degranulaation

Degranulation is the process by which certain cells release the contents of their cytoplasmic granules into the extracellular space. It is a regulated form of exocytosis in which granule membranes fuse with the plasma membrane, allowing mediators stored inside the granules to be released.

Release is triggered by stimuli that raise intracellular calcium and activate SNARE protein complexes that mediate granule docking and fusion. Triggers vary by cell type and include receptor engagement (such as IgE cross-linking on mast cells and basophils), microbial products, inflammatory signals, and platelet activation. Secretory granules differ in composition across cells and are specialized for rapid mediator release.

Key cell types include mast cells and basophils, which degranulate to release histamine, proteases such as tryptase, heparin, and other inflammatory mediators during allergic reactions. Neutrophils and eosinophils degranulate in response to infection, releasing antimicrobial enzymes and toxic proteins. Platelets release contents from alpha and dense granules, contributing to hemostasis, vascular tone, and wound healing. Cytotoxic T cells and natural killer cells also use granule exocytosis to deliver perforin and granzymes to target cells, inducing apoptosis.

Clinical relevance varies with context. In health, degranulation supports host defense, wound healing, and tissue remodeling. In disease, excessive or misdirected degranulation contributes to allergic reactions, asthma, anaphylaxis, and chronic inflammatory conditions. Therapies often target mediators released by degranulation (for example antihistamines) or aim to modulate the degranulation pathway to reduce tissue damage.