6.3 & 11.1 Defense Against
Infectious Disease
Immune System Vocab
Pathogen
An organism or virus that causes a disease
Antigen
Any foreign macromolecule (either proteins,
polysaccharides or structures on the surface of bacteria) that
triggers an immune response
Antibody
Antibodies are proteins that bind to particular antigens and
mark them for elimination from the body
Antibiotics
Any substance that is able to kill or inhibit a microorganism
such as bacteria
Passive versus Active Immunity
Passive immunity is due to the acquisition of
antibodies from another source
Such as
when a developing fetus acquires antibodies from
its mother
when they are artificially injected into a person
Active immunity is when antibodies are
produced by the person themselves after his or
her immune system is triggered by antigens
Immune System Vocab cont.
Virus
An infective agent consisting of a protein coat surrounding
an RNA or DNA core
Are not cells and do not possess membranes or organelles.
They cannot manufacture their own proteins and must
invade living cells to take over their protein production
“machinery”
Leucocytes
White blood cells
Phagocytic leucocytes
Specialized white blood cells that engulf foreign/invading
pathogens and destroy them
Different Types of Leucocytes
The only ones we need to know are monocytes
and macrophages, and lymphocytes
Why are antibiotics effective against
bacteria, but not viruses?
Most antibiotics don’t kill bacteria
Antibiotics disrupt their reproduction (binary
fission) by preventing formation of the bacterial
cell wall in the “daughter cells” (a part of the
cell’s metabolism)
Since viruses aren’t cells and don’t produce
cell walls, antibiotics are not effective against
them
What are the different components
of the immune system?
Skin
Mucous membranes
Phagocytic leukocytes
Antibodies
Skin and Mucous Membranes
These are a form of external defense preventing
pathogens from entering the body
Skin forms a physical barrier
Mucous membranes surround invading
pathogens
Body senses excess mucous, induces coughing
Coughing expels the mucous and the trapped
pathogen
Phagocytic Leucocytes
A type of white blood cell
Float around the body in blood
Phagocyte surrounds the pathogen by endocytosis
A vacuole containing the pathogen travels to a
lysosome
The membranes of the vacuole and lysosome fuse
Digestive enzymes in the lysosome destroy the
pathogen
The pathogen “debris” is released by exocytosis
Phagocytic Leucocyte Diagram
Antibodies
Proteins that recognize one kind of antigen
Similar to enzymes (lock and key)
Lock and key called
“epitope”
React by binding to the antigen
Destroys antigen
Or
Inactivates antigen
Antibody Production
Pathogen is in the body
Phagocytic leucocytes called macrophages ingest the pathogens
Phagocytes “present” the antigens from the pathogens on their cell
surface.
T-helper cells (another type of leucocyte that is specific to that
antigen) bind to the antigen presented by the macrophages and are
activated/stimulated
Meanwhile, B-cells bind to the antigen, and present the antigen as the
phagocytes
did
Antibody Production cont.
The activated T-helper cells then bind to B-cells and activate them;
This triggers the B-cells to undergo mitosis to form memory cells and
plasma cells
Short-lived Plasma B-cells secrete antibodies quickly that neutralize the
pathogen
Memory B-cells stay in the blood for a long time and enable a more rapid
response by the immune system if the same pathogen invades in the future
Monoclonal Antibodies
Monoclonal antibodies—
large quantities of a single type of antibody
produced in a laboratory
Hybridoma cell
memory B cell fused with a tumor cell
divides uncontrollably, producing a large
amount of antibodies
Monoclonal Antibody Production
1. Antigens that correspond to a desired antibody are
injected into an animal
2. B-cells producing the desired antibody are
harvested
3. Tumor cells are obtained from another source
(tumor cells grow and divide endlessly)
4. B-cells are fused with tumor cells, producing
hybridoma cells that divide endlessly, providing the
desired antibodies
5. The hybridoma cells are cultured and the antibodies
they produce are extracted and purified
Application of Monoclonal Antibodies:
Rabies Treatment
Rabies usually causes death in humans before
the immune system can control it.
