Download Chapter_24_HB_Immune

BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 24
The Immune System
Modules 24.1 – 24.2
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Continuing Problem of HIV
• Acquired immune deficiency syndrome (AIDS)
is epidemic throughout much of the world
• 14,000 people are infected with the AIDS virus
every day
– HIV is the virus that causes AIDS
– HIV is transmitted mainly
in blood and semen
– Former L.A. Laker Magic
Johnson is one of 900,000
Americans who are
HIV-positive
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Our immune system is a specific defense system
– It backs up several mechanisms of
nonspecific resistance
• HIV attacks the immune system
– It eventually destroys the body’s ability to
fight infection
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Basic Mechanisms of Defense
• There are three basic lines of defense against
disease
• Vertebrate have all three lines of defense
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Basic Mechanisms of Defense
• The 1st line of defense:
nonspecific external barriers
– Prevent microbes from entering the body
– Examples: skin and mucous membranes
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Basic Mechanisms of Defense
• The 2nd line of defense:
nonspecific internal barriers
– Occurs when microbes breach nonspecific
external barriers
– Broad internal responses to microbe infection
– Examples: phagocytic white blood cells,
inflammation, fever
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Basic Mechanisms of Defense
• The 3rd line of defense:
specific immune response
– Immune cells selectively destroy specific
invading microbes and toxins
– Invaders are “remembered,” allowing for a
rapid future response to invasion
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
NONSPECIFIC DEFENSES AGAINST
INFECTION
24.1 Nonspecific defenses against infection include
the skin and mucous membranes, phagocytic
cells, and antimicrobial proteins
• The body’s first lines of defense against
infection are nonspecific
– They do not distinguish one infectious microbe
from another
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Skin and Mucous Membranes
• The skin is important in blocking microbe
entry and suppressing microbe growth
– Skin is a barrier to microbes
– Skin is continually shed, removing microbes
that gain a foothold on skin
– Many skin secretions contain natural
antibiotics
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Skin and Mucous Membranes
• Mucous membranes have effective microbe
defense mechanisms
– Mucous membrane secretions contain
antibacterial enzymes (example: lysozymes)
– Mucus traps microbes entering the nose or
mouth
– Respiratory tract cilia sweep mucus and
microbes away from lungs
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Nonspecific Internal Defenses
• Broad defenses that attack microbes that
penetrate the skin
• Three major categories of nonspecific
internal defenses
– Phagocytic cells and natural killer cells
– The inflammatory response
– Fever
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Macrophages wander in the interstitial fluid
– They “eat” any bacteria and virus-infected
cells they encounter
Figure 24.1A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Natural Killer Cells
• A type of white blood cell
• Attack body cells that are cancerous or
infected with virus
– Secrete enzymes that poke holes in the cell
membrane of virally-infected or cancerous
cells
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Fever
• Helps combat large-scale infection by
elevating body temperature
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Fever
• Some cells release cytokines in response to
infection
– Antibacterial cytokines
• Macrophages release endogenous pyrogens:
elevate body temperature
• Other cytokines: decrease iron in the blood
• Both act to slow bacterial reproduction
– Antiviral cytokines: Interferon, which helps
cells resist viral attack
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Interferon and complement proteins are
activated by infected cells
Viral nucleic acid
VIRUS
6 Antiviral proteins block
1
viral reproduction
2 Interferon
New viruses
genes
turned on
mRNA
5 Interferon
3
stimulates
cell to turn
on genes
for antiviral
proteins
Interferon
molecules
HOST CELL 1
Makes interferon;
is killed by virus
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
4
HOST CELL 2
Protected against virus
by interferon from cell 1
Figure 24.1B
24.2 The inflammatory response mobilizes
nonspecific defense forces
• Tissue damage triggers the inflammatory
response
Skin surface
Swelling
Pin
Phagocytes
Bacteria
Phagocytes and
fluid move
into area
Chemical
signals
White
blood cell
1 Tissue injury; release of
chemical signals such as
histamine
2 Dilation and increased leakiness
3 Phagocytes (macrophages and
of local blood vessels; migration
of phagocytes to the area
neutrophils) consume bacteria
and cell debris; tissue heals
Figure 24.2
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The inflammatory response can
– disinfect tissues
– limit further infection
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
24.3 The lymphatic system becomes a crucial
battleground during infection
• The lymphatic system is a network of
lymphatic vessels and organs
