Monocytes

2-10% of white blood cells are Monocytes, which are the largest white blood cells and usually measure about 20 μm in diameter two to ten percent of white blood cells are Monocytes, which are the largest white blood cells and usually measure about twenty micrometers in diameter. They can be recognized by the lack of granules in their cytoplasm and their large, single, indented nucleus (which can look like a horse-shoe or kidney bean).

It is not common to see Monocytes in peripheral blood smears because after being produced in the bone marrow they migrate into tissues where they differentiate into macrophages or dendritic cells.

Part of the innate immune system, Monocytes are phagocytic cells, which means that one of their primary functions is to detect, engulf, and destroy invading pathogens such as bacteria, viruses, parasites, and fungi.

Other roles include:

• Presenting the antigens of destroyed pathogens to activate other immune cells (e.g. T cells), which then trigger an adaptive immune response.

• Producing cytokines, which are signaling molecules that regulate and coordinate immune responses

• Tissue repair and wound healing (once differentiated into a Macrophage).

• Activation or suppression of other immune cells (known as immunomodulation).

Figure 1. Monocyte