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Lecture 1: The immune system: an overview

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Title: Lecture 1: The immune system: an overview Author: Department of Pathology Last modified by: Department of Pathology Created Date: 2/12/2001 3:37:02 AM – PowerPoint PPT presentation

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Title: Lecture 1: The immune system: an overview


1
Dr. Fang-Ping Huang Department of
Pathology, Immunology Division, Room 216 Tel.
2855 4864 Email fphuang_at_hkucc.hku.hk
2
Essence and Advances in Contemporary
Immunobiology
  • The immune system - an overview (basic concepts,
    features)
  • Developmental biology of the immune system (Dr.
    L. Lu)
  • Recent advances in lymphocyte lineage commitment
    (Dr. L. Lu)
  • Apoptosis the molecular cell death pathways
    (Dr. L. Lu)
  • Antigen recognition by T cells its MHC
    restrictions
  • Pathways of antigen processing, presentation
    co-stimulations
  • Dendritic cells the initiation of immune
    responses
  • Immune regulation dys-regulation in health in
    diseases

3
The immune system an overview
  • Basic concepts in immunology
  • Vaccination the history of immunology
  • Types of immunity
  • The adaptive immune system
  • Immunological specificity memory
  • B cells humoral immune response
  • T cells cell-mediated immune response
  • The concepts of self/non-self self-tolerance

4
Basic concepts in Immunology
  • Organisms and microorganisms
  • Bacteria, viruses, fungi parasites
  • Infections and diseases
  • Infection disease
  • Mechanisms of defense
  • The immune system
  • Cells soluble factors
  • Immunity and Immunology

5
Immunity
  • Original meaning
  • exemption from taxes
  • Other extended meaning
  • diplomatic immunity
  • In the context of Immunology
  • collective mechanisms against diseases

6
Edward Jenner (1749-1823) The Discovery of
Vaccination (1796) Vaccinia (cowpox)
human smallpox
7
Eradication of smallpox (1979, WHO)
8
Vaccination
  • A process of induction of immunity to a pathogen
    by
  • deliberate injection of a weaken, modified or
    related form of
  • the pathogen which is no longer pathogenic.

9
Other historic events important findings
  • L. Pasteur (1880s)
  • Vaccines against cholera, and rabies
  • R. Kock (late 19th century)
  • Infections caused by microorganisms
  • P. Ehrlich et al. (1890s)
  • Serum factors transfer of immunity
  • Behring Kitasato (1890s)
  • Antibodies in serum bound to pathogens
  • Porter Edelman (1960s)
  • Antibody structure
  • J. Gowans (1960s)
  • Immunological importance of lymphocytes

10
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11
Size of the immune system?
12
Dendritic cell (sentinel)
13
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14
Lymph Node
15
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16
The bursa of Fabricius in birds
17
Cells, tissues and organs of the immune system
  • Immune cells are bone marrow-derived,
    distributed through out the body
  • Primary lymphoid organs
  • Thymus T cell maturation
  • Bone marrow (bursa of Fabricius in birds) B cell
    maturation
  • Secondary lymphoid organs
  • Lymph nodes
  • Spleen
  • Mucosal lymphoid tissues (lung, gut)

18
Questions
  • How may vaccines protect us from infections?
  • What may actually occur in our immune system
    following a vaccination?

19
Types of immunity
  • Innate (natural) immunity
  • Phagocytes etc.
  • Early, rapid responses, but limited
    non-specifc
  • Adaptive (acquired) immunity
  • Lymphocytes (B T cells)
  • Take time but powerful - specificity memory

20
Measles attacks immunological memory
21
Memory in adaptive immunity
  • 1st infection ? memory ? 2nd infection
  • slow response fast response
  • pathogen proliferate pathogen killed
  • disease no disease
  • symptoms no symptom

22
Memory specificity key features of the
adaptive immunity
23
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24
Immunological memory vaccination
  • Natural infections
  • 1st infection ? memory ? 2nd infection
  • slow response fast response
  • pathogens multiply pathogens disposed
  • Symptoms/disease no disease
  • Vaccination ? memory ? nature infections
  • no disease fast response
  • pathogens disposed
  • no disease

25
Vaccination protects us from infection by
inducing the adaptive immune response, but
bypassing the need for a primary infection
26
Theoretical basis for immunological specificity
and memory
  • Theory of Clonal Selection
  • Establishment of lymphocyte memory pool

27
Ehrlichs Side-chain Hypothesis (1900)
1
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4
3
28
Burnets Clonal Selection Theory
Each lymphocyte produces one type of Ag receptors
only, antigen selects and stimulates cells
carrying receptors specific for the antigen
1
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2
2
2
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2
2
2
29
s
s s s s
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s s s s s s s s
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30
Immunological memory
  • The ability of the immune system to respond more
    rapidly and effectively to specific pathogens
    that have been encountered previously.
  • Reflection of the pre-existence of a clonally
    expanded population (pool) of antigen specific
    lymphocytes.

31
The adaptive immune mechanisms
  • Humoral immune responses
  • B cells and antibodies
  • Cell mediated immune responses
  • Cytotoxic T cell (Tc)
  • Helper T cells (TH)

32
  • The Immune Recognition Molecules of the Adaptive
    Immune System
  • Immunoglobulin (Ig)
  • B Cell Receptor (BCR)
  • Antibody (Ab)
  • T Cell Receptor (TCR)
  • Major Histocompatibility Complex (MHC)

33
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34
Ab basic structure
domains
35
Ab V and C regions
36
Antibody functions
  • Neutralization e.g. toxins, viruses
  • Opsonization bind pathogens for recognition by
    other immune cells (e.g. phagocytes)

37
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38
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39
Tc
Target
Tc
40
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41
TH cells play a central role in the immune system
42
CD4 T cells in HIV infection
43
Immunological tolerance
  • A state of unresponsiveness to a particular Ag -
    Ag specific
  • to Ags derived from bodys own tissues/cells -
    self tolerance
  • to pathogen-derived/foreign Ags

44
The concepts of immunological self non-self
  • Immune system does not attack self tissues or
    cells under normal condition, but how?
  • Central tolerance thymic education
  • Peripheral tolerance failed-safe mechanisms

45
Central tolerance thymic education
  • Early in life (foetal stage)
  • T cells are important, which develop in the
    thymus
  • TCR specificities randomly generated ? many
    auto-reactive
  • T cells recognize self components (Ag) in the
    thymus ? removed
  • Non-self reactive cells ? selected, matured
    exported

46
Peripheral tolerance
  • Post-thymic continuing education
  • not all self Ags present in the thymus
  • some auto-reactive cells can escape
  • Mechanisms
  • Deletion
  • Inactivation (anergy)
  • Suppression

47
A question for thoughts
Does the immune system mount responses simply to
anything that is non-self?
48
Summary
  • Immunity
  • Innate (natural)
  • Adaptive (acquired)
  • Humoral (B cells, Abs)
  • Cellular (T, NK, MQ)
  • The adaptive immunity
  • Key features specificity memory
  • Types humoral cell-mediated responses
  • Key players T B lymphocytes
  • TH cells play a central role in the induction
    maintenance of immune responses
  • Principle of vaccination
  • Vaccination protects us from infection by
    inducing protective immunity, through
    establishment of specific immunological memory
    but bypassing the need for primary infection
  • Immunological tolerance
  • Tolerance induction is Ag specific
  • Central peripheral mechanisms
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