The immune system covers all the defenses that the body uses to protect itself from environmental aggressions. These attacks can come from the outside environment, such as infections by pathogenic microorganisms, or from the inside environment, such as cancer cells. Like most biological systems, the main function of the immune system is to maintain homeostasis (i.e. ideal stability) within the body.
Immunology is the science that studies the structures, functions and mechanisms of action of the immune system.
The immune system is not composed of organs in the proper sense of the word. However, the spleen, bone marrow, lymph nodes and tonsils harbor immune cells. In terms of its functional structure, the immune system consists of innate immune defenses and adaptive immune defenses.
Innate immunity exists in plants and all animals and includes non-specific defense mechanisms. These are physical barriers (skin), chemical barriers (saliva or milk enzymes) or biological barriers (commensal flora), inflammatory mechanisms and cells capable of ingesting and destroying pathogens.
On the other hand, adaptive immunity exists only in vertebrates. Specific to the pathogens encountered by the system, this immunity leads to the development of an immune memory allowing the induction of a very rapid and very strong response during a second contact with a given pathogen. This characteristic is the basis for the functioning of vaccines. Certain white blood cells, lymphocytes, confer this adaptive immunity. B lymphocytes produce antibodies. T lymphocytes help destroy pathogens and cancer cells. B and T lymphocytes are also the basis of immune memory. These memory cells are activated during vaccination.
Like all systems, the immune system aims to guarantee a certain homeostasis (a stable environment) within the body. However, this homeostasis can be disturbed by external pathogens (viruses, bacteria, parasites) that seek to infect the body. It can also be harmed by the uncontrolled development of cancer cells. This is then an internal disturbance of the organism.
The immune system possesses the unique property of discriminating what belongs to the body, which is called “the self”, from what is foreign to it, also called “the non-self”. This property allows it to recognize pathogens and cancer cells and to initiate a series of mechanisms to eliminate them. During a transplant, this mechanism of recognition of tissue foreign to the organism is at the root of the phenomenon of rejection.
The immune system may have malformations. These can be of genetic origin and can lead to more or less significant deficiencies in certain parts of the immune system. These deficiencies lead to a decrease in responses and therefore to a greater or lesser susceptibility to attacks by pathogens. This is known as “immunosuppression”.
Other types of immune system disease lead to an increase in its activation. The immune system then begins to react against the body’s cells (autoimmune diseases), or against harmless compounds such as certain allergens (allergies).
It is currently believed that certain deformities of the immune system can also be acquired during the body’s development. The immune system differentiates itself during embryo development and continues to mature in young children. Some hypotheses hold that the environment (in the broad sense) around pregnant women and infants can change the programming of the developing immune system. These changes in programming obviously influence the homeostasis of the system and could be the basis for the rise of autoimmune diseases and allergies in the twentieth century.
One of the most common ways to help the immune system in the elimination of different pathogens (viruses, bacteria, parasites) is through vaccination. During vaccination, a harmless part of a pathogen (antigen) is injected into an organism in order to induce a first response and especially a memory against this antigen. When the vaccinated organism comes into contact with the pathogen, it will develop a new immune response, this time stronger and faster, which in turn will allow it to eliminate the pathogen before it causes damage to the organism.
Another way to help the immune system is to inject some of its components. This is known as immunotherapy. After a snake bite or during an infection with toxin-producing bacteria (diphtheria, botulism), the doctor can, for example, inject antibodies that will directly neutralize venoms and toxins.
Having a healthy daily lifestyle is another, more individual way to help the immune system.
