What is the definition or description of: mast cell?

Controllers: These cells in connective tissue are inconspicuous unless specially stained. When triggered, they release histamine and other substances that direct the flow of blood and encourage entry by other cells, as in some inflammatory reactions. They are best-known for being triggered in common allergy (hay fever, cats, etc.) but they are quiet helpers in health.

Mast cell: Innate immune cell prevalent in tissue and surrounding small blood vessels. Acts as a source of histamine and other rapid acting mediators of an inflammatory response to tissue infection or damage. Inappropriate activation of mast cells is central to many allergy-related diseases including anaphylaxis. Inappropriate population expansion or activity results in mast cell activation disorders