Bone marrow nonneoplastic



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Last staff update: 10 December 2021

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PubMed Search: Bone marrow [title] eosinophils [title]

Dragos C. Luca, M.D.
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Cite this page: Luca DC. Eosinophils. website. Accessed June 3rd, 2023.
Definition / general
  • Named because granules stain deeply with eosin
  • 1 - 4% of all white blood cells (the number of circulating eosinophils is generally low, < 800 / µL)
  • Has a role in response to parasitic infections and allergic conditions
  • Derived from a common progenitor, CFU-GM, together with granulocytes and monocytes / macrophages
  • Progresses from myeloid stem cell to eosinophilic promyelocyte, to eosinophilic myelocyte, to eosinophilic metamyelocyte, then to eosinophil
  • IL5 is growth factor that selectively induces eosinophil formation; also induces enhanced eosinophil function and prolonged survival via inhibition of apoptosis; other factors include IL1, IL3
  • IL9 enhances IL5 receptor expression
  • Eotaxin: eosinophil stimulating chemokine locally produced in tissue (macrophages, eosinophils) but also manifesting systemic effects in bone marrow
  • Other basophil and mast cell derived chemoattractants are ECF-A, PAF and LTB4
  • Degranulation is strictly controlled, which allows it to differentially release its contents in an ordered manner, which prevents tissue injury during migration (Semin Respir Crit Care Med 2006;27:117)
  • Produces IL2, IL3, IL4, IL5, IL7, IL13, IL16, TNF-α, TGF-β, RANTES, eosinophil cationic protein, eosinophil peroxidase (different from myeloperoxidase), eosinophil derived neurotoxin, MBP and Charcot-Leyden crystal lysophospholipase
  • Two main functions: modulation of immediate hypersensitivity reactions initiated by basophil / mast cell degranulation and destruction of parasites; key role played by release of eosinophil secondary granule contents
Eosinophil related diseases
  • Inappropriate release of granule contents, especially major basic protein (MBP), may lead to tissue damage, thrombosis and fibrosis (heart, CNS, etc.)
  • Reactive eosinophilia: allergy / hypersensitivity, parasites, other infections, skin disease, Löffler syndrome, solid tumors, autoimmune diseases, immunodeficiency, drugs, GI disorders, rare multiple myelomas and clonal T or B cell disorders
  • Neoplastic eosinophilia: AML-M4eo with inv(16) or t(16;16), chronic MPD with 8p11 abnormalities, chronic MPD / MDS with t(5;12), other myeloid and lymphoid neoplasms with abnormalities of PDGFRA, PDGFRB and FGFR1
  • Eosinopenia: very uncommon (steroid therapy, acute stress, acute inflammation, severe exercise, normal pregnancy and labor, Cushing syndrome, acromegaly, SLE, aplastic anemia)
Microscopic (histologic) description
  • Eosinophilic promyelocyte: intermediate in development between a myeloblast and myelocyte; 15 microns in diameter with large nucleus and nucleolus; contains a few undifferentiated (primary, coreless) cytoplasmic granules in intensely basophilic cytoplasm
  • Eosinophilic myelocyte: round / oval large cells with moderate cytoplasm containing prominent primary purple granules and secondary red orange, refractile granules of similar size; N/C ratio is 50% with moderately condensed chromatin and indistinct nucleolus
  • Eosinophilic metamyelocyte: round / oval cells with abundant cytoplasm containing large blue orange granules; N/C ratio is 40%; nucleus is indented with moderately condensed chromatin and no nucleolus
  • Eosinophil: 9 - 15 microns with coarsely granular cytoplasm containing refractile orange granules grouped around a single horseshoe shaped nucleus with 2 - 3 lobes (1 lobe - 6%, 2 - 68%, 3 - 22%, 4 - 4%)
Microscopic (histologic) images

Images hosted on other servers:

Eosinophilic metamyelocyte

Developing eosinophils


Various eosinophil precursors

Hypereosinophilic syndrome:

Peripheral blood

Bone marrow aspirate

Bone marrow biopsy

Peripheral blood:


Positive stains
Negative stains
Electron microscopy description
  • Two types of granules: a few rounded homogeneously electron dense granules and many rounded, elongated or oval crystalloid containing ones
Electron microscopy images

Images hosted on other servers:

Normal eosinophil with crystalloid granules

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