Sinh học - Chapter 43: Warm up

Chapter 43 Warm-UpDefine the following terms:PathogenAntigenAntibodyAllergenVaccineWhat are lymphocytes? Where do B cells and T cells mature?Ch. 43 Review Warm-UpWhat is the difference between innate vs. adaptive immunity?Contrast the functions of B cells and T cells.How are antigens recognized by immune system cells? What are memory cells?How does HIV affect the immune system?THE IMMUNE SYSTEMChapter 43What you must know:Several elements of an innate immune responseThe differences between B and T cells relative to their activation and actions.How antigens are recognized by immune system cellsThe differences in humoral and cell-mediated immunityWhy Helper T cells are central to immune responsesTypes of ImmunityInnate ImmunityAdaptive Immunity Non-specific All plants & animals Pathogen-specific Only in vertebrates Involves B and T cellsPlant DefensesNonspecific responsesReceptors recognize pathogen molecules and trigger defense responsesThicken cell wall, produce antimicrobial compounds, cell deathLocalize effectsPathogens(such as bacteria,fungi, and viruses)INNATE IMMUNITY(all animals)• Rapid responseRecognition of traits sharedby broad ranges ofpathogens, using a smallset of receptors•Recognition of traits specific to particularpathogens, using a vastarray of receptors•• Slower responseBarrier defenses:SkinMucous membranesSecretionsInternal defenses:Phagocytic cellsNatural killer cellsAntimicrobial proteinsInflammatory responseHumoral response:Antibodies defend againstinfection in body fluids.Cell-mediated response:Cytotoxic cells defendagainst infection in body cells.ADAPTIVE IMMUNITY(vertebrates only)Figure 43.2Barrier Defenses:SkinMucous membranesLysozyme (tears, saliva, mucus)Inflammatory Response:Mast cells release histamineBlood vessels dilate, increase permeability (redness, swelling)Deliver clotting agents, phagocytic cellsFeverPhagocytic WBCs:Neutrophils (engulf)Macrophage (“big eaters”)Eosinophils (parasites)Dendritic cells (adaptive response)Natural Killer Cells:Virus-infected and cancer cellsAntimicrobial Proteins:Interferons (inhibit viral reproduction)Complement system (~30 proteins, membrane attack complex)Innate Immunity(non-specific)PhagocytosisInflammatory ResponseLymphatic System: involved in adaptive immunityAdaptive ResponseLymphocytes (WBCs): produced by stem cells in bone marrowT cells: mature in thymushelper T, cytotoxic TB cells: stay and mature in bone marrowplasma cells  antibodiesAntigen: substance that elicits lymphocyte responseAntibody (immunoglobulin – Ig): protein made by B cell that binds to antigensMajor Histocompatibility Complex (MHC)Proteins displayed on cell surfaceResponsible for tissue/organ rejection (“self” vs. “non-self”)B and T cells bind to MHC molecule in adaptive responseClass I: all body cells (except RBCs)Class II: displayed by immune cells; “non-self”Origin of Self-ToleranceAntigen receptors are generated by random rearrangement of DNAAs lymphocytes mature in bone marrow or the thymus, they are tested for self-reactivitySome B and T cells with receptors specific for the body’s own molecules are destroyed by apoptosis, or programmed cell deathThe remainder are rendered nonfunctional© 2011 Pearson Education, Inc.Proliferation of B Cells and T CellsIn the body there are few lymphocytes with antigen receptors for any particular epitopeIn the lymph nodes, an antigen is exposed to a steady stream of lymphocytes until a match is madeThis binding of a mature lymphocyte to an antigen initiates events that activate the lymphocyte© 2011 Pearson Education, Inc.Once activated, a B or T cell undergoes multiple cell divisionsThis proliferation of lymphocytes is called clonal selectionTwo types of clones are produced: short-lived activated effector cells that act immediately against the antigen and long-lived memory cells that can give rise to effector cells if the same antigen is encountered again© 2011 Pearson Education, Inc.Humoral Immune Response(antibodies)Cell-Mediated Immune Response(T Cells)Antigen-presenting cellHelper T cellB cellCytotoxic T cellPlasma cellInfected cellAntibodiesIdentify and destroytag for destructionImmunological