Objective: To characterize the circulating cytokine profile and the cellular source of circulating cytokines in polymyalgia rheumatica (PMR).
Methods: The study included 34 patients with active untreated PMR and 17 age-matched healthy controls (HC). Circulating cytokines were measured by CBA and ELISA. Intracellular cytokines were assessed in CD3+ and CD14+ cells by flow cytometry. Cytokines in cell culture supernatants were also determined after polyclonal stimulation of patient’s PBMC.
Results: Circulating levels of IL-6 were significantly higher in active PMR compared to HC. Corticosteroid (CS) treatment was followed by a decrease of IL-6. Intracellular cytokine staining showed that circulating monocytes did not produce higher amounts of proinflammatory cytokines in PMR patients than in HC. There was a discordance between serum levels and cytokine-producing monocyte and T cells and we were not able to demonstrate a Th1 bias in the peripheral compartment.
Conclusion: Active PMR is characterized by increased serum levels of IL-6, but not of other pro-inflammatory cytokines, that are rapidly suppressed by CS therapy. Probably, as circulating monocytes do not show increased production of proinflammatory cytokines, IL-6 might be mainly produced in the inflamed tissue. The study of the circulating cytokine profile and its cellular source may provide a clue to new therapeutic options.