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1. You start a new job in a research lab. The lab protocols state that you should
check your hands for any breaks in the skin before handling infectious agents.
This is because the epidermis fights microbial infections by—
a. making the surface of the skin acidic
b. excreting lysozyme to attack bacteria
c. producing mucus to trap microorganisms
d. all of the above
The correct answer is d—
A. Answer a is incorrect. Although the oil and sweat glands produce substances on
the surface that make the surface acidic enough to inhibit the growth of
microorganisms, this is not the only correct answer.
The correct answer is d—
B. Answer b is incorrect. Although the sweat secreted on the surface of the skin
contains lysozyme that digests bacterial cell walls, this is not the only correct
answer.
The correct answer is d—
C. Answer c is incorrect. Although the epidermal cells that line the respiratory tract
secrete a sticky mucus that traps microorganisms before they enter the lungs, this
is not the only correct answer.
The correct answer is d—all of the above
D. Answer d is correct. The skin is the first line of defense against the invasion of
microorganisms into the body. The skin provides a nearly impenetrable barrier,
but also secretes chemicals that kill microorganisms or traps them so that they
can’t enter the body.
2. Cells that target and kill body cells infected by viruses is are—
a. macrophages
b. natural killer cells
c. monocytes
d. neutrophils
The correct answer is b—
A. Answer a is incorrect. Macrophages engulf a microorganism such as a virus
directly; they do not kill body cells infected by the virus.
The correct answer is b—natural killer cells
B. Answer b is correct. A natural killer cell is a type of leukocyte involved in the
nonspecific immune response. The natural killer cell identifies a body cell that
has been infected by a virus and punctures a hole in the cell with proteins called
perforins. The invading virus dies with the cell.
The correct answer is b—
C. Answer c is incorrect. Monocytes are the precursors of macrophage cells.
Monocytes circulate throughout the body, and in response to an infection they
travel to the site of an infection and transform into a macrophage.
The correct answer is b—
D. Answer d is incorrect. Neutrophils are cells that, like microphages, engulf
invading microorganisms through phagocytosis. But, unlike macrophages,
neutrophils release chemicals that kill microorganisms in the immediate vicinity
of the attacked cell but also end up killing themselves.
3. Structures on invading cells recognized by the immune system are known as—
a. antigens
b. interleukins
c. antibodies
d. lymphocytes
The correct answer a—antigens
A. Answer a is correct. Cells contain proteins and other molecules on their surface,
which are identified by the cells of the immune system. If the cells are recognized
as being body cells, they are left alone. If the surface molecules are determined to
be foreign, they trigger an immune response. Molecules that trigger an immune
response are called antigens.
The correct answer is a—
B. Answer b is incorrect. An interleukin belongs to a class of proteins that are
released from cells of the immune system to trigger steps in the immune response.
They are not surface molecules and they do not induce an immune response; they
are part of the immune response.
The correct answer is a—
C. Answer c is incorrect. An antibody is a molecule that is released from plasma cells
as part of the humoral immune response. Antibodies are not surface molecules
and they do not induce an immune response; they are part of the immune
response.
The correct answer is a—
D. Answer d is incorrect. A lymphocyte is a white blood cell, specifically a T cell or
B cell. These cells carry out the specific immune response and are not surface
molecules.
4. Which one of the following acts as the “alarm signal” to activate the body’s
immune system by stimulating helper T cells?
a. B cells
b. Interleukin-1
c. Complement
d. Histamines
The correct answer is b—
A. Answer a is incorrect. B cells are part of the body’s immune system that provide
humoral immunity, which is activated by the “alarm signal,” and so it cannot be
the alarm signal.
The correct answer is b—Interleukin-1
B. Answer b is correct. Interleukin-1 is released by macrophages after they’ve
encountered an antigen. The release of interleukin-1 stimulates the proliferation
of helper T cells. The helper T cells then release other chemicals that stimulate
macrophage activity and cytotoxic T cells.
The correct answer is b—
C. Answer c is incorrect. Complement proteins are found in the bloodstream; from
there, they form a response to pathogens known as the membrane attack complex.
The correct answer is b—
D. Answer d is incorrect. Histamines are released by mast cells. Although
histamines are important in triggering the inflammatory response, it is not the
“alarm signal” that begins the stimulation of T-cell and B-cell proliferation, which
is the third line of defense.
