How does the immune system work in the human body?

In every second of a human’s life there are bacteria, viruses and fungi that try to enter the body to make it their permanent home. So the body has an effective, fast and smart system to protect itself from these threats: the immune system.

This system is made up of a network of cells, tissues and organs that coordinate the defense of the human body against any threat. Without the help of it, any small injury (such as a paper cut) could be lethal to the human.

This natural defense can be divided into two: a part of the immune system is what the human is born with, which begins to function from the moment the babies leave the womb. The second part of the immune system is the one that adapts, which is what develops when the body is exposed to microbes.

Each of these two parts works thanks to different protective cells that are created in specific organs and have specific tasks. This system has been perfected through human evolution and manages to defend the body from attacks by different bacteria, viruses and fungi.

The actors of the immune system

Like any body system, the immune system works as a team throughout the body. White blood cells, also called leukocytes, are the heroes of the immune system, as they are the ones that fight directly against germs. These are only 1% of the cells in the blood, but their impact is very great.

When a certain area of ​​the body is under attack, it is the white blood cells that rush to destroy the dangerous substance, also called antigen, and prevent disease. These are created in the bone marrow and are stored in the blood and lymphatic system. In fact, the life of leukocytes is not very long, they barely live 1 to 3 days, so the body is always making new ones.

But not all white blood cells work in the same way, in fact there are many types. Some of these are, for example, monocytes that are responsible for attacking bacteria, lymphocytes that create antibodies to any threat, neutrophils that kill bacteria and fungi, basophils that secrete a chemical to warn the body that there are infectious agent, and eosinophils that attack parasites and cancer cells.

Other actors that are part of the immune defense are the skin, which prevents germs from entering the body, the mucous membranes, which protect organs and cavities by trapping germs, and the lymphatic system, which includes organs such as the bone marrow, spleen and lymph nodes.


So if white blood cells are so strong, why do humans get sick? The easiest answer is that diseases appear when there are few white blood cells in the blood or when they are not strong enough. For example, there may be some agent destroying cells faster than they are created, or some microbe preventing the bone marrow from making new blood cells.

Specifically, there are diseases and conditions that can reduce white blood cells. For example, a weak immune system responds to diseases like HIV, cancer treatments, or medicines that reduce production.

However, it is also dangerous to have too many white blood cells, as this can indicate that there is an infection, that there is cancer in the blood (leukemia) or other types of cancer in the body. Other conditions such as extreme stress, the end of a pregnancy or smoking, can also cause excessive white blood cell production.

What happens when a microbe enters the body?

When an infectious agent enters the body through a hole, open wound or intravenously, the immune system will immediately recognize it as a foreign body that must be eliminated. The first cells to detect the foreign agent are phagocytes and lymphocytes, which are constantly navigating the body’s tissues.

Phagocytes and lymphocytes detect the invader, capture it inside the cell, and begin to destroy it into small pieces. Another important task that they do is to release molecules that alert the other actors of the immune system that there is something strange happening in the body.

Sometimes this first cell barrier is enough to eliminate the invader without receiving help from others, but other times, when the infectious agent is more powerful, reinforcements must come in to help.

The next line of defense is the creation of antibodies in the white blood cells, which are proteins that stick to the foreign agent and serve to attack, weaken and destroy infectious agents. Antibodies have a memory of everything they have attacked and are trained to fight it another time.

The second time the antigen enters the body, the immune system has a faster and more adequate response to destroy it in a short time. Simply put, the body creates immunity.

Another barrier of protection is that of the lymph nodes (small organs that are in the neck, armpits, abdomen and groin), which work as filters for germs. When ganglion cells recognize a foreign agent, they become activated, replicate, and go out in search of infection. These nodes become inflamed as an immune response, so doctors often check them to see if the body has an infection.

However, there are germs and viruses that manage to adapt to survive in the body, prevent the immune system from recognizing them, and create an autoimmune disease.