Transcript B cells
IMMUNE SYSTEM Chapter 24 THE KISSING DISEASE The Epstein-Barr virus (EBV) is one of the most common human viruses No vaccine to prevent or an effective treatment Antibiotics are ineffective against viruses Can only get once because the body develops immunity to it During childhood symptoms are mild and often unnoticeable, but causes mononucleosis or mono in newly infected teens and adults Recognizes and fights pathogens, infectious agents that cause disease Acquired immunity backs up innate immunity to form an immune system which limits infections in animals INNATE IMMUNITY First line of defense against potential invaders Respond the same whether invader is novel or not Invertebrates Sole defense is external and internal barriers Exoskeleton, lysozymes to digest cell walls, immune cells to phagocytize foreign invaders, and recognition proteins Vertebrates Coexists with acquired immunity VERTEBRATE DEFENSES External to prevent Skin and mucus membranes protect systems exposed to external environments E.g. nostril hairs to filter particles from the air and respiratory tract mucus to trap those it misses, and cilia to move them up and out Internal fight after infection occurs WBC’s found in interstitial fluid and blood vessels E.g. neutrophils and macrophages phagocytic and wander interstitial fluid ‘eating’ bacteria; natural killer cells release chemicals to promote cell death COMPLEMENT PROTEIN SYSTEM Enhances innate immune responses About 30 different proteins present in an inactive form in the blood at all times Activated by surface receptors of microbes which creates a trigger cascade to activate other proteins Leads to lysing of invaders Some help trigger inflammation response INFLAMMATORY RESPONSE Triggered by any damage to a tissue From microorganisms to insect bites and scratches Seen with improperly treated cuts, also responsible for sore throats Triggering the response Damaged cells release a chemical signal such as histamine Induces nearby blood vessels to dilate and leak Blood flow to the area increases producing the redness, heat, and swelling Other chemicals attract phagocytes Purpose to disinfect and clean injured tissue Engulf bacteria, damaged or dead body cells, and dead WBC’s Pus is dead WBC’s and fluid from leaking capillaries Prevents spreading of infection via clotting proteins and platelets TAKING INFLAMMATION ON THE ROAD Inflammation response can be local, as just described, or widespread (systemic) Once entering the bloodstream, microbes can be carried throughout the body Several responses occur Elevated WBC count is one indicator Fever or abnormally high body temperature Triggered by toxins or macrophages and can stimulate phagocytosis and speed tissue repair Septic shock, an overwhelming inflammatory response Very high fever and low blood pressure Common cause of death in critical care hospital units LYMPHATIC SYSTEM Involved in innate and acquired immunity Includes numerous structures, vessels, and cells Circulates lymph which is similar to interstitial fluid, but with less O2 and fewer nutrients Main functions: Return tissue fluid to circulatory system Lymph drains to veins in chest Vessels have valves to prevent backflow and depend mainly on skeletal muscles to move fluid (like veins) Fight infections Carries invaders to lymphatic organs to be engulfed by permanent macrophage residents (innate of acquired response) Cause lymph nodes to swell from number of cells ACQUIRED IMMUNITY Second line of defense for when innate response fails Only in vertebrates and is active only AFTER exposure to pathogens Varies between individuals depending on exposure Highly specific defense so acts against only 1 agent Can amplify innate responses like inflammation and the complement system Obtained by natural exposure or through vaccinations FIGHTING THE INVADERS Antigens are the foreign molecules responsible for eliciting these responses Molecules from pathogens or other particles such as viruses, bacteria, mold spores, or transplanted organs Body remembers antigens previously exposed to Body responds to antigen presence by: Increasing cells to attack the invader Producing immune proteins called antibodies which attach to specific antigens to counter its’ effects Response is usually quick enough to attack and destroy before symptoms occur; its adaptive Exposure enhances future responses to the same agent VACCINATIONS Exposure to harmless variants, inactivated toxins, or