Increased frequency of activated CD8⁺ T cell effectors in patients with psoriatic arthritis

The aim of this study is to identify subsets of T cells differentially represented in the circulation of patients with psoriatic arthritis and to evaluate the possibility that they can recirculate between peripheral blood and the inflamed joints. We analyzed the phenotype and cytokine expression in circulating CD8⁺ and CD4⁺ T cells in 69 subjects: 28 with cutaneous psoriasis, 15 patients with psoriatic arthritis, and 26 healthy subjects. In the circulation, the percentage of each subset was compared among the groups and correlation was calculated with the serum concentration of C-reactive protein. To investigate the migration of T cells towards the inflamed joints, we performed a transwell migration assay towards patient serum and synovial fluid. In selected patients we analyzed in parallel T cells from peripheral blood and from synovial fluid. In the circulation, we found increased percentage of CD8⁺ CCR6⁺ T cell effectors expressing CD69 and of IL-17-producing T cells in patients with psoriatic arthritis. CD8⁺ effector/effector memory T cells showed increased migration towards synovial fluid. Finally, in synovial fluid we found accumulation of CXCR3⁺ CD8⁺ T cells and CD69⁺ cells. CD4⁺ T cells in the two compartments shared many similarities with CD8⁺ T cells. The results indicate a role for memory T cell effectors in systemic and joint manifestations of psoriatic arthritis.