Mast Cells are granulated white blood cells cells (leucocytes) that play an important part in the immune response. They release granules containing inflammatory mediators such as Histamine and Heparin which is an anticoagulant  when tissue is injured or can be activated by compliment proteins.
- ↑ Alberts et al. Molecular biology of the cell 5th edition. (2008) Garland Science Taylor Francis New York. Chapter 13 Page 804