Macrophage-Mediated Responses to Mycobacterial Infections

Macrophages serve as the primary cellular barrier against mycobacterial pathogens, orchestrating innate defence, antigen presentation and the initiation of adaptive immunity. Upon inhalation of Mycobacterium tuberculosis or related species, alveolar macrophages engulf bacilli into phagosomes and attempt to neutralise them through phagosome maturation, reactive oxygen and nitrogen species, and lysosomal enzymes. Successful pathogens subvert these processes via inhibition of phagosome–lysosome fusion, modulation of host lipid metabolism and escape into the cytosol, thereby creating intracellular niches that favour survival and replication. Distinct macrophage lineages, including alveolar and interstitial subsets, display divergent metabolic programmes that either restrict or permit bacterial growth. Cross-talk with dendritic cells and the release of cytokines such as tumour necrosis factor and interferon-γ shape granuloma architecture and long-term containment of infection. Autophagy and trained immunity offer additional layers of defence by recycling intracellular pathogens and reprogramming haematopoietic stem cells to enhance future responses. Understanding the balance between protective microbicidal functions and pathogen exploitation of macrophage physiology is crucial for the development of host-directed therapies and improved vaccine strategies against tuberculosis and related mycobacterial diseases.

Research from Nature Portfolio

A detailed study revealed that some strains of Mycobacterium tuberculosis bypass the classical phagosomal environment by activating host cytosolic phospholipase A2, enabling rapid escape into the macrophage cytoplasm. This translocation undermines autophagic clearance and promotes intracellular survival through suppression of host antimicrobial pathways. Complementary investigations have shown that Mycobacterium tuberculosis manipulates the expression and activity of cathepsins in human macrophages, down-regulating key proteases such as cathepsins B, S and L to impair phagolysosomal killing. A systematic loss-of-function screen further identified multiple cathepsins required for optimal pathogen clearance, highlighting a targeted evasion strategy that maintains a permissive intracellular niche.

Macrophage-Mediated Responses to Mycobacterial Infections publication trend

The graph below shows the total number of articles in macrophage-mediated responses to mycobacterial infections across all publications each year (not limited to Nature Index journals).

Technical terms

Macrophage: Specialized phagocytic immune cell that engulfs pathogens and orchestrates host defence.

Alveolar macrophage: Resident lung macrophage present in alveolar airspaces, involved in first-line responses to inhaled pathogens.

Interstitial macrophage: Macrophage population within lung tissue interstitium, exhibiting distinct metabolic and immunological characteristics.

Phagosome: Membrane-bound vesicle that encloses ingested pathogens within phagocytic cells.

Phagolysosome: Organellar compartment formed by the fusion of a phagosome with a lysosome, enabling pathogen degradation.

Autophagy: Cellular recycling pathway that can target intracellular pathogens for lysosomal destruction and support immune regulation.

References

1. Mechanopathology of biofilm-like Mycobacterium tuberculosis cords. Cell (2023).
2. Growth of Mycobacterium tuberculosis in vivo segregates with host macrophage metabolism and ontogeny. Journal of Experimental Medicine (2018).
3. M. tuberculosis Reprograms Hematopoietic Stem Cells to Limit Myelopoiesis and Impair Trained Immunity. Cell (2020).
4. The Macrophage: A Disputed Fortress in the Battle against Mycobacterium tuberculosis. Frontiers in Microbiology (2017).
5. Mycobacterial escape from macrophage phagosomes to the cytoplasm represents an alternate adaptation mechanism. Scientific Reports (2016).
6. Single cell analysis of M. tuberculosis phenotype and macrophage lineages in the infected lung. Journal of Experimental Medicine (2021).
7. Role of Cathepsins in Mycobacterium tuberculosis Survival in Human Macrophages. Scientific Reports (2016).