Phagocytosis: strategies for macrophages to hunt Mycobacterium tuberculosis

Abstract Macrophages, as crucial innate immune cells, play a fundamental role in combating Mycobacterium tuberculosis (Mtb). The most powerful strategy for macrophages to eliminate Mtb is phagocytosis. They identify extracellular pathogens through various receptors and then engulf them, eliminating pathogenic microorganisms through reactive oxygen species, reactive nitrogen species, and a range of enzymes derived from phagosome-lysosome fusion. However, this process may also provide a potential ecological niche for Mtb. This is due to the fact that Mtb is capable of ensuring its survival within macrophages. Mtb infection results in obstructing the usual phagosome maturation and acidification. In addition, Mtb is capable of escaping from phagosomes and entering the cytoplasm of its host cell. This process of escaping phagosomes appears to promote necrosis in infected macrophages, and facilitate the expansion of intracellular bacterial populations. Therefore, enhancing the bactericidal capacity of macrophages or preventing Mtb invasion may prove to be a promising strategy for the adjuvant treatment of tuberculosis. This review highlights the processes and outcomes of macrophage recognition and phagocytosis of Mtb, and describes the mechanisms involved in Mtb resistance to phagocytosis. Moreover, recent advances in the modulation of macrophage phagocytosis to assist in the treatment of tuberculosis will be discussed.