NK cell-derived exosomes inhibit survival of Mycobacterium tuberculosis by promoting apoptosis in mice.

Aim: To investigate anti-Mycobacterium tuberculosis (Mtb) influences exerted by natural killer cell-derived exosomes (NK-exo) on mice and to elucidate underlying immunologic mechanisms.

Methods: We established tuberculosis (TB) model in mouse by injecting Mtb H37Ra (1 × 10⁶ colony counting (CFU), i.v.) into tail vein for 14 days. The survival rate of Mtb was assessed through CFU, apoptosis rates were measured utilizing flow cytometry, and inflammation relief was quantified via HE staining. Expressions of apoptosis, inflammation, and pyroptosis-related proteins were quantified by Western blotting and RT-qPCR. ELISA was utilized for detecting inflammatory cytokines production. Intracellular reactive oxygen species (ROS) levels were assessed through DCFH-DA fluorescent probe assay.

Results: NK-exo treatment reduced Mtb load in lung and spleen tissues and alleviated inflammation in mice lung tissues. NK-exo intervention increased protein levels of markers associated with apoptosis, PARP and caspase-3/8/9, downregulating the concentrations of pro-inflammatory cytokines, comprising IL-1β, TNF-α, IL-6, along with protein expressions of biomarkers, ASC, NLRP3, GSDMD, associated to inflammation and pyroptosis. NK-exo also elevated ROS levels without affecting lactate dehydrogenase (LDH) release from macrophages.

Conclusion: NK-exo exhibits anti-tuberculosis activity in experimental TB mice. The underlying mechanism involve regulating caspase-dependent apoptotic signaling pathway to promote cell apoptosis, as well as modulating NLRP3 signaling pathway to suppress the inflammatory response.