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MICROBIOLOGY
WITH DISEASES BY BODY SYSTEM SECOND EDITION
Chapter 16
Adaptive Immunity
Lecture prepared by Mindy Miller-Kittrell, University of Tennessee, Knoxville
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Overview of Adaptive Immunity
• Adaptive immunity is the body’s ability to recognize and defend itself
against distinct invaders and their products
• Five attributes of adaptive immunity
– Specificity
– Inducibility
– Clonality
– Unresponsiveness to self
– Memory
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Overview of Adaptive Immunity
• Involves activity of lymphocytes
• Two main types of lymphocytes
– B lymphocytes (B cells)
– Mature in the bone marrow
– T lymphocytes (T cells)
– Mature in the thymus
• Two types of adaptive immune responses
– Humoral immune responses
– Cell-mediated immune responses
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Overview of Adaptive Immunity
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Overview of Adaptive Immunity
Animation: Host Defenses: Cell-Medicated Immunity: Overview
Animation: Host Defenses: Humoral Immunity: Overview
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Elements of Adaptive Immunity
• The Tissues and Organs of the Lymphatic System
– Screen the tissues of the body for foreign antigens
– Composed of lymphatic vessels and lymphatic cells, tissues, and
organs
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Elements of Adaptive Immunity
• The Tissues and Organs of the Lymphatic System
– Lymphatic vessels and the flow of lymph
– Form a one-way system that conducts lymph from local
tissues and returns it to the circulatory system
– Lymph is a liquid with similar composition to blood
plasma, which arises from fluid leaked from blood
vessels into surrounding tissues
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Elements of Adaptive Immunity
• The Tissues and Organs of the Lymphatic System
– Lymphoid organs
– Primary lymphoid organs
– Red bone marrow
– Thymus
– Secondary lymphoid organs
– Lymph nodes
– Spleen
– Tonsils
– Mucosa-associated lymphatic tissue (MALT)
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Elements of Adaptive Immunity
• Antigens
– Properties of antigens
– Molecules the body recognizes as foreign and worthy of
attack
– Body recognizes antigens by three-dimensional regions
called epitopes
– Include components of bacterial cell walls, capsules, pili, and
flagella, as well as proteins of viruses, fungi, and protozoa
– Food and dust can also contain antigenic particles
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Elements of Adaptive Immunity
• B Lymphocytes (B Cells) and Antibodies
– Arise and mature in the red bone marrow
– Found primarily in the spleen, lymph nodes, and MALT
– Small percentage of B cells circulate in the blood
– Major function is the secretion of antibodies
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Elements of Adaptive Immunity
• B Lymphocytes (B Cells) and Antibodies
– Specificity of the B cell receptor (BCR)
– Each B lymphocyte has multiple copies of a single type of
protein called the B cell receptor
– Each B cell generates a single BCR
– The two variable regions of the BCR form the antigen-binding
sites
– Each BCR recognizes only one epitope
– The entire repertoire of an individual’s BCRs is capable of
recognizing millions of different epitopes
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Elements of Adaptive Immunity
• B Lymphocytes (B Cells) and Antibodies
– Specificity and antibody structure
– Antibodies are immunoglobulins similar to BCRs
– Secreted by activated B cells called plasma cells
– Have identical antigen-binding sites and antigen specificity as
the BCR of the activated B cell
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Elements of Adaptive Immunity
• B Lymphocytes (B Cells) and Antibodies
– Classes of antibodies
– Threats confronting the immune system are variable
– The class involved in the immune response depends on the
type of foreign antigen, the portal of entry, and the antibody
function needed
– Five different classes of antibodies
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Elements of Adaptive Immunity
• B Lymphocytes (B Cells) and Antibodies
• Antibody function
– Antigen-binding sites are complementary to epitopes
– Due to the close match can form strong, noncovalent
interactions
– Hydrogen bonds and other attractions may also be involved
– Antibodies function in several ways
– Activation of complement and inflammation
– Neutralization
– Opsonization
– Killing by oxidation
– Agglutination
– Antibody-dependent cellular cytotoxicity (ADCC)
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Elements of Adaptive Immunity
Animation: Host Defenses: Humoral Immunity: Antibody Function
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Elements of Adaptive Immunity
• T Lymphocytes (T Cells)
– Produced in the red bone marrow and mature under the
influence of the thymus
– Circulate in the lymph and blood and migrate to the lymph
nodes, spleen, and Peyer’s patches
– Antigen-binding sites are complementary to epitopes
– T cells have T cell receptors (TCRs) on their cytoplasmic
membrane
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Elements of Adaptive Immunity
• T Lymphocytes
– Specificity of the T cell receptor (TCR)
– TCRs do not recognize epitopes directly
– TCRs only bind epitopes associated with a MHC protein
– Act primarily against body cells that harbor intracellular
pathogens
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Elements of Adaptive Immunity
• T Lymphocytes
– Types of T lymphocytes
– Based on surface glycoproteins and characteristic functions
– Three types
– Cytotoxic T lymphocyte – directly kills other cells
– Helper T lymphocyte – functions to “help” regulate the
activities of B cells and cytotoxic T cells
– Regulatory T lymphocyte – represses adaptive immune
responses
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Elements of Adaptive Immunity
Animation: Host Defenses: Cell-Mediated Immunity: Cytotoxic T Cells
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Elements of Adaptive Immunity
Animation: Host Defenses: Cell-Mediated Immunity: Helper T Cells
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Elements of Adaptive Immunity
• Clonal Deletion
– Vital that immune responses not be directed against
autoantigens
– Body eliminates self-reactive lymphocytes via clonal deletion
– Lymphocytes that react to autoantigens undergo apoptosis
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Elements of Adaptive Immunity
• Immune System Cytokines
