A Specialized CD107a+ Macrophage Subset Drives Selective Mycobacterial Phagocytosis

Macrophages are critical for host defense against pathogens, yet their diverse roles in phagocytosis remain underexplored. Bone marrow-derived macrophages (BMMs) cultured with L929 conditioned media or M-CSF differentiate into two distinct subsets: FSCloSSCloF4/80loCD11blo and FSChiSSChiF4/80hiCD11bhi cells. Through comprehensive transcriptomic, phenotypic, and functional analyses, we demonstrate that FSCloSSCloF4/80loCD11blo macrophages exhibit a specialized phagocytic program, marked by upregulated actin cytoskeleton regulators (e.g., Arp2/3 complex) and pro-inflammatory pathways (e.g., NF-{kappa}B). This subset excels at internalizing Mycobacterium tuberculosis and M. bovis BCG via actin-dependent mechanisms, inhibited by cytochalasin D. Elevated surface expression of CD107a (LAMP1) and CD195 (CCR5) by FSCloSSCloF4/80loCD11blo macrophages strongly correlates with enhanced mycobacterial uptake (Spearmans {rho} = 1.0, p = 0.0028 for CD107a; {rho} = 0.83, p = 0.06 for CD195), identifying these as key markers of hyperphagocytic macrophages. These cells also produce higher levels of TNF and IL-6 in response to mycobacteria, TLR2 and TLR5 ligands, while maintaining IFN-{gamma}-mediated mycobactericidal activity comparable to the FSChiSSChi subset. In vivo, CD107a+ alveolar macrophages in BCG-infected mice preferentially bind bacilli and upregulate CD195, mirroring in vitro findings. These discoveries highlight a novel hyperphagocytic macrophage subset, offering insights into tuberculosis host defense and potential therapeutic targets. Significance StatementThis study uncovers a specialized group of macrophages that excel at engulfing mycobacteria, a major cause of human disease. In a mouse model, these cells, marked by specific surface proteins, show unique molecular patterns and actin/cytoskeleton pathways that enhance their ability to sense and capture bacteria. By revealing how these macrophages operate differently from others, our work deepens understanding of how the immune system fights infections. The findings highlight the diversity of macrophage roles, offering new avenues for studying immune responses and further exploring targeted therapies to combat bacterial infections.