MICROBIOLOGY
Chapter 17
Specific Defenses of the Host:
The Immune Response
Dr. Abdelraouf A. Elmanama
Ph. D Microbiology
Medical Technology Department, Faculty of Science, Islamic University-Gaza
2008
Specific Defenses of the Host:
The Immune Response
• Innate (nonspecific)
Defenses against any pathogen
• Immunity
Specific antibody and lymphocyte
response to an antigen
• Antigen (Ag)
A substances that causes the
body to produce specific
antibodies or sensitized T cells
• Antibody (Ab)
Proteins made in response to an
antigen
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Terminology
• Serology
Study of reactions between
antibodies and antigens
• Antiserum
Generic term for serum because
it contains Ab
• Globulins
Serum proteins
• Gamma () globulin
Serum fraction containing Ab
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Serum Proteins
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Figure 17.2
The Immune Response
• Acquired immunity
Developed during an
individual's lifetime
• Humoral immunity
Involves Ab produced by
B cells
• Cell-mediated immunity
Involves T cells
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Acquired Immunity
• Naturally acquired active immunity
• Resulting from infection
• Naturally acquired passive immunity
• Transplacental or via colostrum
• Artificially acquired active immunity
• Injection of Ag (vaccination)
• Artificially acquired passive immunity
• Injection of Ab
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Antigenic Determinants
• Antibodies recognize and react with antigenic
determinants or epitopes.
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Figure 17.3
Haptens
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Figure 17.4
Antibody Structure
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Figure 17.5a-c
IgG antibodies
• Monomer
• 80% of serum antibodies
• Fix complement
• In blood, lymph, intestine
• Cross placenta
• Enhance phagocytosis;
neutralize toxins & viruses;
protects fetus & newborn
• Half-life = 23 days
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IgM antibodies
• Pentamer
• 5-10% of serum
antibodies
• Fix complement
• In blood, lymph, on B
cells
• Agglutinates microbes;
first Ab produced in
response to infection
• Half-life = 5 days
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IgA antibodies
• Dimer
• 10-15% of serum
antibodies
• In secretions
• Mucosal protection
• Half-life = 6 days
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IgD antibodies
• Monomer
• 0.2% of serum antibodies
• In blood, lymph, on B cells
• On B cells, initiate immune
response
• Half-life = 3 days
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IgE antibodies
• Monomer
• 0.002% of serum
antibodies
• On mast cells and
basophils, in blood
• Allergic reactions; lysis of
parasitic worms
• Half-life = 2 days
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Clonal Selection
• Bone marrow gives rise to B cells.
• Mature B cells migrate to lymphoid organs.
• A mature B cells recognizes epitopes.
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Clonal Selection
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Figure 17.8
Self-tolerance
• Body doesn't make Ab against self
• Clonal deletion
• The process of destroying B and T cells that react to
self antigens
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The Results of Ag-Ab Binding
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Figure 17.9
Antibody titer:
• Is the amount of Ab in serum
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Figure 17.10
Monoclonal Antibodies
• Hybridomas are produced by fusing a cancer cell with
an Ab-secreting plasma cells
• The hybridoma cell culture is immortal and produces
monoclonal Abs (Mabs)
• Immunotoxins: Mabs conjugated with a toxin to target
cancer cells
• Chimeric Mabs: Genetically modified mice that produce
Ab with a human constant region
• Humanized Mabs: Mabs that are mostly human, except
for mouse antigen-binding
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Monoclonal Antibodies
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Figure 17.11
Immune system cells communicate via cytokines
• Interleukin-1
Stimulates TH cells
• Interleukin-2
Activates TH, B, TC, and NK cells
• Interleukin-12
Differentiation of CD4 cells
• -Interferon
Increase activity of macrophages
• Chemokines
Cause leukocytes to move to an
infection
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Cell-Mediated Immunity
• Specialized lymphocytes, mostly T cells, respond to
intracellular Ags
• After differentiating in the thymus, T cells migrate to
lymphoid tissue
• T cells differentiate into effector T cells when
stimulated by an Ag
• Some effector T cells become memory cells
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Pathogens entering the gastrointestinal or
respiratory tracts pass through:
• M (microfold) cells in
• Peyer's patches which contains
• Dendritic cells which are antigen-presenting cells
and
• T cells
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Dendritic cells present antigens
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Figure 17.12
T Cells
• Helper T Cells (CD4, TH)
• T H1
Activate cells related to cell-mediated
immunity
• T H2
Activate B cells to produce eosinophils, IgM,
and IgE
• Cytotoxic T Cells (CD8, TC)
• Destroy target cells with perforin
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T Cells
• Delayed Hypersensitivity T Cells (TD)
• Associated with allergic reaction, transplant
rejection, and tuberculin skin test
• Suppressor T cells (TS)
• Turn off immune response when Ag no longer
present
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Helper T Cells
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Figure 17.13
Cell-mediated Cytotoxicity
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Figure 17.14
Nonspecific Cells
• Activated
macrophages:
Macrophages
stimulated by
ingesting Ag or by
cytokines
• Natural killer cells:
Lymphocytes that
destroy virusinfected cells,
tumor
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Figure 17.15
T-independent Antigens
B cell
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Figure 17.17
T-independent Antigens
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Figure 17.16
Antibody-Dependent Cell-Mediated Cytotoxicity
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Figure 17.18