IL-23 induces receptor activator of NF-κB ligand expression on CD4⁺ T cells and promotes osteoclastogenesis in an autoimmune arthritis model

IL-23, a clinically novel cytokine, targets CD4⁺ T cells. Recent IL-1Ra^-/- mouse studies have demonstrated that IL-23 indirectly stimulates the differentiation of osteoclast precursors by enhancing IL-17 release from CD4⁺ T cells. IL-17, in turn, stimulates osteoclastogenesis in osteoclast precursor cells. In this study, we found that IL-23 up-regulates receptor activator of NF-κB ligand expression by CD4⁺ T cells, and thus contributes to osteoclastogenesis. This indirect pathway is mediated by NF-κB and STAT3. We have also demonstrated that IL-23 can influence osteoclastogenesis positively under the special conditions in the IL-1-dominant milieu of IL-1Ra^-/- mice. We propose that IL-23-enhanced osteoclastogenesis is mediated mainly by CD4⁺ T cells. The results of this study show that IL-23 is a promising therapeutic target for the treatment of arthritis-associated bone destruction.