Monocyte vs Macrophage
The immune system is composed of few types of cells including lymphocytes, macrophages, monocytes, neutrophils, and other cells such as basophils, eosinophils, and natural killer cells. Macrophages and monocytes are the large irregular shaped white blood cells, which stimulate antibody production in the body. Both these cell types are categorized under agranulocytes due to the presence of cytoplasmic granules. These two types of cells have similar roles in the immune system such as phagocytosis, presenting antigens to T lymphocytes, and production of cytokine that help to initiate and coordinate immune responses.
Monocytes are irregular shaped white blood cells that circulate in the bloodstream. Unlike the other white blood cells, monocytes are larger and have a bean-shaped nucleus in the cell. When monocytes enter an organ or tissue from the bloodstream, they will be differentiated into cells called ‘macrophages’, and thus monocytes are the precursor cells of macrophages.
About 3 – 8% of the white blood cells are monocytes in the human circulatory system. All the white blood cells are derived from progenitor cells. However, in this case, progenitor cells are differentiated into monoblast and then into promonocytes. Promonocytes are finally differentiated into monocytes. The three main functions of monocytes are phagocytosis, presenting antigens, and production of cytokine.
Once monocytes reach an organ or a tissue from the bloodstream, they will differentiate into macrophages. Macrophages are large, irregular shaped, agranulated cells with large bean-shaped nucleus. They are capable of engulfing foreign particles, which could be a threat to human health or cause disease to human. This engulfing process is called phagocytosis. Once they engulf foreign particles or membrane bounded phagosome is formed, lysosomes release their enzymes in order to kill and digest engulfed particles. In addition, rapidly producing oxygen-containing free radicals in phagosomes also help to degrade the pathogens.
Macrophages are capable of engulfing bacteria, viruses, cellular debris, and dust particles in the lungs. When an infection occurs in a tissue or an organ, monocytes in the bloodstream squeeze through the epithelium cells and enter the site of infection. At the site of infection, the monocytes differentiate into active, phagocytic macrophages.
What is the difference between Monocyte and Macrophage?
• Monocytes are the precursor cells of macrophages.
• Monocytes are found in the bloodstream, whereas macrophages are found in extracellular fluid that bathes tissues.