Download 22.4 How Does The Immune System Launch An Attack?

Chapter 22
Defenses against
Disease
Lectures by
Gregory Ahearn
University of North Florida
Copyright © 2009 Pearson Education, Inc..
22.1 How Does The Body Defend Against
Invasion?
 There are three lines of defense that the
body has against invading organisms that
could kill us.
• External barriers, such as the skin, keep
microbes out of the body.
• Nonspecific internal defenses combat invading
microbes.
• The immune system targets specific microbes.
Copyright © 2009 Pearson Education Inc.
22.1 How Does The Body Defend Against
Invasion?
 Levels of defense
against infection
Nonspecific External Barriers
Skin
Mucous membranes
If these barriers are penetrated,
the body responds with
Nonspecific Internal Defenses
Phagocytic and natural killer cells Inflammation Fever
If the nonspecific defenses are insufficient,
the body responds with
Specific Immune Response
Cell-mediated immunity
Humoral immunity
Fig. 22-1
Copyright © 2009 Pearson Education Inc.
22.1 How Does The Body Defend Against
Invasion?
 The skin and mucous membranes are
nonspecific external barriers to invasion.
• The skin is dry and does not provide the water
or nutrients that microbes need to survive.
• Skin also secretes sweat and oil, which
contain natural antibiotics, such as lactic acid,
that kills bacteria and fungus.
Copyright © 2009 Pearson Education Inc.
22.1 How Does The Body Defend Against
Invasion?
 The skin and mucous membranes are
nonspecific external barriers to invasion
(continued).
• The stomach is acidic and has proteindigesting enzymes.
• Mucous membranes of the gut, respiratory
tract, and urogenital tracts secrete mucus with
antibacterial enzymes, such as lysozyme, that
destroys bacteria.
Copyright © 2009 Pearson Education Inc.
22.1 How Does The Body Defend Against
Invasion?
 The protective function of mucus
Bacteria trapped
by mucus and cilia
Fig. 22-2
Copyright © 2009 Pearson Education Inc.
22.1 How Does The Body Defend Against
Invasion?
 Nonspecific internal defenses combat
invaders.
• These defenses attack a wide variety of
microbes rather than target specific invaders;
they fall into three main categories:
• Phagocytic cells
• Natural killer cells
• The inflammatory response
Copyright © 2009 Pearson Education Inc.
22.1 How Does The Body Defend Against
Invasion?
 Phagocytic cells and natural killer cells
destroy invading microbes.
• Phagocytic cells engulf and digest microbes;
one important type is the macrophage.
• Macrophages ingest microbes by
phagocytosis, consuming bacteria and foreign
substances that penetrate the mucous
membranes of the skin.
Copyright © 2009 Pearson Education Inc.
22.1 How Does The Body Defend Against
Invasion?
 The attack of the macrophages
Bacteria visible
through a hole in
the macrophage
membrane
(a) A macrophage leaves a capillary
and enters a wound
(b) A macrophage stuffed with
bacteria that it has ingested
Fig. 22-3
Copyright © 2009 Pearson Education Inc.
22.1 How Does The Body Defend Against
Invasion?
 Phagocytic cells and natural killer cells
destroy invading microbes (continued).
• Viruses leave their proteins on the surface of
infected body cells and are recognized by
natural killer cells.
• Natural killer cells destroy infected body cells
by secreting pore-forming proteins that attach
to the infected cells plasma membrane and
make holes through which the cytoplasm
leaks, killing the cell and the viruses it
contains.
Copyright © 2009 Pearson Education Inc.
22.1 How Does The Body Defend Against
Invasion?
 The inflammatory response defends against
local infections.
• Damaged cells release histamine into the
wound.
• Histamine increases blood flow to the area of
the wound.
• The area around the wound becomes red and
swollen.
Copyright © 2009 Pearson Education Inc.
22.1 How Does The Body Defend Against
Invasion?
 The inflammatory response defends against
local infections (continued).
• Other chemicals from the wound cause blood
clotting, which closes off the wound to
additional microbes.
• Still other chemicals from the wound attract
macrophages, that eat the bacteria.
Copyright © 2009 Pearson Education Inc.
22.1 How Does The Body Defend Against
Invasion?
