fagòcits

Fagòcits, or phagocytes, are specialized cells of the immune system that ingest and digest microbes, dead cells, and debris. They are central to the innate response and also help initiate adaptive immunity through antigen presentation. The main fagòcits are neutrophils, monocytes (which become macrophages in tissues), and dendritic cells. Many tissues harbor resident phagocytes, such as Kupffer cells in the liver and microglia in the brain.

Phagocytosis begins with recognition of targets via pattern-recognition receptors and opsonization by antibodies or complement. After attachment, the cell engulfs the particle to form a phagosome, which matures and fuses with lysosomes to become a phagolysosome. Reactive oxygen species, nitric oxide, and lysosomal enzymes kill and digest the ingested material. Macrophages and dendritic cells can process and present antigen fragments on MHC molecules to T cells, linking innate and adaptive immunity.

Functions of fagòcits include host defense against bacteria, fungi, and parasites; clearance of apoptotic cells and cellular debris; and roles in tissue remodeling and inflammation regulation. Neutrophils are typically short-lived, circulating first responders that rapidly migrate to sites of infection, while macrophages and dendritic cells provide longer-term surveillance and antigen presentation.

Origin and clinical relevance: fagòcits derive from hematopoietic stem cells in the bone marrow. Defects in phagocyte function can lead to increased susceptibility to infections (for example, certain NADPH oxidase deficiencies), whereas excessive phagocyte activation can contribute to inflammatory tissue damage.