Figure17. EM of a human eosinophil; Cr, crystalline body; M, mitochondria
Eosinophils are less numerous than neutrophils, consisting only 2-5% of leukocytes in normal blood.
The cell has a diameter of 12-14 μm and contains a characteristic bilobed nucleus.
Eosinophilic specific granules have a crystalline core an arginine-rich protein called the major basic protein that probably accounts for the eosinophilia of these granules. The less dense material surrounding the internum is known as the externum or matrix. The granules contain histaminase, peroxidase, arylsulfatase and other hydrolytic enzymes. An increase in the absolute number of eosinophils in blood (eosinophilia) is associated with allergic reactions and helmintic (parasitic) infections.
Main functions are:
-eosinophils play an important role in the control of local responses in allergic reactions
-their specific granules contain many enzymes that degrade chemical mediators released by mast cells in association with hypersensitivity reactions
-eosinophils are thought to play an important role in the defense against certain types of parasites
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