Bone marrow nonneoplastic
Normal
Monocytes
Author: Dragos C. Luca, M.D.
Last author update: 1 September 2012
Last staff update: 14 May 2021
Copyright: 2002-2024, PathologyOutlines.com, Inc.
PubMed Search: Bone marrow [title] monocytes [title]
Table of Contents
Definition / general | Clinical features | Microscopic (histologic) description | Microscopic (histologic) images | Positive stains | Negative stains | Electron microscopy images | Additional referencesCite this page: Luca DC. Monocytes. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/bonemarrowmonocytematuration.html. Accessed April 25th, 2024.
Definition / general
- Monocytes usually < 1% of bone marrow cells
- Develop from myeloid stem cell, to monoblast to promonocyte to monocyte (bone marrow) to monocyte (peripheral blood) to macrophage (tissue)
- Same progenitor cell as neutrophils, under the influence of M-CSF
- Difficult to identify monoblasts and promonocytes in normal bone marrow
- Gradual nuclear folding and acquisition of cytoplasmic granules similar to those in neutrophils but fewer and smaller
- Monocytes are also precursors of dendritic cells
- Produce numerous regulatory cytokines in addition to their traditional phagocytic role
- Part of the innate immune system: replenish macrophages and dendritic cells and move quickly to the site of infection (8 - 12 hours)
- A significant proportion (~50%) are stored in the spleen; they spend 1 - 3 days in the bloodstream before moving into tissue
Clinical features
- Causes of monocytosis in bone marrow: reactive / accumulation disorders (high cell turnover states, granulomatous processes, hemophagocytic lymphohistiocytosis, postchemotherapy, fat necrosis, post cytokine therapy, storage diseases, Rosai-Dorfman disease); neoplastic disorders (Langerhans cell histiocytosis, chronic myelomonocytic leukemia, juvenile myelomonocytic leukemia, myeloproliferative diseases, acute myeloid leukemia, malignant histiocytosis, histiocytic sarcoma)
- Causes of monocytopenia in peripheral blood: acute infections, stress, glucocorticoids, aplastic anemia, hairy cell leukemia, acute myeloid leukemia, myelotoxic drugs, genetic syndromes
Microscopic (histologic) description
- Monoblast: 12 - 20 microns, moderate basophilic cytoplasm without granules, may show pseudopod formation, often intense staining on periphery and with perinuclear zone, round / oval nuclei with fine chromatin and 1 - 4 large prominent nucleoli; nucleus may show indentations or folding
- Promonocyte: features intermediate between monoblast and monocyte, more irregular nuclear contour, less basophilic and more granulated cytoplasm
- Monocyte: largest of leukocytes (12 - 20 microns); round with smooth margins or pseudopod-like cytoplasmic extensions; abundant light blue cytoplasm with fine pink azurophilic granules; may have vacuoles or phagocytized material; large bilobed, kidney shaped or U shaped nucleus with moderately clumped chromatin; no nucleolus; N/C ratio is 65 - 80%
Microscopic (histologic) images
AFIP images
Promonocyte
Bone marrow in acute monocytic leukemia (AML M4):
Monoblasts are larger cells with abundant
cytoplasm and round nuclei and
promonocytes are two cells with folded and
creased nuclei next to monoblast in center
Images hosted on other servers:
Monocyte
Positive stains
- Mainly CD14
- Also CD4, CD7, CD11a, CD11b, CD11c, CD11d, CD12, CD13, CD15 (variable), CD15u, CD17, CD18, CD23 (activated), CD29, CD30, CD32, CD33, CD36, CD37, CD38, CD39, CD40, CD43, CD44R, CD45, CD45RB, CD45RC, CD45RO, CD48, CD49a, CD49b, CD49d, CD49e, CD49f, CD51, CD52, CD54, CD61, CD62L, CD64, CD65, CD65s, CD68, CD83 (transient), CD84, CD85A, CD85B, CD85D, CD85E, CD85F, CD85I, CD85J, CD85K, CD85M, CD86, CD87, CD88, CD89, CD91, CD92, CD93, CD97, CD101, CD102, CD105 (activated), CD111, CD112, CD114, CD116, CD122, CD123 (plasmacytoid), CD126, CD127, CD128, CD132, CD137, CD139, CD141, CD148, CD156, CD157, CD163, CD165, CD166 (activated), CD171, CD180, CD210, CD226 and CD227
Electron microscopy images
Images hosted on other servers:
Monocyte - TEM and SEM
Additional references
