Chapter 67
Review of the Immune System
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
Review of the Immune System
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Two types of immune responses
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Natural immunity (innate)
Specific acquired immunity
• Cell-mediated
• Antibody-mediated: humoral
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Immune System: Cells
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B lymphocytes (B cells)
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Cytolytic T lymphocytes
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Make antibodies
Cytolytic T cells, CD8 cells
Do not produce antibodies
Attack and kill target cells directly
Helper T lymphocytes
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Helper T cells, CD4 cells
• Antibody production by B cells
• Promote delayed-type hypersensitivity (DTH)
• Activation of cytolytic T cells
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Immune System: Cells
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Helper T lymphocytes
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Helper T cells, CD4 cells
• Required for an effective immune response
• Antibody production by B cells
• Promote DTH
• Activation of cytolytic T cells
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Immune System: Cells
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Macrophages
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Begin in bone marrow, enter blood as monocytes,
and infiltrate tissues, where they evolve into
macrophages
Principal scavengers of the body
Specific acquired immunity
• Activation of T cells
• Final mediators of DTH
• Phagocytize cells tagged with antibodies
Also play key roles in natural immunity and
inflammation
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Fig. 67–1. Maturation of blood cells.
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Immune System: Cells
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Dendritic cells
Mast cells and basophils
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Neutrophils (polymorphonuclear leukocytes)
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Mediate immediate hypersensitivity reactions
Phagocytize bacteria and other foreign particles
Eosinophils
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Attack and destroy foreign particles that have
been coated with antibodies of the
immunoglobulin (Ig)E class
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Antibodies
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Alternative names
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Immunoglobulins
Gamma globulins
Family of structurally related glycoproteins
Mediate humoral immunity
Recognize and bind with specific antigens
Produced by B lymphocytes
Five classes of antibodies
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IgA, IgD, IgE, IgG, and IgM
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Fig. 67–2. Antibody structure.
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Antigens
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Molecules that induce specific immune
responses
May trigger production of antibodies or
cytotoxic T cells, or both
Antibodies recognize and bind selected small
portions of the antigen
More than one antibody can bind to the
antigen
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Fig. 67–3. Memory and time limitation of immune responses.
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
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Characteristic Features of the
Immune Response
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Specificity
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Diversity
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Millions of different antigenic determinants
Memory
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Immune responses are triggered by specific antigens
Exposure to an antigen affects the immune system such that
re-exposure produces a faster, larger, and more prolonged
response
Time limitation
Selectivity for antigens of nonself origin
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Targets only foreign antigens (normal conditions)
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Phases of the Immune Response
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Recognition phase
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Activation phase
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Antigen recognition by B cells and T cells
Proliferation
Differentiation of activated lymphocytes
Effector phase
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Elimination of antigen
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Antibody-Mediated
(Humoral) Immunity
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Production of antibodies
 Interaction of three types of cells
• B cells
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Make antibodies
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Stimulate B cells
• Helper T cells (CD4 cells)
• Antigen-presenting cells (macrophage or
dendritic)
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Activate CD4 cells
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Antibody-Mediated
(Humoral) Immunity
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Antibody effector mechanisms
Opsonization of bacteria
Activation of the complement system
Neutralization of viruses and bacterial toxins
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Fig. 67–4. Major events in antibody-mediated (humoral) immunity.
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Cell-Mediated Immunity
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Two branches
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Delayed-type hypersensitivity (DTH)
• Activation of helper T cells
• Activation of macrophages
Cytolytic T lymphocytes (CTLs, CD8 cells)
• Activation of cytolytic T cells
• Recognition of virally infected target cells
• Mechanism of cell kill
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Binding of a CTL to its target cell
Release of mediators that kill the target
• Cause target cell lysis
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Fig. 67–5. Cell-mediated immunity: delayed-type hypersensitivity.
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Fig. 67–6. Cell-mediated immunity: cytolytic T cells.
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