MemoryPrimary immune response: 1st exposure to antigenMemory cells:Secondary immune response: repeat exposure  faster, greater responseAntigenAntigenreceptorAntibodyPlasma cellsMemory cellsB cells thatdiffer inantigenspecificityFigure 43.14Concept 43.3: Adaptive immunity defends against infection of body fluids and body cellsAcquired immunity has two branches: the humoral immune response and the cell-mediated immune responseIn the humoral immune response antibodies help neutralize or eliminate toxins and pathogens in the blood and lymphIn the cell-mediated immune response specialized T cells destroy affected host cells© 2011 Pearson Education, Inc.Helper T Cells: A Response to Nearly All AntigensA type of T cell called a helper t cell triggers both the humoral and cell-mediated immune responsesSignals from helper T cells initiate production of antibodies that neutralize pathogens and activate T cells that kill infected cellsAntigen-presenting cells have class I and class II MHC molecules on their surfaces© 2011 Pearson Education, Inc.Class II MHC molecules are the basis upon which antigen-presenting cells are recognizedAntigen receptors on the surface of helper T cells bind to the antigen and the class II MHC molecule; then signals are exchanged between the two cellsThe helper T cell is activated, proliferates, and forms a clone of helper T cells, which then activate the appropriate B cells© 2011 Pearson Education, Inc.Figure 43.16Antigen-presentingcellPathogenAntigen fragmentClass II MHC moleculeAccessory proteinAntigen receptorHelper T cellCytokinesHumoralimmunityCell-mediatedimmunityB cellCytotoxic T cell321Cytotoxic T Cells: A Response to Infected CellsCytotoxic T cells are the effector cells in the cell-mediated immune responseCytotoxic T cells recognize fragments of foreign proteins produced by infected cells and possess an accessory protein that binds to class I MHC moleculesThe activated cytotoxic T cell secretes proteins that disrupt the membranes of target cells and trigger apoptosis© 2011 Pearson Education, Inc.Figure 43.17-3Cytotoxic T cell312AccessoryproteinClass I MHCmoleculeInfectedcellAntigenreceptorAntigenfragmentPerforinPoreGran-zymesReleasedcytotoxicT cellDyinginfected cellB Cells and Antibodies: A Response to Extracellular PathogensThe humoral response is characterized by secretion of antibodies by B cellsActivation of the humoral immune response involves B cells and helper T cells as well as proteins on the surface of pathogensIn response to cytokines from helper T cells and an antigen, a B cell proliferates and differentiates into memory B cells and antibody secreting effector cells called plasma cells© 2011 Pearson Education, Inc.Figure 43.18-3Pathogen312Antigen-presentingcellAntigenfragmentClass IIMHCmoleculeAntigenreceptorAccessoryproteinHelper T cellB cellCytokinesActivatedhelper T cellMemory B cellsPlasma cellsSecretedantibodiesAntibody FunctionAntibodies do not kill pathogens; instead they mark pathogens for destructionIn neutralization, antibodies bind to viral surface proteins preventing infection of a host cellAntibodies may also bind to toxins in body fluids and prevent them from entering body cells© 2011 Pearson Education, Inc.In opsonization, antibodies bind to antigens on bacteria creating a target for macrophages or neutrophils, triggering phagocytosisAntigen-antibody complexes may bind to a complement protein—which triggers a cascade of complement protein activationUltimately a membrane attack complex forms a pore in the membrane of the foreign cell, leading to its lysis© 2011 Pearson Education, Inc.Figure 43.19OpsonizationNeutralizationAntibodyVirusBacteriumMacrophageActivation of complement system and poreformationComplement proteinsFormation of membraneattack complexFlow of waterand ionsPoreAntigenForeigncellB cells can express five different forms (or classes) of immunoglobulin (Ig) with similar antigen-binding specificity but different heavy chain C regionsIgD: Membrane boundIgM: First soluble class producedIgG: Second soluble class; most abundantIgA and IgE: Remaining soluble classes© 2011 Pearson Education, Inc.Immunizations/vaccines: induce