CHAPTER 24 – THE BODY’S DEFENSES
AGAINST PATHOGENS
STATE STANDARDS
Standard 10.a. – The role of the skin is to provide nonspecific defenses
against infection
Standard 10.b. – Antibodies play a role in the body’s response to
infection
Standard 10.c. – Vaccination protects an individual from infectious
diseases
Standard 10.d. – There are important differences between bacteria and
viruses with respect to their requirements for growth and replication, the
body’s primary defenses against bacterial and viral infections, and
effective treatments of these infections
Standard 10.e. – Individuals with a compromised immune system may
be unable to fight off and survive infections by microorganisms that are
usually benign
PATHOGENS
PATHOGENS
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•
•
Pathogens are disease causing agents
They are usually microorganisms
- Viruses – cold, influenza, HIV, SARS
- Bacteria – E. coli, stomach ulcers, strep throat, MRSA
- Fungi – ringworm, yeast infections
- Protozoa – malaria
- Parasites – trichinosis, round worm, tapeworm
- Protein – BSA Mad Cow disease
Bacteria and viruses are everywhere in nature, but only a
few cause disease.
PATHOGENS
Pathogenic Bacteria
• Some bacteria damage
the bodies cells and
tissues by breaking
down the cells for food.
• Other bacteria release
toxins (poisons) that
travel throughout the
body interfering with the
normal activity of the
host.
Pathogenic Viruses
• Viruses can attack and
destroy certain cells in
the body, causing
symptoms of the
disease.
• Other viruses cause
infected cells to change
patterns of cell/tissue
growth and development.
EVERYDAY STEPS TO PROTECT YOUR HEALTH
•
•
•
•
•
Cover your nose and mouth with a tissue when you
cough or sneeze. Throw tissue in the trash after you
use it.
Wash your hands often with soap and water. Alcohol
based hand cleaners are also effective.
Avoid touching your eyes, nose or mouth. Germs
spread this way.
Try to avoid close contact with sick people.
Cook food thoroughly.
PREVENTING INFECTIONS
•
•
•
Sterilization (medical, tattoo, piercing equipment)
Disinfectants/Antiseptics (bleach, “Lysol” type
cleaners)
- Chemicals that oxidize or inactivate the
infecting organism
- Useful in decontaminating surfaces with
which the body may come into contact
Food processing (canning and packaging
hygienically)
Preventing & Dealing with Infections
Viral
•Antiviral drugs:
limit virus ability to
replicate and infect
new cells of your
body
–Ex: tamiflu, AZT
Both
•Immune response
•Vaccine: a weakened
form of pathogen 
immune system makes
memory cells that remember
how to fight off infection
*over the counter medications like
Tylenol and Nyquil treat the
symptoms not the infection!!!
Bacterial
•Antibiotics: drugs that
KILL bacteria by
interfering with their
growth and
reproductive processes
–Ex: penicillin,
erythromycin
TREATING BACTERIAL INFECTIONS - ANTIBIOTICS
Antibiotics
• Chemicals that inhibit (slow/stop) the growth
of bacteria
• Function by
- reducing the number of bacteria or
- slowing the growth rate of the population
giving the body’s defenses time to fight the
bacteria
TREATING BACTERIAL INFECTIONS - ANTIBIOTICS
•
•
Effective in treating
bacterial infections only
Ex: penicillin interferes with
the growth of bacterial cell
walls
Also work by
• Destroying bacterial cell walls
(lysozyme)
• Interfering with the function
of the bacterial cell wall
• Inhibiting the bacteria from
synthesizing DNA, RNA, or
proteins (erythromycin,
streptomycin, tetracycline)
•
•
Why doesn’t penicillin affect
your cells?
Why doesn’t penicillin affect
a virus infection?
ANTIBIOTIC RESISTANCE
•
•
When a strain of bacteria is
exposed to an antibiotic
- the bacteria that are
susceptible to the
antibiotic die.
- the ones that have
genetic resistance
survive and multiply.
Complication: Antibiotics
also kill beneficial bacteria
(that live on and in you) that
normally keep the harmful
strains in check.
THE BODY’S DEFENSES
NONSPECIFIC DEFENSES AGAINST INFECTION
•
The body’s first lines of defense against
pathogens are nonspecific
- They do not distinguish one pathogen from
another
NONSPECIFIC DEFENSES – 1ST LINE OF DEFENSE
Skin
• Outer layer is a barrier of dead cells that most
bacteria and viruses can’t penetrate.
• Acids in sweat and oils inhibit growth of
microorganisms.
• Sweat contains lysozyme that attacks cell walls
of bacteria. (Found in saliva and tears, too)
NONSPECIFIC DEFENSES – 1ST LINE OF DEFENSE
Digestive system
Stomach acid kills most
bacteria swallowed in food
Respiratory system
• Hairs in nostrils filter air.
