Effector mechanisms of interleukin-17 in collagen-induced arthritis in the absence of interferon-γ and counteraction by interferon-γ

INTRODUCTION: Interleukin (IL)-17 is a pro-inflammatory cytokine in rheumatoid arthritis (RA) and collagen-induced arthritis (CIA). Since interferon (IFN)-γ inhibits Th17 cell development, IFN-γ receptor knockout (IFN-γR KO) mice develop CIA more readily. We took advantage of this model to analyse the mechanisms of action of IL-17 in arthritis. The role of IFN-γ on the effector mechanisms of IL-17 in an in vitro system was also investigated. METHODS: IFN-γR KO mice induced for CIA were treated with anti-IL-17 or control antibody. The collagen type II (CII)-specific humoral and cellular autoimmune responses, myelopoiesis, osteoclastogenesis, and systemic cytokine production were determined. Mouse embryo fibroblasts (MEF) were stimulated with IL-17, tumor necrosis factor (TNF)-α and the expression of cytokines and chemokines were determined. RESULTS: A preventive anti-IL-17 antibody treatment inhibited CIA in IFNγR KO mice. In the joints of anti-IL-17-treated mice, neutrophil influx and bone destruction were absent. Treatment reduced the cellular autoimmune response as well as the splenic expansion of CD11b(+ )cells, and production of myelopoietic cytokines such as granulocyte macrophage colony-stimulating factor (GM-CSF) and IL-6. IL-17 and TNF-α synergistically induced granulocyte chemotactic protein-2 (GCP-2), IL-6 and receptor activator of NFκB ligand (RANKL) in MEF. This induction was profoundly inhibited by IFN-γ in a STAT-1 (signal transducer and activator of transcription-1)-dependent way. CONCLUSIONS: In the absence of IFN-γ, IL-17 mediates its pro-inflammatory effects mainly through stimulatory effects on granulopoiesis, neutrophil infiltration and bone destruction. In vitro IFN-γ profoundly inhibits the effector function of IL-17. Thus, aside from the well-known inhibition of the development of Th17 cells by IFN-γ, this may be an additional mechanism through which IFN-γ attenuates autoimmune diseases.