Download Immune System

Infectious Agents
 Pathogen – an organism that causes disease
 A pathogen that can be spread from one
organism to another is contagious.
 A pathogen is infectious when it finds a tissue
that will support its growth.
 A parasite obtains nutrients and shelter from an
organism while contributing nothing.
 Bacteria and viruses are the most common
infectious microbes.
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Infectious Agents - Bacteria
 Bacteria are single-celled prokaryotes,
are very diverse, and can be categorized
into 3 basic shapes
Pili
Rod shaped (bacilli)
Gelatinous capsule
Cell wall
Plasma membrane
Flagellae
Nucleoid region
containing circular
DNA chromosome
Spherical (cocci)
Plasmid
Spiral (spirochetes)
1 µm
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Figure 18.1
Infectious Agents - Bacteria
 Bacteria reproduce through binary fission.
1
2
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3
4
Figure 18.2
Infectious Agents - Bacteria
 Bacteria can
reproduce
rapidly.
 Under ideal
conditions a
population can
double in 20
minutes
Noon
2
bacteria
Chicken salad
sandwich
2:00 p.m.
128
bacteria
4:00 p.m.
8192
bacteria
8:00 p.m.
Over
33
million
bacteria
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Figure 18.3
Infectious Agents - Bacteria
Bacterial
diseases
are caused
by toxins
secreted
by bacteria.
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Table 18.1
Infectious Agents - Bacteria
 Bacterial infections are usually treated with
antibiotics.
 Many bacteria – including those which cause
gonorrhea, ear infections, and TB – have
become resistant to antibiotics.
 This is likely due to natural selection through
overuse.
 Methicillin-resistant Staphylococcus aureus
(MRSA) has recently caused the deaths of
otherwise healthy young athletes.
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Infectious Agents - Viruses
 Viruses consist of nucleic acid surrounded
by a protein sheath or coat, and are not
classified as living organisms because
they..
1. Cannot reproduce by themselves; require a
host cell
2. Are not composed of cells
3. Also do not have cytoplasm or organelles,
and cannot produce toxins
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Infectious Agents - Viruses
 The genome of
a virus can be
DNA or RNA.
Surface
protein
Membrane
envelope
Reverse
transcriptase
Capsid
0.01 µm
Genome:
Single-stranded
DNA or RNA
or
Double-stranded
DNA or RNA
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Figure 18.4
Infectious Agents - Viruses
 Viral replication is carried out by hijacking
the host cell’s transcription and
translation processes.
3
2
1
RNA
Reverse
transcription
Transcription and
translation
DNA
Host
cell
Viral genomes
(RNA)
4
Viral proteins
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Figure 18.5
Infectious Agents - Viruses
PLAY
Animation—Structure and Reproduction of Viruses
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Infectious Agents - Viruses
Examples of
Viral Diseases
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Table 18.2
Infectious Agents - Eukaryotic Pathogens
 Protozoans,
worms, and
some fungi
can infect
animals,
including
humans.
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Table 18.3
Infectious Agents - Prions
 A prion is a misfolded protein.
(a) Normal prion protein has more
helical regions.
(b) Misfolded prion protein has
more pleated regions.
Amino acid chain
0.001 µm
0.001 µm
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Figure 18.6
Transmission of Infectious Agents
 Common Methods of Transmission
(a) Direct contact
(c) Indirect contact
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(b) Vector-borne
(d) Inhalation
(e) Ingestion
Figure 18.8
Transmission of Infectious Agents Ingestion
 Spongiform encephalopathy can be
spread by ingestion of food containing
misfolded prions.
 Cows can become infected by eating feed
made from infected cows.
 Humans who eat infected cows can become
infected.
 Prions occur in the nervous system; these
parts are not commonly eaten in the US, but
meat can be exposed during processing.
