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Download line of defense - De Anza College
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Our body has several lines of defense The body’s defenses virus antibody Dead Keratinized Skin Cells 1st line of defense: External barriers–Skin 1st line of defense: External barriers Dead Keratinized Epidermal Cells Sweat has enzymes (“lysozymes”) that digest bacteria Sebaceous glands (around hair) secrete oil (“sebum”) that is acidic Keratin is a durable, waterproof protein Secretions from sebaceous glands & sweat glands kill microbes on skin 1st line of defense: External barriers The 2nd line of defense Gastric Juice pH ~2.0 Acidic Gastric Juices Protect One of the Main Body Entrances Bio 11 (De Anza) - Schinske Act when an invader penetrates the body’s external barriers Nonspecific – combats all invading microbes Depend on white blood cells and defensive proteins. White Blood Cells (cells that fight infection) 1 The 2nd line of defense The 2nd line of defense: protective proteins Infected cells send “warnings” to neighboring cells Phagocytes Ingest (“Eat”) Invaders Proteins called Interferons tell other cells to prepare for attack–to produce substances that interfere with viral reproducton http://www.youtube.com/watch?v=PXUNEJkjQt4&feature=related The 2nd line of defense How do NK cells know which cells to kill? Key to Immunity: Recognizing self vs. non-self NK Cell Attacks If: • Cell has no HLA proteins • Cell has different HLA proteins Natural Killer (NK) cells: WBCs that destroy cells infected with viruses and cancer cells Granules release chemicals that break down the target cell’s membranes and burst the cell NK cell is unharmed, looks for other abnormal cells NK cells are one of our main natural defenses against cancer Like wearing uniforms for identification HLA = Protein markers on cell surfaces Your HLA proteins are unique to you, just like your fingerprints & DNA! Another defense mechanism: Inflammation Even though cancer cells start from our own body cells, they make strange HLA proteins. NK cells recognize and force cancer cells to commit suicide! Abnormal HLA proteins Poison oak on the hand Bio 11 (De Anza) - Schinske Any type of tissue injury triggers the inflammatory response Sx: Redness, warmth, swelling and pain 2 Inflammation brings defenses & repairs to a specific area What happens when you cut your finger? Need Help Here! Phagocytes engulf bacteria Tissue heals Like Putting Up Signs & Opening Gates to Attract Help Responding cells eat microbes & release histamine Histamine makes vessels leaky to bring nutrients & more defenses to area = swelling, redness Antihistamines (ex. Benadryl) block effects of histamine Recap: 1st line of defense External barriers Protective proteins: “Complement” Plasma proteins that automatically assemble, create holes in the membrane of bacteria and cause them to burst Physical barriers Chemical barriers 2nd line defenses Bacteria Viruses Inflammation phagocytes Complement Bio 11 (De Anza) - Schinske NK cells Secretions - inhibit growth of microbes Specific immunity requires special forces B cells and T cells 3 Fighting the Invaders B cells The specific defenses Special weapon: antibodies Target: bacteria and viruses T cells A large number of cells work together to respond to a specific microbe or foreign invader Helper T cells Cytotoxic (or “killer”) T cells Memory cells Target: infected cells, some cancer cells and transplanted tissue X Example: E. coli 0157 Two properties Specificity for a particular foreign (non-self) Memory for previously encountered invaders molecule The immune system can react more promptly to a second exposure to infection. Copyright 2009, John Wiley & Sons, Inc. B-cells Specific Antibody-mediated Defenses response T-cells Recognizing the invaders Cell mediated response Digests Pathogen • Displays its Proteins Macrophages engulf invaders and display information about them to other defense cells Type of WBC Recognizes Display Antigens = any foreign particles Secretes antibodies Kills Infected Cells Helper T Cells Initiate Specific Attacks Scouts Cytotoxic T Cells Stimulated by Helper T Cells Each helper T cell recognizes a different antigen. Over a billion different types of T Cell receptors in our bodies! (Antigens = any foreign particles) Attack infected body cells Send signals to cytotoxic T cells and B