BATF regulates collagen-induced arthritis by regulating T helper cell differentiation

Background: We recently demonstrated that BATF, a member of the activator protein-1 (AP-1) family, regulates osteoarthritic cartilage destruction. Here, we explored the roles and regulatory mechanisms of BATF in collagen-induced arthritis (CIA) in mice. Methods: CIA and K/BxN serum transfer were used to generate inflammatory arthritis models in wild-type (WT) and Batf(-/-) mice. RA manifestations were determined by examining CIA incidence, clinical score, synovitis, synovial hyperplasia, angiogenesis in inflamed synovium, pannus formation, bone erosion, and cartilage destruction. Immune features in RA were analyzed by examining immune cell populations and cytokine production. Results: BATF was upregulated in the synovial tissues of joints in which inflammatory arthritis had been caused by CIA or K/BxN serum transfer. The increases in CIA incidence, clinical score, and autoantibody production in CIA-induced WT mice were completely abrogated in the corresponding Batf(-/-) DBA/1 J mice. Genetic ablation of Batf also inhibited CIA-induced synovitis, synovial hyperplasia, angiogenesis in synovial tissues, pannus formation, bone erosion, and cartilage destruction. Batf knockout inhibited the differentiation of T helper (Th) 17 cells and the conversion of CD4(+) Foxp3(+) cells to CD4(+) IL-17(+) cells. However, BATF did not modulate the functions of fibroblast-like synoviocytes (FLS), including the expressions of chemokines, matrixdegrading enzymes, vascular endothelial growth factor, and receptor activator of NF-kappa B ligand (RANKL). Conclusion: Our findings indicate that BATF crucially mediates CIA by regulating Th cell differentiation without directly affecting the functions of FLS.