Eosinophil

Eosinophils, also less commonly known as acidophilesacidophils, are myeloid granulocytes and form one of the main types of white blood cells. Their counts are routinely measured as part of a full blood count. They have important roles in fighting parasitic infections, but are increasingly recognised as having a vital role in the immune defence against bacteria and viruses. 

Definitions

• normal level: <450 cells/μlμL
• eosinophilia: >450-500 cells/μlμL
• hypereosinophilia: >1500 cells/μlμL

Normal development

Eosinophils develop in the bone marrow from myeloid precursor cells under stimulation from interleukins, namely IL-3, IL-5 and GM-CSF, and maturation takes ~1 week ¹.

Function

Eosinophils have a relatively short half-life within the circulation and attach themselves to the endothelial cells of the vascular wall to enter the tissues via diapedesis. The release of proteins, cytokines, and chemokines help produce the acute inflammatory response while also directly killing invading organisms.².

They are particularly abundant in the mucosa of the GI, respiratory, and urinary tracts where they are the primary defence against parasitic organisms. Their numbers are also increased in allergic responses such as asthma.  

History and etymology

Eosinophil derives from the Ancient Greek root "phil" meaning love. Eosin is a histological acidic dye; therefore, eosinophil means "eosin loving".