Abstract
Phagocytosis is an essential mechanism in innate immune defense, and in maintaining homeostasis to eliminate apoptotic cells or microbes, such as Mycobacterium tuberculosis, Salmonella enterica, Streptococcus pyogenes and Legionella pneumophila. After internalizing microbial pathogens via phagocytosis, phagosomes undergo a series of ‘maturation’ steps, to form an increasingly acidified compartment and subsequently fuse with the lysosome to develop into phagolysosomes and effectively eliminate the invading pathogens. Through this mechanism, phagocytes, including macrophages, neutrophils and dendritic cells, are involved in the processing of microbial pathogens and antigen presentation to T cells to initiate adaptive immune responses. Therefore, phagocytosis plays a role in the bridge between innate and adaptive immunity. However, intracellular bacteria have evolved diverse strategies to survive and replicate within hosts. In this review, we describe the sequential stages in the phagocytosis process. We also discuss the immune evasion strategies used by pathogens to regulate phagosome maturation during intracellular bacterial infection, and indicate that these might be used for the development of potential therapeutic strategies for infectious diseases.
Highlights
Phagocytosis is a mechanism for the uptake and digestion of large particles (0.5 > μm) in vacuoles surrounded by the plasma membrane [1,2]
Microbial pathogens are recognized directly by receptors expressed on the cell surface of phagocytes that interact with pathogen-associated molecular patterns (PAMPs), or indirectly by receptors that interact with opsonins
Phagocytosis can occur in all types of cells, but it is most effective in professional phagocytes, including macrophages, neutrophils and dendritic cells
Summary
Phagocytosis is a mechanism for the uptake and digestion of large particles (0.5 > μm) in vacuoles surrounded by the plasma membrane [1,2]. Phagocytosis plays a role in maintaining cellular homeostasis by removing dead cells, microbes and cellular or foreign debris [4,5]. It is a fundamental defense mechanism that activates immune and inflammatory responses against invading pathogens. Nonprofessional phagocytic cells, such as epithelial cells [6], endothelial cells [7], fibroblasts [8] and B cells [9], are involved in phagocytosis These cells recognize foreign pathogens and internalize them into phagosomes. We focused on a novel molecular finding regarding the regulation of phagosome maturation during microbial pathogen infection
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