FLS are able to interact with macrophages via the CD97/CD55 receptor-ligand system. In this respect, the CD97/CD55 pair may account for the specific architecture of the intimal lining layer and may be of primary importance in maintaining and amplifying synovial inflammation. The specific increase in sCD97 levels in RA SF might be related to the presence of activated proteolytic systems or to the increase in synovial mass, rather than a consequence of local receptor-ligand interaction.
authors.affiliation: Central Laboratory of the Netherlands Red Cross Blood Transfusion Service, and University of Amsterdam.
authors.forename: J
authors.initials: J
authors.lastname: Hamann
authors.forename: J O
authors.initials: JO
authors.lastname: Wishaupt
authors.forename: R A
authors.initials: RA
authors.lastname: van Lier
authors.forename: T J
authors.initials: TJ
authors.lastname: Smeets
authors.forename: F C
authors.initials: FC
authors.lastname: Breedveld
authors.forename: P P
authors.initials: PP
authors.lastname: Tak
mesh_terms: D000328:Adult; D000368:Aged; D000911:Antibodies, Monoclonal; D015703:Antigens, CD / Q000032:analysis; D015214:Antigens, Differentiation, Myelomonocytic / Q000032:analysis; D001172:Arthritis, Rheumatoid / Q000276:immunology / Q000378:metabolism*; D018958:CD55 Antigens / Q000032:analysis*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005455:Fluorescent Antibody Technique; D006801:Humans; D008297:Male; D008562:Membrane Glycoproteins / Q000032:analysis* / Q000097:blood / Q000134:cerebrospinal fluid; D008875:Middle Aged; D010003:Osteoarthritis / Q000276:immunology / Q000378:metabolism; D000091402:Prohibitins; D043562:Receptors, G-Protein-Coupled; D013583:Synovial Membrane / Q000737:chemistry* / Q000276:immunology; D000097382:CD68 Molecule
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D018958:CD55 Antigens; D008562:Membrane Glycoproteins; D000091402:Prohibitins; D043562:Receptors, G-Protein-Coupled; C095004:ADGRE5 protein, human; C067980:CD68 antigen, human; D000097382:CD68 Molecule; C000717331:PHB2 protein, human