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Bone marrow nonneoplastic

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Eosinophils

Author: Dragos C. Luca, M.D.

Last author update: 1 August 2012

Last staff update: 28 September 2023

Copyright: 2002-2025, PathologyOutlines.com, Inc.

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

Table of Contents

Cite this page: Luca DC. Eosinophils. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/bonemarroweosinophils.html. Accessed January 10th, 2025.

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

Physiology

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

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