Bhlhe40 is an essential repressor of IL-10 during Mycobacterium tuberculosis infection

The cytokine IL-10 antagonizes pathways that control Mycobacterium tuberculosis (Mtb) infection. Nevertheless, the impact of IL-10 during Mtb infection has been difficult to decipher because loss of function studies in animal models have yielded only mild phenotypes. We have discovered that the transcription factor Bhlhe40 is required to repress Il10 expression during Mtb infection. Loss of Bhlhe40 in mice results in higher Il10 expression, higher bacterial burden, and early susceptibility similar to that observed in mice lacking IFN-g. Deletion of Il10 in Bhlhe40-/- mice reverses these phenotypes. Bhlhe40 deletion in T cells or CD11c+ cells is sufficient to cause susceptibility to Mtb. Bhlhe40 represents the first transcription factor found to be essential during Mtb infection to specifically regulate Il10 expression, revealing the importance of strict control of IL-10 production by innate and adaptive immune cells during infection. Our findings uncover a previously elusive but significant role for IL-10 in Mtb pathogenesis. Bhlhe40+/+ and Bhlhe40-/- GM-CSF-cultured bone marrow-derived cells were stimulated in the presence of 10 µg/ml heat-killed Mycobacterium tuberculosis (H37Ra strain, Difco) for 4 hours. Bhlhe40+/+ and Bhlhe40-/- in vitro-polarized TH1 cells were stimulated with PMA (50 ng/ml, Enzo Life Sciences) and ionomycin (1 µM, Enzo Life Sciences) for 1.5 hours. After stimulation, cells were fixed and genomic DNA was immunoprecipitated with anti-Bhlhe40 antibody.