phagocytosis, engulfment

Definition

Target type: biologicalprocess

The internalization of bacteria, immune complexes and other particulate matter or of an apoptotic cell by phagocytosis, including the membrane and cytoskeletal processes required, which involves one of three mechanisms: zippering of pseudopods around a target via repeated receptor-ligand interactions, sinking of the target directly into plasma membrane of the phagocytosing cell, or induced uptake via an enhanced membrane ruffling of the phagocytosing cell similar to macropinocytosis. [GOC:curators, ISBN:0781735149]

Phagocytosis is a fundamental process in cellular defense and tissue homeostasis, involving the engulfment and internalization of particulate matter, such as bacteria, apoptotic cells, and cellular debris. This intricate process is orchestrated by a complex interplay of cellular signaling, cytoskeletal rearrangements, and membrane dynamics.

Initiation of phagocytosis is triggered by the recognition of specific ligands on the surface of the target particle by receptors on the phagocytic cell. These receptors, such as Fc receptors, complement receptors, and scavenger receptors, bind to various targets, including antibodies, complement proteins, and pathogen-associated molecular patterns (PAMPs). Ligand binding triggers a cascade of intracellular signaling events, leading to the activation of small GTPases, such as Rac and Cdc42, which play crucial roles in cytoskeletal reorganization and membrane dynamics.

Upon receptor engagement, the phagocytic cell extends pseudopods, finger-like projections of the plasma membrane, towards the target particle. These pseudopods, driven by actin polymerization, surround the target, forming a phagocytic cup. The actin filaments, anchored to the plasma membrane by proteins like Arp2/3 complex and WASP, provide the force required for engulfment. As the phagocytic cup closes around the target, the plasma membrane fuses, creating a phagosome – a membrane-bound vesicle containing the engulfed particle.

Once the phagosome is formed, it undergoes a maturation process involving fusion with lysosomes, acidic organelles containing hydrolytic enzymes. The lysosomal enzymes degrade the ingested material, breaking it down into smaller molecules that can be recycled or excreted by the cell. This process, known as phagolysosome formation, effectively eliminates pathogens and cellular debris, preventing their harmful effects.

Phagocytosis is essential for maintaining tissue integrity, clearing apoptotic cells, and mounting an immune response against invading pathogens. Dysregulation of phagocytosis can contribute to various diseases, including autoimmune disorders, infections, and cancer. The intricate choreography of this cellular process underscores the importance of understanding its molecular mechanisms and potential for therapeutic intervention.'
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Proteins (4)

Compounds (21)