fagosomien

Fagosomien (phagosomes) are membrane-bound vesicles formed inside phagocytic cells during phagocytosis. They enclose extracellular particles such as bacteria, apoptotic cells, or debris, by plasma membrane invagination and pseudopod extension.

After formation, phagosomes undergo maturation, involving sequential fusion with early and late endosomes and ultimately lysosomes to form phagolysosomes. This process lowers pH via V-ATPase, delivers hydrolytic enzymes, and recruits antimicrobial effectors. Phagolysosomes can generate reactive oxygen species via NADPH oxidase and, in some cells, reactive nitrogen species, contributing to microbe killing.

In professional phagocytes, processed material can be loaded onto MHC class II molecules in phagolysosomes, enabling antigen presentation to CD4+ T cells. Dendritic cells may also cross-present some antigens on MHC I. Antigen presentation links innate and adaptive immunity.

Pathogens have evolved strategies to block phagosome maturation, such as Mycobacterium tuberculosis and Legionella; others escape killing by residing in modified phagosomes. Defects in phagosome formation or maturation can lead to increased susceptibility to intracellular pathogens and are implicated in certain immunodeficiencies.