Injecting monoclonal antibodies when a person
gets infected will control the virus
At the same time, the person's body begins
making its own antibodies
Triggers two-fold immune response
Passive through injection
Active through body’s production
Application of Monoclonal Antibodies:
Malaria Diagnosis
1. Monoclonal antibodies are made to bind to
antigens in malarial parasites
2. A test plate is covered with antibodies
3. The sample is left on the plate long enough
for malaria antigens (if present) to bind to
antibodies
4. The sample is rinsed off
Any bound antigens are detected using more
monoclonal antibodies with attached colorchanging enzyme
Challenge and Response,
Clonal Selection, and Memory Cells
B-cells make antibodies
The immune system can make 1015 different types of
antibodies (but not all at once)
A few of each type of B-cell are produced and they
wait until the body is infected with an antigen
When this occurs, they multiply to form many clones
This is called clonal selection
A clone of B-cells can produces large amounts of
antibodies quickly and give immunity to a disease
Only after the immune system is challenged by a disease
This is called the challenge and response system
Vaccination
A weakened or dead version of a pathogen is injected
into the body, causing the immune system to mount a
primary response
This results in the production of B memory cells
The B-cells "remember" the antibodies to produce in
response to the pathogen
When the real pathogen strikes, a secondary response
occurs, aided by the memory cell production of
pathogen-specific antibodies
This response is much stronger than the primary
response and prevents any ill effects
HL Only: Benefits and Dangers of Vaccines
Benefits
prevent disease and epidemics
results in a healthier society
reduces long-term medical costs
speed up the body's response to a future
disease by memory B-cells
Dangers
possible allergic reactions
danger of side-effects
HIV and the Immune System
HIV virus kills Helper T-cells
Helper T-Cells tell B-cells there is a pathogen
Immune system cannot mount an effective
defense against invading pathogens
Patients then succumb to secondary infections
Blood Clotting
Damaged cells in the blood vessel release
compounds called “clotting factors”
These factors trigger the formation of the
enzyme thrombin
Thrombin catalyzes the conversion of soluble
fibrinogen in the blood to the fibrous protein
fibrin
Fibrin forms threads which create an
interwoven net
Platelets and blood cells get caught in the net
and plug up the wound
Blood Clotting Diagram
IB Exam Question
1. Which is not true of active immunity?
A.
B.
C.
D.
(1 mark)
It can be produced by exposure to a disease
causing organism.
It can be produced artificially.
It can be produced by a virus.
It can be transferred via the colostrum.
Correct answer: D
If you’ve never heard of it, it’s probably a trick
question!
IB Exam Question
2. Describe how human skin and mucous
membranes act as barriers to pathogens.
(4 marks)
To receive full marks, responses must have two answers for each.
Skin
lower pH / acid to keep bacteria from growing / chemical
barrier;
fatty acids / waxes antimicrobial;
physical barrier to prevent entry / dry skin inhibits bacterial
growths;
bacteria on skin / mucous membranes prevent other bacteria
from growing;
antimicrobial / lysozyme in sweat and saliva (mucous
membrane) to keep bacterial growth in check;
Mucous membranes
mucous traps bacteria / sticky / mucus slightly acidic i.e. vagina
cilia sweep mucous up to be swallowed to kill bacteria;
contain macrophages / phagocytes;
IB Exam Question
3. Outline how phagocytic leucocytes ingest
pathogens in the blood and in body tissues.
The phagocytic cell surround the pathogen by
endocytosis
A vacuole containing the pathogen travels to a
lysosome and the membranes of the vacuole
and lysosome fuse
Digestive enzymes in the lysosome destroy the
pathogen
The pathogen “debris” is released by exocytosis
IB Exam Question
4. Which of the following represents the correct sequence
of events when the body is responding to a bacterial
infection?
(1 mark)
I.
Antigen presentation by macrophages
II. Activation of B-cells
III. Activation of helper T-cells
A. I, II, III
B. I, III, II
C. III, II, I
D. II, III, I
Correct answer: B
IB Exam Question
5. Explain antibody production.
A vaccine is injected into body
This vaccine contains killed / weakened pathogen or fragments of
pathogens
Phagocytic leucocytes called macrophages ingest the pathogens and
“present” the antigens from the pathogens on their cell surface.
