The mast cell is an important player in the body's immune system. People with mastocytosis have been found to have these extra cells in a variety of places, such as the skin, the liver, the gastrointestinal tract, the bone marrow, and the spleen.
Mast cells function to promote an inflammatory response to things the cells perceive as foreign.
When the granules release the chemicals outside of the cell, it is called degranulation. The best known chemical released in this manner is histamine. This chemical is well known by anybody who has allergies and has taken antihistamines to treat them. In mastocytosis, histamine can cause more than just a runny nose. It is one of the culprits in many of the symptoms of the disease.