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Bone marrow - nonneoplastic

Normal

Eosinophils


Reviewers: Dragos Luca, M.D. (see Reviewers page)
Revised: 28 September 2012, last major update August 2012
Copyright: (c) 2001-2012, PathologyOutlines.com, Inc.

General
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● 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

Physiology
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● 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
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● 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)

Micro description
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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%)

Micro images
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Eosinophilic metamyelocyte

   
Left: developing eosinophils; right: eosinophilic promyelocyte

   
Eosinophilic myelocyte

   
Eosinophil

AML-M4eo:
           
Various eosinophil precursors

Other:
       
Hypereosinophilic syndrome: left to right is peripheral blood, bone marrow aspirate, bone marrow biopsy

Peripheral blood:
           
Eosinophils

Positive stains
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● CD9; also CD15, CD16, CD23, CD32, CD35, CD47R (weak), CD49d, CD50, CD52, CD62L, CD69, CD85A, CD85D, CD88, CD89, CD116, CDw125, CD183, myeloperoxidase, Sudan Black and PNL2
Cytochemistry: the naphthol-ASD-chloroacetate esterase reaction is normally negative, but characteristically faintly positive in the abnormal eosinophils of AML-M4eo

Negative stains
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● CD114, tryptase

Electron microscopy description
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● Two types of granules: a few rounded homogeneously electron-dense granules and many rounded, elongated or oval crystalloid-containing ones

Electron microscopy images
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Normal eosinophil with crystalloid granules

Additional references
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Wikipedia, eMedicine

End of Bone Marrow - nonneoplastic > Normal > Eosinophils


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