What is the Immune System?

The immune system is the body's natural system of the innate and adaptive defenses, in charge of providing resistance to diseases.

In the innate system, the first barriers, the skin and associated mucus membranes keep invading microorganisms out of the body via a number of protective mechanisms.

For example, skin is both acidic and contains various bactericidal chemicals to inhibit bacterial growth and elements like mucus-coated hairs in the nose trap inhaled particles to prevent passage through the nasal passages.

Although these surface barriers are rather effective, when they are compromised, the second line of internal defense is activated.

Now, phagocytic cells such as macrophages and mast cells, along with other non-specific cells and chemicals are in charge. They mount an inflammatory response to prevent the spread of infection.

The third line of defense, the adaptive system, responds by employing specific cells called lymphocytes to precisely destroy the infectious agent themselves or through circulating antibodies.

However, before such protection can be provided, the system must be primed, that is it must have previously encountered the foreign substance, forming a memory to produce a stronger attack.