 The inflammatory response
Tissue damage carries
bacteria into the wound
Wounded cells
release chemicals (red)
that stimulate mast cells
Mast cells release
histamine (blue)
Histamine increases capillary
blood flow and permeability
Phagocytes leave the
capillaries and ingest bacteria
and dead cells
Fig. 22-4
Copyright © 2009 Pearson Education Inc.
22.1 How Does The Body Defend Against
Invasion?
PLAY
Animation—Inflammation
Copyright © 2009 Pearson Education Inc.
22.1 How Does The Body Defend Against
Invasion?
 Fever combats large-scale infections.
• A fever is produced after a population of
microbes becomes established; it slows
microbial reproduction and increases the
body’s defenses.
• Macrophages release hormones, called
endogenous pyrogens, as they respond to an
infection.
Copyright © 2009 Pearson Education Inc.
22.1 How Does The Body Defend Against
Invasion?
 Fever combats large-scale infections
(continued).
• These endogenous pyrogens travel to
hypothalamus (the body’s thermostat) and
alter body temperature, causing a fever; fever
slows bacterial reproduction.
• Fever helps fight viral infections by inducing
infected cells to release interferon, which
helps uninfected cells resist viral attack.
Copyright © 2009 Pearson Education Inc.
22.2 What Are The Key Characteristics Of
The Immune System?
 The immune system targets specific
invading organisms.
• It is composed of an army of separate cells
that is coordinated in its actions through the
use of hormones, receptors, cells, antigens,
and antibodies.
Copyright © 2009 Pearson Education Inc.
22.2 What Are The Key Characteristics Of
The Immune System?
 The immune system targets specific
invading organisms (continued).
• It attacks one kind of microbe, overcomes it,
and provides future protection against that
particular microbe but to no others.
• That is why the immune response is specific in
its effect.
Copyright © 2009 Pearson Education Inc.
22.2 What Are The Key Characteristics Of
The Immune System?
 The immune system consists of cells and
molecules dispersed throughout the body.
• The immune system includes blood cells
called lymphocytes that are clustered in the
thymus, lymph nodes, spleen, and throughout
the blood.
• The immune cells produce proteins called
antibodies and cytokines, which help destroy
microbes.
Copyright © 2009 Pearson Education Inc.
22.2 What Are The Key Characteristics Of
The Immune System?
Copyright © 2009 Pearson Education Inc.
22.2 What Are The Key Characteristics Of
The Immune System?
 Immune cells originate in the bone marrow.
• Two important lymphocytes are the B cells
and T cells, which originate in the bone
marrow and bring about the immune
response.
• Step 1: recognition of the invader
• Step 2: launch the attack
• Step 3: retention of a memory of the invader
for future protection
Copyright © 2009 Pearson Education Inc.
22.3 How Does The Immune System
Recognize Invaders?
 Immune cells recognize invader’s complex
molecules.
• Invading microbes have surface proteins that
act as antigens against which the immune
cells generate other specific proteins, called
antibodies.
Copyright © 2009 Pearson Education Inc.
22.3 How Does The Immune System
Recognize Invaders?
 Antibodies and T-cell receptors recognize
and bind to antigens.
• Antibody proteins are produced by B cells,
and may remain attached to the surface of the
cell that produced them or may be released
into the blood plasma.
• T-cell receptor proteins are produced by T
cells and always remain attached to the
surfaces of the T cells that produced them;
they are never secreted into the plasma.
Copyright © 2009 Pearson Education Inc.
22.3 How Does The Immune System
Recognize Invaders?
 Antibodies both recognize and help to
destroy invaders.
• Antibodies are Y-shaped molecules composed
of a pair of large (heavy) chains and a pair of
small (light) chains.
• Both heavy and light chains have constant
and variable regions each.
Copyright © 2009 Pearson Education Inc.
22.3 How Does The Immune System
Recognize Invaders?
 Antibody structure
antigen
light
chain
heavy
chain
ss
Variable regions form
antigen binding sites
Constant regions are
the same in all antibodies
of a given type
Fig. 22-5
Copyright © 2009 Pearson Education Inc.
22.3 How Does The Immune System
Recognize Invaders?
 Antibodies both recognize and help to
destroy invaders (continued).
• The variable regions form binding sites for
specific antigens on microbes.
