What Is the Function of Monocytes?

Victoria Blackburn

Monocytes are a type of white blood cell and are a part of the immune response system. The function of monocytes is to carry out the process of phagocytosis. During this process, large molecules found within the blood are ingested and then broken down. The two main purposes of phagocytosis are to protect the organism from attack by harmful pathogens, and to remove dead, dying or damaged cells from the blood.

The healing action of monocytes causes the heat and swelling associated with infections.
The healing action of monocytes causes the heat and swelling associated with infections.

When pathogens enter an organism, they cause an infection. In most cases, the pathogens are bacterial or viral cells. As the pathogens carry out their natural life processes, they produce and release chemicals. These chemicals attract white blood cells to the area of infection, including those that release antibodies and those that carry out phagocytosis. There are also proteins within the blood that attach to the bacteria or virus, which makes it easier for the cells of the immune system to recognize the pathogens.

Pus is a normal part of the immune system response process.
Pus is a normal part of the immune system response process.

The surface of a monocyte is not smooth as it has specific proteins on it that allow it to bind to the bacteria or virus cell. The function of monocytes is to move towards the specific pathogenic cell and eventually adhere to it when it is close enough. Attaching to the pathogen stimulates the production of a pseudopodium. This occurs due to the monocyte bending into a C shape around the pathogen, and the ends of the C meeting, so that the pathogen is engulfed.

The pathogen is then trapped within a phagosome inside of the monocyte. Engulfing the pathogen or dead or damaged cells is only one part of the function of monocytes. Once the cells or debris have been engulfed, they are broken down within the phagosome.

A lysosome is a type of cellular organelle that is found within the monocytes. When a phagosome is formed, the lysosomes attach to it and release digestive enzymes, called lytic enzymes, into the phagosome. These enzymes break down the cell within the phagosome, and the products that remain are absorbed by the monocyte.

Inflammation occurs at the site of the infection where phagocytosis occurs. The function of monocytes and other cells of the immune system causes the signs and symptoms associated with an inflammation. For example, heat and swelling are due to the activities of these cells. Moreover, pus is formed from the dead bacteria and the phagocytes, including monocytes, involved in fighting the infection.

A diagram showing different types of white blood cells, including monocytes.
A diagram showing different types of white blood cells, including monocytes.

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Discussion Comments


I think part of the reason an area near wound will become hot is in order to help the monocytes destroy the infection.

Often the infecting cells are less able to survive the heat because they have no backup, while the human cells they are attacking can call on the reserves from the rest of the body to continue to survive.

This is one reason a high fever for a long time can be fatal, because those temperatures are fatal to your cells too, and if it's happening everywhere there is no backup to call.

I didn't realize it was the monocytes themselves that caused the heat though.


@pastanaga - If you want to compare monocytes to warriors you can also bring in some of the battle tactics.

There are some diseases that use a kind of "Trojan horse" maneuver in order to get past the body's defenses.

They will let themselves be "eaten" through phagocytosis in order to get inside the poor monocyte, and then they will use the cell in order to produce more copies of themselves.

It is usually viruses that use these kinds of tactics and they can be very difficult to eliminate, even with modern medicine, simply because they are so difficult to get apart from our own cells.


It's no wonder people who are sick will sometimes imagine that their insides are fighting with the disease. Because, really, they are literally fighting the disease.

Monocytes are actually eating the invaders, and according to the article, puss is made up of the bodies of the fallen.

I know I'm being a little bit silly, but I find it quite extraordinary how many tiny dramas are happening inside even your little finger tip right this second that we barely have any idea about and probably will never even notice.

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