Specific Immune Response

Overview of the Immune System

• One of the purposes of the immune system is to protect the body against micoorganisms such as viruses. When viruses enter the body, they invade individual cells, take over the cell and use the cell's own machinery to produce more viruses.
• The immune system activates immune cells to destroy the invader. This activation of the immune system involves two main types of cells: B cells and T cells. B cells make antibodies, molecules that attach to and neutralize viruses floating free in the bloodstream, thereby preventing the viruses from infecting other cells. T cells can be helper cells or killer cells. Helper T cells organize the immune response. Killer T cells (known as CTLs) attack cells infected by viruses.
• Microorganisms such as viruses contain many molecules that are seen as foreign to the body. These different molecular shapes are called antigens, or epitopes. The B cells and T cells are activated by recognizing these antigens. Each individual T cell or B cell will only recognize and respond to its individual "destiny antigen".
• Once a T cell or B cell is activated by its destiny antigen, the B or T cell clones itself, making many duplicate copies of itself. Some of these cloned T cells attack and destroy cells infected by the invading virus. Other cloned B or T cells remain in the body as memory cells.
• If the body is re-invaded by the virus in the future, the memory cells will be reactivated and respond faster and more powerfully to destroy the virus. This is the principle behind vaccines, such as the vaccinations we received in childhood against measles or mumps.