Helper-T cells (another type of leucocyte that is specific to that
antigen) bind to the antigen presented by the macrophages and are
activated/stimulated
Meanwhile, B-cells bind to the antigen, and present the antigen as the
T cells did
The activated T-helper cells then bind to B-cells and activate them;
This triggers the B-cells to undergo mitosis to form memory cells and
plasma cells
Short-lived Plasma B-cells secrete antibodies quickly that neutralize
the pathogen
Memory B-cells stay in the blood for a long time and enable a more
rapid response by the immune system if the same pathogen invades
in the future
IB Exam Question
6. Which type of cell is responsible for secondary
immune responses to a pathogen?
(1 mark)
A.
B.
C.
D.
Cytotoxic T-cells
Phagocytes
Macrophages
Memory cells
Correct answer: D
IB Exam Question
HL Only: 7. Outline the principles of challenge and response,
clonal selection, and memory cells as the basis of immunity.
B-cells make antibodies
The immune system can make 1015 different types of
antibodies (but not all at once)
A few of each type of B-cell are produced and they
wait until the body is infected with an antigen
When this occurs, they multiply to form many clones;
this is called clonal selection
A clone of B-cells can produces large amounts of
antibodies quickly and give immunity to a disease,
only after the immune system is challenged by a
disease
This is called the challenge and response system
IB Exam Question
8. Which type of immunity usually results
from vaccination?
(1 mark)
A.
B.
C.
D.
active, natural
active, artificial
passive, natural
passive, artificial
Correct answer: B
IB Exam Question
9. Discuss the benefits and dangers of
vaccination.
(8 marks)
Benefits [5 max]
prevent disease;
eliminate diseases: like smallpox
prevent epidemics;
healthier society;
reduce medical cost;
disease free cattle / more food;
Dangers [3 max]
allergic reactions / anaphylactic shock;
weakened virus becomes virulent / causes the disease;
harmful side-effects;
IB Exam Question
10. Which curve shows the response of the immune
system to a vaccine, followed by an infection?
(1 mark)
Correct answer: B
IB Exam Question
HL Only: 11. Describe the production of
monoclonal antibodies along with one use of
them in diagnosis and one use in treatment.
Monoclonal antibodies - large quantities of a single type of
antibody, produced using the procedure outlined below.
1. Antigens that correspond to a desired antibody are
injected into an animal.
2. B-cells producing the desired antibody are extracted.
3. Tumor cells are obtained from another source (tumor
cells grow and divide endlessly).
4. B-cells are fused with tumor cells, producing hybridoma
cells that divide endlessly, providing the desired
antibodies.
5. The hybridoma cells are cultured and antibodies they
produce are extracted and purified.
IB Exam Question
HL Only: 11. Describe the production of
monoclonal antibodies along with one use of
them in diagnosis and one use in treatment. cont.
Treatment of rabies
Rabies usually causes death in humans before the immune system
can control it.
Injecting monoclonal antibodies when a person gets infected will
control the virus and at the same time, the person's body begins
making its own antibodies.
Diagnosis of malaria
1. Monoclonal antibodies are made to bind to antigens in malarial
parasites.
2. A test plate is covered with antibodies.
3. The sample to be tested is left on the plate long enough for malaria
antigens (if present) to bind to antibodies.
4. The sample is rinsed off and any bound antigens are detected
using more monoclonal antibodies with attached color-changing
enzyme.
IB Exam Question
12. Outline the effect of HIV on the immune system.
The HIV virus results in the death of Helper
T-cells
Therefore, the immune system of the infected
individual cannot mount an effective defense
against invading pathogens
Patients can then succumb to secondary
infections
IB Exam Question
13. Describe the process of blood clotting.
Damaged cells in the blood vessel release
compounds called “clotting factors”
These factors trigger the formation of the
enzyme thrombin
Thrombin catalyzes the conversion of soluble
fibrinogen in the blood to the fibrous protein
fibrin
Fibrin forms threads which create an
interwoven net. Platelets and blood cells get
caught in the net and plug the open cut