Fagocytere

Fagocytere, or phagocytosis, is a cellular process in which certain cells engulf and digest extracellular particles, including pathogens, dead cells, and debris. It is carried out primarily by professional phagocytes such as macrophages, neutrophils, and dendritic cells, but can also occur in non-professional phagocytes under certain conditions.

During recognition, target particles are detected by pattern recognition receptors and opsonin receptors. Opsonization involves antibodies or complement fragments (for example IgG and C3b) that enhance binding. The plasma membrane extends around the target and internalizes it into a phagosome.

Phagosome maturation involves fusion with lysosomes to form a phagolysosome. The internal environment acidifies, and hydrolytic enzymes degrade the contents. A respiratory burst produced by NADPH oxidase generates reactive oxygen species that contribute to microbial killing; nitric oxide may also be produced by some cells.

Phagocytosed material can be presented to the adaptive immune system by antigen-presenting cells, linking innate and adaptive immunity. The process is controlled by the actin cytoskeleton and signaling molecules such as Rac, Cdc42, and PI3K. Some pathogens have evolved strategies to evade phagocytosis or to survive within phagosomes, such as capsules or inhibition of phagosome-lysosome fusion.

Defects in phagocytic function contribute to susceptibility to recurrent infections and impaired wound healing. For example, chronic granulomatous disease results from defects in NADPH oxidase, reducing the respiratory burst; leukocyte adhesion deficiencies impair phagocyte recruitment to sites of infection.