• After the B cell antibody binds to an antigen
on a microbe, the B cell engulfs the antigenbearing microbe and removes it.
Copyright © 2009 Pearson Education Inc.
22.3 How Does The Immune System
Recognize Invaders?
 Antibodies
B cell
antibody
antigen
(a) Antibody receptor function
macrophage
antibody
antigen
(b) Antibody effector function
Fig. 22-6
Copyright © 2009 Pearson Education Inc.
22.3 How Does The Immune System
Recognize Invaders?
 T-cell receptors recognize invaders and help
to trigger the immune response.
• T-cell receptors are only found on the surfaces
of T cells, and have both similarities and
differences from antibodies.
• Like antibodies, they consist of peptide chains
that form highly specific binding sites for
antigens.
Copyright © 2009 Pearson Education Inc.
22.3 How Does The Immune System
Recognize Invaders?
 T-cell receptors recognize invaders and help
to trigger the immune response (continued).
• Unlike antibodies, T-cell receptors are not
released into the bloodstream.
• T-cell receptors trigger a response in the T cell
only when it encounters an antigen on the
surface of a cancerous or infected cell.
Copyright © 2009 Pearson Education Inc.
22.3 How Does The Immune System
Recognize Invaders?
 The immune system can recognize millions
of different molecules.
• Immune cells produce millions of types of
antibodies and T-cell receptors capable of
binding to almost all of the possible antigens a
person might encounter.
Copyright © 2009 Pearson Education Inc.
22.3 How Does The Immune System
Recognize Invaders?
 The immune system can recognize millions
of different molecules (continued).
• Antibodies and T-cell receptors are proteins,
and proteins are encoded by genes; there are
21,000 genes in the human genome.
• This means that a relatively small number of
genes must code for millions of antibodies and
T-cell receptors.
Copyright © 2009 Pearson Education Inc.
22.3 How Does The Immune System
Recognize Invaders?
 Antibody genes are assembled from several
segments of DNA.
• B cell genes do not code for entire antibodies,
but instead, code for antibody fragments that
can be pieced together in millions of
combinations.
• Each B cell has DNA to produce the constant
regions of antibodies but different pieces of
DNA for the variable parts, so that each B cell
makes a unique antibody.
Copyright © 2009 Pearson Education Inc.
22.3 How Does The Immune System
Recognize Invaders?
 Recombination of segments of DNA from
antibody genes
heavy
chain
V2
V1
V3
V4
light
chain
V200
V2
V1
V3
D1 D2
V4
D50
J1
J1
V150
J2
J2
J3
J4
J6
CM CD CG CE CA
J5
CK
(a) Genes for parts of the heavy chain (top) and light chain (bottom) of antibodies
heavy
chain
V2 D11 J4
light
chain
V80 J2
CG
V87 D8
CK
J1
V101 J5
CG
V111 D40 J1
CK
Cell 1
Cell 2
(b) Complete antibody genes in three different B cells
V2
D11
J4
V80
J2
CK
V80
J2
CK
CG
CG
Cell 1
V87
D8
J1
V101
J5
CK
V101
J5
CG
Cell 2
CK
Cell 3
CK
CG
J1
V6
CG
V111
D40
J1
V6
J1
CK
V6
J1
CK
CG
CG
Cell 3
(c) Antibodies synthesized by these three B cells
Fig. 22-7
Copyright © 2009 Pearson Education Inc.
22.3 How Does The Immune System
Recognize Invaders?
 Antibody genes are assembled from several
segments of DNA (continued).
• Some immunologists think that perhaps 15–20
billion different antibodies are possible.
• T-cell receptors are made of different genes,
but the process is similar.
• There are more parts available for T-cell
receptor genes, so there may be as many as a
quadrillion (1015) different possible T-cell
receptors!
Copyright © 2009 Pearson Education Inc.
22.3 How Does The Immune System
Recognize Invaders?
 Antibodies are not tailor-made for antigens.
• The immune system does not design
antibodies to fit invading antigens.
• Instead, it randomly synthesizes millions of
different antibodies, and this array is simply
there, waiting for an appropriate antigen.
• Virtually every antigen can be bound by at
least a few antibodies because of the
immense numbers of antibodies present in the
body.
