PowerPoint® Lecture
Presentations prepared by
Bradley W. Christian,
McLennan Community
College
C H A P T E R
© 2016 Pearson Education, Inc.
Adaptive
Immunity:
Specific
Defenses of
the Host
17
© 2016 Pearson Education, Inc.
© 2016 Pearson Education, Inc.
The Adaptive Immune System
• Adaptive immunity: defenses that target a
specific pathogen
• Acquired through infection or vaccination
• Primary response: first time the immune system
combats a particular foreign substance
• Secondary response: later interactions with the same
foreign substance; faster and more effective due to
"memory"
© 2016 Pearson Education, Inc.
The Immune Response
Three Key Features
1. Recognition of self
2. Specificity
3. Memory
© 2016 Pearson Education, Inc.
Anatomy of the Immune System
Blind-ended capillaries in tissues collect
lymph and cells and drain to vena cava
Lymph nodes filter the lymph
© 2016 Pearson Education, Inc.
© 2016 Pearson Education, Inc.
Anatomy of the Immune System
Bone marrow and thymus are primary
lymphoid organs
Lymph nodes and spleen are secondary
lymphoid organs
© 2016 Pearson Education, Inc.
Figure 17.1 Differentiation of T cells and B cells.
Stem cells develop
in bone marrow or
in fetal liver
Red bone
marrow
of adults
Stem cell
(diverges into
two cell lines)
Thymus
Differentiate to
T cells in thymus
T cell
Migrate to lymphoid
tissue such as spleen,
but especially lymph
nodes
B cell
Differentiate to
B cells in adult
red bone marrow
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Humoral Immunity
Protection by antibody (Ab) molecules
Soluble proteins
Produced by B lymphocytes which
differentiate to plasma cells
Identify and bind to antigens
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Cell-Mediated Immunity
Protection by T lymphocytes that react to cellular antigen
Specialized cells that act by a variety of non-phagocytic mechanisms
Respond to infected, cancerous, and foreign cells
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Antigen
Foreign substance that stimulates the
immune system
Almost always protein
Antigen (Ag) means “antibody generating”
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Antibodies
Also called immunoglobulins (Ig)
Structure:
2 pairs of identical polypeptide chains
“Y”-shaped molecule with 2 binding sites
Five classes of Ig (IgG,IgM,IgA, IgD, IgE)
© 2016 Pearson Education, Inc.
© 2016 Pearson Education, Inc.
Antibody Function
Identification molecule – no direct activity
Agglutination
Opsonization
Activate complement (C’)
Neutralize soluble proteins and virus
© 2016 Pearson Education, Inc. Figure 17.7 - Overview (1 of 6)
© 2016 Pearson Education, Inc. Figure 17.14 - Overview
© 2016 Pearson Education, Inc.
Antigens
• Antigens: substances that cause the production
of antibodies
• Usually components of invading microbes or foreign
substances
• Antibodies interact with epitopes, or antigenic
determinants, on the antigen
• Haptens: antigens too small to provoke immune
responses; attach to carrier molecules
© 2016 Pearson Education, Inc.
Figure 17.2 Epitopes (antigenic determinants).
Antibody A
Epitopes (antigenic determinants)
on antigen
Antigens:
components
of cell wall
Antibody B
Bacterial cell
Binding sites
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Figure 17.3 Haptens.
© 2016 Pearson Education, Inc.
Table 17.1 A Summary of Immunoglobulin Classes
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Clonal Selection of Antibody-Producing Cells
• Major histocompatibility complex (MHC) genes
encode molecules on the cell surface
• Class I MHC are on the membrane of nucleated animal
cells
• Identify "self"
• Class II MHC are on the surface of antigen-presenting
cells (APCs), including B cells
© 2016 Pearson Education, Inc.
B Cells
Proliferate in response to Ag and a “co-stimulatory signal”
Differentiate to antibody-producing plasma cells and memory cells
Memory cells respond to Ag much faster than virgin B cells
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T Cell “Help”
Most B cells only respond to Ag with the
“help” of Ag-specific T cells
Some B cells do not require T cell help to
make responses to Ag
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Clonal Selection of Antibody-Producing Cells
• T-dependent antigen
• Antigen that requires a TH cell to produce antibodies
• T-independent antigens
• Stimulate the B cell without the help of T cells
• Provoke a weak immune response, usually producing
IgM
• No memory cells generated
© 2016 Pearson Education, Inc.
© 2016 Pearson Education, Inc.
© 2016 Pearson Education, Inc.
© 2016 Pearson Education, Inc.
Clonal Selection of Antibody-Producing Cells
• Clonal selection differentiates activated B cells
into:
• Antibody-producing plasma cells
• Memory cells
• Clonal deletion eliminates harmful B cells
© 2016 Pearson Education, Inc.
Antibody Diversity
In humans, maybe as many as 1015
different B cells
Genes for these are formed through
rearrangements of the germline DNA
and later modified by mutational events
