Immune System Genetics

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 and the complement proteins in the bloodstream. We shall not deal further with these defenses.

Specific immunity is the set of defenses mounted against a specific invader. It involves the action of three major types of cells: B cells, T cells, and macrophages. In broad, somewhat oversimplified terms, B cells make proteins called antibodies that attach to foreign antigens, serving as warning flags. T cells coordinate the immune attack and destroy virus-infected cells. Macrophages consume flagged antigens and clean up the debris from a T cell attack on infected cells.

An antibody binds to an invader when its shape fits some shape (the antigen) on the invader's surface. Any particular invader, such as a bacterial cell, may have dozens of such antigens.