This table in our kitchen, stab the

This lesson will teach you about certain white blood cells of the innate immune system. Namely, we’ll learn about phagocytes, monocytes, macrophages, mast cells, and NK cells.

Cell Eating

In this lesson, we will cover some of the major types of white blood cells involved in the innate immune system.

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This is the immune system that is on the front lines of your body’s defense against foreign invaders, such as bacteria, fungi, viruses, and so forth. Specifically, one of the cells we are going to talk about is really famous for phagocytosis, or the process of cell eating for the purposes of destroying a foreign entity; so, let’s step into our kitchen along with a bunch of dinner guests as we go over some important terms and concepts.

Monocytes and Macrophages

In the kitchen, there is a plate filled with kidney beans. However, these aren’t what you think they are. These are actually cells called monocytes, which are white blood cells of the innate immune system. They have a very characteristic kidney bean shaped nucleus, which makes them readily identifiable under the microscope.One of the most important roles monocytes have is the ability to morph, or turn, into a cell called a macrophage.

This is a cell involved in engulfing and digesting pathogens and debris. While it is part of the innate immune system, it does play some roles in the adaptive immune system as well, which will be covered in another lesson.

The Role of Phagocytes

For now, it’s important to think of the macrophage as kind of like the clean-up crew that comes in after the kitchen closes.

Someone has to clean up the mess made by all of that cooking! Well, these are the most famous cells involved in phagocytosis.When they encounter either a dead cell, part of a bacteria, or even a whole pathogen, they try to essentially eat, or phagocytize, this particle. In order to do this, the macrophage, or any phagocyte, attaches the receptors on its cell surface to the receptors on the surface of, say, a bacteria. It’s basically like having the macrophage take a fork off of the table in our kitchen, stab the bacteria with the fork, thereby making it attach to the fork, and put the bacteria into its mouth thereafter. Once inside the macrophage’s stomach, its cytoplasm, it will be digested and killed using enzymes, kind of like the gastric juices of our own stomach digest food and kill pathogens.

Now that’s good eating!As a side note, there are many different types of phagocytes, besides macrophages, that utilize this process in order to defend us against pathogens or clean up debris or dead cells. These phagocytes include neutrophils, monocytes, mast cells, and dendritic cells. The latter of which, like our macrophages, are also involved in adaptive immunity, despite being part of the innate immune system.

That’s because both of them basically serve as a go between for the two systems, as another lesson explains in more detail.

Mast Cells and NK Cells

Another cell that is technically a part of the innate immune system, but plays a big role in the adaptive immune system, is called a mast cell. This is a cell responsible for the body’s defense against pathogens and plays an important part in allergic reactions.

Finally, after eating our kidney beans and having the clean-up crew clean the kitchen up after dinner, we all decide to watch a movie before going to bed. As we’re watching a movie, a killer enters our room and for some reason kills only some of our dinner guests before leaving. The name of this killer is the NK cell, and it’s a white blood cell, called a natural killer cell, that is responsible for killing tumor cells and cells infected by a virus.Basically, as soon as the NK cell recognizes via receptors that a cell in our body has been compromised by something like a virus, it releases chemicals that cause the cell to die, along with any virus that may be inside of it.This is super important. Think of everyone who came over for dinner tonight as an individual cell comprising the entire collection of guests, the entire body.

If a virus enters the body, it can be recognized by a lot of different defense mechanisms and may be killed. However, if the virus enters a friendly cell before it is killed, and hides inside of this friendly cell, no one will be able to see it from the outside.That’s a problem, because the virus will replicate inside of that cell and will end up infecting the entire body, or all of the dinner guests. So, our body has a defense system by which an infected cell cries out for help after it is infected by a virus.

It cries out for help by using special receptors that NK cells recognize. As soon as the killer cells hear this cry for help, or rather see the receptor, they kill the infected dinner guest, which ends up killing the virus inside of them, in order to save the entire body, or all the other guests from being infected.

Lesson Summary

Now you know why the killer only went after some of our dinner guests.

I hope that little tidbit about a killer won’t give you nightmares tonight, so let’s divert our attention to reviewing some important terms we went over.Your body has cells called monocytes, which are white blood cells of the innate immune system.One of the most important roles monocytes have is the ability to morph, or turn, into a cell called a macrophage.

This is a cell involved in engulfing and digesting pathogens and debris.Besides macrophages, any white blood cell that uses the process of phagocytosis is called a phagocyte.Other cells of the innate immune system include mast cells, which are cells responsible for the body’s defense against pathogens and play an important part in allergic reactions, and NK cells, which are white blood cells, called natural killer cells, that are responsible for killing tumor cells and those infected by a virus.

Learning Outcomes

After this lesson, you will have the ability to:

  • Describe the structure and function of monocytes
  • Explain how phagocytes, including macrophages, function to destroy pathogens
  • Summarize the importance of mast cells and NK cells to the innate immune system
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