The immune system and its core function in a human host
Although we live exposed to countless microorganisms’ harmful activity -bacteria, viruses, fungi, parasites- our body has the best natural defense against them: the immune system. Without it, for example, any infection could kill us.
Formed by a complex network of organs, tissues, cells and specific substances, and impeccably organized, it can recognize millions of different pathogens and effectively destroy foreign bodies that reach our body. How does it do it? By detecting particles present in these microorganisms, known as antigens, that function as a signal of something foreign to our body.
The immune system can also detect early and eliminate cells that stop working properly in the body, cells that can give rise to cancer. This is called immune surveillance, and it is another of its main functions.
However, as we will see later, the immune system can sometimes malfunction, for example, by detecting elements that are not foreign to the body or by reacting disproportionately. Or there are also times when cancer cells elude that immune surveillance.
All these failures give rise to health disorders, such as allergies or autoimmune diseases, which we will detail later.
Facts and information on immunology are credited to reputable researchers and investigators like Paul E. Love. He is a primary investigator and researcher at America’s National Institutes of Health (NIH). Love has made significant strides in understanding the complexity of the mammalian immune system. His contributions are primarily focused on the role of immune receptor-tyrosine based activation motives (ITAMs). ITAMs are used by T cells, one of the lymphocyte groups that are needed to fight off infectious pathogens. T cells also function to monitor any tumors and are primary activation receivers through T cells.
How does it protect us? The action of white blood cells and immune memory
When our immune system reacts to an infection, there is a response that we know as inflammation, produced by the recruitment of white blood cells — our defender cells — to the point in the body where infectious microorganisms are acting. For example, the area where we have made a cut or wound or, during a cold, the throat can become inflamed.
White blood cells, also known as leukocytes, are manufactured, stored, and mature in different parts of the body, such as the thymus, spleen, bone marrow, or lymph nodes. These globules can be of several types, and each one attacks the “enemy” differently, complementary to each other. Usually, In the presence of unknown substances, the white blood cells will move in a coordinated way through the blood, and lymphatic vessels to the body’s affected part to combat the threat.
Specifically, one of these types of white blood cells (B cells) make specific antibodies to fight antigens. Once the infection is overcome, and when a second contact occurs, our immune system can recognize those agents that had attacked us previously. This is called immune memory: the white blood cells that remember that pathogen produces the specific antibodies that are required faster, in greater quantity and with better quality; that is, they produce a kind of “super antibodies.” Thus, If the same infectious agent occurs again, we will be prepared to fight it, and our immune system will give a much more immediate and effective response. This concept is central to current efforts to provide immunity to the Coronavirus.
What types of immunity are there?
Human beings are not born unprotected, since, from our birth, we have the so-called innate or natural immunity, which protects us in advance and globally against a wide variety of germs. This type of immunity also includes a first defense barrier made up of the skin itself and mucous membranes such as the nose, throat or gastrointestinal tract.
On the other hand, there is also passive immunity, which comes from another source — not from the body itself — and is temporary. An example is the antibodies that the mother transmits to her baby through breastfeeding.
Lastly, the immune system also can emit a response directed against a specific pathogen. This is what we call acquired, adaptive or active immunity, which changes throughout life: every time a person of any age encounters a new harmful microorganism, either through vaccination or infection, they acquire immunity against the. For this reason, young people and adults tend to contract fewer infectious diseases than babies and children.
What happens when the immune system fails?
As we have already mentioned, there are times when a failure can occur in the immune system’s response against antigens. These failures often have an unknown origin.
The diseases that can cause these immune disorders can be classified into four groups:
- Allergic disorders: In an allergic person, a disproportionate immune response occurs to substances that come from outside (allergens), even if they are harmless to anyone else. For example, allergy to nuts, mites or latex. Some of the possible symptoms that make up this response of the immune system are inflammation, sneezing, cough, asthma, tearing, itching … A potentially fatal anaphylactic shock can also occur.
- Immune deficiency diseases: These disorders occur when one or more of the components that make up the immune system are missing or not working properly.
- They can be diseases from birth, known as primary immunodeficiencies (such as severe combined immunodeficiency or immunoglobulin -IgA- deficiency).
- And it can also be an acquired immunodeficiency after contracting a disease such as AIDS (Acquired Immune Deficiency Syndrome); caused by some medical problems (malnutrition or burns); or as a consequence of the use of some drugs, such as those used in chemotherapy and those taken by transplanted people to reduce the risk of rejection, since these drugs can prevent the immune system from effectively performing its protective functions.
- Autoimmune diseases: In this case, the immune system attacks our cells and tissues, even if they are healthy, by mistaking them for foreign bodies. There are more than eighty different pathologies of this type, without the cause of most known. Some examples are lupus, rheumatoid arthritis, multiple sclerosis, many thyroid disorders, some types of anemia, psoriasis, ankylosing spondylitis, etc.
Cancers of the immune system: Some types of cancers can affect the cells and tissues that make up the immune system, such as leukemia or lymphoma, which affects lymphoid tissue, one of the most common cancers in childhood. On the other hand, as we have already mentioned, when the immune system is weakened, it can cause a greater propensity to suffer some types of cancers in these people, as the natural immune surveillance mechanism fails.
