A type of leukocyte (white blood cell), also called a granular leukocyte, filled with granules of toxic chemicals, that can digest micro-organisms. Basophils are responsible for the symptoms of allergy. Despite similarities, basophils appear to be a distinct cell type from mast cells .

Basophils are derived from bone marrow progenitors (psc) and contain granules that bind basic dyes. They are capable of synthesizing many of the same mediators as mast cells . Both express the same high affinity for Fce receptors (FceRI) and can be triggered by antigen binding to IgE . Basophils, like other inflammatory granulocytes , enter tissues only when they are recruited into inflammatory sites. Basophils, like neutrophils , express a number of adhesion molecules important for homing, such as LFA-1 (CD11aCD18), Mac-1 (CD11bCD18) and CD44.

When basophils are triggered, they release two kinds of mediators :

1. Preformed granule-associated mediators such as histamine , serotonin , bradykinin , heparin , cytokines .
2. Newly-generated mediators , prostaglandins and leukotrienes , made from arachidonic acid in surrounding tissues.