Immune-Responsive Gene 1 expression in myeloid cells prevents neutrophil mediated immunopathology during Mycobacterium tuberculosis infection, in vivo neutrophil data

Immune-Responsive Gene 1 (Irg1) is a mitochondrial enzyme that produces itaconate under inflammatory conditions principally in cells of myeloid lineage. Cell culture studies suggest that itaconate regulates inflammation through inhibitory effects on cytokine and reactive oxygen species production. To evaluate the functions of Irg1 in vivo, we challenged wild-type (WT) and Irg1 KO mice with Mycobacterium tuberculosis (Mtb) and monitored disease progression. Irg1 KO but not WT mice succumbed rapidly to Mtb, and mortality was associated with increased infection, inflammation, and pathology. Infection of LysM-Cre Irg1 flox, MPR8-Cre Irg1 flox, and CD11c-Cre Irg1 flox conditional knockout mice along with neutrophil depletion experiments revealed a role for Irg1 in alveolar macrophages and LysM+ myeloid cells in preventing neutrophil-mediated immunopathology and disease. RNA-seq analyses suggest that Irg1 and its production of itaconate temper Mtb-induced inflammatory responses in myeloid cells at the transcriptional level. Thus, Irg1 modulates inflammation to curtail Mtb-induced lung disease. Overall design: C57BL/6N (WT) mice were purchased from Charles River. B6.SJL (CD45.1) mice were obtained from Jackson Laboratories. Irg1-/- mice (embryonic stem cells obtained from KOMP (C57BL/6N background), MGI: 103206) were generated at Washington University. Adult mice (6-13 weeks of age) of both sexes were used, and sex was randomized between experiments. Neutrophils were purified by magnetic-activated cell sorting from the bone marrow of naïve mice (negative selection) or the lungs of Mtb-infected mice at 16 dpi (selection for Ly6G+ cells) (Miltenyi).

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Nair S, Huynh JP, Lampropoulou V, Loginicheva E, Esaulova E, Gounder AP, Boon ACM, Schwarzkopf EA, Bradstreet TR, Edelson BT, Artyomov MN, Stallings CL, Diamond MS