University of Virginia Health System

Segmented Eosinophil

Bone marrow aspirate smear, Wright-Giemsa stain, 1000x

Description:

When the first segmentation occurs the cell is referred to as a segmented eosinophil. The majority are bilobed, but cells with three or four segments may be seen. The cytoplasm is pink and the number of eosinophilic granules is quite variable due to an increased tendency of eosinophils to degranulate in the circulation.

Function:

Eosinophils share many functions with neutrophils such as phagocytosis of microorganisms through either Toll-like receptors (innate immune response) or phagocytosis of antibody- or complement- coded microorganisms through Fc or complement receptors (adaptive immune response), and antigen presentation.

Other more specific functions are:

• Immune response to parasites- eosinophils bind to antibody- or complement- coded parasites resulting in the release of their granular contents (e.g. eosinophilic basic proteins, cationic proteins, peroxidase), all of which are toxic to the parasites.
• Participation in many other inflammatory and allergic responses, including response to tumors.
• Regulation of mast cell function.

Trafficking:

The exit of mature eosinophils from the bone marrow is regulated by Il-5. The half-life of circulating eosinophils is approximately that of neutrophils, about 6 hours. Eosinophils exit the circulation and home mostly to the gastrointestinal tract but also to the breast, uterus, and thymus. Their survival in tissues and organs is longer than for neutrophils, on the order of 10 days. The life span of histiocytes in tissues and organs is approximately 2 weeks but may be longer.

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