• Mucus in respiratory tubes
trap microorganisms
• Cilia sweep mucus up and
out
NONSPECIFIC DEFENSES – 2ND LINE OF DEFENSE –
INTERNAL DEFENSES
Internal defenses
• When an invader penetrates the body’s
external barriers, a set of nonspecific internal
defenses that depend mostly on white blood
cells acts as a second line of defense.
2ND LINE OF NONSPECIFIC DEFENSES
Figure 24.4
2ND LINE OF NONSPECIFIC DEFENSES - WBC
Types of white blood cells
(WBC)
• Macrophages – large cells
that move in the interstitial
fluid and “eat” any bacteria
and virus-infected cell they
come in contact with
• Neutrophils and monocytes
– engulf bacteria and
viruses in infected tissues
• Natural killer cells – attack
cancer cells and infected
body cells
2ND LINE OF NONSPECIFIC DEFENSES
Chemical Warfare
1. Interferons
Virus infects cell & then the
infected cell produces and
releases interferon molecules
to warn neighboring cells of
viral infection
Interferon binds to healthy cell,
activating antiviral protein
production
-What do you think happens
when virus tries to infect this
cell ?
2. Complement Proteins
• Found in blood in
inactive form.
• Activated by immune
system or microbes.
• Make microbes easier
to engulf by
macrophages.
• Or cut lethal holes in
membranes of
microbes.
INFLAMMATORY RESPONSE – NONSPECIFIC
RESPONSE TO INJURY
Figure 24.6
INFLAMMATORY RESPONSE
•
•
•
•
Can be local… like getting
a splinter
- Or
Widespread due to severe
tissue damage or
infection
Increase in the number
of white blood cells
Cells release Pyrogens
(“firemakers”), chemicals
that tell your brain’s
thermostat to turn up the
temperature.
•
Causing a fever!
103oF/39.4oC
•
Will this reduce viral
replication or bacterial
growth?
THE LYMPHATIC SYSTEM
•
•
•
The lymphatic system is
a network of lymphatic
vessels and organs
It returns tissue fluid to
the circulatory system
It fights infections
• Lymph nodes can
become infected
during this war
LYMPHATIC SYSTEM
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
SPECIFIC DEFENSES – THE IMMUNE SYSTEM
The Immune System
• Recognizes and defends
against invading microbes
and cancer cells
• When detects an antigen
increases the number of
cells that either
- Attack the antigen
directly
- Produce defensive
proteins, antibodies
SPECEFICE DEFENSES – THE IMMUNE SYSTEM
The immune system
• Is very specific
• Has memory
- remembers antigens it has been exposed
to
- reacts against the antigens more quickly
and more vigorously
RECOGNIZING THE INVADERS - LYMPHOCYTES
Lymphocytes
• are white blood cells
found most often in the
lymphatic system
• produce the immune
response
• originate from stem
cells in the bone
marrow
RECOGNIZING THE INVADERS - LYMPHOCYTES
•
•
Human body has 2 trillion
WBC produced by stem cells
in bone marrow
Two kinds of lymphocytes
carry out the immune
response
•
•
B cells secrete
antibodies that attack
antigens
T cells attack cells
infected with
pathogens
THE IMMUNE RESPONSE
THE IMMUNE RESPONSE
THE CELL MEDIATED IMMUNE RESPONSE
In the cell-mediated immune response T cells
fight pathogens that have already entered body
cells
Helper T cells
• help activate cytotoxic T cells and macrophages
• stimulate B cells to produce antibodies
Cytotoxic T cells
• Attack body cells infected with pathogens
•
CELL-MEDIATED IMMUNE RESPONSE
Cytotoxic T cells are the only T cells that actually
kill other cells
CELL MEDIATED IMMUNE RESPONSE
•
•
Cytotoxic T cells may
attack cancer cells
The surface
molecules of cancer
cells are altered by
disease
HUMORAL IMMUNE RESPONSE
B cells secrete specific antibody proteins as a form of defense
against given identified antigen*.
