The Key Players of the Immune System — Immunology #3
How does the immune system respond to an invasion? The key players of the immune system sense impending danger and aggressively attack.
The immune system is an amazing but very complex system that works all day, every day, to keep us alive.
By knowing how the immune system functions you will be able to understand how medications and vaccines work, as well as appreciate the healing process (which can sometimes be a pain, literally).
In the last article The Four Lines of Defense — Immunology #2 we took a look at the structure of the immune system as a whole.
In this article, we’ll take a look at the key players of the immune system: the sensor cells.
Important Terminology
Here is a list of some terms that will come up in this article.
The Key Players in the Immune System
Although there are many cells vital to the immune response, you’ll often hear the leukocytes being referred to as the key players of the immune system. Leukocytes are more commonly known as white blood cells (WBCs).
The sensor cells — or white blood cells — are also called granulocytes because they contain granules with enzymes that destroy invading pathogens through a process called degranulation. We’ll discuss degranulation in detail in a future article.
There are other immune cells that we will discuss later, but here’s an overview of some of the WBCs which act as sensor cells. These are important in the second line of defense.
Neutrophils
Neutrophils are the most abundant granulocyte. They make up about 50–60% of white blood cells. They are the first cell to get to the site of injury or infection. Their main function in the immune system is to phagocytose (eat and digest) and destroy pathogens. They’re aggressive and dedicate their lives to keeping you alive. Once they start attacking, they only have a few hours until they die of exhaustion.
Macrophages
Macrophages are not white blood cells, but they do come from a precursor WBC. The macrophage precursor is called a monocyte. When a pathogen invades the body or there is damage to tissues (such as a cut in your skin), monocytes move from the bloodstream into the tissues and become macrophages.
Macrophages are the largest immune cell. If the average body cell was the size of a human, then a macrophage would be the size of a black rhino. Incidentally, they also have the temperament of a black rhino — they will aggressively attack any threat.
Macrophages destroy pathogens and damaged cells through a process called phagocytosis (more on this later). Macrophages are often referred to as being ‘partners in crime’ with neutrophils. Macrophages and neutrophils are both very quick to the site of infection or injury and set out to destroy pathogens together.
Macrophages are also able to present bits of the digested pathogen to other immune cells. This provides a link between the innate and adaptive parts of the immune system.
Fun Fact: Tattoos are stored in macrophages. Essentially, getting a tattoo is introducing an invader into your body. Tattoo ink is not ‘self’ which means the immune cells want to get rid of it.
Macrophages gobble up the tattoo ink and try to digest and destroy it. However, most of the ink particles are too large for the macrophage to digest, so it simply stores it. Some of the ink particles are small enough to be digested, which is why the tattoo fades a little when you first get it.
As time goes on, tattoos fade. This is, at least in part, due to macrophages dying. When an old macrophage dies, the ink particles are left behind. Some of these particles float away, others are gobbled up by new, younger macrophages. Since some of the ink has floated away, the tattoo appears to be fading.
Mast Cells
Like macrophages, mast cells are not WBCs, but, they are made from a precursor white blood cell. The precursor WBC travels into the skin, intestines, and airway mucosa from the blood and becomes a mast cell.
Mast cells destroy pathogens via degranulation and are also involved in the allergy response. These cells contain a chemical called histamine which, during an allergic reaction, is released more than it should. This is why many people with allergies take antihistamines after being exposed to an allergen.
Eosinophils
Eosinophils make up 1–6% of white blood cells in your body. Their main responsibility is to destroy pathogens through degranulation. They are also involved in allergic reactions.
Basophils
Basophils are even less abundant than eosinophils; they make up less than 1% of the WBCs in the body. Like eosinophils, their main responsibility is to destroy pathogens via degranulation and they are also involved in allergies.
Natural Killer Cells
Natural killer cells (NK cells) are white blood cells that recognize and kill body cells that have been infected. They also are good at recognizing and targeting cancer cells. NK cells are granulocytes and one of the ways they kill infected cells is through degranulation.
Conclusion
The sensor cells — or white blood cells — are the key players of the immune system. We’ll be talking about these cells throughout the whole series, so hopefully, you’re a bit more familiar with them now.
Here are the key takeaways from this article:
- The key players of the innate immune system are the sensor cells.
- The sensor cells are the white blood cells, which are:
- Neutrophils
- Macrophages
- Mast cells
- Eosinophils
- Basophils
- Natural killer cells
In the next article, we’ll dive into the innate immune system. We’ll cover the first line of defense in more detail.
Other articles in this series
