Pre-AP Biology Chapter 40-2 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

Inflammatory response

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

Yellow objects are killer T cells attaching cancer cell (SEM)

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 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