The immune system is the set of cells and glands that protects the body from invasion and infection by viruses, bacteria, and other pathogens. The immune system must be able to recognize any foreign target, or antigen, of which there are potentially millions. Pathogenic organisms change over time, and new antigens evolve that must also be targeted. At the same time, the immune system must distinguish pathogenic antigens from the body's own tissues, attacking the former and sparing the latter. The key to the scope and specificity of the immune system response is in the genes that give rise to it.

Overview of the Immune System

The immune system includes several interacting components. Nonspecific immunity (protection against any invasion) is provided by the barriers of the skin and mucous membranes lining the lungs and gut. Additional non-specific defenses are provided by the inflammatory response...