Bone Marrow - nonneoplastic

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Bone marrow - nonneoplastic

Normal

Osteoclasts

Reviewers: Dragos Luca, M.D. (see Reviewers page)
Revised: 4 February 2013, last major update September 2012
Copyright: (c) 2001-2013, PathologyOutlines.com, Inc.
PubMed Search: osteoclast
Broken links/comments: click here or email CommentsPathOut@gmail.com, subject=bonemarrowosteoclasts

General
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● Cells derived from hematopoietic progenitor cells involved in bone resorption, primarily due to remodeling and not calcium homeostasis
● Along endosteal surface of bony trabeculae (reside in Howship lacunae) or along margins in marrow smears
● Common in children (active bone remodelling); in adults associated with metabolic or neoplastic diseases
● Some overlapping immunophenotypic features with monocytes / macrophages
● Relatively recently identified osteoclast colony stimulating factor and transcription factors involved in osteoclastogenesis
● Activated by parathyroid hormone and by cytokines RANKL and macrophage colony-stimulating factor (Arthritis Res Ther 2006;8:201)
● Osteoclasts use their ruffled borders (with villous extensions) to bind to matrix adhesion proteins, produce resorption pits / bays (shallow concavities) called Howship’s lacunae
● Plasma membrane forms a seal with bone; osteoclast acidifies extracellular area, which solubilizes the mineral and releases enzymes which dissolve the matrix

Diagrams
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Left to right: cross-section; bone resorptive cycle; osteoclast differentiation

Micro description
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● Very large (up to 100 microns), multinucleated (2-12 nuclei) giant cells associated with bone surface
● Abundant, blue-purple-pale pink cytoplasm containing many fine, red-purple granules
● Also contain bone sand in the cytoplasm
● Multiple, relatively uniform but widely separated nuclei, each with one nucleolus and dense chromatin
● Generally, less mature osteoclasts have basophilic cytoplasm and mature forms have brightly eosinophilic cytoplasm

Micro images
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Osteoclasts

Very large cell with multiple nuclei with distinct nucleoli, cytoplasm has coarse azurophilic granules

Positive stains
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● CD13, CD31, CD51 (Histochemistry 1991;96:169)
● CD53, CD54, CD61, CD63, CD68, CD115, acid phosphatase, microphthalmia transcription factor and TRAP

Electron microscopy description
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● Numerous mitochondria, rare lysosomes
● Ruffled edge in area of cell membrane is associated with bone resorption

Electron microscopy images
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Left: osteoclast resorbing bone

Additional references
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● Keio J Med 2003;52:1, Wikipedia, Anat Embryol (Berl) 1984;170:51

End of Bone Marrow - nonneoplastic > Normal > Osteoclasts

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