国外动物学35.PPT

国外动物学35 Still waters run deep.流静水深流静水深,人静心深人静心深 Where there is life,there is hope。有生命必有希望。有生命必有希望The Immune SystemlAn animal must defend itself from the many dangerous pathogens it may encounter in the environment.The Immune SystemlA host is susceptible to a parasite if it cant eliminate a parasite before it becomes established.lThe parasite is infective.lThe host is resistant if it is able to prevent establishment of the parasite.lThe parasite is noninfective.The Immune SystemlImmune cells,red blood cells,and other white blood cells are derived from multipotential stem cells in the bone marrow.The Immune SystemlLymphocytes arise from stem cells in the bone marrow.lNewly formed lymphocytes are all alike,but they later develop into B cells or T cells,depending on where they continue their maturation.The Immune SystemlAs B and T cells are maturing in the bone marrow and thymus,their antigen receptors are tested for possible self-reactivity.lLymphocytes bearing receptors for antigens already present in the body are destroyed by apoptosis or rendered nonfunctional.The Immune SystemlTwo major kinds of immunity have evolved that counter these invaders:lInnate immunitylAcquired immunityInnate ImmunitylInnate immunity is present before any exposure to pathogens and is effective from the time of birth.lInvolves nonspecific responses to pathogens.Acquired ImmunitylAcquired immunity develops only after exposure to inducing agents such as microbes,toxins,or other foreign substances.lInvolves a very specific response to pathogens.A Summary of Innate and Acquired ImmunityExternal DefenseslIntact skin and mucous membranes form physical barriers that block the entry of microorganisms and viruses.lCertain cells of the mucous membranes produce mucus-a viscous fluid that traps microbes and other particles.External DefenseslIn the trachea,ciliated epithelial cells sweep mucus and any entrapped microbes upward,preventing the microbes from entering the lungs.External DefenseslSecretions from the skin give the skin a pH between 3 and 5,which is acidic enough to prevent colonization of many microbes.lAlso include proteins such as lysozyme,an enzyme that digests the cell walls of many bacteria.Internal Cellular and Chemical DefenseslInternal cellular defenses depend mainly on phagocytosis.lPhagocytes are types of white blood cells that:lIngest invading microorganisms.lInitiate the inflammatory response.Phagocytic CellslPhagocytes attach to their prey via surface receptors and engulf them,forming a vacuole that fuses with a lysosome.Phagocytic CellslMacrophages,a specific type of phagocyte,can be found migrating through the body.lAlso found in various organs of the lymphatic system.The Lymphatic SystemlThe lymphatic system plays an active role in defending the body from pathogens.Antimicrobial ProteinslNumerous proteins function in innate defense by attacking microbes directly or by impeding their reproduction.Antimicrobial ProteinslAbout 30 proteins make up the complement system,which can cause lysis of invading cells and help trigger inflammation.lInterferons provide innate defense against viruses and help activate macrophages.Inflammatory ResponselIn local inflammation,histamine and other chemicals released from injured cells promote changes in blood vessels that allow more fluid,more phagocytes,and antimicrobial proteins to enter the tissues.Natural Killer CellslNatural killer(NK)cells patrol the body and attack virus-infected body cells and cancer cells.lTrigger apoptosis(programmed cell death)in the cells they attack.Acquired ImmunitylAcquired immunity is the bodys second major kind of defense.lInvolves the activity of lymphocytes.Acquired ImmunitylAn antigen is any foreign molecule that is specifically recognized by lymphocytes and elicits a response from them.lA lymphocyte actually recognizes and binds to just a small,accessible portion of the antigen called an epitope.Antigen Recognition by LymphocyteslThe vertebrate body is populated by two main types of lymphocytes which circulate through the blood:lB lymphocytes(B cells)lT lymphocytes(T cells)B Cell Receptors for AntigenslB cell receptors bind to specific,intact antigens.lY-shaped:two identical heavy chains&two identical light chains.lVariable regions at the tip provide diversity.T Cell Receptors for Antigens and the Role of the MHClEach T cell receptor consists of two different polypeptide chains.lThe variable regions form the antigen binding site and provide a diversity of T cells.VVCCT Cell Receptors for Antigens and the Role of the MHClT cells bind to small fragments of antigens that are bound to normal cell-surface proteins called MHC molecules.lMHC molecules are encoded by a family of genes called the major histocompatibility complex.T Cell Receptors for Antigens and the Role of the MHClInfected cells produce MHC molecules which bind to antigen fragments and then are transported to the cell surface in a process called antigen presentation.lA nearby T cell can then detect the antigen fragment displayed on the cells surface.T Cell Receptors for Antigens and the Role of the MHClDepending on their source,peptide antigens are handled by different classes of MHC molecules.T Cell Receptors for Antigens and the Role of the MHClClass I MHC molecules,found on almost all nucleated cells of the body,display peptide antigens to cytotoxic T cells.T Cell Receptors for Antigens and the Role of the MHClClass II MHC molecules,located mainly on dendritic cells,macrophages,and B cells,display antigens to helper T cells.Clonal Selection of LymphocyteslIn a primary immune response,binding of an antigen to a mature lymphocyte induces the lymphocytes proliferation and differentiation,a process called clonal selection.Clonal Selection of LymphocyteslClonal selection of B cells generates a clone of short-lived activated effector cells and a clone