Multiple defects in macrophage antibacterial responses support intracellular survival of Mycobacterium abscessus in cystic fibrosis.

The prevalence of Mycobacterium abscessus (MABS) infections in people with cystic fibrosis (pwCF) is increasing. Macrophages are key phagocytic cells that recognize bacteria via cell surface receptors, engulf them into phagosomes, and then utilize diverse killing strategies. Here, we used human primary monocyte-derived macrophages (MDMs) from healthy controls (HCs) and pwCF to investigate how they processed and killed MABS. Expression of phagocytosis-related pattern recognition receptors (TLR2, Dectin-1, Dectin-2, and MARCO), engulfment of MABS, and lysosomal acidity were all reduced in CF-MDMs. MABS-infected CF-MDMs also had reduced mitochondrial mass, mitochondrial reactive oxygen species (mitoROS) production, relative intracellular zinc levels and inducible mRNA expression of the antibacterial zinc transporters, SLC30A1 and SLC39A8. Stimulation of mitoROS production in HC-MDMs with antimycin A reduced intracellular loads of MABS, confirming that MABS are sensitive to this mechanism of killing and suggesting that the mitoROS defect in MABS-infected CF-MDMs compromises bacterial killing. Accordingly, CF-MDMs failed to control MABS infection, with these cells allowing significantly increased intracellular MABS survival and expansion over 6 d. While treatment with the CFTR modulator, elexacaftor-tezacaftor-ivacaftor (ETI) did increase CFTR channel function and corrected CF macrophage functions to some degree, this was not sufficient to increase MABS killing. Taken together, our findings suggest important roles for functional CFTR in internalization and killing of MABS within macrophages, with CFTR dysfunction supporting MABS survival and replication in macrophages. Under our experimental conditions, ETI treatment failed to fully restore macrophage functions against MABS, highlighting the need for alternative, host-targeted approaches for improving macrophage functions in CF.