Immune System

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• Immune System

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

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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?

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THE IMMUNE SYSTEM
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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

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Types of Immunity
Innate Immunity Adaptive Immunity
Non-specific All plants animals Pathogen-specific Only in vertebrates Involves B and T cells
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Plant Defenses

• Nonspecific responses
• Receptors recognize pathogen molecules ? trigger
  defense responses
• Thicken cell wall, produce antimicrobial
  compounds, cell death
• Localize effects

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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
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• 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)

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Phagocytosis
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Inflammatory Response
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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
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• Bioflix chapter 43

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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

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

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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

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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

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• 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

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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
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Immunological Memory

• Primary immune response 1st exposure to antigen
• Memory cells
• Secondary immune response repeat exposure ?
  faster, greater response

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Figure 43.14
B cells thatdiffer inantigenspecificity
Antigen
Antigenreceptor
Antibody
Plasma cells
Memory cells
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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

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Types of Cells (and molecules) InvolvedBasic
Response video
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Helper T Cells A Response to Nearly All Antigens

• 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

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• 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

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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
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Cytotoxic T Cells A Response to Infected Cells

• the effector cells in the cell-mediated immune
  response
• recognize fragments of foreign proteins produced
  by infected cells
• activated cytotoxic T cell secretes proteins that
  disrupt the membranes of target cells and trigger
  apoptosis

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Figure 43.17-3
Cytotoxic T cell
ReleasedcytotoxicT cell
Accessoryprotein
Dyinginfected cell
Antigenreceptor
Perforin
Class I MHCmolecule
Gran-zymes
Pore
Infectedcell
Antigenfragment
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B Cells and Antibodies A Response to
Extracellular Pathogens

• The humoral response is characterized by
  secretion of antibodies by B cells
• 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

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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
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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

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• In opsonization, antigen is marked for
  phagocytosis and destruction (by antibodies)
• leads to lysis of foreign cell

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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
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• 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

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• 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

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vaccines
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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

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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

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Figure 43.22
Histamine
IgE
Allergen
Granule
Mast cell
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Allergies

• the allergen enters the body, it binds to mast
  cellassociated IgE molecules
• Mast cells release histamine ? vascular changes ?
  allergy symptoms

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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)

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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

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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

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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

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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

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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
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1
2
3
4
5
6
7
8
10
Years after untreated infection
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• 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

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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