cells Bio 11 (De Anza) - Schinske 4 T-cells T cell defenses Cell mediated response Digests Pathogen • Displays its Proteins 1st step B-cells B cell defenses Antibody-mediated response Activated B Cells Produce Antibodies Activates 2nd Recognizes Display step Secretes antibodies Kills Infected Cells Antibodies eliminate specific invaders (antigens) Y-shaped proteins that bind a particular foreign molecule (antigen) Specific Memory T Cells & B Cells respond if a familiar invader returns Familiar Invader Antigen Immediately divide into active cytotoxic T cells Immediately divide into active helper T cells Immediately divide into plasma cells Specific immunity: Abs 1:01 http://www.youtube.com/watch?v=Ys_V6FcYD5I&NR=1 Definitions Antigens Antibodies mark foreign cells for phagocytosis Are foreign substances that trigger an immune response Most are pathogens Antibodies Are proteins made by our body that attack one particular foreign invader (or antigen) Antibody immune response 0:53 (no narration) http://www.youtube.com/watch?v=lrYlZJiuf18&feature=fvw Bio 11 (De Anza) - Schinske 5 Antibodies inactivate bacteria and viruses In-class exercise Compare and contrast the roles of B cells and cytotoxic (killer) T cells in our immune defenses. How are they similar? How are they different? Differences in the response of B cells and T cells? Role of helper T cells B cells secrete antibodies that inactivate foreign invaders APC Sends signal s The specific defenses Specificity for foreign molecules (antigens) Memory for previously encountered “invaders” The immune system can react more promptly to a second exposure to infection. Bio 11 (De Anza) - Schinske Cell-mediated immunity Autoimmune diseases “Special forces” of B and T cells work together to respond to a specific microbe or foreign invader. Two properties T cells circulate in the blood and lymph, attacking infected body cells Antibodymediated The immune response Antibody-mediated immunity Due to loss of self-tolerance The immune system attacks the person’s own tissues Examples Type 1 diabetes - T cells attack the insulinproducing pancreatic beta cells Multiple sclerosis (MS) - T cells attack myelin sheaths around axons of neurons 6 Memory: How vaccinations work Test your understanding Vaccines trigger the immune reaction, stimulating the body to defend itself and create memory B and T cells. What makes a secondary immune response faster than a primary immune response? It takes a week or two for B and T cells to be formed during the primary response. In a secondary response, preexisting memory cells can respond more quickly. Copyright 2009, John Wiley & Sons, Inc. How does the body respond to a viral infection? The common cold A contagious viral disease of the upper respiratory track Primarily caused by rhinoviruses The most common infectious disease in humans Cold viruses live only in the nose Inflammatory response This increases mucus secretion NK cells attack virus-infected cells Virus-infected cells also produce interferon Interferon stimulates healthy cells to make antiviral proteins Bio 11 (De Anza) - Schinske First line of defense – external barriers mucous membranes of the nose Cold viruses attach to cells lining the nasopharynx The virus is taken into the cell, where it starts an infection 3rd line of defense Specific immune responses 2nd line of defense The major entry point for the virus is the nose The host's immune system effectively deals with the cold virus. The B cells begin producing antibodies that bind to the virus and prevent it from infecting cells. 7 Specific immune responses Infected cells display viral antigens on their surface If a cytotoxic T cell recognizes a viral fragment there, it will destroy the infected cell How does the body respond to a viral infection? External barriers Skin, mucous membranes, secretions The first responders Specific responses B cells produce antibodies to the virus NK cells Interferon Helper T cells Rhinovirus Cytotoxic T cells attack virus-infected cells Inflammation HIV Infects Helper T Cells Helper T Cell Why is HIV so lethal? Replicated HIV Budding Off From Cell HIV infects and kills helper T Cells How does this impact the body’s immune responses? X X X X Antibodymediated AIDS HIV cripples both antibody- and T cell-mediated immunity. AIDS is a worldwide epidemic that kills millions of people each year. Bio 11 (De Anza) - Schinske 8