of long-lived memory cells.lEffector cells produce antibodies for a specific antigen.Clonal Selection of LymphocyteslIn the secondary immune response,memory cells facilitate a faster,more efficient response.Humoral vs.Cell-Mediated ResponselAcquired immunity includes two branches:lThe humoral immune response involves the activation and clonal selection of B cells,resulting in the production of secreted antibodies.lThe cell-mediated immune response involves the activation and clonal selection of cytotoxic T cells.Humoral vs.Cell-Mediated ResponselThe roles of the major participants in the acquired immune response.Helper T Cells:A Response to Nearly All AntigenslHelper T cells produce CD4,a surface protein that enhances their binding to class II MHC moleculeantigen complexes on antigen-presenting cells.lActivation of the helper T cell then occurs.The Role of Helper T Cells in Acquired ImmunitylActivated helper T cells secrete several different cytokines(protein hormones)that stimulate other lymphocytes.Cytotoxic T Cells:A Response to Infected Cells and Cancer CellslCytotoxic T cells make CD8-a surface protein that greatly enhances the interaction between a target cell and a cytotoxic T cell.The Role of Helper T Cells in Acquired ImmunitylCytotoxic T cells bind to infected cells,cancer cells,and transplanted tissues.lBinding to a class I MHC complex on an infected body cell activates a cytotoxic T cell and differentiates it into an active killer.The Role of Helper T Cells in Acquired ImmunitylThe activated cytotoxic T cell secretes proteins that destroy the infected target cell.B Cells:A Response to Extracellular PathogenslActivation of B cells is aided by cytokines and antigen binding to helper T cells.lThe clonal selection of B cells generates antibody-secreting plasma cells,the effector cells of humoral immunity.Antibody ClasseslA secreted antibody has the same Y-shaped structure as a B cell receptor,but isnt anchored in the cell membrane.lThe five major classes of antibodies differ in their distributions and functions within the body.Antibody-Mediated Disposal of AntigenslThe binding of antibodies to antigens is also the basis of several antigen disposal mechanisms.lLeads to elimination of microbes by phagocytosis and complement-mediated lysis.Active and Passive ImmunizationlActive immunity develops naturally in response to an infection.lCan also develop following immunization,also called vaccination.Active and Passive ImmunizationlIn immunization,a nonpathogenic form of a microbe or part of a microbe elicits an immune response to an immunological memory for that microbe.Active and Passive ImmunizationlPassive immunity,which provides immediate,short-term protection,is conferred naturally when IgG crosses the placenta from mother to fetus or when IgA passes from mother to infant in breast milk.lCan be conferred artificially by injecting antibodies into a non-immune person.Distinguishing Self from NonselflThe immune system can wage war against cells from other individuals.lTransplanted tissues are usually destroyed by the recipients immune system.Blood Groups and TransfusionslCertain antigens on red blood cells determine whether a person has type A,B,AB,or O blood.lAntibodies to nonself blood types already exist in the body.lTransfusion with incompatible blood leads to destruction of the transfused cells.Blood Groups and TransfusionslAnother red blood cell antigen,the Rh factor creates difficulties when an Rh-negative mother carries successive Rh-positive fetuses.Tissue and Organ TransplantslMHC molecules are responsible for stimulating the rejection of tissue grafts and organ transplants.lThe chances of successful transplantation are increased if the donor and recipient MHC tissue types are well matched and if the recipient is given immunosuppressive drugs.Disrupting the BalancelIf the delicate balance of the immune system is disrupted,the effects on the individual can range from minor to often fatal consequences.AllergieslAllergies are exaggerated(hypersensitive)responses to certain antigens called allergens.lIn localized allergies such as hay fever,IgE antibodies produced after first exposure to an allergen attach to receptors on mast cells.AllergieslThe next time the allergen enters the body,it binds to mast cellassociated IgE molecules.lThe mast cells then release histamine and other mediators that cause vascular changes and typical symptoms.AllergieslAn acute allergic response sometimes leads to anaphylactic shock a whole-body,life-threatening reaction that can occur within seconds of exposure to an allergen.Autoimmune DiseaseslIn individuals with autoimmune diseases,the immune system loses tolerance for self and turns against certain molecules of the body.Autoimmune DiseaseslRheumatoid arthritis is an autoimmune disease that leads to damage and painful inflammation of the cartilage and bone of joints.Autoimmune DiseaseslOther examples of autoimmune diseases include:lSystemic lupus erythematosuslMultiple sclerosislInsulin-dependent diabetesImmunodeficiency DiseaseslAn inborn or primary immunodeficiency results from hereditary or congenital defects that prevent proper functioning of innate,humoral,and/or cell-mediated defenses.Immunodeficiency DiseaseslAn acquired or secondary immunodeficiency results from exposure to various chemical and biological agents.Stress and the Immune SystemlGrowing evidence shows that physical and emotional stress can harm immunity.Acquired Immunodeficiency Syndrome(AIDS)lPeople with AIDS are highly susceptible to opportunistic infections and cancers that take advantage of an immune system in collapse.Acquired Immunodeficiency Syndrome(AIDS)lBecause AIDS arises from the loss of helper T cells,both humoral and cell-mediated immune responses are impaired.lThe loss of helper T cells results from infection by the human immunodeficiency virus(HIV).