dead/weakened microbes to stimulate the immune system Almost eliminated numerous viral diseases Resulting immunity from antigen exposure, naturally or artificially, is active immunity E.g. polio, smallpox, mumps and measles Body actively produces antibodies Receiving premade antibodies is passive immunity When travelers go to foreign countries or treatment of a snakebite with antivenom Temporary results because body isn’t stimulated by antigens, the immunity ends once antibodies are gone LYMPHOCYTES WBC’s that reside in tissues and organs of the lymphatic system Responsible for acquired immune responses Originate from stem cells in bone marrow Remain and become B cells Move to the thymus and become T cells Both eventually to spleen and other organs Work to form a dual defense Humoral immune response Cell-mediated immune response IMMUNE RESPONSE TYPES Humoral Secretion of B cells into blood and lymph Defends against bacteria and viruses in body fluids (outside cells) Passively transferred via blood plasma containing antibodies from immune to nonimmune individuals Defensive proteins responsible Cell-Mediated Produced by T cells Attack body cells infected with bacteria or viruses Promote phagocytosis by other WBC’s Stimulating B cells to make antibodies Defensive cells responsible PRODUCTION OF B CELLS AND T CELLS Certain genes are turned on in developing cells Synthesizes proteins to be incorporated onto the PM called antigen receptors which bind specific antigens All receptors on a single cell are identical B cells to the particular antibody it produces ANTIGEN AND ANTIBODY BINDING Antigens don’t usually belong to the host animal Proteins or polysaccharides on foreign cell surfaces Antibodies bind to an antigenic determinant or epitope of an antigen E.g parts of capsules, bacterial cell walls, and macromolecules on the surface of other organisms Complementary shapes on both facilitate it Antigens possess several determinants so multiple antibodies can bind Single antigens can stimulate production of multiple types of antibodies HUMORAL RESPONSE WEAPONS B cells secrete antibodies (proteins) Made of 2 heavy chains and 2 light chains Functions to: Recognize and bind certain antigens (light chains) Assist in neutralizing the antigen it recognizes (heavy chains) Antigen-binding site varies in shape to enable it to react to any antigen Tail for disposal and groups them into 1 of 5 major classes of antibodies Differ in body location and function ELIMINATING ANTIGENS Antibodies must be able to mark invaders Form an antigen-antibody complex held by weak bonds Actual binding of antibodies trigger destruction called effector mechanisms Specific recognition-and-attack phase followed by a nonspecific destruction phase Blocks viral binding sites Attach and poke holes in the PM=lysis Group cells Group dissolved molecules T CELL TYPES Respond to antigens on cell surfaces = infection inside cells Cytoxic T cells attack body cells infected with pathogens Helper T cell roles are multifaceted, and interact with WBC’s that function as antigenpresenting cells Interaction activates helper T cells to activate other cells of immune system Macrophage ingests a microbe o Self-proteins bind microbe pieces = nonself molecules o Helper T recognizes selfnonself complex o Activating Helper T Cells Has 2 binding sites oActivates Helper T which promotes the immune response o Only T cells that actually kill infected cells o Identify infected cells like Helper T cells o Binding activates so new proteins produced o Produce holes in cell membrane o Enzymes enter to promote apoptosis o Cytotoxic T Cells ALLERGIES Hypersensitive responses to antigens in our surroundings Allergens are antigens that cause allergies Feces of tiny mites in dust and animal dander (shed skin cells) Bed Bugs (Cimex lectularius) Dog/cat allergies commonly to saliva proteins deposited on fur Symptoms from 2 stage reaction Sensitization Allergic response Reactions can vary Anaphylactic shock when allergens make mast cells release inflammatory chemicals suddenly Blood vessels dilate so blood pressure drops rapidly Epinephrine injections can counter ALLERGIC REACTIONS Allergen enters bloodstream and binds B cells B cells proliferate and secrete lots of antibodies Attach to mast cells which produce histamine for inflammatory response Allergen enters body and bind to antibodies on mast cells Releases histamine to trigger symptoms Antihistamines interfere with and so provide relief