fagosoma

Fagosoma is a membrane-bound vesicle formed by phagocytic cells during phagocytosis, enclosing a particle such as a microbe, dead cell, or debris. In many languages, the term corresponds to the English “phagosome.” It serves as the initial intracellular compartment for degradation and antigen processing.

Formation of a fagosoma begins when a target particle binds to phagocytic receptors, including Fc receptors, complement receptors, and scavenger receptors. The actin cytoskeleton rearranges to extend pseudopods that enclose the particle, and a closed vesicle is internalized into the cytoplasm.

Maturation involves sequential fusion with endosomal compartments and lysosomes. Early phagosomes acquire Rab proteins and nutrients from endosomes, then fuse with lysosomes to form phagolysosomes. The lumen becomes increasingly acidic due to vacuolar ATPases, while hydrolytic enzymes, antimicrobial peptides, and reactive oxygen and nitrogen species digest the cargo. The degradative products can be recycled or transported for antigen presentation.

Functions of the fagosoma include microbial killing, clearance of apoptotic cells, and generation of peptide fragments for MHC class II presentation. Some phagosomes also participate in cross-presentation to CD8+ T cells. Pathogens have evolved strategies to modulate phagosome maturation, enabling survival or replication within modified vacuoles.

Clinical relevance includes defects in phagosome formation or maturation contributing to susceptibility to infections, as seen in certain immunodeficiencies and chronic granulomatous disease.