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ADAPTIVE IMMUNITY
CHAPTER 16
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Third Line of Defense
Is called adaptive immunity
The bodys ability to recognize and defend itselfagainst distinct invaders and their products
Is a smart system whose memory allows it torespond rapidly to a second encounter with a pathogen
Antigens trigger specific immune responses
Various cells, tissues, and organs are part of specificimmunity
Includes B and T lymphocytes
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Antigens
Molecules that trigger a specific immune response
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
Enter the body by various methods
Through breaks in the skin and mucous membranes
Direct injection, as with a bite or needle
Through organ transplants and skin grafts
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Antigen Processing and Presentation
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Antigens
Figure 16.1
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The Lymphatic System
Figure 16.2
Screens the tissues
of the body forforeign antigens
Composed oflymphatic vessels
and lymphaticcells
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Lymphatic Vessels
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 that arises from fluid leaked from blood vesselsinto surrounding tissues
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Lymphoid Cells
Develop from stem cells in the red bone marrow
Includes lymphocytes, the smallest of the leukocytes
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Lymphocytes
Figure 16.3
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Lymph Node
Figure 16.4
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Lymph Nodes
Houses leukocytes that recognize and attack foreign
antigens present in the lymphConcentrated in the cervical (neck), inguinal (groin),
axillary (armpit), and abdominal regions
Receives lymph from afferent lymphatic vessels anddrains lymph into efferent lymphatic vessels
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Other Lymphoid Tissues and Organs
Spleen
Similar in structure and function to the lymph nodes
Filters bacteria, viruses, toxins, and other foreignmatter from the blood
Tonsils and mucosa-associated lymphoid tissue(MALT)
Physically trap foreign particles and microbes
MALT includes the appendix, lymphoid tissue of the
respiratory tract, vagina, urinary bladder, mammaryglands, and Peyers patches in the wall of the smallintestine
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B Lymphocytes
Arise and mature in the red bone marrow
Found primarily in the spleen, lymph nodes, andMALT
Small percentage of B cells circulate in the blood
Major function is the secretion of antibodies
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Antibodies
Also called immunoglobulins (Ig)
Soluble proteins that bind antigen
Secreted by plasma cells, which are B cells activelyfighting exogenous antigen
Considered part of the humoral immune responsesince bodily fluids such as lymph and blood were oncecalled humors
A ib d S
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Antibody Structure
Figure 16.5
Antigen-binding sites are complementary to antigenicdeterminants (epitopes)
F i f A ib di
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Functions of Antibodies
Figure 16.6
Function in several ways
Activation ofcomplement
Stimulation ofinflammation
Neutralization
Opsonization
Agglutination
Cl f A ib di
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Classes of Antibodies
A single type of antibody is not sufficient for the
multiple types of invaders to the bodyThe class involved in the immune response depends
on the type of foreign antigen, the portal of entry, andthe antibody function needed
Five different classes of antibodies
Cl f A tib di
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Classes of Antibodies
Figure 16.7
Ch t i ti f th Fi Cl
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Characteristics of the Five Classesof Immunoglobulins
Table 16.1
B C ll R t (BCR)
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B Cell Receptor (BCR)
Is an antibody that remains associated with the cytoplasmicmembrane
Each B lymphocyte has multiple copies of a single type of BCR
Antigen binding site is identical to that of the secreted antibodyfor that particular cell
The randomly generated antibody variable region determines theBCR (it is not formed in response to antigens)
Each BCR is complementary to only one antigenic determinant
The BCRs on all of an individuals B cells are capable ofrecognizing millions of different antigenic determinants
T L h t
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T Lymphocytes
Produced in the red bone marrow and mature under
the influence of the thymusCirculate in the lymph and blood and migrate to the
lymph nodes, spleen, and Peyers patches
Part of the cell-mediated immune response becausethey act directly against various antigens
Endogenous invaders
Many of the bodys cells that harbor intracellular
pathogens Abnormal body cells such as cancer cells that produce
abnormal cell surface proteins
T C ll R t
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T Cell Receptor
Figure 16.9
C t t i T ll (T C ll )
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Cytotoxic T cells (TC Cells)
Distinguished by the CD8 cell-surface glycoprotein
Directly kill certain cells Cells infected with viruses and other intracellular
pathogens
Abnormal cells, such as cancer cells
Helper T Cells (T Cells)
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Helper T Cells (TH Cells)
Distinguished by the CD4 cell-surface glycoprotein
Function to help regulate the activities of B cellsand cytotoxic T cells during an immune response
Secrete various soluble protein messengers, calledcytokines, that determine which immune response willbe activated
Helper T Cells (T Cells)
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Helper T Cells (TH Cells)
Two types
Type 1 helper T cell (TH1) Assist cytotoxic T cells
Express a cytokine receptor named CCR5
Type 2 helper T cell (TH2
) Assist B cells