5. Cytotoxic T cells are called into action by the—
a. presence of histamine
b. presence of interleukin-1
c. presence of interleukin-2
d. interferon
The correct answer is c—
A. Answer a is incorrect. Histamines are released by mast cells and stimulate the
inflammatory response by causing vasodilation and increased permeability of
capillaries to lymphocytes. However, histamines do not stimulate cytotoxic T
cells.
The correct answer is c—
B. Answer b is incorrect. Although interleukin-1 stimulates the proliferation of
helper T cells, it does not trigger the proliferation of cytotoxic T cells.
The correct answer is c—presence of interleukin-2
C. Answer c is correct. Interleukin-1 is released from macrophages that have
encountered an antigen. Interleukin-1 then stimulates the proliferation of helper T
cells. The helper T cells then in turn release interleukin-2, which stimulates the
proliferation of cytotoxic T cells that can attack cells that carry the antigen.
The correct answer is c—
D. Answer d is incorrect. Interferon works at the nonspecific response level. It is
released by virus-infected cells and serves to stimulate nearby (uninfected) cells
to produce antiviral proteins.
6. The primary response to invading microorganisms involves ________, and the
secondary response involves ________.
a. IgG; IgA
b. IgM; IgE
c. IgE; histamines
d. IgM; IgG
The correct answer is d—
A. Answer a is incorrect. IgG is the immunoglobin primarily involved in the
secondary response and IgA is primarily found in body secretions.
The correct answer is d—
B. Answer b is incorrect. Although it is true that IgM is involved in the primary
response, IgE is not involved in the secondary response. IgE is involved in the
inflammatory response, promoting the release of histamines.
The correct answer is d—
C. Answer c is incorrect. IgE and histamines are involved in the inflammatory
response, not in the general humoral immune response.
The correct answer is d—IgM; IgG
D. Answer d is correct. The first antibodies produced in the humoral immune
response are the IgM antibodies, which are very effective at activating the
complement system. This initial wave of antibody production peaks after about
one week; this is called the primary response. The primary response is followed
by a far more extended production of IgG antibodies, which is the secondary
response.
7. How is your body able to detect millions of different antigens?
a. The few hundred immunoglobulin genes can be rearranged or can undergo
mutations to form millions of antibody molecules.
b. There are millions of different antibody genes.
c. The few hundred immunoglobulin genes undergo antigen shifting.
d. Each B cell has a different set of immunoglobulin genes, and so the
activation of different B cells produces different antibodies.
The correct answer is a—The few hundred immunoglobulin genes can be rearranged or
can undergo mutations to form millions of antibody molecules.
A. Answer a is correct. There are only a few hundred genes encoded for
immunoglobulins, but those genes can be rearranged, a process called somatic
rearrangement, or can undergo mutations, a process called somatic mutation, to
produce millions of gene combinations. Each gene combination produces a
different immunoglobulin molecule.
The correct answer is a—
B. Answer b is incorrect. The human genome only has some 30,000 genes, therefore
it could not contain a separate gene for every immunoglobulin molecule that is
produced in the body.
The correct answer is a—
C. Answer c is incorrect. Antigen shifting is the process whereby a pathogen is able
to “get around” the immune system by the mutation of genes that encode for
surface proteins (antigens) so that the antibodies that were produced to fight the
pathogen are no longer effective.
The correct answer is a—
D. Answer d is incorrect. There is only one set of genes per organism and each and
every cell in the body contains the same genes (although gametes only contain
one copy of each gene). Different cells cannot have a different set of genes.
8. If you have type AB blood, which of the following results would be expected?
a. Your blood agglutinates with anti-A antibodies only.
b. Your blood agglutinates with anti-B antibodies only.
c. Your blood agglutinates with both anti-A and anti-B antibodies.
d. Your blood would not agglutinate with either anti-A or anti-B antibodies.
The correct answer is c—
A. Answer a is incorrect. AB blood contains red blood cells that carry both A and B
antigens on their cell surfaces, and so their blood would react with anti-B
antibodies and not just with anti-A antibodies.
The correct answer is c—
B. Answer b is incorrect. AB blood contains red blood cells that carry both A and B
antigens on their cell surfaces, and so their blood would react with anti-A
antibodies and not just with anti-B antibodies.
