Overview of the Immune System

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Chapter 1 Overview of the Immune System
Sept 19 21, 2006
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• ??????? (immunity)?
• ?????????
• ?????????? (innate immunity)?
• ?????????? (adaptive immunity)?
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• ??????????????? ?????
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• ????????,??????

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• Outlines
• Historical Perspective ?????
• Early Studies of Humoral and Cellular Immunity
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• Theoretical Challenges ??????
• Infection and Immunity ??????
• Innate and Adaptive Immunity
• ??????????
• 6. Immune Dysfunction and its Consequences
• ????????

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The immune system evolved to protect
multicellular organisms from pathogens. -
Pathogens are diverse. - The immune system is
highly adaptable. There are two systems of
immunity - Innate immunity - Adaptive
immunity Two systems collaborate to protect
the body. How to protect? - recognition
response
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??? - immunis exempt ??- immunity
the state of protection from
infectious disease
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Historical Perspective
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Peloponnesian War (431 404 B.C.)
??????? Thucydides ????? (?????????) Only
those who had recovered from the plague
could nurse the sick because they would not
contract the disease a second time.
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• 15th Century Chinese and Turks
• Inhale the dried crusts derived from smallpox
  pustules
• into the nostrils (??) or insert into small cuts
  in the skin.
• Variolation (???)
• 18th Century Jenner (1798)
• Milkmaids who had contracted cowpox (a mild
  disease)
• were subsequently immune to smallpox (a
  disfiguring and
• often fatal disease).
• Jenner introduced fluid from a cowpox pustule
  into people.

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• Louis Pasteur (???,1822 - 1895)
• The chicken which were injected with
• fowl cholera bacterium (old culture)
• survived from a subsequent injection
• of fresh culture of bacteria.
• Aging had weakened the virulence of the
  pathogen.
• An attenuated (weakened) strain could protect
  the
• chickens against the disease.

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• Vaccine ??
• vacca, meaning cow, in honor of
• Jenners work

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1881, vaccination of the sheep with
heat-attenuated anthrax bacilli (Bacillus
anthracis,??) 1885, Pasteur administered the
first vaccine to a human, a young boy who had
bitten by a rabid (rabies ???) dog.
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Early Studies of Humoral and Cellular Immunity
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Mechanism of Immunity Early studies revealed
humoral and cellular components of the immune
system.
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Humoral Immunity Serum Serum
from animals previously
immunized to bacteria could transfer
the immune state to unimmunized
animals g-globulin (gG) immunoglobulin
(Ig) antibody (Ab, ??? antigen Ag) Because
immunity was mediated by antibodies contained in
body fluid (known as humors), it was called
humoral immunity.
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Cellular Immunity Phagocytes Certain white
blood cells were able to
ingest microorganisms and
other foreign material. Metchnikoff (1883)
demonstrated that cells contribute to the
immune state of an animal. He hypothesized that
cells, rather than serum components, were the
major effector of immunity. - Cell-mediated
Immunity
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Theoretical Challenges
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Is humoral or cell-mediated immunity responsible
for the protection? The full immune response
requires both cellular and humoral responses. The
lymphocyte was identified as the cell responsible
for both cellular and humoral immunity due to the
improved cell culture techniques in 1950s. T
lymphocyte derived from the thymus mediated
cellular immunity B
lymphocyte derived from bone marrow,
responsible for humoral immunity
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How is the immunological specificity
generated? - the selective theory
Ehrlich (1900) side-chain theory
Jerne, Talmadge, Burnet (1950s)
clonal-selection theory - the instructional
theory Breinl Haurowitz (1930)
antigens serve as templates Pauling
(1940s) protein folding
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Infection and Immunity
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• The immune system evolves to protect
• organisms from pathogens.
• An effective defense relies heavily on the
• nature of the individual microorganism.
• The immune system must deal with all
• types of microbes and has evolved
• multiple strategies for combating the
• invasion of pathogens.

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Pathogens representing the major categories of
microorganisms causing human diseases
Fungi Candida albicans
Viruses - rotavirus
Bacteria - Pseudomonas
Parasites - filaria
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Innate and Adaptive Immunity
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Innate Immunity (1) - A set of
disease-resistance mechanisms that are present
before the onset of infection and not specific to
a particular pathogen - Respond immediately. It
is the 1st line of defense during the critical
period just after the hosts exposure to a
pathogen.
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• Innate Immunity (2)
• Consist of cellular and molecular components
• that recognize classes of molecules peculiar
• to frequently encountered pathogens.
• Barriers (skin, mucosa, acids, sweat, tears,
• etc.), phagocytic cells (macrophages,
• neutrophils, etc.) and antimicrobial
• components (lysozyme, interferon,
• complement, collectins, etc.)

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• Innate Immunity (3)
• Many of the molecules involved in innate
• immunity have the property of pattern
• recognition the ability to recognize a
  given
• class of molecules.
• Members with pattern recognition ability
• may be soluble (lysozyme, complement
• components,..) or cell-associated receptors,
• such as Toll-like receptors (TLRs).

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red cell
Macrophages attacking Escherichia coli The
bacteria are phagocytized and breakdown products
secreted. The monocyte has been recruited to the
vicinity of the encounter by soluble factors
secreted by the macrophage.
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• Adaptive Immunity
• - Occurs within 5 or 6 days after the initial
• exposure to an Ag.
• - Displays a high degree of specificity.
• Exposure to the same Ag some time in the
• future results in a memory response
• respond more quickly, stronger, and often
• more effective in neutralizing and clearing
• the pathogen.
• - Lymphocytes antibodies (Ab)

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Adaptive and innate immunity do not operate
independently of each other they function as a
highly interactive and cooperative system,
producing a total response more effective than
either could alone.
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Major components barriers (e.g.,
Lymphocytes
skin) antigen-specific
phagocytes
receptors antibodies
pattern
recognition
molecules
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• The Hallmarks (??) of Adaptive Immunity
• Antigenic specificity
• Diversity
• Immunological memory
• Self-nonself recognition

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Distinctive Membrane Molecules on
Lymphocytes
B lymphocyte
T lymphocyte
T cell receptor
T helper (TH) cell T cytotoxic (TC) cell
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Antigen is Recognized Differently by B and T
Lymphocytes B lymphocytes recognize an
antigenic determinants,
or epitope T lymphocytes recognize peptide
epitopes associated
with a major
histocompatibility complex
(MHC) molecule on the
surface of a self-cell
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The MHC Molecules Bind Antigenic Peptides
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Cooperation between T lymphocytes and
antigen-presenting cells
Mf
T cell
Association of an antigen-presenting cell (APC)
with a T lymphocyte
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Numerous T Lymphocytes Interact with a Single
Macrophage
L
M
L
L
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Clonal Selection of Lymphocytes
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Immunological Memory Ab response
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Overview of the T cell and B cell Responses
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Immune Dysfunction and Its Consequences
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• - Allergy and Asthma
• ?????
• Autoimmune disease
• ??????
• - Immunodeficiency
• ???? (?????)
• - Graft rejection and
• graft-versus-host (GVH) disease
• ?????????????

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Questions 1. What is innate immunity ? 2. What
is adaptive immunity ? 3. What components does
the innate branch of the immune system consist of
? 4. What components does the adaptive branch of
the immune system consist of ? 5. How do innate
and adaptive immunity interact and cooperate?