Copyright © 2009 Pearson Education Inc.
22.3 How Does The Immune System
Recognize Invaders?
PLAY
Animation—The Immune Response
Copyright © 2009 Pearson Education Inc.
22.3 How Does The Immune System
Recognize Invaders?
 The immune system distinguishes “self”
from “non-self”.
• It does so by destroying immune cells that
respond to the body’s own molecules and
retaining those that do not.
• Some cell-surface proteins, called the major
histocompatibility complex (MHC), are unique
to each person.
• Transplants are rejected because the immune
system of the recipient recognizes the MHC of
the donor as foreign antigens.
Copyright © 2009 Pearson Education Inc.
22.4 How Does The Immune System
Launch An Attack?
 The immune system launches two types of
attack on invading microbes.
• Humoral immunity: B cells and the antibodies
they secrete attack invaders before they enter
body cells.
• Cell-mediated immunity: T-cells attack
invaders after they have entered body cells.
Copyright © 2009 Pearson Education Inc.
22.4 How Does The Immune System
Launch An Attack?
 An immune response takes time to develop.
• Although the immune system has millions of
different types of antibodies and T-cell
receptors, there are only a few of each type at
any one time in the body.
• Therefore, the immune system takes time to
recognize the invader, multiply, and
differentiate.
Copyright © 2009 Pearson Education Inc.
22.4 How Does The Immune System
Launch An Attack?
 It usually takes one or two weeks to mount a
good response; it is then a race to
overcome the multiplying microbes.
immune
response
(amount of
antibody
produced)
first
exposure
to antigen
0
1
2
3
4
5
6
7
8
time since exposure (weeks)
9
Fig. 22-8
Copyright © 2009 Pearson Education Inc.
22.4 How Does The Immune System
Launch An Attack?
 Humoral immunity is produced by antibodies
dissolved in blood.
• The B cell that binds to a particular antigen
starts to divide very rapidly, making more of
itself with its particular antibody; this is called
clonal selection.
• The daughter cells differentiate into two kinds
of cells: memory B cells and plasma cells.
Copyright © 2009 Pearson Education Inc.
22.4 How Does The Immune System
Launch An Attack?
 Clonal selection among B cells by invading
antigens
B cell
plasma
cell
endoplasmic
reticulum
(b) Selected B cells differentiate into plasma cells
Fig. 22-9
Copyright © 2009 Pearson Education Inc.
22.4 How Does The Immune System
Launch An Attack?
 Humoral immunity is produced by antibodies
dissolved in blood (continued).
• Plasma cells make thousands of copies of the
antibody that originally bound the antigen.
• Memory B cells do not release antibodies, but
rather, remember the antigen that started the
process for a future immunity event.
Copyright © 2009 Pearson Education Inc.
22.4 How Does The Immune System
Launch An Attack?
 Humoral antibodies have multiple modes of
action.
• Humoral immunity is produced by antibodies
in the blood, which combats invading
molecules or microbes in three ways.
Copyright © 2009 Pearson Education Inc.
22.4 How Does The Immune System
Launch An Attack?
 Circulating
antibodies may
bind to a foreign snake
venom
molecule, virus, enzyme
or cell and render
it harmless, a
process called
neutralization.
active
site
antibody
Antibodies block the
active site of the toxic
enzymes in snake venom
Fig. 22-10
Copyright © 2009 Pearson Education Inc.
22.4 How Does The Immune System
Launch An Attack?
antibodies
 Antibodies
may coat the
Variable regions of
surface of an
antibodies bind to a
microbe
microbe; the constant
regions are exposed
invading
molecules,
virus, or cell,
Constant regions of
make it easier
the antibodies bind to the
microbe
surface of a macrophage,
promoting phagocytosis
for phagocytic
cells to
destroy them.
macrophage
Fig. 22-11
Copyright © 2009 Pearson Education Inc.
22.4 How Does The Immune System
Launch An Attack?
 When antibodies bind to antigens on the
surface of a microbe, they attract other
proteins, called complement proteins.
• Some complement proteins punch holes in the
plasma membrane of the microbe.
• Others promote phagocytosis of the invaders.
Copyright © 2009 Pearson Education Inc.
22.4 How Does The Immune System
Launch An Attack?
