chapter 67

Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.

Chapter 67

Review of the Immune System

2Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.

Review of the Immune System Two types of immune responses

Natural immunity (innate) Specific acquired immunity

• Cell-mediated• Antibody-mediated: humoral


Immune System: Cells B lymphocytes (B cells)

Make antibodies Cytolytic T lymphocytes

Cytolytic T cells, CD8 cells Do not produce antibodies Attack and kill target cells directly

Helper T lymphocytes Helper T cells, CD4 cells

• Antibody production by B cells• Promote delayed-type hypersensitivity (DTH)• Activation of cytolytic T cells


Immune System: Cells Helper T lymphocytes

Helper T cells, CD4 cells• Required for an effective immune response• Antibody production by B cells• Promote DTH• Activation of cytolytic T cells


Immune System: Cells Macrophages

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


Fig. 67–1. Maturation of blood cells.


Immune System: Cells Dendritic cells Mast cells and basophils

Mediate immediate hypersensitivity reactions Neutrophils (polymorphonuclear leukocytes)

Phagocytize bacteria and other foreign particles Eosinophils

Attack and destroy foreign particles that have been coated with antibodies of the immunoglobulin (Ig)E class


Antibodies Alternative names

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

IgA, IgD, IgE, IgG, and IgM


Fig. 67–2. Antibody structure.


Antigens 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


Fig. 67–3. Memory and time limitation of immune responses.


Characteristic Features of the Immune Response

Specificity Immune responses are triggered by specific antigens

Diversity Millions of different antigenic determinants

Memory 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

Targets only foreign antigens (normal conditions)


Phases of the Immune Response Recognition phase

Antigen recognition by B cells and T cells Activation phase

Proliferation Differentiation of activated lymphocytes

Effector phase Elimination of antigen


Antibody-Mediated (Humoral) Immunity

Production of antibodies Interaction of three types of cells

• B cells Make antibodies

• Helper T cells (CD4 cells) Stimulate B cells

• Antigen-presenting cells (macrophage or dendritic)

Activate CD4 cells


Antibody-Mediated (Humoral) Immunity

Antibody effector mechanisms Opsonization of bacteria Activation of the complement system Neutralization of viruses and bacterial toxins


Fig. 67–4. Major events in antibody-mediated (humoral) immunity.


Cell-Mediated Immunity Two branches

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

Binding of a CTL to its target cell Release of mediators that kill the target

• Cause target cell lysis


Fig. 67–5. Cell-mediated immunity: delayed-type hypersensitivity.


Fig. 67–6. Cell-mediated immunity: cytolytic T cells.

chapter 67

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