Monocyte Count

Aka: Monocyte Count, Macrophage Count, Monocyte, Macrophage, Granuloma, Epithelioid Cell, Alveolar Macrophage, Dendritic Cell, Kuppfer Cell, Langerhans Cell, Mesangial Cell, Microglial Cell, Microglia

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II. Characteristics

  1. Monocytes form in Bone Marrow from Myeloblasts as with other Granulocytes (Basophils, Eosinophils, Neutrophils)
    1. Monocytes move from peripheral blood into tissue and become Macrophages
    2. Transformation to Macrophages controlled by Cytokines
  2. Functions
    1. Bacteriocidal activity without Phagocytosis
      1. Release of antibacterial enzymes (Lysozymes) contained within secreted vacuoles (Lysosomes)
    2. Phagocytosis of dead or damaged cells and Bacteria (similar to Neutrophils)
      1. Macrophages directly perform the Phagocytosis
      2. Resulting Phagosome fuses with Lysosomes to digest the ingested material within the Phagosome
      3. Phagocytosis.jpg
    3. Granuloma formation (epitheliod cells, multinucleated giant cells)
      1. Walling off of infection in response to chronic inflammation
      2. Result when Macrophages cannot lyse phagocytized material (e.g. silica, Asbestos, immune complexes)
      3. Macrophages expand, increasing cytoplasm, to form epitheliod cells
      4. Macrophages fuse to form multinucleated giant cells
  3. Monocyte Morphology on Blood Smear
    1. Mononuclear Leukocyte (same class as Lymphocyte)
    2. Slightly larger than a Lymphocyte
    3. Kidney shaped nucleus
  4. Macrophages (and related phagocytic cells) have specific names in certain tissues
    1. Alveolar Macrophage (lung)
    2. Dendritic Cells (Spleen, Lymph)
      1. Antigen Presenting Cells to Lymphocytes
    3. Kuppfer Cell (Liver)
    4. Langerhans Cell (Skin)
      1. Dendritic Cell precursors
      2. Acute inflammation results in Langerhans Cell transit to regional Lymph Nodes
      3. Langerhans Cells transition to Dendritic Cells, carrying Antigen to present to Lymphocytes
    5. Mesangial Cell (Kidney)
    6. Microglia (Central Nervous System)
    7. Osteoclast (Bone)

III. Labs: Normal

  1. Range: 2-8% of White Blood Cells

IV. Causes: Increased

  1. Infection
    1. Viral Infection
    2. Parasitic Infection
  2. Inflammatory Bowel Disease
  3. Sarcoidosis
  4. Neoplasms
  5. Monocytic Leukemia
  6. Lymphoma
  7. Multiple Myeloma

V. Causes: Decreased

  1. Aplastic Anemia
  2. Lymphocytic Anemia
  3. Glucocorticoids

VI. Evaluation: Monocytosis (Monocytes >880/mm3)

  1. See Leukocytosis
  2. History and potential causes
    1. Travel and contagious contacts
  3. Diagnostics (consider)
    1. Chest XRay
    2. Specific infection testing (e.g. Monospot, PPD or quantiferon)
    3. Acute phase reactants (ESR, CRP)

VII. References

  1. Goldberg (2014) Clinical Physiology, Medmaster, Miami, p. 68-9
  2. Saiki in Friedman (1991) Medical Diagnosis, p. 227
  3. Abramson (2000) Am Fam Physician 62(9):2053-60 [PubMed]
  4. Riley (2015) Am Fam Physician 92(11):1004-11 [PubMed]

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