title: Predominance of CD8+ T lymphocytes in psoriatic arthritis.
abstract: OBJECTIVE
  To characterize the synovial fluid (SF) derived T cell populations in psoriatic arthritis (PsA) and compare with similar populations from rheumatoid arthritis (RA).
  
  
  METHODS
  Paired peripheral blood (PB) and SF samples were analyzed by 3 color flow cytometry using monoclonal antibodies to CD3, CD4, CD8, HLA-DR, CD25, CD45RA, and CD45RO.
  
  
  RESULTS
  There was a significantly increased CD8+ T cell population in PsA SF compared to RA: PsA mean 61% (range 35-93), RA mean 46% (range 6-72) (p < 0.005). This resulted in a reversal of the CD4:CD8 ratio in PsA SF compared to RA SF (p < 0.001). Patients with oligoarticular PsA had the most pronounced differences in SF derived T cell populations compared to RA (p < 0.0005) but these results were not significantly different from PsA patients with a polyarticular disease pattern. PB PsA T cell populations were not different from controls, in contrast to RA, where the CD4+ T cell population was increased (p < 0.0026), giving an exaggerated PB CD4:CD8 ratio. The majority of PsA SF CD8+ T cells expressed CD45RO, mean 73% (range 58-95), and HLA-DR antigen: mean 72% (range 38-94). Low levels of CD25 were detectable in this population, indicating a nonclassical activation pattern: mean 2% (range 0.3-4.4).
  
  
  CONCLUSIONS
  In PsA, activated (HLA-DR+) and mature (CD45RO+) CD8+ T cells predominate in SE Analysis of this population may uncover clues to pathogenesis in this HLA class I mediated disease.
authors.affiliation: Department of Rheumatology and Education and Research Centre, St. Vincent's University Hospital, Elm Park, Dublin, Ireland.
authors.forename: P
authors.initials: P
authors.lastname: Costello
authors.forename: B
authors.initials: B
authors.lastname: Bresnihan
authors.forename: C
authors.initials: C
authors.lastname: O'Farrelly
authors.forename: O
authors.initials: O
authors.lastname: FitzGerald
mesh_terms: D000328:Adult; D000368:Aged; D015535:Arthritis, Psoriatic / Q000097:blood / Q000276:immunology*; D001172:Arthritis, Rheumatoid / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D005260:Female; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000276:immunology; D008213:Lymphocyte Activation; D016131:Lymphocyte Subsets / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D013582:Synovial Fluid / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology