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 alpha (TNFalpha) 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-gamma, 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 TNFalpha 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.