Fagocit

Fagocit, or phagocyte, is a cell of the immune system that ingests and digests foreign particles, microbes, and cellular debris. In humans the main fagocytes are neutrophils, monocytes (which differentiate into macrophages) and dendritic cells. These cells form a core part of the innate immune system and also link to adaptive immunity.

Phagocytosis begins when a target is recognized by surface receptors and often aided by opsonization, where antibodies or complement mark the particle for ingestion. The cell engulfs the target, creating a phagosome. The phagosome then fuses with lysosomes to form a phagolysosome, where enzymes and antimicrobial substances break down the contents. Many phagocytes generate reactive oxygen species and other reactive molecules in a respiratory burst to kill ingested microbes; macrophages can also produce nitric oxide with antimicrobial effects.

Beyond destruction, phagocytes play a key role in immune signaling. Macrophages and dendritic cells process and present antigens on MHC class II molecules to helper T cells, helping to initiate and tailor adaptive immune responses. They also secrete cytokines that coordinate inflammation and recruitment of other immune cells. Phagocytes are involved in tissue homeostasis by clearing apoptotic cells and participating in remodeling after injury.

Clinical relevance includes susceptibilities arising from impaired phagocytosis or respiratory burst, such as chronic granulomatous disease, which increases infection risk. In healthy individuals, fagocytes provide essential surveillance, rapid response to infection, and initiation of longer-term adaptive immunity.