Fagocytos

Fagocytos, or phagocytosis, is a cellular process in which specialized cells, called phagocytes, internalize and destroy particulate matter from the external environment. It is a fundamental mechanism of innate immunity and tissue homeostasis.

Professional phagocytes include neutrophils, macrophages, and dendritic cells. Non-professional phagocytes such as epithelial or endothelial cells can perform limited phagocytosis. Phagocytosis contributes to defense against bacteria, fungi, and parasites, as well as the clearance of apoptotic cells and debris.

Phagocytosis proceeds through a sequence of steps. Recognition and attachment occur via pattern recognition receptors and opsonins, such as antibodies or complement, that coat the target. The particle is then ingested to form a phagosome. The phagosome matures by acidification and fusion with lysosomes to create a phagolysosome, where lysosomal enzymes and antimicrobial molecules digest the contents. Digestion products are degraded or processed for antigen presentation on MHC molecules, linking innate and adaptive immunity.

Microbicidal mechanisms include a respiratory burst that generates reactive oxygen species through NADPH oxidase, along with nitric oxide production in macrophages. Lysosomal enzymes, antimicrobial peptides, and pH changes contribute to killing and digestion. Some pathogens have evolved strategies to evade phagocytosis or survive within phagolysosomes.

Clinical relevance includes increased infection susceptibility when phagocytosis or oxidative killing is impaired. For example, chronic granulomatous disease results from NADPH oxidase deficiency. Proper phagocytic function is also important for resolving inflammation and maintaining tissue homeostasis.