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The Immune System The Body’s Defense • Pathogens are everywhere. • We stay healthy because our body has defenses to keep pathogens out. • The immune system fights infection through the production of cells that inactivate unwanted cells • A lymphocyte engulfing an invader Nonspecific Defenses fight or defend against any pathogen First line of defense: – – – – Skin Mucus Sweat Tears Second line of defense: inflammatory response fever interferons (fight viruses) Specific Defenses guard against certain invaders • When a pathogen gets past the body’s nonspecific defenses, the immune system attacks. • The antigen (invader) triggers the immune response. • Future attacks will be met by memory cells Organs of the Immune System Humoral Immunity-B cells • B lymphocytes (B cells) provide immunity against antigens and pathogens in body fluids • B cells recognize invader and produce large numbers of plasma cells and memory B cells • Plasma cells release antibodies – Antibodies are proteins that recognize & bind to antigens – As antibodies overcome infection, plasma cells die off and stop producing antibodies – Memory B cells remain in blood stream so they can make plasma cells immediately if ever exposed to the same pathogen again Cell Mediated Immunity-T Cells • Killer T cells track down and destroy bacteria, fungi, protists, or other foreign tissue. – Primary defense against the body’s own cells when they have become cancerous or infected by pathogens • Helper T cells produce memory T cells. • Memory T cells will attack if the same pathogen ever returns. • Suppressor T cells shut down the killer T cells when the infection is under control. HIV attacks T cells • HIV (Human Immunodeficiency Virus) attacks the body’s T cells. • The immune system is disabled. • Victim is not able to fight infection • HIV eventually causes AIDS Vaccines • Edward Jenner invented first vaccine in 1769 – Injected boy with cowpox virus (weak similar virus to smallpox) – Later injected with deadly smallpox virus. • Boy had immunity to the virus • Vaccines are weakened or “killed” virus or bacteria pathogen. • The body responds by creating an immunity to the pathogen (antibodies)