Fagocitoz

Fagocitoz, or phagocytosis, is a cellular process by which specialized immune cells called phagocytes ingest and digest large particles such as bacteria, dead cells, and debris. It is a central component of innate immunity and also shapes adaptive responses through antigen processing.

During phagocytosis, targets are recognized and bound by receptors on phagocytes (including Fc receptors for opsonized particles, complement receptors, and pattern recognition receptors). The cell then rearranges its actin cytoskeleton to engulf the particle, forming a membrane-bound phagosome. The phagosome matures through fusion with endosomes and lysosomes to become a phagolysosome, where ingested material is degraded by acidic enzymes and reactive oxygen and nitrogen species. The resulting fragments may be released by exocytosis or used for antigen presentation to T cells.

Phagocytosis serves to kill and clear pathogens, remove apoptotic cells, and support tissue remodeling. In macrophages and dendritic cells, degraded material is loaded onto MHC class II molecules for presentation to helper T cells, linking innate and adaptive immunity.

Its efficiency is influenced by opsonization and receptor signaling, and some pathogens have evolved strategies to evade phagocytosis. Defects in phagocytic function or in the oxidative burst can lead to increased susceptibility to infections, as seen in diseases affecting NADPH oxidase or phagocyte function.

Professional phagocytes include neutrophils, macrophages, and dendritic cells; non-professional phagocytes can engulf particles in certain contexts, such as epithelial cells during tissue injury.