Have cytokine receptors CCR3 and CCR4
Cytokines
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Cytokines
Soluble regulatory proteins that act as intercellular
signals when released from certain body cells Immune system cytokines signal among various
leukocytes
The complex web of signals among all the cell typesof the immune system is referred to as the cytokinenetwork
Cytokines of the Immune System
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Cytokines of the Immune System
Interleukins (ILs)signal among leukocytes
Interferons (IFNs)antiviral proteins that may act ascytokines
Growth factorsproteins that stimulate stem cells todivide, maintaining a adequate supply of leukocytes
Tumor necrosis factor (TNF)Secreted bymacrophages and T cells to kill tumor cells andregulate immune responses and inflammation
Chemokinessignal leukocytes to go to a site ofinflammation or infection and stimulate otherleukocytes
Lymphocyte Editing by Clonal Deletion
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Lymphocyte Editing by Clonal Deletion
Vital that immune responses not be directed against
autoantigensBody edits lymphocytes to eliminate any self-
reactive cells
Lymphocyte Editing by Clonal Deletion
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Lymphocyte Editing by Clonal Deletion
Figure 16.10
Major Histocompatibility Complex (MHC)
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Major Histocompatibility Complex (MHC)
Important in determining the compatibility of tissues
in successful tissue graftingMajor histocompatibility antigens are glycoproteins
found in the membranes of most cells of vertebrateanimals
Function to hold and position antigenic determinantsfor presentation to T cells
Antigens bind in the antigen-binding groove of MHC
moleculesTwo classes of MHC proteins
MHC class I
MHC class II
MHC: Two Classes
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MHC: Two Classes
Figure 16.11
Antigen Processing
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Antigen Processing
T-independent antigen
Large antigen molecules with readily accessible,repeating antigenic determinants
B cells can bind these directly without being processed
Stimulates B cells to differentiate into a plasma celland produce antibodies
Antigen Processing
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Antigen Processing
T-dependent antigens
Smaller antigens with less accessible antigenicdeterminants
B cells require involvement from helper T cells totarget these antigens
Helper T cells are assisted by leukocytes that processthe antigen to make the antigenic determinants moreaccessible
Processing is different based on whether the antigenis exogenous or endogenous
Processing of Exogenous Antigens
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Processing of Exogenous Antigens
APC internalizes the invading pathogen and
enzymatically digests it into smaller antigenicfragments which are contained within aphagolysosome
Phagolysosome fuses with a vesicle containing MHC
II moleculesEach fragment binds to the antigen-binding groove of
a complementary MHC II molecule
The fused vesicle then inserts the MHC II-antigencomplex into the cytoplasmic membrane so theantigen is presented on the outside of the cell
Processing of Endogenous Antigens
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Processing of Endogenous Antigens
The intracellular pathogens are also digested into
smaller antigenic determinantsEach fragment binds to a MHC I molecule located in
the endoplasmic reticulum membrane
The membrane is packaged into a vesicle by a Golgibody which is inserted into the cytoplasmic membraneso the antigen is displayed on the cells surface
Humoral Immune Response
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Humoral Immune Response
Body mounts humoral immune responses against
exogenous pathogensComponents of a humoral immune response
B cell activation and clonal selection
Memory B cells and the establishment ofimmunological memory
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Humoral Immunity
Humoral Immune Response
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Humoral Immune Response
Figure 16.14
Plasma Cells
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Plasma Cells
Make up the majority of cells produced during B cell
proliferationEach plasma cell secretes only antibody molecules
complementary to the specific antigenic determinant
Are short-lived cells that die within a few days ofactivation, though their antibodies and progeny canpersist
Memory B Cells
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Memory B Cells
Cells produced by B cell proliferation that do not
secrete antibodiesCells that have BCRs complementary to the specific
antigenic determinant that triggered their production
Long-lived cells that divide only a few times and thenpersist in the lymphoid tissue
Are available to initiate antibody production if thesame antigen is encountered again
Primary and Secondary Responses
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Primary and Secondary Responses
Figure 16.15
Cell-Mediated Immune Response
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Cell Mediated Immune Response
Responds to intracellular pathogens and abnormal
body cellsThe most common intracellular pathogens are viruses
but the response is also effective against intracellularbacteria
Triggered when antigenic determinants of thepathogen are displayed on the host cells surface
Activation of TC Cells
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Activation of TC Cells
Figure 16.16
A Cell-Mediated Immune Response
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A Cell Mediated Immune Response
Figure 16.17
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Cell-Mediated Immunity
Acquired Immunity
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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 introducedvia 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
A Comparison of the Types of Acquired
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A Comparison of the Types of AcquiredImmunity
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