Fifty kDa γ-PGA was obtained from Bioleaders (Daejeon, Korea) and its purity was more than 97%. The levels of endotoxin and peptidoglycan Histone Methyltransferase inhibitor contained in a 40 µM γ-PGA solution were <0·01 EU/ml and <10 pg/ml when measured by the Limulus amebocyte lysate assay using E-toxate kits (Sigma-Aldrich, St Louis, MO, USA) and by the silkworm larvae plasma assay (Wako Pure Chemicals, Osaka, Japan), respectively. Lipopolysaccharide (LPS) derived from Escherichia coli 026:B6 was purchased from Sigma-Aldrich. IL-6, TGF-β, anti-TGF-β antibody and mouse IgG1 isotype control

antibody were from R&D Systems (Minneapolis, MN, USA) and IL-2 was from Peprotech (Rocky Hill, NJ, USA). Anti-interferon (IFN)-γ antibody (XMG1·2) and anti-IL-4 antibody (11B11) were obtained from BD Biosciences (San Jose, CA, USA). T cells were stained with an appropriate mixture of monoclonal antibodies (mAbs), as described [27]. Data were acquired on a BD FACSCantoII. The mAbs used were: anti-CD17A-phycoerythrin (PE) (BD Biosciences), and anti-CD4-allophycocyanin (APC), anti-CD25-PE, anti-FoxP3-fluorescein isothiocyanate (FITC), anti-IFN-γ-FITC, anti-RORγt-PE, anti-CTLA-4-PE, anti-CD11c-FITC, anti-CD44-PE and anti-glucocorticoid-induced tumour necrosis factor (GITR)-PE (all from eBioscience, San Diego, CA, USA). Single-cell suspensions were obtained from BGJ398 cell line the spleens and lymph nodes of mice, and erythrocytes were lysed in ammonium

chloride (ACK) solution [150 mM NH4Cl, 1 mM potassium

hydrogen carbonate (KHCO3), 0·1 mM ethylenediamine tetraacetic acid (EDTA)]. To sort naive non-Treg CD4+ T cells, cells were stained with a mixture of anti-CD4, anti-CD44 and anti-CD11c or a mixture of anti-CD4, anti-CD44, and anti-CD25, and sorted by FACSAriaIII (BD Biosciences). The purity of the CD4+CD44loCD11c– and CD4+CD25-CD44lo populations was >98%. CD4+ T cells were purified to >98% of the purity using anti-CD4 magnetic microbeads and columns (Miltenyi Biotec, Bergisch Gladbach, Germany). Cells were cultured in RPMI-1640 medium supplemented with 10% Carnitine palmitoyltransferase II fetal bovine serum (FBS). For Th cell differentiation, purified whole CD4+ or naive CD4+ T cells (2 × 106 cells/ml) were stimulated with soluble 1 µg/ml anti-CD3 mAb (145-2C11; eBioscience) and soluble 1 µg/ml anti-CD28 mAb (37·51; BD Biosciences). Four ng/ml IL-2 was added for non-polarizing conditions (referred to as Th0) and 20 ng/ml IL-6, 5 ng/ml TGF-β, 5 µg/ml anti-IFN-γ mAb and 5 µg/ml anti-IL-4 mAb were added for Th17-polarizing conditions. After 4 days, IL-17 concentrations in culture supernatants were measured by sandwich enzyme-linked immunosorbent assay (ELISA) (R&D Systems), and the cells were restimulated with 40 ng/ml phorbol myristate acetate (PMA) (Sigma-Aldrich) and 1 µg/ml ionomycin (Sigma-Aldrich) in the presence of Golgi Stop (BD Biosciences) for 6 h and assayed by intracellular FACS methods.