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Bone marrow - nonneoplastic

Normal

Basophils


Reviewers: Dragos Luca, M.D. (see Reviewers page)
Revised: 5 September 2012, last major update August 2012
Copyright: (c) 2001-2012, PathologyOutlines.com, Inc.

General
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● 0.5% of all white blood cells (least numerous granulated cells in peripheral blood)
● Named because it stains with basic dyes

Development
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● Similar to mast cells, but apparently generated by different CD34+ precursor cells in bone marrow (basophils mature in marrow, mast cells in connective tissue)
● Progresses from the multipotent myeloid stem cell via a committed progenitor (basophil colony-forming unit, CFU-Baso) to basophilic promyelocyte, to basophilic myelocyte, to basophilic metamyelocyte, to basophil
● Leaves bone marrow as terminally differentiated granulocyte

Pathophysiology
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● Basophils and mast cells are effector cells in allergen / IgE-mediated immune responses
● They induce type 1 immediate immune response in airways and elsewhere, causing bronchial asthma and other allergic diseases (Allergol Int 2006;55:105)
● Also play a critical role in host defense against helminths (Allergol Int 2006;55:99)
Factors thought to play key role in basophil production: IL3 (main cytokine), GM-CSF, IL4, IL5 (primary cytokine linked to specific eosinophil and basophil production), stem cell factor (SCF)
● Basophils and their granules contain histamine, sulphated mucopolysaccharides (mostly chondroitin sulfate), peroxidase, low levels of chymase, negligible amount of tryptase, Charcot-Leyden crystal protein, PAF and ECF-A

Clinical features
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● Basophil activation test, using CD203c or CD63 as an activation marker, has become a reliable test for in vitro investigation of immediate allergy, complementing other in vitro tests (Clin Mol Allergy 2005;3:9)
● Significant basophilia is more likely to represent neoplasia (chronic myelogenous leukemia, other chronic myeloproliferative disorders, myelodysplastic syndromes, acute leukemias) than reactive processes
Non-neoplastic basophilia: allergic / hypersensitivity reactions, hypothyroidism, ulcerative colitis, rheumatoid arthritis, renal disease, rare infections (varicella, influenza), irradiation, rare carcinomas and rare drugs (estrogens, antithyroid agents)
Decreased number of basophils (basophilopenia): certain medications (steroids, epinephrine, thyrotoxicosis therapy), acute stress, acute inflammation

Micro description
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● Basophilic granules are metachromatic (reddish-purple) with toluidine blue and Alcian blue; are also water-soluble
Basophilic myeloblast: difficult to distinguish from other granulocyte blasts; large round cell with basophilic cytoplasm without granules; N/C ratio is 80%; dispersed chromatin with nucleolus
Basophilic promyelocyte: intermediate in development between basophilic myeloblast and myelocyte; large round cell with a few undifferentiated cytoplasmic granules; slight chromatin clumping, nucleolus present
Basophilic myelocyte: round / oval cell; cytoplasm with slight basophilia, moderate cytoplasmic purple-black granules of varying size and shape; granules are usually larger than neutrophilic granules; N/C ratio is 50%; chromatin moderately condensed, no distinct nucleolus
Basophilic metamyelocyte: oval cell with abundant pale cytoplasm, large and fairly uniform specific granules; N/C ratio is 40%; nucleus is small and indented with condensed chromatin, no nucleolus
Basophil: smaller than other white blood cells (10-15 microns); cytoplasm is homogenous pale-blue but often obscured by purple-blue granules (containing heparin and histamine); N/C is 20%; nucleus is often unsegmented or bilobed, chromatin is coarse

Micro images
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Basophilic myelocyte

   
Basophilic metamyelocyte

           
Basophil

Positive stains
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Commonly used: CD9, CD25, CD38
● Also CD11a, CD11b, CD11c, CD13, CD15u, CD17, CD18, CD26, CD31, CD32, CD33, CD35, CD38, CD43, CD44, CD45, CD46, CD47, CD49d, CD50, CD55, CD58, CD59, CD63, CD68, CD71 (dim by flow cytometry), CD85A, CD85H, CD87, CD88, CD99, CD102, CD116, CD121b, CD123, CD125, CD126, CDw128a (CD181), CD203c, HLA-DR (immature basophils, Allergy 2006;61:1063), histidine decarboxylase, 2D7 (J Clin Pathol 2006;59:396) and basogranulin (Am J Clin Pathol 2006;125:273)
Allergic subjects: CD32, CD122, CD124, CD130 and CD154 (J Allergy Clin Immunol 2000;106:1190)
Variable: CD14, CD15, myeloperoxidase (usually negative) and a small proportion are chloroacetate esterase-positive
Cytochemistry: PAS-positive (not the granules), Sudan-black-positive and phosphatase (acid & alkaline)-negative

Negative stains
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● CD2, CD3, CD7, CDw12, CD16, CD19, CD20, CD21, CD22, CD23, CD56, CD57, CD114, CD117, CD122, CD124 and tryptase

Electron microscopy description
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● Granules ~20nm in diameter, with a particulate substructure

Electron microscopy images
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Basophil

Additional references
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Basophil granulocyte, Wikipedia
Flow cytometry markers, Cytometry 1999;35:249
Allergy 1994;49:861, Blood 1987;70:1872

End of Bone Marrow - nonneoplastic > Normal > Basophils


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