A specialized CD107a+ macrophage subset drives hyperphagocytosis of mycobacteria

Macrophages are essential for pathogen clearance, yet phagocytic specialization among subsets is poorly defined. Bone marrow-derived macrophages cultured with L929 supernatant or macrophage colony-stimulating factor (M-CSF) separate into FSC lo SSC lo F4/80 lo CD11b lo (FSC lo SSC lo ) and FSC hi SSC hi F4/80 hi CD11b hi (FSC hi SSC hi ) subsets. Transcriptomic and functional analyses reveal that FSC lo SSC lo cells possess a hyperphagocytic program driven by enhanced actin cytoskeleton regulators (e.g., Arp2/3) and pro-inflammatory signaling (NF-κB). These cells excel at internalizing Mycobacterium tuberculosis virulent H37Rv and BCG through actin-mediated, cytochalasin D-sensitive mechanisms. High surface CD107a (LAMP1) expression marks this hyperphagocytic subset and correlates strongly with mycobacterial uptake. FSC lo SSC lo macrophages produce more TNF and IL-6 upon mycobacterial or Toll-like receptor 2 (TLR2)/TLR5 stimulation yet retain IFN-γ-mediated killing capacity. In vivo , CD107a + alveolar macrophages in BCG-infected lungs preferentially capture bacilli and upregulate CD195, recapitulating the in vitro phenotype. These findings establish CD107a as a key surface marker of a hyperphagocytic macrophage subset, providing new mechanistic understanding relevant to tuberculosis host defense and therapeutic development.