Immune-Responsive Gene 1 expression in myeloid cells prevents neutrophil mediated immunopathology during Mycobacterium tuberculosis infection, in vitro neutrophils 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: Neutrophils were purified from bone marrow of naïve mice by negative selection using magnetic-activated cell sorting beads (Miltenyi). Neutrophil purity (>95%) was assessed by flow cytometry as the percentage of Ly6G+ CD11b+ cells. Neutrophils were cultured in RPMI-1640 supplemented with 1% non-essential amino acids at 37°C, 5% CO2. GFP-Mtb was grown to mid-log phase, washed with PBS, sonicated to disperse clumps, and resuspended in neutrophil culture media. GFP-Mtb then was opsonized prior to infection by mixing with an equal volume of normal mouse sera (Sigma) and incubation at room temperature for 30 min. Neutrophils were mock-infected or infected with opsonized GFP-Mtb at MOI 1 and incubated at 37°C, 5% CO2.

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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