Frontline Science: Antibiotic treatment routes Mycobacterium avium to phagolysosomes without triggering proinflammatory cytokine production in human Mϕs.

Mycobacterium avium (Mav) causes chronic infections in immunocompromised patients that require long-term antibiotic treatment. We have previously shown that Mav takes residence in host Mϕs and establishes a compartment (MavC) in which it is hidden from host defenses. Failure to establish the MavC traps Mav in Lamp1+ phagolysosomes where growth is prevented, and inflammatory signaling activated through TLRs 7/8. To elucidate how antibiotic treatment affects mycobacterial trafficking and host defenses, we infected human primary Mϕs with Mav for 4 days prior to treatment with a macrolide, aminoglycoside, and ethambutol. We show that Mav is killed and the MavC fuses with Lamp1+ lysosomes following antibiotic treatment. However, this does not result in nuclear translocation of NF-κB or production of inflammatory cytokines, suggesting different Lamp1+ lysosomal compartments can form that differ in their innate signaling capabilities. Thus, we show that upon antibiotic treatment of a chronic infection, Mav is quietly disposed of by Mϕs.