Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsOverview: Reconnaissance, Recognition, andResponse• An animal must defend itself from the manydangerous pathogens it may encounter• Two major kinds of defense have evolved: innateimmunity and acquired immunityCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Innate immunity is present before any exposure topathogens and is effective from the time of birth• It involves nonspecific responses to pathogens• Innate immunity consists of external barriers plusinternal cellular and chemical defenses• Key internal defenses are macrophages and otherphagocytic cellsLE 43-13 µmCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Acquired immunity, or adaptive immunity,develops after exposure to agents such asmicrobes, toxins, or other foreign substances• It involves a very specific response to pathogens• Recognition is by white blood cells calledlymphocytes• Some lymphocytes produce antibodies; othersdestroy infected cells, cancer cells, or foreigntissueLE 43-2Invadingmicrobes(pathogens)External defensesSkinMucous membranesSecretionsINNATE IMMUNITYRapid responses to abroad range of microbesACQUIRED IMMUNITYSlower responses tospecific microbesInternal defensesPhagocytic cellsInflammatory responseHumoral response(antibodies)Antimicrobial proteinsNatural killer cellsCell-mediated response(cytotoxiclymphocytes)Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsConcept 43.1: Innate immunity provides broaddefenses against infection• A pathogen that breaks through external defensesencounters innate cellular and chemicalmechanisms that impede its attackCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsExternal Defenses• Skin and mucous membranes are physicalbarriers to entry of microorganisms and viruses• Mucous membrane cells produce mucus, aviscous fluid that traps microbes and otherparticles• In the trachea, ciliated epithelial cells sweepmucus and any entrapped microbes upward,preventing microbes from entering the lungsLE 43-310 µmCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Secretions of the skin and mucous membranesprovide an environment hostile to microbes• Secretions give the skin a pH between 3 and 5,acidic enough to prevent colonization of manymicrobes• Skin secretions include proteins such aslysozyme, which digests bacterial cell wallsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsInternal Cellular and Chemical Defenses• Internal cellular defenses depend mainly onphagocytosis• White blood cells called phagocytes ingestmicroorganisms and initiate inflammationCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsPhagocytic Cells• Phagocytes attach to prey via surface receptorsand engulf them, forming a vacuole that fuses witha lysosomeLE 43-4PseudopodiaMicrobesMACROPHAGELysosomecontainingenzymesVacuoleCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Macrophages, a type of phagocyte, migratethrough the body and are found in organs of thelymphatic system• The lymphatic system defends against pathogensLE 43-5AdenoidTonsilLymphnodesPeyer’s patches(small intestine)SpleenAppendixLymphaticvesselsLymphnodeMasses oflymphocytes andmacrophagesLymphaticvesselBloodcapillaryTissuecellsLymphaticcapillaryInterstitialfluidCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsAntimicrobial Proteins• Proteins function in innate defense by attackingmicrobes directly or impeding their reproduction• About 30 proteins make up the complementsystem, which causes lysis of invading cells andhelps trigger inflammation• Interferons provide innate defense against virusesand help activate macrophagesCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsInflammatory Response• In local inflammation, histamine and otherchemicals released from injured cells promotechanges in blood vessels• These changes allow more fluid, phagocytes, andantimicrobial proteins to enter tissuesLE 43-6PathogenPinChemical signalsCapillaryPhagocytic cellsMacrophageRed blood cellBloodclottingelementsBlood clotPhagocytosisCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsNatural Killer Cells• Natural killer (NK) cells attack virus-infected bodycells and cancer cells• They trigger apoptosis in the cells they attackCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsInvertebrate Immune Mechanisms• Many invertebrates defend against infection bymany of the same mechanisms in the vertebrateinnate responseCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsConcept 43.2: In acquired immunity, lymphocytesprovide specific defenses against infection• Acquired immunity is the body’s second major kindof defense• An antigen is a foreign molecule that is recognizedby lymphocytes and elicits a response from them• A lymphocyte recognizes and binds to a smallportion of the antigen called an epitopeLE 43-7Antigen-bindingsitesEpitopes(antigenicdeterminants)Antibody AAntibody BAntibody CAntigenCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsAntigen Recognition by Lymphocytes• Two main types of lymphocytes circulate in theblood of vertebrates: B lymphocytes (B cells) andT lymphocytes (T cells)• A single B cell or T cell has about 100,000identical antigen receptors• All antigen receptors on a single cell recognize thesame epitopeCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsB Cell Receptors for Antigens• B cell receptors bind to specific, intact antigens• Secreted antibodies, or immunoglobulins, arestructurally similar to B cell receptors but lacktransmembrane regions that anchor receptors inthe plasma membraneLE 43-8Antigen-bindingsiteDisulfidebridgeLightchainVVCCCCVVAntigen-binding siteVariable regionsConstant regionsTransmembraneregionAntigen-binding siteCVCVPlasmamembraneT cellβ chainα chainDisulfide bridgeCytoplasm of T cellA T cell receptor consists of one αchain and one β chain linked by adisulfide bridge.A B cell receptor consists of two identical heavychains and two identical light chains linked byseveral disulfide bridges.Heavy chainsCytoplasm of B cellB cellCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsT Cell Receptors for Antigens
View Full Document
Unlocking...