Interleukin‐1 drives pathogenic Th17 cells during spontaneous arthritis in interleukin‐1 receptor antagonist–deficient mice

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Abstract
Objective Interleukin-1 receptor antagonist–deficient (IL-1Ra−/−) mice spontaneously develop an inflammatory and destructive arthritis due to unopposed excess IL-1 signaling. In this study, the role of Th17 cells and the effect of neutralization of IL-17, IL-1, and tumor necrosis factor α (TNFα) were investigated in this IL-1–driven murine arthritis model. Methods T cells isolated from IL-1Ra−/− and wild-type (WT) mice were stained for IL-17 and interferon-γ, with results assessed by fluorescence-activated cell sorting analysis. To investigate the contribution of IL-1 and IL-17 in further progression of arthritis in this model, mice were treated with neutralizing antibodies after the onset of arthritis. Results Compared with WT mice, IL-1Ra−/− mice had similar levels of Th1 cells but clearly enhanced levels of Th17 cells; this increase in the number of Th17 cells was evident even before the onset of arthritis, in young, nonarthritic IL-1Ra−/− mice. The percentage of Th17 cells increased even more after the onset of arthritis and, similar to the serum levels and local messenger RNA levels of IL-17, the percentage of IL-17+ Th17 cells clearly correlated with the severity of arthritis. Anti–IL-17 treatment prevented any further increase in inflammation and bone erosion, whereas blocking of TNFα after the onset of arthritis had no effect. In contrast, neutralization of IL-1 resulted in a complete suppression of arthritis. Interestingly, this anti–IL-1 treatment also significantly reduced the percentage of IL-17+ Th17 cells in the draining lymph nodes of these arthritic mice. Conclusion Increased levels of Th17 cells can be detected in IL-1Ra−/− mice even preceding the onset of arthritis. In addition, the results of cytokine-blocking studies demonstrated that IL-17 contributes to the inflammation and bone erosion in this model, which suggests that IL-1 is the driving force behind the IL-17–producing Th17 cells.

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