Contribution of pathogenic T helper 1 and 17 cells to bursitis and tenosynovitis in polymyalgia rheumatica

Background: Although polymyalgia rheumatica (PMR) is a very common rheumatic inflammatory disease, current insight into the pathobiology of PMR is limited and largely based on studies in blood. We investigated T helper 1 (TH1) and T helper 17 (TH17) cell responses in blood, synovial fluid and bursa tissue of patients with PMR. Materials and methods: Blood samples were collected from 18 patients with new-onset PMR and 32 healthy controls. Synovial fluid was aspirated from the inflamed shoulder bursae or biceps tendon sheath of 13 patients. Ultrasound-guided biopsies of the subacromial-subdeltoid (SASD) bursa were obtained from 11 patients. T cells were examined by flow cytometry, immunohistochemistry and immunofluorescence staining. Results: Besides an increase of TH17 (CD4+IL-17+IFN-γ-) cells and T cytotoxic 17 (TC17; CD8+IL-17+IFN-γ-) cells, no other major changes were noted in the circulating T cell compartment of patients with PMR. Absolute numbers of CD4+ and CD8+ T cells were similar in blood and synovial fluid of patients with PMR. Synovial fluid T cells showed an effector-memory (CD45RO+CCR7-) phenotype. Percentages of TH1 (CD4+IFN-γ+IL-17-) cells and TH1/TH17 (CD4+IFN-γ+IL-17+) cells, but not TH17 or TC17 cells, were increased in the synovial fluid. Bursa tissue biopsies contained a small number of T cells, which were mostly CD8 negative. The majority of bursa tissue T cells produced IFN-γ but not IL-17. For comparison, B cells were scarcely detected in the bursa tissue. Conclusion: Although the circulating TH17 cell pool is expanded in patients with PMR, our findings indicate that TH1 cells are involved in the inflammation of bursae and tendon sheaths in this condition. Our study points towards the TH1 cell pathway as a potential target for therapy in PMR