Hemachromatosis (iron-overload) increases host susceptibility to siderophilic bacterial infections that cause serious complications, but the underlying mechanisms remain elusive. The present study demonstrates that oral infection with hyperyersiniabactin (Ybt) producing Yersinia pseudotuberculosis Δfur mutant (termed Δfur) results in severe systemic infection and acute mortality to hemochromatotic mice due to rapid disruption of the intestinal barrier. Transcriptome analysis of Δfur-infected intestine revealed up-regulation in cytokine–cytokine receptor interactions, the complement and coagulation cascade, the NF-κB signaling pathway, and chemokine signaling pathways, and down-regulation in cell-adhesion molecules and Toll-like receptor signaling pathways. Further studies indicate that dysregulated interleukin (IL)-1β signaling triggered in hemachromatotic mice infected with Δfur damages the intestinal barrier by activation of myosin light-chain kinases (MLCK) and excessive neutrophilia. Inhibiting MLCK activity or depleting neutrophil infiltration reduces barrier disruption, largely ameliorates immunopathology, and substantially rescues hemochromatotic mice from lethal Δfur infection. Moreover, early intervention of IL-1β overproduction can completely rescue hemochromatotic mice from the lethal infection.

Control of Mycobacterium tuberculosis (Mtb) infection requires the generation of T cells that migrate to granulomas, specialized immune structures surrounding sites of bacterial replication. Here we report that persistent influx of neutrophils impedes T-cell recruitment to the lung and limits bacterial control in tuberculosis (TB) granulomas. We found that type I interferons (IFN-1) induced by Mtb infection dampens T-cell production in the bone marrow by driving a granulocyte-biased hematopoietic program. Neutrophil-intrinsic IFN-1 signaling, and bacterial type VII secretion system are critical for this process. Mechanistically, we demonstrate that IFN-1 facilitates neutrophil influx to the lung, where these cells produce granulocyte colony stimulating factor (G-CSF) in response to Mtb and neutrophil extracellular traps (NETs). Augmented and sustained release of G-CSF support granulopoiesis and impair lymphopoiesis, causing sub-optimal T-cell responses in the lung and spleen. Therapeutically, inhibiting IFN-1 signaling or neutralizing G-CSF limits neutrophil-driven immunopathology and bacterial replication by restoring optimal T-cell responses. Thus, we identify a mechanism by which neutrophils limit T-cell immunity during TB by disrupting the hematopoietic equillibrium and propose “IFN-1→NETosis→GCSF” immune axis as targets for host-directed therapy and immunization

Mycobacterium tuberculosis (Mtb) infection induces persistent influx of neutrophils that precludes both CD4 and CD8 T cells from tuberculosis (TB) lesions in genetically susceptible mice. Depletion of neutrophils restores T cell number and ameliorated disease. High neutrophil to T lymphocyte ratio in the peripheral blood of pulmonary TB (PTB) patients correlate with sputum smear positivity and disease severity. These observations led us to hypothesize that infiltration of neutrophils negatively affect the normally protective T cell response in TB lesions. By employing various mouse strains that present neutrophil-rich lung lesions, we demonstrated that instead of serving as canonical myeloid derived suppressor cells (MDSCs), neutrophils produce granulocyte colony stimulating factor (CSF3/G-CSF) to indirectly regulate T cell numbers in TB lesions. Neutrophil-derived G-CSF reprograms the bone marrow towards a granulocyte-biased hematopoiesis at the expense of lymphocyte progenitors. Transcriptome profiling of the isolated neutrophils from the lung, spleen and bone marrow revealed a type I interferon (IFN-I) response signature in these neutrophils. Hematopoietic cell-intrinsic IFN-I signaling (IFNAR1) is both necessary and sufficient to promote the pathologic granulopoiesis generating Mtb-permissive neutrophils while suppressing lymphocyte progenitors (CLPs) production. Finally, blockade of IFNAR1-signaling ameliorates disease pathology by preserving the hematopoietic equilibrium. Collectively, our work uncovers a mechanism by which type I IFN response in neutrophils along with G-CSF perturbs hematopoiesis in the bone marrow and negatively impacts T cell immunity in TB lesions.

Mycobacterium tuberculosis (Mtb) infection induces persistent influx of neutrophils that associates with poor bacterial control and clinical outcome from tuberculosis (TB). Although implicated in TB pathology, the mechanism by which these cells contribute to pathogenesis is poorly understood. Using Cell-DIVE multiplexed immunofluorescence imaging and spatial analysis of inflammatory TB lesions, we demonstrated that persistent neutrophil infiltration affects the spatiotemporal organization of T-lymphocytes and impairs their function. Instead of directly suppressing T-cells, neutrophils produce granulocyte colony stimulating factor (CSF3/G-CSF) that collaborates with type I interferon (IFN-I) to promote a granulocyte-skewed hematopoiesis impacting T-lymphocyte production. Importantly, neutrophil-intrinsic IFN-I receptor 1 (IFNAR1) is both necessary and sufficient to promote pathologic granulopoiesis. Finally, inhibition of IFNAR1-signaling alone mitigates immunopathogenesis by restoring hematopoietic equilibrium. Collectively, our work uncovers a potential immunevasion strategy by which virulent Mtb strains induce IFN-I to generate pathogen-permissive neutrophils that produce G-CSF and sustain pathogenic hematopoiesis to impair T-cell immunity during TB.