The immune system is the body’s defense system which is constantly protecting us from the foreign particles which enter our body. The Immune System is the name of a collection of molecules, Cells and organs whose complex interactions form an efficient system that is usually able to protect an individual from both outside invaders and its own altered internal cells.
In most cases, the immune system does a great job of keeping people healthy and preventing infections. But sometimes problems with the immune system can lead to illness and infection. When a baby is born, its immune system is poorly developed, as it has not been exposed to the pathogens around it. Substances such as Lactoferrin and MSM in the mother's milk are important elements in building the new system and preparing it for a germ filled world.
Two body features which are not normally associated with the Immune System also serve important functions: the Skin, and the Mucosa. While it seems elementary, the importance of Skin in resisting infection can not be overlooked. It is the location at which most Micro-organisms are stopped. The less effective, but close cousin of the skin is the Mucosa: the tissue which covers our eyes, alimentary and genital & urinary tracts.
There are two types of cells that serve the Immune system namely B Cells and T Cells. T-Cells are responsible for destroying infected or cancerous cells, and for coordinating all acquired immune responses. B-Cells are the generators of humeral immunity, so called because it consists of soluble proteins found in the "Humors" (Blood).
The Human Biology site has a complete description about the immune system and ill effects of reduced immunity.