– Soluble regulatory proteins that act as intercellular signals when
released from certain body cells
– Immune system cytokines secreted by various leukocytes
– The complex web of signals among all the cell types of the
immune system is referred to as the cytokine network
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Elements of Adaptive Immunity
• Immune System Cytokines
– Interleukins (ILs) – signal among leukocytes
– Interferons (IFNs) – antiviral proteins that may act as cytokines
– Growth factors – proteins that stimulate stem cells to divide
– Tumor necrosis factor (TNF) – Secreted by macrophages and T
cells to kill tumor cells and regulate immune responses and
inflammation
– Chemokines – chemotactic cytokines that signal leukocytes to
move
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Preparation for an Adaptive Immune Response
• The Roles of the Major Histocompatibility Complex
– Group of antigens first identified in graft patients
– Important in determining the compatibility of tissues in successful
grafting
– Major histocompatibility antigens are glycoproteins found in the
membranes of most cells of vertebrate animals
– Function to hold and position antigenic determinants for
presentation to T cells
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Preparation for an Adaptive Immune Response
• The Roles of the Major Histocompatibility Complex
– Antigens bind in the antigen-binding groove of MHC molecules
– Two classes of MHC proteins
– MHC class I
– MHC class II
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Preparation for an Adaptive Immune Response
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Preparation for an Adaptive Immune Response
• Antigen Processing
– Antigens must be processed for MHC proteins to display
epitopes
– Antigen processing occurs by different processes for
endogenous and exogenous antigens
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Preparation for an Adaptive Immune Response
Animation: Host Defenses: Antigen Processing and Presentation: Overview
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Preparation for an Adaptive Immune Response
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Preparation for an Adaptive Immune Response
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Preparation for an Adaptive Immune Response
Animation: Host Defenses: Antigen Processing and Presentation: Steps
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Preparation for an Adaptive Immune Response
Animation: Host Defenses: Antigen Processing and Presentation: MHC
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Cell-Mediated Immune Responses
• Responds to intracellular pathogens and abnormal body cells
• The most common intracellular pathogens are viruses but the response is also
effective against cancer cells, intracellular protozoa, and intracellular bacteria
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Cell-Mediated Immune Responses
• Activation of T Cell Clones and Their Functions
– Steps involved in activation of cytotoxic T cells
– Antigen presentation
– Helper T cell differentiation
– Clonal expansion
– Self-stimulation
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Cell-Mediated Immune Responses
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Cell-Mediated Immune Responses
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Cell-Mediated Immune Responses
Animation: Host Defenses: Cell-Mediated Immunity: Cytotoxic T Cells
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Cell-Mediated Immune Responses
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Cell-Mediated Immune Responses
• Memory T Cells
– Some activated T cells become memory T cells
– Persist for months or years in lymphoid tissues
– Become functional immediately upon subsequent contacts with
epitope specific to its TCR
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Cell-Mediated Immune Responses
• T Cell Regulation
– Careful regulation of cell-mediated immune response to prevent
T cells from responding to autoantigens
– T cells require additional signals from an antigen-presenting cell
– Interaction of the T cell and antigen-presenting cell at an
immunological synapse stimulates the T cell to respond to
the antigen
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Humoral Immune Responses
• Body mounts humoral immune responses against exogenous pathogens
• Activates only in response to specific pathogens
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Humoral Immune Responses
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Humoral Immune Responses
Animation: Host Defenses: Humoral Immunity: Clonal Selection and Expansion
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Humoral Immune Responses
• Inducement of T-Dependent Humoral Immunity
– Plasma cells
– Make up the majority of cells produced during B cell
proliferation
– Each plasma cell secretes only antibody molecules
complementary to the specific antigen
– Are short-lived cells that die within a few days of activation,
though their antibodies and progeny can persist
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Humoral Immune Responses
• Memory B Cells and the Establishment of Immunological
Memory
– Cells produced by B cell proliferation that do not secrete
antibodies
– Cells that have BCRs complementary to the specific antigenic
determinant that triggered their production
– Long-lived cells that persist in the lymphoid tissue
– Available to initiate antibody production if the same antigen is
encountered again
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Humoral Immune Responses
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Humoral Immune Responses
Animation: Host Defenses: Humoral Immunity: Primary Immune Response
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Humoral Immune Responses
Animation: Host Defenses: Humoral Immunity: Secondary Immune Response
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Humoral Immune Responses
Animation: Host Defenses: The Big Picture
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Types of Acquired Immunity
• Specific immunity acquired during an individuals life
• Two types
– Naturally acquired – immune response against antigens encountered in daily
life
– Artificially acquired – response to antigens introduced via a vaccine
• Further distinguished as either active or passive
– Active – active response to antigens via humoral or cell-mediated responses
– Passive – passively receive antibodies from another individual
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Types of Acquired Immunity
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