Objective: Arthralgias and overt arthritides are often associated with viral infections. Viral infections expose the infected host to proinflammatory double-stranded RNA (dsRNA), which can cause joint inflammation and is a potent activator of interferon-alpha (IFNalpha). The aim of this study was to determine the role of IFNalpha and dsRNA-related signaling molecules in the onset of joint inflammation induced by viral dsRNA.
Methods: IFNalpha and different forms of RNA were injected into the knee joints of wild-type mice, mice lacking the type I interferon receptor (IFNAR(-/-)), and mice deficient in dsRNA-dependent protein kinase (PKR(-/-)). Histologic evidence of joint damage and the ability of splenocytes to produce cytokines in response to dsRNA or IFNalpha were assessed.
Results: Viral dsRNA, but not short single-stranded RNA, induced arthritis. The arthritis was aggravated by intracellular delivery of dsRNA. The expression of PKR was not mandatory for dsRNA-induced joint inflammation. In contrast, IFNalpha/beta signaling was important for dsRNA-induced joint inflammation because IFNAR(-/-) mice did not develop arthritis. Furthermore, intraarticular deposition of IFNalpha induced arthritis in PKR(-/-) and control mice, whereas IFNAR(-/-) mice were protected. The arthritogenic effect of IFNalpha was attenuated by in vivo depletion of monocyte/macrophages.
Conclusion: Arthritis triggered by dsRNA is not dependent on the expression of the dsRNA-signaling molecule PKR (or Toll-like receptor 3, as previously shown), but is associated with the ability to produce type I IFN and is critically dependent on type I IFN receptor signaling. The intrinsic arthritogenic properties of IFNalpha implicate a role of this cytokine in joint manifestations triggered by various interferogenic stimuli.