– It returns tissue fluid to the circulatory system
– It fights infections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
LYMPHATIC
VESSEL
Adenoid
Tonsil
Right lymphatic
duct, entering
vein
Thoracic
duct
VALVE
Lymph nodes
Thoracic duct,
entering vein
Blood
capillary
Tissue cells
Interstitial
fluid
Thymus
Appendix
Spleen
LYMPHATIC
CAPILLARY
Masses of
lymphocytes and
macrophages
Bone
marrow
Lymphatic
vessels
Figure 23.3
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• This lymphatic vessel is taking up fluid from
tissue spaces in the skin
• It will return it as lymph to the blood
– Lymph contains less oxygen and fewer
nutrients than interstitial fluid
LYMPHATIC
VESSEL
VALVE
Blood
capillary
Tissue cells
Interstitial
fluid
LYMPHATIC
CAPILLARY
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 23.3B
• Lymph nodes are key sites for fighting infection
– They are packed with lymphocytes and
macrophages
Masses of
lymphocytes and
macrophages
Outer capsule of
lymph node
Macrophages
Lymphocytes
Figure 23.3C, D
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
SPECIFIC IMMUNITY
24.4 The immune response counters specific
invaders
• Our immune systems responds to foreign
molecules called antigens
• Infection or vaccination triggers active
immunity
• The immune system reacts to antigens and
“remembers” an invader
• We can temporarily acquire passive immunity
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Key Characteristics
• The immune response involves specialized
white blood cells called lymphocytes
• The immune system: lymphocytes, the
chemicals they produce, and the organs that
they live in
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
24.5 Lymphocytes mount a dual defense
• Two kinds of
lymphocytes carry
out the specific
immune response
BONE MARROW
Stem cell
THYMUS
Via
blood
Immature
lymphocytes
– B cells secrete
antibodies that
attack antigens
Antigen
receptors
HUMORAL
IMMUNITY
– T cells attack cells
infected with
pathogens
Figure 24.5
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
T cell
B cell
OTHER PARTS
OF THE
LYMPHATIC
SYSTEM
Via
blood
CELLMEDIATED
IMMUNITY
Lymph nodes,
spleen, and other
lymphatic organs
Final
maturation of
B and T cells
in lymphatic
organ
An immune response has three steps
– First: recognizing an invader
– Second: launching an attack
– Third: remembering specific
invaders to ward off future
infections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Step 1: Recognizing an Invader
• Foreign invaders exhibit characteristic
antigens
– Foreign molecules that are particular to an
invading microbe or toxin
– Immune cells respond to the presence of
antigens
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Antibodies and T-cell Receptors
• Antibodies and T-cell receptors recognize
and bind to foreign antigens
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Antibodies
• Antibodies are proteins that can be
attached to B cells or free-floating in the
blood
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Antibodies
• Antibodies
– Y-shaped molecules made of light peptide
chains and heavy peptide chains
– Both chains have constant and variable
regions that form highly specific antigen
binding sites
– Each type of antibody is unique to the B cell
that makes them
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
24.10 Antibodies are the weapons of humoral
immunity
• An antibody molecule
Figure 24.10A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Antibodies
• There are five different classes of antibodies,
which perform various functions
– Inactivate their antigens by binding them and
causing them to clump together
– Assist white blood cells to engulf microbes
– Activate natural killer cells
– Bind to blood proteins of the complement
system…
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Antibodies
– Some classes of antibodies can cross the
placenta and provide immunity to a
developing child
– Another class is secreted in breast milk
– Both help the newborn, whose immune
system is not fully developed
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
24.6 Antigens have specific regions where
antibodies bind to them
• Antigenic
determinants
(epitopes) are
the molecules
to which
antibodies bind
Antibody A
molecules
Antigenbinding
sites
Antigen
Antigenic
determinants
Antibody B
molecule
Figure 24.6
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Immune Cells Launch an Attack
• Once an invading antigen has been detected,
two forms of attack occur
–Humoral immunity
–Cell-mediated immunity
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
24.7 Clonal selection musters defensive forces
against specific antigens
• When an antigen enters the body, it activates
only lymphocytes with complementary
receptors
– B and T cells multiply into clones of specialized
effector cells that defend against the triggering
antigen
– This is called clonal selection
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Humoral Immunity
• Provided by B cells and circulating
antibodies
• Attack antigens circulating in the
bloodstream and lymph
• Each B cell has a unique antibody attached to
its surface that will only bind with properly
shaped antigens
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Humoral Immunity
•
The mechanism of humoral immunity
occurs in the following series of steps
1.
