Predominance of CD8+ T lymphocytes in psoriatic arthritis.

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). CONCLUSION: 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.