 Humoral immunity fights invaders that are outside
cells.
• Because antibodies are large proteins that usually do
not cross plasma membranes, humoral immunity
defends against invaders that are in the blood or
extracellular fluid.
• Bacteria, toxic molecules that are in venoms or are
released by bacteria, some fungi, and protists are all
susceptible to the humoral immune response.
• Viruses that penetrate the body’s cells are only
vulnerable to antibodies when they are outside a body
cell, and are safe when they are inside a cell.
Copyright © 2009 Pearson Education Inc.
22.4 How Does The Immune System
Launch An Attack?
 Cell-mediated immunity is produced by cytotoxic
T cells.
• Cytotoxic T cells are the body’s defense against
cancerous cells or cells invaded by viruses.
• T-cell receptors on T-cell plasma membranes bind to
viral antigens on the surface of an infected cell.
• After binding to a viral antigen, the T cell releases a
pore-forming protein that punches holes in the
infected cell’s plasma membrane, killing the infected
cells.
• This prevents the replication of the enclosed viruses.
Copyright © 2009 Pearson Education Inc.
22.4 How Does The Immune System
Launch An Attack?
 Both humoral and cell-mediated immunity are
enhanced by helper T cells.
• Helper T cells bear receptors that bind to antigens,
either on the surfaces of infected cells or of
macrophages that have engulfed and digested
invading microbes.
• When a helper T cell receptor binds to an appropriate
invading cell antigen, the T cells multiply rapidly and
release chemicals, called cytokines.
• Cytokines stimulate the division of B cells and
cytotoxic T cells, which respond to the same invasion.
Copyright © 2009 Pearson Education Inc.
22.4 How Does The Immune System
Launch An Attack?
 Both humoral and cell-mediated immunity
are enhanced by helper T cells (continued).
• Both B cells and cytotoxic T cells only make a
significant defense against disease if they
receive stimulation by cytokines from helper T
cells.
• Human immunodeficiency virus (HIV), which
causes AIDS, kills off helper T cells, leading to
an ineffective defense against many diseases.
Copyright © 2009 Pearson Education Inc.
HUMORAL IMMUNITY
Targets invaders outside cells
(e.g., viruses, bacteria, fungi,
protists, and toxins)
HELPER T CELLS
CELL-MEDIATED IMMUNITY
Stimulate both humoral and
cell-mediated immunity by
releasing cytokines
Targets defective body cells
(e.g., infected cells and
cancer cells), transplants
virus
viral
antigen
B-cell antibodies
bind to viral
antigens and
stimulate the B
cells to divide and
differentiate
macrophage
Viral antigens
presented on
the surfaces of
macrophages
and infected
cells
infected cell
T-cell receptors
bind to viral
antigens
antibody
B cell
helper T cell
cytotoxic T cell
Cytokines released by helper
T cells stimulate B cells and
cytotoxic T cells
plasma
cell
memory B cell
memory
helper
T cell
memory
cytotoxic
T cell
cytotoxic T cell
infected
cell
Plasma cells
secrete antibodies
into the blood and
extracellular fluid
Memory cells
confer future
immunity to this
virus
Cytotoxic T cells
release poreforming proteins
that destroy
infected cells
Fig. 22-12
Copyright © 2009 Pearson Education Inc.
22.5 How Does The Immune System
Remember Its Past Victories?
 During the early stages of a disease—while
B cells, cytotoxic T cell, and helper T cells
are dividing rapidly—some of their daughter
cells differentiate into memory cells that may
survive for years.
• If the body is re-invaded by this same type of
microbe, the memory cells will recognize the
invader and mount an immune response.
Copyright © 2009 Pearson Education Inc.
22.5 How Does The Immune System
Remember Its Past Victories?
 At a second infection, memory cells produce
a second immune response that is so fast
and large that the microbes are destroyed
before any noticeable symptoms appear.
immune
response
(amount of
antibody
produced)
interval:
months
or years
first
exposure
0
Copyright © 2009 Pearson Education Inc.
1
2
3
second
exposure
0
1
time since exposure (weeks)
2
3
Fig. 22-13
22.5 How Does The Immune System
Remember Its Past Victories?
PLAY
Animation—Humoral vs. Cell-mediated Immunity
Copyright © 2009 Pearson Education Inc.
