- Eosinophils are leukocytes found throughout the body's tissues which contain granules of vasoactive, inflammatory, and toxic substances. Eosinophils are part of a functional class of leuckocytes which we have termed "Anti-parasites" that include mast cells and basophils. All of these cells possess Fc Receptor for the IgE isotype of antibody and degranulate when their Fc-bound IgE becomes cross-linked with antigen. This reaction is thought to have evolved as part of host defense against large, extracellular parasites which cannot be phagocytosed by other immune cells. However, because parasitic infections are now clinically less important, the anti-parasites are primarily known for their role in allergic responses.
- Eosinophils are derived from Hematopoietic Stem Cells in the bone marrow. Development of Eosinophils is more fully described as part of hematopoiesis.
- The nucleus of eosinophils is characteristically bi-lobed, justifying their classification as Polymorphonuclear Leukocytes (PMNs). These cells are also abundantly packed with eosinophilic cytoplasmic granules, giving these cells their moniker, and justifying their classification as granulocytes.