What is an Eosinophil?
The eosinophil is a specialized cell of the immune system. This proinflammatory white blood cell generally has a nucleus with two lobes (bilobed) and cytoplasm filled with approximately 200 large granules containing enzymes and proteins with different (known and unknown) functions.
Eosinophils are formed exclusively in the bone marrow where they spend about 8 days in the process of maturation before moving into the blood vessels. They travel through the vessels for 8 to 12 hours before they finally arrive at destination tissues, where they remain for 1 to 2 weeks. Interleukin 5 (IL-5) appears to be the major growth factor for this type of cell.
Microscopic pictures of eosinophils obtained from nasal mucosa.
The functions of the eosinophil are varied, some of which are very similar to other white blood cells. They are implicated in numerous inflammatory processes, especially allergic disorders. In addition, eosinophils may have a physiological role in organ formation (e. g. postgestational mammary gland development).
Eosinophilic functions include: movement to inflamed areas, trapping substances, killing cells, antiparasitic and bactericidal activity, participating in immediate allergic reactions, and modulating inflammatory responses. Eosinophils can be either helpful or harmful. At one extreme, such as in the illness erythema toxicum, eosinophils play the role of a beneficial modulatory element or an innocent bystander. At the other extreme, represented by conditions like Loeffler’s disease and idiopathic hypereosinophilic syndrome, eosinophils are linked with permanent pathologic changes.