Mast cell degranulation

Mast cell degranulation is the rapid release of histamine and other stored chemicals from a mast cell, the event that sets off an allergic reaction.

Mast cells hold hundreds of granules packed with histamine, heparin, the enzyme tryptase and other mediators. When an allergen bridges IgE antibodies on the cell surface, or when a physical trigger such as pressure, heat or certain drugs activates the cell directly, calcium floods in and the granules fuse with the outer membrane, dumping their contents within seconds. The cell then begins making a second wave of mediators, including prostaglandins and leukotrienes, over the following minutes and hours. The result is vessel widening, swelling, itching and, in the airways, constriction.

Clinicians assess degranulation indirectly, most often by measuring tryptase in blood after a suspected reaction. The term appears in discussions of allergy, anaphylaxis, urticaria and mast cell activation syndrome. Laboratory and animal experiments have reported that CBD reduced antigen-triggered degranulation under controlled conditions; those findings are preclinical, and no human study has shown a corresponding effect.