Their numbers increase greatly during infection due to increased synthesis of them in the bone marrow.
Basophils are present in blood.
They contain granules of histamine and other inflammatory mediators. In response to infection or allergens, basophils degranulate , meaning that they release the granule contents by exocytosis. The release of histamine and other factors leads to inflammation and other symptoms associated with allergic reactions and infections. Mast cells are almost identical to basophils. Mast cells are present in tissues.