Immune System Notes: Part I

Immune System Notes: Part I The body protects itself by using three lines of defense… I. 1st Line of Defense: Non-specific body defenses A. Surface membrane barriers  Skin has keratin filled cells used as barriers  Sweat and vaginal secretions are acidic(pH of 3-5)  Saliva and tears have an enzyme called lysozyme which kills bacteria by breaking down the cell walls of bacteria  Sticky mucous in nose and throat trap invaders and cilia sweeps them up to be coughed or sneezed out  Gastric juice of the stomach kills most microbes II.2nd Line of Defense: Cells and Chemical Defenses A. Non-specific cells  Phagocytes are white blood cells (leukocytes) that engulf pathogens by phagocytosis. Monocytes (which become macrophages) and neutrophils wander through the circulatory system using amoeboid motion  As they wander, they engulf viruses and bacteria, produce vacuoles to hold the viruses and bacteria, and then fuse the vacuoles with a lysosome (a sac of enzymes that kills bacteria).  Cells called Natural Killer cells also wander around and attack foreign cells by producing a toxin that disintegrates the invader’s cell membrane and causes the cell to lyse (These cells are not specific to their targets) B. Inflammation  Injured cells release inflammatory chemicals such as histamine (vasodilator, except in the lungs). This creates heat and redness because of increased blood flow  Kinins are chemicals that are also released and they activate pain receptors to cause pain and swelling  Chemotaxis then occurs which attracts phagocytes to the area Steps involved in inflammation: 1. Neutrophils enter the area and engulf pathogens and cell debris 2. Monocytes follow and become macrophages within 8- 12 hours (they engulf many more cells than neutrophils) 3. Clotting proteins (fibrinogen and thromboplastin) leak into the area and build a wall of fibrin around the inflamed area so pathogens don’t spread 4. Sometimes the third line of defense comes into play (I’ll talk about that later.) 5. Sometimes, macrophages don’t fully cleanse the area and an abscess of pus is formed. This pus must be drained before healing can occur. Pus = pathogens, dead or dying neutrophils, and broken down tissues C. Chemicals  Complement – a group of 20 or more plasma proteins that are activated when an antigen enters the body a. complement attaches to the antigen when it enters the body b. complement forms holes in the invader c. water leaks out of the invader and the cell lyses d. this may initiate inflammation because activation of complement causes release of vasodilators and chemotaxis chemicals  Interferon – (viruses must enter cells to do their work) a protein produced by a viral infected cell to be released and bind to nearby cell receptors to prevent infection even further  Fever – when macrophages attack invaders, they release pyrogens in the process and this “turns up” the body heat a. excessive fever may denature enzymes b. mild fevers denature bacterial enzymes, and deprive them of iron because the liver gathers up iron during a fever c. fever speeds up cell repair activities

III.3rd line of defense: Developing immunity through the use of antigens and antibodies See Handout on Humoral (Antibody-mediated) immunity! Proteins of the Immune System

Antibodies – (aka Immunoglobulins or Igs)  Produced naturally in our bodies and are found on the surface of B Cells (lymphocytes)  Y shaped protein  Each has a specific receptor site on it’s surface called a combining site (concave shape)  Each antibody has a complimentary antigen that fits like a lock and key with the antibody  Produced in response to only one antigen

Antigens – (Ag) Foreign substances such as proteins, pollen, bacteria or viruses  Usually found on the cell surfaces of invading cells  Have a specific receptor site, called an epitope, that fits with the antibody  Self antigens are normally present in our bodies and lymphocytes do not recognize these  Foreign antigens are called non-self antigens

Major Histocompatability Complex (MHC)-  Collection of glycoproteins (protein and carbohydrate) that exist on the membrane of all body cells  Only identical twins carry the same set of MHC molecules White Blood Cells of the Immune System Lymphocytes –

B-lymphocytes – known as the antibody producers  Lymphoid stem cells produce immature lymphocytes (occurs before birth and is completed a few months after birth)  Immature B cells produce antibodies while still in the bone marrow and insert these antibodies into their cell membranes (genes determine this)  Antibody bearing B cells enter the blood stream and travel to the lymph nodes, spleen and liver  They are now immunocompetent

T-lymphocytes – known as the cell mediators  Lymphoid stem cells produce lymphocytes and send them to the thymus gland  In the thymus gland, T cells develop antibodies over a period of 2-3 days, and display them on their cell surface (These antibodies fit with only one type of antigen)  The cells are now immunocompetent, before they even meet the antigen (genetic)  T cells travel to the lymph nodes, liver, and spleen to live and fight antigens  T cells take on different roles o Killer T cells (aka cytotoxic T cells) inject toxins into the foreign cells and the cell ruptures o Helper T cells produce interleukins (communication chemicals between leukocytes) to stimulate killer T cells and tell B cells to divide and form antibodies o Suppressor T cells suppress the helper T cells and the killer T cells to prevent unnecessary immune activity

Phagocytes - Neutrophils Monocytes (which become macrophages) (These are non-specific)