Each second, human beings are exposed to bacteria, viruses and fungi, which try to enter the body to make it their permanent home. Therefore, to protect itself from these threats, the body has an effective, fast and intelligent system called: the immune system.
This system is composed of a network of cells, tissues and organs that coordinate the defense of the body against any threat. Without the help of this network, any small injury (such as a paper cut) could be lethal.
This natural defense can be divided into two parts. The first part is the one each individual was born with, which starts working from the moment the baby comes out of the womb. And, the second part of the immune system develops when the body is exposed to microbes.
Each of these two parts works thanks to different protective cells produced in specific organs to perform specific tasks. The evolution of human beings has enhanced this system. It is now able to defend the body from different bacteria, viruses and fungi attacks.
Actors of the immune system
Like any body’s system, the immune system teams up with other elements of the body. White blood cells, also called leukocytes, are the immune system heroes, as they are the ones that fight germs directly. They only represent 1% of the total blood cells, but play an important role.
When a part of the body is under attack, the white blood cells are the ones that destroy the dangerous substance, also called antigen, and prevent the body from getting sick. They are made in the bone marrow and are stored in the blood and lymphatic system. In fact, white blood cells do not live very long. Their lifespan ranges from 1 to 3 days, so the body is always making new ones.
But not all white blood cells work the same way. There are many types of white cells. Indeed, monocytes are in charge of attacking bacteria, lymphocytes produce antibodies to fight any threat, neutrophils kill bacteria and fungi, basophils release a chemical as a warning message when an infectious agent invades the body, and eosinophils attack parasites and cancer cells.
Other actors that are part of the immune system include the skin (prevents germs from entering the body), mucous membranes (protect organs and cavities by trapping germs) and the lymphatic system (bone marrow, spleen and lymph nodes).
They are not indestructible
So, if white blood cells are so strong, why do humans get sick? The easiest answer is that diseases appear when there are few leucocytes in the blood or when they are not strong enough. For instance, an agent may be destroying cells faster than they are produced, or some microbe may prevent the bone marrow from producing new cells.
In fact, a weak immune system due to a disease (HIV), cancer treatments or drugs can reduce the production of white blood cells.
However, it is also dangerous to have too many white blood cells, as it may indicate an infection, blood cancer (leukemia) or any other type of cancer. Other conditions, such as extreme stress, the end of a pregnancy or quitting smoking, can also cause an excessive production of white blood cells.
What happens when a microbe enters the body?
When an infectious agent enters the body through a break in the skin, an 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.
The phagocytes and lymphocytes detect the intruder, capture it inside the cell and start destroying it in small pieces. They also release molecules to alert the other system’s actors to the fact that there is something strange going on in the body.
Sometimes this first barrier of cells alone can eliminate the intruder. However, when the infectious agent is more powerful, reinforcement is needed.
The next line of defense is the production of antibodies in the white blood cells, which are proteins that stick to the foreign agent and are used to attack, weaken and destroy infectious agents. Antibodies keep in memory everything they have attacked and are trained to fight it again.
Therefore, if the same antigen enters the body a second time, the immune system is able to give a faster and more adequate response to it. In short, the body creates immunity.
Another protective barrier is that of the lymph nodes (small organs in the neck, armpits, abdomen and groin), which work as filters for germs. When the lymph nodes cells recognize a foreign agent, they become activated, replicate and seek for the infection. As an immune response, these nodes become inflamed so doctors usually check them to see if there is an infection.
Nevertheless, 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.
Sometimes a failure in the immune system may occur. In these cases, the immune system is not able to distinguish what is nonself (foreign) from what is self. Consequently, instead of fighting against external agents, it attacks its own cells and tissues.
This process is known as autoimmunity and is part of the so-called autoimmune diseases such as lupus, rheumatoid arthritis, myositis or a simple allergy. Although the causes of autoimmune diseases are unknown, science has developed medicines, which help fight them.
The role of science
The immune system is strong and is made to protect humans. However, it may fail. This is why science has been used to improve the quality of life of human beings. Thus, medications such as methotrexate, which blocks specific steps of the immune process, can be used against autoimmune diseases.
There are also antibiotics, which disable or kill specific bacteria and help the immune system fight off external agents. This also means that an antibiotic used for skin bacteria will not work for stomach bacteria.
In fact, taking the wrong antibiotic can lead to antibiotic resistance, which means that it will not work in the future. For this reason, medical supervision is important as well as to take the antibiotic as prescribed.
On the other hand, vaccines are a scientific aid for the immune system to prepare for future attacks. They contain part of the germs, which trick the immune system into thinking that it has already fought the disease. This is one of the most effective tools for preventing diseases.
Although scientists have learned much about the immune system, the way the body responds to foreign attacks is still being studied. With the help of technology, it has been possible to understand the role of all white blood cells. This will be of great help in combating future viruses, bacteria and fungi, which may appear in the world.