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^loSSC^loF4/80^loCD11b^lo (FSC^loSSC^lo) and FSC^hiSSC^hiF4/80^hiCD11b^hi (FSC^hiSSC^hi) subsets. Transcriptomic and functional analyses reveal that FSC^loSSC^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^loSSC^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.