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Immune System

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Title: Immune System


1
  • Immune System

2
  • terms
  • Pathogen
  • Antigen
  • Antibody
  • Allergen
  • Vaccine
  • What are lymphocytes? Where do B cells and T
    cells mature?

3
  1. What is the difference between innate vs.
    adaptive immunity?
  2. Contrast the functions of B cells and T cells.
  3. How are antigens recognized by immune system
    cells?
  4. What are memory cells?
  5. How does HIV affect the immune system?

4
THE IMMUNE SYSTEM
5
What you must know
  • Several elements of an innate immune response
  • The differences between B and T cells relative to
    their activation and actions.
  • How antigens are recognized by immune system
    cells
  • The differences in humoral and cell-mediated
    immunity
  • Why Helper T cells are central to immune responses

6
Types of Immunity
Innate Immunity Adaptive Immunity
Non-specific All plants animals Pathogen-specific Only in vertebrates Involves B and T cells
7
Plant Defenses
  • Nonspecific responses
  • Receptors recognize pathogen molecules ? trigger
    defense responses
  • Thicken cell wall, produce antimicrobial
    compounds, cell death
  • Localize effects

8
Figure 43.2
Pathogens(such as bacteria,fungi, and viruses)
Barrier defenses
INNATE IMMUNITY(all animals)
SkinMucous membranesSecretions
Internal defenses
Phagocytic cellsNatural killer
cellsAntimicrobial proteinsInflammatory response
Rapid response
Humoral response
ADAPTIVE IMMUNITY(vertebrates only)
Antibodies defend againstinfection in body
fluids.
Cell-mediated response
Cytotoxic cells defendagainst infection in body
cells.
Slower response
9
  • Antimicrobial Proteins
  • Interferons (inhibit viral reproduction)
  • Complement system (30 proteins, membrane attack
    complex)
  • Barrier Defenses
  • Skin
  • Mucous membranes
  • Lysozyme (tears, saliva, mucus)

Innate Immunity (non-specific)
  • Natural Killer Cells
  • Virus-infected and cancer cells
  • Inflammatory Response
  • Mast cells release histamine
  • Blood vessels dilate, increase permeability
    (redness, swelling)
  • Deliver clotting agents, phagocytic cells
  • Fever
  • Phagocytic WBCs
  • Neutrophils (engulf)
  • Macrophage (big eaters)
  • Eosinophils (parasites)
  • Dendritic cells (adaptive response)

10
Phagocytosis
11
Inflammatory Response
12
Lymphatic System involved in adaptive immunity
- network of tissues and organs that consists
of lymph vessels, lymph nodes and lymph
(fluid) - lymphatic tissue of these organs
filters and cleans the lymph of any debris,
abnormal cells, or pathogens
13
Adaptive Response
  • Lymphocytes (WBCs) produced by stem cells in
    bone marrow
  • T cells mature in thymus
  • helper T, cytotoxic T
  • B cells stay and mature in bone marrow
  • plasma cells ? antibodies

14
  • Antigen substance that elicits lymphocyte
    response
  • Antibody (immunoglobulin Ig) protein made by B
    cell that binds to antigens

15
Major Histocompatibility Complex (MHC)
  • Proteins displayed on cell surface
  • Responsible for tissue/organ rejection (self
    vs. non-self)
  • B and T cells bind to MHC molecule in adaptive
    response
  • Class I all body cells (except RBCs)
  • Class II displayed by immune cells non-self

16
Proliferation of B Cells and T Cells
  • In the body there are few lymphocytes with
    antigen receptors for any particular epitope
  • In the lymph nodes, an antigen is exposed to a
    steady stream of lymphocytes until a match is
    made
  • This binding of a mature lymphocyte to an antigen
    initiates events that activate the lymphocyte

17
  • Once activated, a B or T cell undergoes multiple
    cell divisions
  • This proliferation of lymphocytes is called
    clonal selection
  • Two 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

18
Antigen-presenting cell
Cell-Mediated Immune Response (T Cells)
Humoral Immune Response (antibodies)
Helper T cell
B cell
Cytotoxic T cell
Plasma cell
Identify and destroy
tag for destruction
Infected cell
Antibodies
19
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20
Immunological Memory
  • Primary immune response 1st exposure to antigen
  • Memory cells
  • Secondary immune response repeat exposure ?
    faster, greater response

21
Figure 43.14
B cells thatdiffer inantigenspecificity
Antigen
Antigenreceptor
Antibody
Plasma cells
Memory cells
22
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23
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24
Adaptive immunity defends against infection of
body fluids and body cells
  • Acquired immunity has two branches
  • humoral immune response and
  • cell-mediated immune response
  • humoral immune response antibodies help
    neutralize or eliminate toxins and pathogens in
    the blood and lymph
  • cell-mediated immune response specialized T cells
    destroy affected host cells

25
Types of Cells (and molecules) Involved
26
Helper T Cells A Response to Nearly All Antigens
  • a helper t cell triggers both the humoral and
    cell-mediated immune responses
  • initiate production of antibodies that neutralize
    pathogens and activate T cells that kill infected
    cells
  • Antigen-presenting cells have class I and class
    II MHC molecules on their surfaces

27
  • Class II MHC molecules are the basis upon which
    antigen-presenting cells are recognized
  • Antigen 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 cells
  • The helper T cell is activated, proliferates, and
    forms a clone of helper T cells, which then
    activate the appropriate B cells

