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)