Attached B cell antibodies bind to an invading
antigen in the blood
2. Bound B cell divides rapidly forming many
identical copies (clonal selection)
3. B cell clones differentiate to form memory B
cells and plasma cells
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Antigen molecules
Variety of
B cells in a
lymph node
Antigen receptor
(antibody on
cell surface)
Cell growth
division, and
differentiation
Clone of many
effector cells
secreting
antibodies
Endoplasmic
reticulum
Antibody
molecules
Figure 24.7
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Humoral Immunity
• Memory B cells: saved to fight future
infection
• Plasma cells: mass-produce the specific
antibody into the blood
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
24.11 Antibodies mark antigens for elimination
• Antibodies may
– block harmful antigens on microbes
– clump bacteria or viruses together
– precipitate dissolved antigens
– activate complement proteins
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Binding of antibodies to antigens
inactivates antigens by
Neutralization
(blocks viral binding sites;
coats bacterial toxins)
Agglutination
of microbes
Precipitation of
dissolved antigens
Complement
molecule
Bacteria
Virus
Antigen
molecules
Bacterium
Enhances
Phagocytosis
Activation
of complement
Foreign cell
Hole
Leads to
Cell lysis
Macrophage
Figure 24.11
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
24.8 The initial immune response results in a type
of “memory”
• In the primary immune response, clonal
selection produces memory cells
– These cells may confer lifelong immunity
Figure 24.8A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• When memory
cells are activated
by subsequent
exposure to an
antigen, they
mount a more
rapid and
massive
secondary
immune response
Unstimulated lymphocyte
First exposure to antigen
FIRST CLONE
Memory cells
Second exposure to antigen
Effector cells
SECOND CLONE
More memory cells
New effector cells
Figure 24.8B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
24.9 Overview: B cells are the main warriors of
humoral immunity
• Triggered by a specific antigen, a B cell
differentiates into an effector cell
– The effector cell is called a plasma cell
– The plasma cell secretes antibodies
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
PRIMARY RESPONSE
(initial encounter
with antigen)
Antigen
Antigen receptor
on a B cell
Antigen binding
to a B cell
Cell growth,
division, and
differentiation
Clone of
cells
Memory B cell
Plasma cell
Antibody
molecules
SECONDARY RESPONSE
(can be years later)
Cell growth,
division, and further
differentiation
Later
exposure
to same
antigen
Larger clone
of cells
Plasma cell
Memory B cell
Antibody
molecules
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 24.9
24.12 Connection: Monoclonal antibodies are
powerful tools in the lab and clinic
• These molecules are
produced by fusing
B cells specific for a
single antigenic
determinant with
easy-to-grow tumor
cells
Antigen injected
into mouse
B cells
(from spleen)
Tumor cells grown
in culture
Tumor cells
Cells fused to
generate hybrid
cells
Single hybrid cell
grown in culture
Antibody
Figure 24.12A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Hybrid cell culture,
producing monoclonal antibodies
• These cells are useful
in medical diagnosis
– Example: home
pregnancy tests
• They are also useful
in the treatment of
certain cancers
Figure 24.12B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
24.13 T cells mount the cell-mediated defense and
aid humoral immunity
• Provided by T cells, which attack cancer cells
and cells that have been invaded by viruses
• Three types of T cells are involved
– Helper T cells
– Cytotoxic T cells
– Memory T cells
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Cell-Mediated Immunity
• Helper T cells
– Bind to antigens “presented” by a
macrophage that consumed them