*antigen could be from the surface of a cancer cell, virus,
bacteria, or other pathogen…
•
The variable region of the
Antibody that allows it to
Bind onto only 1 specific
type of antigen
ANTIBODIES MARK ANTIGENS FOR ELIMINATION
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
ANTIBODIES MARK ANTIGENS FOR ELIMINATION
Antibodies
• Bind to a certain antigen that triggers
mechanisms to neutralize or destroy the
invaders by
1. Blocking harmful antigens on microbes
2. Clumping bacteria or viruses together
3. Precipitating dissolved antigens
4. Activating complement proteins
IMMUNITY
Immunity is resistance to
specific invaders
Passive immunity TEMPORARY
• Antibodies produced by
another animal are
transferred to you
• Mother to child: before
birth + by breast milk
• If bitten by rabid animal,
treatment injection of
antibodies against rabies
IMMUNITY
Active immunity – LONG
TERM
• Exposed to a pathogen
which triggers the
immune response and the
development of Memory B
cells
• Developing active
immunity by…
- Get sick and
survive
•
Get vaccinated (weakened
form of pathogen)
•
More than 20 different
vaccines available today
IMMUNE RESPONE HAS MEMORY
•
In the primary immune response, memory cells
are produced
- These cells may give the person lifelong
immunity
IMMUNE
RESPONSE HAS A
MEMORY
 Remembers antigens it

Antigen
binding
to B cell
Antigen
B cell
Primary Immune
response
has been exposed to
Reacts against the
antigens more quickly
and more vigorously
Some B cells
develop into
memory B
cells.
2nd Exposure
to Antigen
Memory
B cell
Memory B cell
Divides producing
A LOT more Plasma cells to
Produce HUGH Quantities of
antibodies against reinvading antigen
More memory B cells
Secondary
Immune response
IMMUNE RESPONSE HAS MEMORY
Primary Immune
Secondary Immune
Response
Response
• Occurs when
• Occurs when exposed to
lymphocytes are first
same antigen again
exposed to an antigen
• Immune response is
• Antibodies are produced
faster and stronger
by B cells
• Memory cells divide
• Memory cells are
quickly producing a large
produced
number of lymphocytes
that attack the antigen
• Usually takes several
days
VACCINATIONS
•
•
•
•
•
Person receives a harmless form of an antigen
(Ex: Sabin vaccine used against polio)
Causes the primary immune response
Produces memory cells
When person exposed to actual antigen,
secondary immune response occurs
Person does not get sick
IMMUNODEFICIENCY DISEASES
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•
•
Immune components are lacking, and
infections recur.
May arise through inborn conditions
-SCID: Severe combined immunodeficiency
(lack T& B cells)
Or from disease.
-Example: AIDS (Acquired immune
deficiency syndrome)
HIV/AIDS
Transmission of HIV
• HIV is not transmitted
through casual contact.
• HIV can ONLY be
transmitted through the
exchange of
blood
semen
vaginal secretions
breast milk
HIV: Human Immunodeficiency Virus
HIV/AIDS
How HIV replicates in helper T cell
1. Viral envelope fuses w/ plasma
membrane. Virus disassembles
2. HIV’s Reverse transcriptase enzyme
copies RNA Genome into DNA
3. Double stranded DNA from new DNA
4. HIV’s DNA inserted into cell’s nuclear
DNA (lytic or lysogenic cycle?)
5. Provirus DNA transcribed into RNA
6. Viral RNA translated into viral proteins
(capsomeres and enzymes)
7. New HIV viruses assembled
8. New HIV viruses released
*Helper T cell eventually dies!
•
Why are T cells important to your
immune system?
HIV/AIDS
When helper T cell count drops below …
TH cells per ml of blood
•500 TH cells per milliliter of blood you become vulnerable to opportunistic infections
•200 TH cells per milliliter of blood you go from “HIV positive”  having “AIDS”
HIV/AIDS
•
•
•
•
Can AIDS Be Cured?
No!!!
Scientists have no vaccine yet! Why? The high
mutation rate of the retrovirus genome is
problematic
The virus can be controlled by expensive multidrug
antiviral “cocktails” that fight the virus.
How can new HIV infections be avoided?
With knowledge!
HIV/AIDS
Preventing HIV Infection
• The only no-risk behavior with respect to HIV
and AIDS is abstinence.
• People who share contaminated needles to
inject themselves with drugs are at a high risk
for contracting HIV.
• People who have sex with IV drug abusers are
also at high risk.
RATING THE RISK OF TRANSMISSION
(H) High risk of HIV exposure
(R) Reduced risk of HIV exposure
(N) No HIV exposure
1. Abstinence (NO sexual intercourse of ANY kind)
2. Unprotected sex of ANY kind
3. Sharing needles
4. Getting blood on yourself while helping an injured person
5. _______ Wearing Latex* gloves when helping a person who
is bleeding
*if person has latex allergy, can be substitute with
polyurethane
RATING THE RISK OF TRANSMISSION
6. Sexual intercourse between two UNINFECTED
people who remain monogamous (no other partners)
and NEITHER person shares needles.
7. Receiving a blood transfusion in the USA where all
blood is tested for HIV.
8. An HIV positive mother breast feeding her baby.
9. Using a NEW LATEX condom or oral barrier during
sexual intercourse.
10. Sexual intercourse between two people who
remain monogamous (no other partners) AND one
person shares needles.