Immune System Chapter 18

What is its function? PROTECTION FROM INVADERS! Three Lines of Defense: Innate Immunity- born with it! 1. Barrier Defenses – BROAD 2. Internal Cellular Defenses - BROAD 3. Acquired Immunity –develops only after exposure to a SPECIFIC pathogen!

Barrier Defenses / 1st line of defense The Skin and Mucous Membranes Physical barriers; trap microbes Secrete substances (oil, sweat, etc.) that makes the skin too acidic (pH= 3-5) for microbes to live there. Also secrete lysozyme, an enzyme that can destroy bacterial cell walls (in saliva, mucous secretions, & tears.) INNATE=you’re born with it!

2. Internal Cellular Defenses If an invader gets inside the body, the internal defenses (2nd line of defense!) take over A) Phagocytes (“to eat”/”cell”) White blood cells that “eat”/engulf invaders NEUTROPHILS-most numerous phagocyte MONOCYTES BECOME MACROPHAGES (can patrol lymphatic system/ spleen, lymph nodes for pathogens) EOSINOPHILS- phagocytize parasitic invaders Invaders (bacteria/virus/etc) are then digested by lysosomes.

2. Internal Cellular Defenses B) Antimicrobial Proteins Interferon = “Warning Protein” sent out by virus infected cells. Other body cells then make other substances to inhibit viral replication. Complement System- 30 proteins w/ variety of functions. Many lyse invaders.

2. Internal Celluar Defenses C) Inflammatory Response Damage to tissue (from physical injury or the entry of pathogens) leads to inflammation Histamine (signal molecule) is released by basophyls & mast cells (leukocytes). This causes increased vasodilation & & increased permeability of capillaries. (Clotting factors, platelets, phagocytes, etc. diffuse into interstitial fluid to help REPAIR) Redness, edema, & increased temperature occur.

2. Internal Cellular Defenses D) Natural Killer (NK) Cells- Patrol the body and attack virus-infected cells and cancer cells Surface receptors (“nametags”) identify these infected/damaged cells All 4 of these internal defenses (phagocytes, interferons, inflammatory response, and natural killer cells) occur INNATELY.

3. Acquired Immunity Acquired immunity is the third line of defense. Acquired immunity only comes after EXPOSURE to a specific pathogen. Receptor proteins in cell membrane provide pathogen-specific recognition. Acquired immunity occurs more slowly than innate immunity.

3. Acquired Immunity Acquired immunity is performed by lymphocytes Made from stem cells in the bone marrow B-cells: mature in the bone marrow T-cells: mature in the thymus

3. Acquired Immunity Antigen = foreign molecule that is recognized by lymphocytes and causes them to respond An antigen is usually a surface marker (“nametag”) Lymphocytes Have antigen receptors (100,000 on each cell!) that recognize a SPECIFIC antigen by shape SPECIFIC!!

3. Acquired Immunity B-lymphocytes are responsible for the humoral immune response They are responsible for pathogens OUTSIDE of cells (in body fluids, etc.) B-lymphocyte is “activated” when specific antigen binds to its receptors. Activated B-lymphocytes reproduce using clonal selection in order to destroy the invader

3. Acquired Immunity These B-lymphocytes produce two types of cloned cells: Effector cells (Plasma Cells) Make antibodies! Special proteins that bind onto the ANTIGENS of the “invaders,” which flags them for destruction (usually by macrophages) Memory cells These cells live a long time, and can respond quickly if this same antigen is seen again

3. Acquired Immunity T-lymphocytes are responsible for the cell-mediated immune response Guard against invaders hiding out inside infected cells A) Cytotoxic T cells They are the effectors (“hit men”) of the cell-mediated immune response by lysing infected cells or “punching holes” in the membrane They kill infected body cells (display foreign antigens on Major Histocompatability Complex (MHC) or other cells that don’t belong (like tumors) Class I MHCs = on almost all body cells except RBCs. Class II MHCs= made by dendritic cells, macrophages, & B cells. Some of these cells will become memory cells, so they can be reactivated if the pathogen “strikes again.”

Cytotoxic T Cells & MHC

Acquired Immunity B) Helper T Cells When activated by binding to MHC protein of an antigen presenting cell, Helper T-cells secrete cytokines (like interleukin) which stimulate & activate B cells & Cytotoxic-T cells. “Master Switch of acquired immunity” HIV destroys Helper T cells, and shuts down both humoral & cell-mediated immunity!

Primary v. Secondary Immune Response Primary Response Upon first exposure to an antigen, the immune response is delayed for several days while plasma cells are being formed Secondary Response If antigen is seen again, the next response is quicker and more potent because of memory cells

The Immune System Key Features of the Immune System Specificity Recognizes SPECIFIC invaders – species of bacteria, for example Due to ANTIGENS dispayed on the MHC (Major Histocompatibility Complex) Diversity The immune system can respond to millions of different invaders because it has so many different lymphocytes “on reserve”

The Immune System Key Features of the Immune System Memory The immune system can “remember” antigens it’s seen before and react more quickly the second, third, etc. time it sees them Acquired immunity Because of memory cells (B & T cells)! Self/Nonself Recognition The immune system can distinguish between the body’s own molecules from foreign molecules Autoimmune disorders (example: lupus, MS, rheumatoid arthritis) means that this part of the immune system is not working – the immune system destroys the body’s own tissues

Passive vs. Active Immunity Passive Immunity Transferring antibodies from one person to another, without the B-lymphocytes having to make them! The person will already have the memory cells and antibodies, so the next response will be quicker! Example: Pregnant mother passes antibodies to her fetus through the placenta Antibodies in breast milk Immunoglobulins (antibodies) may be given to a person who is exposed to a disease to prevent them from getting the disease.

Passive vs. Active Immunity Immunity to a specific pathogen that comes after having come in contact with the pathogen. Can come naturally Been sick with the pathogen before Example: had measles before, 2nd time won’t take as long to respond Can come artificially Immunization (weakened or dead form of the pathogen is used to induce immune response.) Edward Jenner - smallpox Stimulates B-lymphocytes to make antibodies AND memory cells

Allergies Allergies are hypersensitivies of the immune system to an environmental molecule because of its ANTIGENS Anaphylactic shock Life-threatening allergic reactions to ingested or injected allergens Peanuts, shellfish, bee stings, etc.