22.5 How Does The Immune System
Remember Its Past Victories?
PLAY
Animation—Humoral Immunity
Copyright © 2009 Pearson Education Inc.
22.6 How Does Medical Care Assist The
Immune Response?
 Antibiotics slow down microbial
reproduction.
• Organisms affected by antibiotics include
bacteria, fungi, and protists.
• Antibiotics do not destroy every single
disease-causing microbe in the body, but they
may kill enough of them to give the immune
system time to finish the job.
• Some microbes become resistant to
antibiotics.
Copyright © 2009 Pearson Education Inc.
22.6 How Does Medical Care Assist The
Immune Response?
 Drugs are available that target different
stages of a viral cycle of infection, which
include the following:
• Attachment to a host cell
• Replication of viral parts using the host cell’s
machinery
• Assembly of the virus within the host cell
• Release of the virus into the extracellular fluid
to infect new cells
Copyright © 2009 Pearson Education Inc.
22.6 How Does Medical Care Assist The
Immune Response?
 Vaccinations stimulate the development of
memory cells.
• A vaccine exposes an individual to antigens produced
by a disease organism to stimulate an immune
response.
• Vaccines often consist of weakened or killed disease
microbes or antigens from the disease organism,
which are synthesized using genetic engineering.
• When the body is exposed to these antigens, it
produces swarms of memory cells that confer
immunity against living microbes of the same type.
Copyright © 2009 Pearson Education Inc.
22.7 What Happens When The Immune
System Malfunctions?
 Allergies are misdirected immune
responses.
• A foreign substance, such as pollen, enters
the bloodstream and is recognized as an
antigen by a B cell.
• The B cell then proliferates, producing plasma
cells that secrete antibodies against the pollen
antigen.
Copyright © 2009 Pearson Education Inc.
22.7 What Happens When The Immune
System Malfunctions?
 Allergies are misdirected immune responses
(continued).
• The allergy antibodies bind to the membranes
of mast cells of the respiratory and digestive
tracts, triggering release of histamine.
• Histamine causes leaky capillaries and other
symptoms of the immune response.
• In the lungs, histamine causes mucus
secretion that results in a runny nose,
sneezing, and congestion.
Copyright © 2009 Pearson Education Inc.
22.7 What Happens When The Immune
System Malfunctions?
 An allergic reaction
First exposure to pollen
(yellow) stimulates B cells to
produce “allergy” plasma cells
Plasma cells
produce allergy
antibodies
mast
cell
plasma
cell
Allergy antibodies
bind to mast cells
Reexposure to
pollen results in pollen
binding to allergy
antibodies on mast cells
Binding of pollen
stimulates mast cells to
release histamine (blue),
triggering the
inflammatory response
Fig. 22-14
Copyright © 2009 Pearson Education Inc.
22.7 What Happens When The Immune
System Malfunctions?
 An autoimmune disease is an immune
response against the body’s own cells.
• Some types of anemia are caused by
antibodies that destroy a person’s red blood
cells.
• Juvenile-onset diabetes begins when the
immune system attacks the insulin-secreting
cells of the pancreas.
• Rheumatoid arthritis results when the immune
system attacks cartilage in the joints.
• There are no known cures for autoimmune
diseases.
Copyright © 2009 Pearson Education Inc.
22.7 What Happens When The Immune
System Malfunctions?
 Immune deficiency diseases occur when the
body cannot mount an effective immune
response against invaders.
Copyright © 2009 Pearson Education Inc.
22.7 What Happens When The Immune
System Malfunctions?
 There are two very different disorders in
which the immune system cannot combat
routine infections—one inherited, the other
acquired.
• Severe combined immune deficiency (SCID)
is a family of genetic defects in which few or
no immune cells are formed.
• Acquired immune deficiency syndrome (AIDS)
is a viral infection that destroys a formerly
functional immune system.
Copyright © 2009 Pearson Education Inc.
22.7 What Happens When The Immune
System Malfunctions?
 Severe combined immune deficiency
• A child with SCID may survive the first few
months of life, protected by antibodies from
the mother during pregnancy or in her milk.
• Once these antibodies are lost, common
infections prove fatal because the child is
lacking an immune system.
