Basophils and mast cells secrete histamines and heparin. These immune cells share morphology and function, but basophils are found in the bloodstream while mast cells are embedded in tissues of the body.
Upon release, heparin slows clotting and thins the blood, which allows more blood to reach the affected area. Histamines actively draw blood cells to the area. These compounds, which are both important for the body's inflammatory response, are stored in compact granules inside the basophils and mast cells until infection or injury causes the cell to release them.
Produced in the bone marrow, basophils and mast cells are part of the innate immune system and make up approximately 0.5 percent of all white blood cells. They belong to the class of white blood cells called granulocytes. When basophils and mast cells are placed on a slide and stained with a dye, the granules containing histamine and heparin are visible under a microscope.
Improper release of histamines by basophils can cause allergies and asthma. When histamines are released as a response to harmless particles that enter the body, they cause a runny nose, watery eyes and itchy skin. Antihistamines block the action of histamines released by basophils and relieve allergy symptoms.