Divergent Pro- and Antiinflammatory Roles for IL-23 and IL-12 in Joint Autoimmune Inflammation

TLDR

IL‑23 is a heterodimeric cytokine (p19+p40) that regulates memory T‑cell and macrophage function via the IL‑23R receptor. IL‑23 promotes end‑stage joint autoimmune inflammation, while IL‑12 deficiency exacerbates arthritis, indicating that IL‑23 drives disease and IL‑12 confers protection.

Abstract

Interleukin (IL) 23 is a heterodimeric cytokine composed of a p19 subunit and the p40 subunit of IL-12. IL-23 affects memory T cell and inflammatory macrophage function through engagement of a novel receptor (IL-23R) on these cells. Recent analysis of the contribution of IL-12 and IL-23 to central nervous system autoimmune inflammation demonstrated that IL-23 rather than IL-12 was the essential cytokine. Using gene-targeted mice lacking only IL-12 (p35−/−) or IL-23 (p19−/−), we show that the specific absence of IL-23 is protective, whereas loss of IL-12 exacerbates collagen-induced arthritis. IL-23 gene-targeted mice did not develop clinical signs of disease and were completely resistant to the development of joint and bone pathology. Resistance correlated with an absence of IL-17–producing CD4+ T cells despite normal induction of collagen-specific, interferon-γ–producing T helper 1 cells. In contrast, IL-12–deficient p35−/− mice developed more IL-17–producing CD4+ T cells, as well as elevated mRNA expression of proinflammatory tumor necrosis factor, IL-1β, IL-6, and IL-17 in affected tissues of diseased mice. The data presented here indicate that IL-23 is an essential promoter of end-stage joint autoimmune inflammation, whereas IL-12 paradoxically mediates protection from autoimmune inflammation.