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The Body’s Response to Infection: The
Immune System
Pathogens
3 Lines of Defense
 Nonspecific Physical
1 Nonspecific
 Skin, Mucous
 Nonspecific Cellular
 Macrophage, Phagocytes
Skin
2 Nonspecific
 Specific
 Antibodies
 Lymphocytes:
 B-Cells, T-Cells
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Macrophage
3 Specific
Lymphocytes
Figure 18.9
The Body’s Response to Infection: The
Immune System - Skin and Mucous
Membranes
Nonspecific Immune Response
 Skin
 Sheds, takes pathogens with it
 Has low pH, repels microorganisms
 Glands in skin secrete chemicals to slow
bacterial growth
 Mucous Membranes
 Mucous traps pathogens
 Can be sneezed, coughed away
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The Body’s Response to Infection: The
Immune System - White Blood Cells
Nonspecific Immune Response
 White blood cells:
macrophages and
phagocytes
 Engulf and digest
invasive organisms
 Also digest old red blood
cells and cellular debris
 Can release chemicals
to stimulate production
of more white blood cells
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Figure 18.10
The Body’s Response to Infection: The
Immune System - White Blood Cells
Nonspecific Immune Response
 natural killer cells
 Attack tumor cells and virus-infected
cells
 Release chemicals that break apart cell
membranes
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The Body’s Response to Infection: The
Immune System - Inflammation
Nonspecific Immune Response
 Inflammation: response which produces
redness, warmth, swelling, and pain
 After tissue injury, damaged cells release
histamine
 Histamine causes vasodilation which
increases blood flow (redness)
 More blood in area brings more oxygen and
nutrients, also more fluid (swelling/pain)
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The Body’s Response to Infection: The
Immune System - Inflammation
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The Body’s Response to Infection: The
Immune System – Defensive Proteins
Nonspecific Immune Response
 Interferons – produced by
infected cells
 Bind to healthy cells
 Stimulate production of
anti-viral chemicals
 Complement proteins –
class of about 20 different proteins
 Can coat surface of bacteria to facilitate
phagocytosis
 Can make holes in bacterial membrane
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Figure 18.11
The Body’s Response to Infection: The
Immune System - Fever
Nonspecific Immune Response
 Fever – temperature above range of 9799º F
 Macrophages can release pyrogens, which
cause temperature to increase
 Increased temperature inhibits bacterial
growth
 Increases metabolism of healthy cells
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The Body’s Response to Infection: The
Immune System - The Third Line of Defense:
Lymphocytes
Specific Immune Response
 Lymphocytes are a specific defense
because they recognize specific antigens.
 Lymphocytes travel throughout the body in
spaces between the cells and are carried
in the blood and lymphatic system.
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The Body’s Response to Infection: The
Immune System - The Third Line of Defense:
Lymphocytes
Specific Immune Response
Tonsils and adenoid: Type of
lymph node
Thymus: Where some lymphatic
cells go to mature
Bone marrow: Produces some
lymphatic cells
Spleen: Stores and purifies
blood; contains high
concentration of lymphocytes
Lymph nodes: Store cells and
filter out bacteria and other
unwanted substances to purify the
lymphatic fluid; become swollen
and painful when infection occurs
Lymphatic vessels: Transport
fluid from tissues to lymph nodes
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Figure 18.12
The Body’s Response to Infection: The
Immune System - The Third Line of Defense:
Lymphocytes
 B and T cells produce antigen receptors
that fit on a portion of a particular antigen.
(a) B lymphocyte
(b) T lymphocyte
B-cell receptors Antibodies
B cell
T-cell receptors
T cell
Viruses
Bacteria
Antigen
Antigen
Virus-infected cell
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Figure 18.13
The Body’s Response to Infection: The
Immune System - The Third Line of Defense:
Lymphocytes
Specific Immune Response
 B cells
 Recognize small organisms such as bacteria
 Produce antibodies
 T cells
 Respond to larger organisms, virally infected
cells, body cells that have gone awry and
transplanted tissues
 Attack antigen directly
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The Body’s Response to Infection: The
Immune System - The Third Line of Defense:
Lymphocytes
Specific Immune Response
 Passive Immunity – short-term immunity,
lasts as long as antibodies are in bloodstream.
 Ex: Given antibodies as antitoxin
 Active Immunity – long-term, caused by
exposure to antigen and production of B and T
cells. Example: Vaccinations/memory
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The Body’s Response to Infection: The
Immune System - Allergy
 Allergy – immune response that occurs
even though no pathogen is present
 Body reacts to a non-harmful substance as if
it were pathogenic
 Common allergies include ragweed pollen
and peanuts
 Asthma might be caused by allergy
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The Body’s Response to Infection: The
Immune System - Self vs. Non-self
 B- and T-cells must be able to distinguish
between body cells and other cells.
 All cells of an individual have characteristic
proteins, like an ID badge.
 Developing lymphocytes are tested to insure
they do not bind to body cells.
 Normal immune system is self-tolerant.
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The Body’s Response to Infection: The
Immune System - Self vs. Non-self
 When the immune system is not selftolerant, it can result in auto-immune
disease – when the system attacks some
part of the body.
 Multiple sclerosis is the result of T cells
attacking a protein on neurons.
 Insulin-dependent diabetes is when T and
B cells attack the insulin-producing cells in
the pancreas.
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The Body’s Response to Infection: The
Immune System - Humoral and Cell-Mediated
Immunity
 Humoral Immunity: provided by antibodies
produced by B cells, extracellular
pathogens
 Cell-Mediated Immunity: provided directly
by T cells, intracellular pathogens (viruses)
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The Body’s Response to Infection: The
Immune System - Humoral and Cell-Mediated
Immunity
 Humoral Immunity – B
cells produce:
1. Antibodies
2. Clonal copies of
themself, providing
long-term immunity
B-cell
receptors
B cell
Antigen
Antibodies
Clonal
population
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Figure 18.17
Specific Host Defense:
Humoral Immunity
1
Clonal Selection:
1)
Ag binds specific Ab only
2)
Clonal Proliferation
3)
Plasma Cell or Memory Cell
4)
Ab Produced
5)
Memory for next encounter
with pathogen
2
3-5
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Specific Host Defense:
Humoral Immunity
Memory Cells
1)
Inject Rabbit with tetanus
toxin
2)
Primary response:
Several days for Clonal
Proliferation (Plasma and
Memory Cells)
3)
Secondary Response:
Faster and Stronger
(have memory cells)
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Specific Host Defense:
Humoral Immunity
Vaccines:
1) Give an innocuous dose
of tetanus toxin
-Not a toxic level, primes
immune system
2) Actual encounter with
tetanus is stronger
and faster
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The Body’s Response to Infection: The
Immune System - Humoral and Cell-Mediated
Immunity
 Vaccinations attempt to take advantage
of long-term immunity through exposure to
parts of antigens
 Produces population of memory cells
 Some antigens, such as flu, mutate quickly
and require frequent vaccinations
 Some antigens are difficult to make vaccines
for
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The Body’s Response to Infection: The
Immune System - Humoral and Cell-Mediated
Immunity
 Cell-Mediated Immunity – T lymphocytes
divide to make different types of cells,
some of which directly attack pathogens
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The Body’s Response to Infection: The
Immune System - Humoral and Cell-Mediated
Immunity
Macrophage presents
antigen to T cell.
T cell
Viruses
T-cell receptors
Virus antigen
1 Memory cells
will help the body respond
more quickly if the pathogen
is encountered again.
2 Cytotoxic T cells
attack and kill body cells
that have become
infected with a pathogen.
3 Helper T cells
secrete a substance that enhances
humoral immunity (B cells) and
cell-mediated immunity (T cells).
Body cell
Clonal
population
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Virus
Interleukin 2 amplifies immune response.
Figure 18.18
The Body’s Response to Infection: The
Immune System - AIDS Weakens the Immune
System
 Acquired Immune Deficiency Syndrome (AIDS) is
caused by the Human Immunodeficiency Virus
(HIV).
 HIV kills or disables helper T cells.
 Loss of helper T cells causes immune deficiency;
individuals can become infected by pathogens to
which they should be immune.
 Opportunistic infections occur when the immune
system is weakened.
 HIV is only transmitted through contact with
bodily fluids: semen, blood, vaginal fluids, and
occasionally breast milk.
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18.3 The Body’s Response to Infection: The
Immune System
PLAY
Animation—The Body’s Response to Infection
PLAY
Animation—HIV: The AIDS Virus
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