immune memory to nonpathogenic microbe or toxinPassive immunity: via antibodies in breast milkAllergies: hypersensitive responses to harmless antigensAutoimmune Diseases:Lupus, rheumatoid arthritis, Type I diabetes, multiple sclerosisHIV: infect Helper T cellsAIDS = severely weakened immune systemImmune RejectionCells transferred from one person to another can be attacked by immune defensesThis complicates blood transfusions or the transplant of tissues or organs © 2011 Pearson Education, Inc.Blood GroupsAntigens on red blood cells determine whether a person has blood type A (A antigen), B (B antigen), AB (both A and B antigens), or O (neither antigen)Antibodies to nonself blood types exist in the bodyTransfusion with incompatible blood leads to destruction of the transfused cellsRecipient-donor combinations can be fatal or safe© 2011 Pearson Education, Inc.Tissue and Organ TransplantsMHC molecules are different among genetically nonidentical individualsDifferences in MHC molecules stimulate rejection of tissue grafts and organ transplantsChances of successful transplantation increase if donor and recipient MHC tissue types are well matchedImmunosuppressive drugs facilitate transplantationLymphocytes in bone marrow transplants may cause the donor tissue to reject the recipient© 2011 Pearson Education, Inc.Figure 43.22IgEAllergenHistamineGranuleMast cellThe next time the allergen enters the body, it binds to mast cell–associated IgE moleculesMast cells release histamine and other mediators that cause vascular changes leading to typical allergy symptomsAn acute allergic response can lead to anaphylactic shock, a life-threatening reaction, within seconds of allergen exposure© 2011 Pearson Education, Inc.Autoimmune DiseasesIn individuals with autoimmune diseases, the immune system loses tolerance for self and turns against certain molecules of the bodyAutoimmune diseases include systemic lupus erythematosus, rheumatoid arthritis, insulin-dependent diabetes mellitus, and multiple sclerosis© 2011 Pearson Education, Inc.Exertion, Stress, and the Immune SystemModerate exercise improves immune system functionPsychological stress has been shown to disrupt immune system regulation by altering the interactions of the hormonal, nervous, and immune systemsSufficient rest is also important for immunity© 2011 Pearson Education, Inc.Immunodeficiency DiseasesInborn immunodeficiency results from hereditary or developmental defects that prevent proper functioning of innate, humoral, and/or cell-mediated defensesAcquired immunodeficiency develops later in life and results from exposure to chemical and biological agentsAcquired immunodeficiency syndrome (AIDS) is caused by a virus© 2011 Pearson Education, Inc.LatencySome viruses may remain in a host in an inactive state called latencyHerpes simplex viruses can be present in a human host without causing symptoms© 2011 Pearson Education, Inc.Attack on the Immune System: HIVHuman immunodeficiency virus (HIV) infects helper T cellsThe loss of helper T cells impairs both the humoral and cell-mediated immune responses and leads to AIDSHIV eludes the immune system because of antigenic variation and an ability to remain latent while integrated into host DNA© 2011 Pearson Education, Inc.LatencyAIDSHelper T cellconcentrationYears after untreated infectionHelper T cell concentration(in blood (cells/mm3)Relative anti-HIV antibodyconcentrationRelative HIVconcentration8006004002000012345678910Figure 43.25People with AIDS are highly susceptible to opportunistic infections and cancers that take advantage of an immune system in collapse The spread of HIV is a worldwide problemThe best approach for slowing this spread is education about practices that transmit the virus© 2011 Pearson Education, Inc.Cancer and ImmunityThe frequency of certain cancers increases when adaptive immunity is impaired20% of all human cancers involve virusesThe immune system can act as a defense against viruses that cause cancer and cancer cells that harbor virusesIn 2006, a vaccine was released that acts against human papillomavirus (HPV), a virus associated with cervical cancer© 2011 Pearson Education, Inc.