What is the role of our immune system?

The immune system is a network of cells that organise themselves to defend our body against external organisms, such as microbes. This defence is carried out by directly eliminating the aggressor with specific cells (white blood cells) that swallow the intruder or that produce different defence substances such as antibodies (synonymous with immunoglobulins), enzymes, cytokines, or antimicrobial peptides. In some situations, this defence can even keep the "memory" of the infection, and thus respond more effectively to other similar infections. It is this principle of memory of the immune system that is used during vaccination and protects us from bacteria, viruses and other microorganisms, such as parasites and fungi.

How is the immune system formed?

The immune system exists in all living beings and is formed by two levels of immune defence that have a complementary role.

The first level of immune defence, innate immunity, is formed by tissues that make a barrier such as the skin or mucous membranes and immunity cells, such as certain white blood cells (polymorphonuclear cells and monocytes). The role of this immunity is to eliminate the microbe by digesting it and by causing an inflammatory reaction. The constituents of this inflammatory reaction (enzymes, free radicals, cytokines) contribute to the elimination of the intruder. Once digested, the debris of the microbe will be used to accurately activate the cells (lymphocytes) of the second level of immune defence. Innate immunity is immediately effective but it does not give rise to immunological memory.

The second level of immune defence, adaptive immunity, is specific and relies on white blood cells called T and B lymphocytes. These lymphocytes, once educated, specifically recognise the aggressor or its debris, then respond appropriately to remove any intruders that have survived the action of the first level of immune defence. Each aggressor is then eliminated by the action of T lymphocytes and by the action of antibodies produced by B lymphocytes. During the first encounter with the aggressor, the lymphocyte response is quite slow compared to the innate immunity response which is more immediate. However, in the case of a next aggression, the lymphocyte response is much faster, more intense and more lasting because the lymphocytes have kept the memory of the aggressor. It is this memory that protects us after a vaccination.