28
Figure 43.16
Antigen-presentingcell
Antigen fragment
Pathogen
Class II MHC molecule
Accessory protein
Antigen receptor
Helper T cell
?
?
Cytokines
Cell-mediatedimmunity
Humoralimmunity
?
?
B cell
Cytotoxic T cell
29
Cytotoxic T Cells A Response to Infected Cells
  • Are the effector cells in the cell-mediated
    immune response
  • recognize fragments of foreign proteins produced
    by infected cells
  • possess an accessory protein that binds to class
    I MHC molecules
  • activated cytotoxic T cell secretes proteins that
    disrupt the membranes of target cells and trigger
    apoptosis

30
Figure 43.17-3
Cytotoxic T cell
ReleasedcytotoxicT cell
Accessoryprotein
Dyinginfected cell
Antigenreceptor
Perforin
Class I MHCmolecule
Gran-zymes
Pore
Infectedcell
Antigenfragment
31
B Cells and Antibodies A Response to
Extracellular Pathogens
  • The humoral response is characterized by
    secretion of antibodies by B cells
  • Activation of the humoral immune response
    involves B cells and helper T cells as well as
    proteins on the surface of pathogens
  • In 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

32
Figure 43.18-3
Antigen-presentingcell
Pathogen
Antigenfragment
B cell
Memory B cells
Class IIMHCmolecule
?
Accessoryprotein
Cytokines
Antigenreceptor
Activatedhelper T cell
Plasma cells
Helper T cell
Secretedantibodies
33
Antibody Function
  • Antibodies do not kill pathogens instead they
    mark pathogens for destruction
  • In neutralization, the antigen can no longer
    cause damage because its physically bound
  • Antibodies may also bind to toxins in body fluids
    and prevent them from entering body cells

34
  • In opsonization, antigen is marked for
    phagocytosis and destruction (by antibodies)
  • Antigen-antibody complexes may bind to a
    complement proteinwhich triggers a cascade of
    complement protein activation and inflammation
  • leads to lysis of foreign cell

35
Figure 43.19
Activation of complement system and poreformation
Opsonization
Neutralization
Complement proteins
Antibody
Formation of membraneattack complex
Bacterium
Virus
Flow of waterand ions
Pore
Antigen
Foreigncell
Macrophage
36
  • B cells can express five different forms (or
    classes) of immunoglobulin (Ig) with similar
    antigen-binding specificity but different heavy
    chain C regions
  • IgD Membrane bound
  • IgM First soluble class produced
  • IgG Second soluble class most abundant
  • IgA and IgE Remaining soluble classes

37
  • Immunizations/vaccines induce immune memory to
    nonpathogenic microbe or toxin
  • Passive immunity via antibodies in breast milk
  • Allergies hypersensitive responses to harmless
    antigens
  • Autoimmune Diseases
  • Lupus, rheumatoid arthritis, Type I diabetes,
    multiple sclerosis
  • HIV infect Helper T cells
  • AIDS severely weakened immune system

38
Immune Rejection
  • Cells transferred from one person to another can
    be attacked by immune defenses
  • This complicates blood transfusions or the
    transplant of tissues or organs
  • ABO Blood Groups

39
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40
Tissue and Organ Transplants
  • MHC molecules are different among genetically
    non-identical individuals
  • Differences in MHC molecules stimulate rejection
    of tissue grafts and organ transplants
  • bone marrow transplants lymphocytes may cause
    the donor tissue to reject the recipient
  • Immunosuppressive drugs facilitate
    transplantation

41
Figure 43.22
Histamine
IgE
Allergen
Granule
Mast cell
42
Allergies
  • the allergen enters the body, it binds to mast
    cellassociated IgE molecules
  • Mast cells release histamine ? vascular changes ?
    allergy symptoms

43
Autoimmune Diseases
  • the immune system turns against certain molecules
    of the body
  • diseases - systemic lupus erythematosus,
    rheumatoid arthritis, insulin-dependent diabetes
    mellitus, and multiple sclerosis (ms)

44
Exertion, Stress, and the Immune System
  • Moderate exercise improves immune system function
  • Psychological stress has been shown to disrupt
    immune system regulation by altering the
    interactions of the hormonal, nervous, and immune
    systems
  • Sufficient rest is also important for immunity

45
Immunodeficiency Diseases
  • Inborn immunodeficiency results from hereditary
    or developmental defects that prevent proper
    functioning of innate, humoral, and/or
    cell-mediated defenses
  • Acquired immunodeficiency develops later in life
    and results from exposure to chemical and
    biological agents
  • Acquired immunodeficiency syndrome (AIDS) is
    caused by a virus

46
Latency
  • Some viruses may remain in a host in an inactive
    state called latency
  • Herpes simplex viruses can be present in a human
    host without causing symptoms

47
Attack on the Immune System HIV
  • Human immunodeficiency virus (HIV) infects helper
    T cells
  • The loss of helper T cells impairs both the
    humoral and cell-mediated immune responses and
    leads to AIDS
  • HIV eludes the immune system because of antigenic
    variation and an ability to remain latent while
    integrated into host DNA

48
Figure 43.25
Latency
AIDS
Relative anti-HIV antibodyconcentration
800
Relative HIVconcentration
600
Helper T cell concentration(in blood (cells/mm3)
Helper T cellconcentration
400
200
0
0
9
1
2
3
4
5
6
7
8
10
Years after untreated infection
49
  • People 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 problem
  • The best approach for slowing this spread is
    education about practices that transmit the virus

50
Cancer and Immunity
  • The frequency of certain cancers increases when
    adaptive immunity is impaired
  • 20 of all human cancers involve viruses
  • The immune system can act as a defense against
    viruses that cause cancer and cancer cells that
    harbor viruses
  • In 2006, a vaccine was released that acts against
    human papillomavirus (HPV), a virus associated
    with cervical cancer
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