Basophils are a type of white blood cell (leukocyte) that contain granules filled with chemicals that are toxic to other cells and are used to destroy invading bacteria and other pathogens. They belong to a group of leukocytes known as granular leukocytes or granulocytes.
Basophils are heavily involved in the inflamatory response and allergic reactions. They destroy pathogens by engulfing them and then destroying them by releasing their toxic granules in a process known as phagocytosis.
Basophils are manufactured and matured in the bone marrow. They only leave the blood except when recruited by cytokines released by a variety of leukocytes. They express a number of adhesion molecules which "stick to" those expressed by the endothelium layer of the blood vessels in response to the cytokines.
When basophils are triggered they release a number of immune system mediators including those that regulate granulocytes (histamine, serotonin, bradykinin, heparin and cytokines) and newly-generated mediators such as prostaglandins and leukotrienes which stimulate hypersensitivity and inflammation.
Basophils are very similar, but appear to be distinct from, mast cells. It is hypothesised that they are the same type of leukocyte, basophils being the blood version and mast cells the tissue version. This is contraversial.
Recent research suggests that basophils and mast cells may play a role in the destruction of myelin in multiple sclerosis - see this news article.
HON Allergy Glossary Basophil
Blood cells and the CBC
Mast cells and basophils