• One form of therapy is to transplant bone
marrow from a healthy donor so enough
immune cells can be produced to confer
normal immune responses.
Copyright © 2009 Pearson Education Inc.
22.7 What Happens When The Immune
System Malfunctions?
 Acquired immune deficiency syndrome
• AIDS is caused by two viruses: human
immunodeficiency viruses 1 and 2 (HIV-1 and
HIV-2).
Fig. 22-15
Copyright © 2009 Pearson Education Inc.
22.7 What Happens When The Immune
System Malfunctions?
 Acquired immune deficiency syndrome
(continued)
• HIV viruses harm the immune system by
destroying the helper T cells that are essential
for stimulating both cell-mediated and humoral
immune responses.
• AIDS does not kill people directly, but rather,
makes them susceptible to other diseases as
their helper T cell populations decline.
Copyright © 2009 Pearson Education Inc.
22.7 What Happens When The Immune
System Malfunctions?
 Acquired immune deficiency syndrome
(continued)
• HIV can be transmitted only by direct contact
with body fluids containing the virus, including
blood, semen, vaginal secretions, and breast
milk.
• The infection can be spread by sexual activity,
by sharing needles among drug users, or by
blood transfusions.
• A woman infected with HIV can transmit the
virus to her child during pregnancy, childbirth,
or through breast feeding.
Copyright © 2009 Pearson Education Inc.
22.7 What Happens When The Immune
System Malfunctions?
 Acquired immune deficiency syndrome
(continued)
• For persons infected with AIDS, there are two
categories of therapy.
• First, infections that result from the impaired
immune system must be treated as they
would be in any patient.
• Second, there are drugs that slow the
multiplication of HIV and slow the progress
of AIDS.
• The best solution would be to develop an
AIDS vaccine.
Copyright © 2009 Pearson Education Inc.
22.7 What Happens When The Immune
System Malfunctions?
PLAY
Animation—The Immune Response
Copyright © 2009 Pearson Education Inc.
22.7 What Happens When The Immune
System Malfunctions?
PLAY
Animation—A Detailed View of the HIV Virus
Copyright © 2009 Pearson Education Inc.
22.7 What Happens When The Immune
System Malfunctions?
PLAY
Animation—Effects of HIV on the Immune Response
Copyright © 2009 Pearson Education Inc.
22.8 How Does The Immune System
Combat Cancer?
 Cancer is a failure of the mechanisms that
control the growth of the body’s own cells—
the body destroys itself.
• Cancer is basically the unchecked growth of
malignant tumor cells.
• A tumor is a population of cells that has
escaped the normal regulatory processes and
grows at an abnormal rate.
Copyright © 2009 Pearson Education Inc.
22.8 How Does The Immune System
Combat Cancer?
 Most cancerous cells are recognized as
foreign.
• Cancer cells normally are produced every day,
but natural killer cells and cytotoxic T cells
screen the body for them and destroy most of
them before they can proliferate and spread.
• The processes that cause cancer often cause
new and slightly different proteins to appear
on the surfaces of cancer cells.
Copyright © 2009 Pearson Education Inc.
22.8 How Does The Immune System
Combat Cancer?
 Natural killer and cytotoxic cells recognize
these as “non-self” antigens and destroy the
cells.
cytotoxic T cell
cancer cell
Fig. 22-16
Copyright © 2009 Pearson Education Inc.
22.8 How Does The Immune System
Combat Cancer?
 Most cancerous cells are recognized as
foreign (continued).
• Some cancer cells evade detection because
they do not bear antigens that allow the
immune system to recognize them as foreign.
• Cancers such as leukemia suppress the
immune system.
• Others grow so fast that the immune system
can’t keep up.
Copyright © 2009 Pearson Education Inc.
22.8 How Does The Immune System
Combat Cancer?
 Treatments for cancer depend on
distinguishing and selectively killing
cancerous cells.
• Surgery may not remove all of the cancer if it
has started to spread throughout the body.
• Radiation can be used to kill small clusters of
cancer cells that surgery cannot find, but the
whole body cannot be radiated without
dangerous effects.
• Chemotherapy prevents normal cell division
and can result in damage to dividing hair
follicle cells and intestinal cells.
Copyright © 2009 Pearson Education Inc.