Understanding the role of innate immunity in the lung pathogenesis of Mycobacterium abscessus infection 2303168

Abstract Introduction Infections by Mycobacterium abscessus (MAB), a saprophytic bacterium, are rising globally. While most people exposed do not get infected, immunocompromised individuals, or those with lung conditions like cystic fibrosis, can develop pulmonary MAB disease (MAB-PD). Our research shows GM-CSF is crucial for early pulmonary MAB clearance. GM-CSF is vital for alveolar macrophage (AM) and granulocyte maturation. We hypothesize that both AM and neutrophils are needed to control bacterial growth in early infection stages. Methods We measured the bacterial load in the lungs of immunocompetent C57BL/6 mice depleted of neutrophils and/or AM. To demonstrate that AM are essential for MAB clearance, we depleted AM using clodronate liposomes and neutrophils, combined with two monoclonal antibodies (anti-Ly6G and anti-Ly6C). After depletion, mice were exposed to a MAB aerosol. Mice were euthanized, and lungs, blood, bone marrow, and bronchoalveolar lavage were collected. Bacterial burden in the lungs was assessed, and the presence or absence of AMs and neutrophils during infection was determined by flow cytometry. Results We monitored the frequency of AM and neutrophils in the lungs using flow cytometry at 3, 10, and 15 days post-infection (DPI). While control mice (untreated) and mice depleted of AM or neutrophils showed a significant reduction in bacterial burden in the lungs at 10 and 15 days post-infection, mice depleted of both AM and neutrophils were unable to control the infection by day 10. However, their bacterial load was reduced by day 15. Conclusion Our preliminary results demonstrate the essential, cooperative roles of both AM and neutrophils in the early containment and control of MAB infection within the pulmonary environment. We are currently employing multi-parameter flow cytometry to analyze potential compensatory cellular mechanisms in secondary lymphoid organs, specifically the bone marrow and blood, following the depletion of these key subsets. Funding Source RO1 AI155922 Topic Categories Microbial, Parasitic, and Fungal Immunology (MPF)