Chapter 37 Immunity Sections 7-12

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Chapter 37ImmunitySections 7-12
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37.7 Overview of Adaptive Immunity

• Vertebrate adaptive immunity adapts to different
  antigens an individual encounters during its
  lifetime
• Lymphocytes and phagocytes interact to effect
  four defining characteristics self/nonself
  recognition, specificity, diversity, and memory

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4 Characteristics of Adaptive Immune Responses

• Self/Nonself recognition is based on the ability
  of T cell receptors to recognize self (MHC)
  markers TCRs and other antigen receptors
  recognize nonself, in the form of antigen
• Specificity means the adaptive immune response
  can be tailored to combat specific antigens

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4 Characteristics of Adaptive Immune Responses

• Diversity refers to the billions of different
  antigen receptors that a persons B and T cells
  can make
• Memory refers to the capacity of the adaptive
  immune system to remember an antigen the
  second time an antigen shows up, the response is
  faster and stronger

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Two Arms of Adaptive Immunity

• Antibody-mediated immune response
• B cells produce antibodies that bind to specific
  antigen particles in blood or interstitial fluid
• Cell-mediated immune response
• Cytotoxic T cells and NK cells detect and destroy
  infected or altered body cells

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Antigen Processing

• Once a B or T cell recognizes and binds to a
  specific antigen, it begins to divide by mitosis
• All descendent cells recognize the same antigen
• T cells do not recognize an antigen unless it is
  presented by an antigen-presenting cell
• Macrophages, B cells, and dendritic cells digest
  particles and display antigen-MHC complexes

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Antigen Processing
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lysosome
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MHC molecule
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Intercepting Antigen

• A dendritic cell or macrophage migrates to a
  lymph node, where it presents antigen to T cells
• The T cell secretes cytokines, which signal other
  B or T cells with the same antigen receptor to
  divide and differentiate
• Effector cells are differentiated B and T cells
  that act at once to fight infection
• Memory cells are long-lived B and T cells
  reserved for future encounters with the same
  antigen

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Clearing Out Antigen

• Effector cells destroy most antigen-bearing
  agents
• Antibodyantigen complexes form large clumps that
  are quickly cleared from the blood by the liver
  and spleen
• Complement proteins assist in the cleanup

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memory cells
memory cells
B or T cell
effector cells
effector cells
primary immune response
secondary immune response
second exposure
first exposure
Figure 37-15 p661
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Take-Home MessageWhat is the adaptive immune
system?

• Phagocytes and lymphocytes interact to bring
  about vertebrate adaptive immunity, which has
  four defining characteristics self/nonself
  recognition, specificity, diversity, and memory.
• The two arms of adaptive immunity work together.
  Antibody-mediated responses target antigen in
  blood or interstitial fluid cell-mediated
  responses target altered body cells.

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37.8 The Antibody-Mediated Immune Response

• Antibody-mediated immune response
• Antigen activates naïve B cells and dendritic
  cells
• Naïve T cell binds to APC and differentiates into
  effector and memory helper T cells
• Helper T cells bind antigen-MHC complexes on
  activated B cell and secrete cytokines
• B cell differentiates into effector B cells,
  which produce antibodies, and memory B cells

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Stepped Art
Figure 37-16a p662
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Antibody Action

• Circulating antibodies attach themselves to
  pathogens
• An antibody coating prevents bacteria from
  attaching to body cells and brings them to the
  attention of phagocytic cells
• Antibodies also cause agglutination of foreign
  cells clumps are removed from the circulatory
  system by the spleen
• Antibodies also initiate a complement cascade in
  innate immune responses

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Lymphocyte Activity in a Lymph Node
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Clonal Selection

• Only B and T cells with receptors that bind
  antigen divide (clone) and differentiate into
  effector and memory cells
• Primary response produces memory B and T cells
  secondary response is stronger and faster

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antigen
Antigen binds only to a matching B cell receptor.
mitosis
clonal population of effector B cells
Many effector B cells secrete many antibodies.
Figure 37-18 p663
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Take-Home Message What happens during an
antibody-mediated immune response?

• T cells, B cells, and antigen-presenting cells
  carry out an antibody-mediated immune response.
• Effector B cells that form during an
  antibody-mediated immune response make and
  secrete antibodies that recognize and bind
  antigen-bearing particles in blood or tissue
  fluids. Antibody binding can neutralize a
  pathogen or toxin and facilitate its elimination
  from the body.
• Memory cells also form, and these are reserved
  for a potential future encounter with the antigen.

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37.9 The Cell-Mediated Response

• Cell-mediated immune response
• Dendritic cell ingests altered body cell,
  displays antigen-MHC complexes, and migrates to
  lymph node
• Naïve helper T and cytotoxic T cells bind to APC
• Activated helper T divides and differentiates
  into memory and effector cells cytokines signal
  division of activated cytotoxic T cells
• Cytotoxic T cells circulate and touch-kill
  altered body cells

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Stepped Art
Figure 37-19a p664
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APC and T Cell
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TCR Binding
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Antigen/TCR/ MHC Complex
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Cytotoxic T Cells

• Cytotoxic T cells kill body cells displaying
  antigen-MHC markers including cancer cells that
  display altered body proteins, and body cells
  infected with intracellular pathogens
• T cell releases protein-digesting enzymes and
  perforins
• Perforins assemble into complexes that insert
  themselves into a plasma membrane as a
  transmembrane channel enzymes enter the cell and
  induce it to commit suicide

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Natural Killer Cells

• Cytokines secreted by helper T cells also
  stimulate natural killer (NK) cell division
• Unlike cytotoxic T cells, NK cells can kill
  infected cells that are missing all or part of
  their MHC markers

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Take-Home Message What happens during a
cell-mediated immune response?

