Galectin-9 expands immunosuppressive macrophages to ameliorate T-cell-mediated lung inflammation

Galectin-9 (Gal-9) plays pivotal roles in the modulation of innate and adaptive immunity to suppress T-cell-mediated autoimmune models. However, it remains unclear if Gal-9 plays a suppressive role for T-cell function in non-autoimmune disease models. We assessed the effects of Gal-9 on experimental hypersensitivity pneumonitis induced by Trichosporon asahii. When Gal-9 was given subcutaneously to C57BL/6 mice at the time of challenge with T. asahii, it significantly suppressed T. asahii-induced lung inflammation, as the levels of IL-1, IL-6, IFN-γ, and IL-17 were significantly reduced in the BALF of Gal-9-treated mice. Moreover, co-culture of anti-CD3-stimulated CD4 T cells with BALF cells harvested from Gal-9-treated mice on day 1 resulted in diminished CD4 T-cell proliferation and decreased levels of IFN-γ and IL-17. CD11b⁺ Ly-6C^highF4/80⁺ BALF M/ expanded by Gal-9 were responsible for the suppression.We further found in vitro that Gal-9, only in the presence of T. asahii, expands CD11b⁺Ly-6C ^highF4/80⁺ cells from BM cells, and the cells suppress T-cell proliferation and IFN-γ and IL-17 production. The present results indicate that Gal-9 expands immunosuppressive CD11b⁺Ly-6C ^high Mφ to ameliorate Th1/Th17 cell-mediated hypersensitivity pneumonitis.