The skin is the body’s largest organ and provides incredible protection against infections. Despite its efficiency, some external agents still manage to get inside the body. These agents are recognised by the immune system as foreign (non-self) and potentially dangerous (responsible for illnesses and infections). Therefore, they must be eliminated.
The immune system is our best natural defense system against illness: it fights viruses, bacteria, fungi and parasites.
As soon as they enter the body, agents deemed as foreign to the body (known as antigens) are attacked by the immune system’s cells and organs: the natural defenses. This immune reaction involves:
- So-called lymphoid organs: red bone marrow, lymph nodes, the spleen and the thymus.
- Cells like leukocytes (white blood cells), lymphocytes and phagocytic cells from lymphoid organs.
Generally, when a foreign agent is detected by the immune system, an immediate elimination reaction is triggered. This reaction involves phagocytic cells and lymphocytes that are constantly circulating the body. This reaction is fast and non-specific, i.e. the immune system attacks the antigen without knowing what it is. This type of reaction results in inflammation, the clinical signs of which are the appearance of redness, pain and heat.
Depending on the severity of the infection, this rapid and non-specific immune reaction may not be enough to eliminate the foreign agent. A second, slower and more specific reaction will then take place: this involves the recognition of the foreign agent by the immune cells, which takes place in the lymph nodes in particular. Following recognition, these immune cells, which are specifically adapted to the destruction of the foreign agent (lymphocytes), will multiply rapidly in the lymphoid organs. Afterwards, the body keeps a record of this encounter with the foreign agent (thanks to B lymphocytes). We call this the immunological memory. This optimises the specific immune response so that it is faster the next time the body encounters the same foreign agent. This is the principle of vaccination whereby pathogenic (safe) foreign agents are inoculated. The immune system learns to fight against them and, by remembering them, will be able to get rid of them quickly when they are encountered for real.