• T cells, NK cells, and antigen-presenting cells
  carry out a cell-mediated immune response.
• Effector cytotoxic T cells and NK cells that form
  during a cell-mediated immune response kill
  infected body cells or those that have been
  altered by cancer.
• Memory cells also form, and these are reserved
  for a potential future encounter with the antigen.

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37.10 When Immunity Goes Wrong

• An allergy is an immune response to something
  that is ordinarily harmless to most people
• Autoimmune disorders occur when an immune
  response is misdirected against a persons own
  healthy body cells
• In immunodeficiency, the immune response is
  insufficient to protect a person from disease

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Allergies

• Allergy
• An immune response to a typically harmless
  substance (allergen)
• First exposure stimulates production of IgE,
  which becomes anchored to mast cells and
  basophils
• Later exposure stimulates secretion of histamine
  and cytokines that initiate inflammation

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Allergies Hives
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Allergies Hay Fever
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Overly Vigorous Responses

• Acute illnesses arise when mechanisms that limit
  immune responses fail
• Severe episodes of asthma or septic shock occur
  when too many neutrophils degranulate at once
• Anaphylactic shock is a severe and potentially
  fatal allergic reaction

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Anaphylactic Shock
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Autoimmune Disorders

• Sometimes lymphocytes and antibodies fail to
  discriminate between self and nonself
• Autoimmune response is an immune response that is
  misdirected against the persons own tissues
• Autoimmune diseases include rheumatoid arthritis,
  Graves disease, and multiple sclerosis

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Table 37-4 p667
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Immunodeficiency

• In immunodeficiency, the immune response is
  insufficient to protect a person from disease
• Primary immune deficiencies such as SCIDs and ADA
  are present at birth
• Secondary immune deficiency such as AIDS results
  from exposure to an outside agent, such as a virus

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Take-Home Message What happens when the immune
system does not function properly?

• Normally harmless substances may induce an immune
  response in some people. Sensitivity to such
  allergens is called an allergy.
• Misdirected or compromised immunity, which
  sometimes occurs as a result of mutation or
  environmental factors, can have severe or lethal
  outcomes.

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37.11 HIV and AIDS

• Acquired immune deficiency syndrome (AIDS)
• A group of disorders resulting from a failure of
  the immune system due to HIV infection
• Includes rare cancers and infections caused by
  normally harmless microorganisms
• Human immunodeficiency virus (HIV)
• A retrovirus that attacks specific cells of the
  immune system, including helper T cells

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Table 37-5 p669
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Symptoms

• Early symptoms include fever, enlarged lymph
  nodes, chronic fatigue and weight loss, and
  drenching night sweats
• AIDS results in infections caused by normally
  harmless microorganisms, and cancers such as
  Kaposis sarcoma

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Transmission of HIV through Mothers Milk
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Kaposis Sarcoma
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HIV Revisited

• HIV is a retrovirus with a lipid envelope
  consisting of a small piece of the hosts plasma
  membrane
• Viral proteins enclose two RNA strands and
  reverse transcriptase enzymes
• Reverse transcriptase copies viral RNA into DNA,
  which becomes integrated into the host cells DNA
• The host then begins to produce viral proteins

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Cellular Struggle

• HIV infects macrophages, dendritic cells, and
  helper T cells
• For years or decades, IgG antibodies keep the
  level of HIV in the blood low, and cytotoxic T
  cells kill HIV-infected cells
• Eventually the immune system becomes less
  effective at fighting the virus, and HIV
  demolishes the immune system
• Secondary infections and tumors kill the patient

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Infected T Cell with Budding HIV Virus
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Transmission and Testing

• Common modes of HIV transmission include
  unprotected sex, mother to child, and shared
  syringes
• Most AIDS tests check blood, saliva, or urine for
  antibodies that bind to HIV antigens
• One test can detect viral RNA at about eleven
  days after exposure
• Home test kits are not reliable

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Treatments

• Drugs
• There is no cure protease inhibitors and reverse
  transcriptase inhibitors can slow its progress
• Education
• The best option for preventing the spread of HIV
  is teaching people how to avoid being infected

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Take-Home MessageWhat is AIDS?

• AIDS is a secondary immune deficiency caused by
  HIV infection.
• HIV infects lymphocytes and so cripples the human
  immune system.

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Video Vaccinating Against Cancer
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37.12 Vaccines

• Immunization
• The administration of an antigen-bearing vaccine
  designed to elicit immunity to a specific disease
• Vaccine (active immunization)
• A preparation containing an antigen that elicits
  a primary immune response
• Passive immunization
• Administration of antibodies no immune response

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The First Vaccine

• Benjamin Jesty showed that people deliberately
  infected with cow pox became immune to the more
  deadly smallpox
• In 1796, Edward Jenner used cowpox to created the
  first vaccine against smallpox
• The vaccine has now eradicated smallpox

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A Case of Smallpox
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Table 37-6 p670
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Progress on an HIV Vaccine

• HIV vaccines are notoriously ineffective because
  the HIV virus has a very high mutation rate
• One promising strategy involves reverse
  engineering HIV antibodies isolated from people
  with AIDS
• Genes encoding effective antibodies are also
  being inserted into viral vectors for use in gene
  therapy

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Take-Home MessageHow do vaccines work?

• Immunity to many diseases can be elicited by
  administering antigen-bearing vaccines, a process
  called immunization

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Video Restarting the Immune System