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Cell-mediated immunity
– An antigenpresenting cell
(APC) first
displays a
foreign antigen
and one of the
body’s own self
proteins to a
helper T cell
Microbe
Macrophage
(will become APC)
1
Antigen from microbe
(nonself molecule)
Self protein
Self protein
displaying
antigen
T cell receptor
3
2
Helper
T cell
Binding
site for
self
protein
4
APC
Binding site
for antigen
Figure 24.13A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Cell-Mediated Immunity
• Helper T cells
– Produce cytokines that stimulate T cell
division and differentiation
• Will form memory T cells and cytotoxic
T cells
• Will also stimulate division of B cells
(humoral response) that are bound to an
antigen
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The helper T cell’s receptors recognize the selfnonself complexes on the APC
– The interaction activates the helper T cells
– The helper T cell can then activate cytotoxic T
cells with the same receptors
Self protein
displaying
an antigen
T cell
receptor
APC
Interleukin-2
stimulates
cell division
Helper
T cell
Cytotoxic
T cell
Interleukin-2
activates
other T cells
and B cells
B cell
Interleukin-1
activates
helper T cell
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Cell-mediated
immunity
(attack on
infected cells)
Humoral
immunity
(secretion of
antibodies by
plasma cells)
Figure 24.13B
• Cytotoxic T cells
– Bind directly to cancerous or virally-infected
cells
– Release proteins that poke holes in
cancer/infected cell membrane, killing the
cell
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Cell-Mediated Immunity
• Cytotoxic T cells bind to infected body cells and
destroy them
1 Cytotoxic T cell binds
to infected cell
2 Perforin makes holes
in infected cell’s membrane
Foreign
antigen
3 Infected cell is destroyed
Hole
forming
INFECTED CELL
Perforin
molecule
Cytotoxic
T cell
Figure 24.13C
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Cell-Mediated Immunity
• Memory T cells
– Dormant helper T cells that fight future
infection by the antigen that produced it
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
24.14 Cytotoxic T cells may help prevent cancer
• Cytotoxic T cells may
attack cancer cells
– The surface molecules
of cancer cells are
altered by the disease
Figure 24.14
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
24.15 The immune system depends on our
molecular fingerprints
• The immune system normally reacts only
against nonself substances
– It generally rejects transplanted organs
– The cells of transplanted organs lack the
recipient’s unique “fingerprint” of self proteins
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
DISORDERS OF THE IMMUNE SYSTEM
24.16 Connection: Malfunction or failure of the
immune system causes disease
• Autoimmune diseases
– The system turns against the body’s own
molecules
• Immunodeficiency diseases
– Immune components are lacking, and infections
recur
• Physical and emotional stress may weaken the
immune system
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
24.17 Connection: Allergies are overreactions to
certain environmental antigens
• Allergies are abnormal sensitivities to
allergens in the surroundings
B cell
(plasma cell)
Histamine
Antigenic
determinant
Allergen
(pollen grain)
Mast
cell
B cells make
antibodies
Antibodies
attach to
mast cell
SENSITIZATION: Initial exposure to allergen
Allergen binds to
antibodies on
mast cell
Histamine is
released, causing
allergy symptoms
LATER EXPOSURE TO SAME ALLERGEN
Figure 24.17
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
24.18 Connection: AIDS leaves the body
defenseless
• The AIDS virus attacks helper T Cells
– This cripples both cell-mediated and humoral
immunity
• So far, AIDS is incurable
– Drugs and vaccines offer hope for the future
• Practicing safer sex could save many lives
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings