MONOCYTES
MONOCYTES are agranulocytes, are the largest cells and the second line of defense against infection. Histiocytes are large macrophagic phagocytes, which are also classified as monocytes and each can be changed into the other. These cells remove injured and dead cells, microorganisms and other insoluble products from the circulating blood. Monocytes contain interferon (antiviral agent) and escape from the upper and lower respiratory, gastrointestinal and genitourinary systems performing scavenger hunts
THE MONOCYTE, MACROPHAGE, AND THE RETICULAR ENDOTHELIAL SYSTEM
It takes up to eight hours for a monocyte to become a macrophage.
The combination of monocytes, mobile, and fixed tissue macrophages, the
spleen, lymph nodes, and the liver are collectively called the “reticular
endothelial system.
Tissue macrophages are found in the skin, lymph nodes, lung alveoli, liver (Kupfer cells and sinusoids), central nervous system (microglial cells), connective tissue (histiocytes), and synovium as type A and type C cells.
The main purpose of macrophages is phagocytosis. Tissue macrophages are considered the first line of defense, followed by neutrophils being the second line of defense, the third being mononuclear cells, and the fourth being granulocytes and monocytes.
The spleen and bone marrow trap blood-born bacteria, debris and old red blood cells via filtration through the red pulp by phagocytosis.
ABSOLUTE COUNT 100-500/mm3
DIFFERENTIAL 3-7% OF TOTAL WBC's
Monocytes (monocytosis >500 cell/mm3 are increased in:
1. Bacterial infections
2. TB
3. Syphilis
4. Carcinoma of the stomach, breast and ovary
5. Hodgkin;s disease
6. Myeloproliferative diseases
7. Chronic ulcerative colitis
8. Collagen diseases and sarcoidosis
9. Surgical trauma
10. Lipid storage diseases (Gaucher's disease)
11. Severe infections
12. Lupus erythematosus
13. Hemolytic anemias
14. Breakdown of non-diseased tissue
Monocytes are decreased (monocytopenia 100 cells/mm3) in:
1. Prednisone treatment
2. HIV
3. Aplastic anemia
4. Overwhelming infection
5. toxic reactions