Immune System Pre-AP Biology Chapter 40-2 Immune System Overview • Function: fight infection through the production of [specialized] cells that inactivate foreign substances or cells • It is main defense against pathogens ▫ Recognizes, attacks, destroys, and “remembers” each type of pathogen that enters the body • 2 general categories: ▫ Nonspecific defenses (fortress walls of the body) ▫ Specific defenses (security guards of the body) Nonspecific Defenses • First line of defense: skin ▫ Most important nonspecific defense! ▫ Very few pathogens can penetrate the skin Must have an opening – a cut, scratch, mouth, nose ▫ Mucus, saliva, and tears have lysozyme – enzyme that breaks down bacteria’s cell wall ▫ Oil and sweat glands produce acidic environment ▫ Mucus and cilia in nose and throat trap and push pathogens away from lungs ▫ Acid and enzymes destroy bacteria that make it to your stomach Nonspecific Defenses • Second line of defense: inflammatory response ▫ Reaction to tissue damage caused by injury/infection ▫ When pathogens are detected: White blood cells flood area through blood vessels near wound Many WBC are phagocytes – engulf and destroy Releases chemicals that increase core body temperature (fever) Many pathogens only survive in narrow temp. range Increased temp also increases heart rate = more WBC Nonspecific Defense to Viruses • Sometimes, virus-infected cells produce a group of proteins that help other cells resist infection: Interferons ▫ Named this because they “interfere” with growth of the virus ▫ Slows the progress of infection and gives specific defense system time to respond Specific Defenses • Called “immune response” • Triggered by antigens • 2 types of lymphocytes ▫ B lymphocytes (B cells) – work in body fluids Humoral immunity ▫ T lymphocytes (T cells) – work in living cells Cell-mediated immunity Humoral Immunity • B cells detect pathogen and multiply rapidly ▫ Produces large numbers of plasma cells and memory B cells • Plasma cells release antibodies (proteins that recognize and bind to antigens – recall blood types!) ▫ Antibodies carried in the blood stream to attack • Memory B cells remain capable of producing antibodies specific to that pathogen after exposure Antibody Structure • Antibody is shaped like a “Y” and has two identical antigen binding sites ▫ Differences in amino acids affect shape of binding sites ▫ Shape of binding site is how antibody recognizes antigen ▫ Healthy adult can produce about 100 million different types of antibodies! Cell-Mediated Immunity • Primary defense against own cells when cancerous or infected • Also important for fighting fungi and protists • Process: T cells divide and differentiate into… ▫ Killer T cells – destroy bacteria, fungi, protozoan or foreign tissue with the antigen ▫ Helper T cells – produce memory T cells ▫ Suppressor T cells – shut down killer T cells after pathogenic cells brought under control ▫ Memory T cells – cause response if same antigen enters again Transplants • Killer T cells make organ transplants difficult ▫ Recognize new organ as foreign and attack it Called “rejection” ▫ To prevent rejection, donor should have cell markers nearly identical to recipient; and ▫ Recipient usually takes drugs for the rest of their life to suppress cell-mediated immune response. Acquired Immunity • Remember Jenner’s smallpox?? ▫ Cowpox infection to create immunity to smallpox • Can be active or passive Active vs. Passive Immunity Active Passive • Type of immunity produced by reaction to a vaccine • Vaccination: injection of weakened or mild form of pathogen • Stimulate immune system to create plasma cells • Plasma cells are ready to make specific antibodies • Appears AFTER exposure • Can be natural or deliberate • Antibodies produced by other animals injected into the bloodstream • Lasts for short time – body eventually destroys them • Can be natural or deliberate • Natural: from mother to fetus or in breastmilk • Deliberate: vaccine ▫ Tropical diseases ▫ Rabies