The basophilic granulocyte at 10 to 14 µm is smaller than the other granulocytes. The coarse, dark violet granules are tightly packed and extensively overlay the nucleus and cytoplasm.
The normal range for basophilis is to x 109/L. Consequently, they are very rarely found in the blood film. An increase of the basophil count is termed basophilia.
Basophils have an important role to play in hypersensivity reactions (immediate-type hypersensitivity = type I). They contain granules with heparin and immflamatory mediators such as histamin and platelet activating factor (PAF). They are also able to leave the bloodstream and to emigrate to the surrounding tissue.
Basophilia is typical in cases of chronic myelocytic leukemia or the other myeloproliferative syndromes, particularly polycythemia vera.