The correct answer is c—Your blood agglutinates with both anti-A and anti-B antibodies.
C. Answer c is correct. AB blood contains red blood cells that carry both A and B
antigens on their cell surfaces, and so their bodies do not produce antibodies
against either of these two proteins because they are not seen as foreign. If either
anti-A or anti-B antibodies are mixed with these red blood cells, the blood would
agglutinate.
The correct answer is c—
D. Answer d is incorrect. AB blood contains red blood cells that carry both A and B
antigens on their cell surfaces, and so their blood would reaction with either anti-
A antibodies or anti-B antibodies. The addition of either antibody would result in
agglutination.
9. The HIV virus is particularly dangerous because it attacks—
a. cells with the CD4+ coreceptor
b. helper T cells
c. 60–80% of circulating T cells in the body
d. all of the above
The correct answer is d—
A. Answer a is incorrect. Although it is true that HIV attacks all cells with the CD4+
coreceptor, which are T cells, and eventually kills the cells it attacks, essentially
wiping out the immune system, this is not the only correct answer.
The correct answer is d—
B. Answer b is incorrect. Although it is true that the HIV virus attacks and kills
helper T cells in the body, which are key to mounting a specific immune response,
this is not the only correct answer.
The correct answer is d—
C. Answer c is incorrect. Although it is true that the HIV virus attacks helper T cells,
which make up 60–80% of circulating T cells in the body, this is not the only
correct answer.
The correct answer is d—all of the above
D. Answer d is correct. The HIV virus is so destructive to the body because it
recognizes, attacks, and eventually kills cells that carry the CD4+ coreceptor,
which is present on the surfaces of the helper T cells. Helper T cells make up 60–
80% of the circulating T cells in the body and are necessary for the stimulation of
cytotoxic T-cell and B-cell proliferation. Without helper T cells, the immune
system essentially shuts down.
Hint: One mechanism for defeating the vertebrate immune system is to attack the
immune mechanism itself. Helper T cells and inducer T cells are CD4+ T cells.
Therefore any pathogen that inactivates CD4+ T cells leaves the immune system
unable to mount a response to any foreign antigen. HIV attacks cells with the CD4+
coreceptor and essentially eliminates 60–80% of the circulating T cells in the body.
10. Diseases in which the person’s immune system no longer recognizes its own
MHC proteins are called—
a. allergies
b. autoimmune diseases
c. immediate hypersensitivity
d. delayed hypersensitivity
The correct answer is b—
A. Answer a is incorrect. Allergies are caused by an overactive immune system, not a
failure of the immune system to recognize “self”-proteins. Allergies, also called
hypersensitivity, occur when the immune system overreacts to harmless antigens,
called allergens, and triggers a full-blown immune response when it is not needed.
The correct answer is b—autoimmune diseases.
B. Answer b is correct. Autoimmune diseases occur when the body’s immune system
doesn’t recognize the self-MHC proteins on one’s own cells and mounts an
immunological attack of self-antigens. This results in inflammation and organ
damage against the tissues of the body.
The correct answer is b—
C. Answer c is incorrect. Immediate hypersensitivity is a form of allergic reaction
that involves an abnormal B-cell response to an allergen, producing symptoms in
seconds or minutes of exposure. This is not the body attacking its own tissues,
but rather the body acting in a hypersensitive way to a harmless allergen.
The correct answer is b—
D. Answer d is incorrect. Delayed hypersensitivity is a form of allergic reaction that
involves an abnormal T-cell response to an allergen, producing symptoms within
48 hours of exposure. This is not the body attacking its own tissues, but rather the
body acting in a hypersensitive way to a harmless allergen.
Hint: Autoimmune diseases are produced by failure of the immune system to
recognize and tolerate self-antigens. This failure results in the activation of
autoreactive T cells and the production of autoantibodies by B cells, causing
inflammation and organ damage. There are over 40 known or suspected autoimmune
diseases that affect 5–7% of the population.
11. Suppose that you get a paper cut while studying. Which of the following
responses will occur last?
a. Injured epidermal cells release histamine
b. Bacteria enter the cut
c. Helper T cells are activated
d. Macrophages engulf bacteria
The correct answer is c—
A. Answer a is incorrect. The release of histamine would be one of the earlier events
in this sequence, not the last.
The correct answer is c—
B. Answer b is incorrect. The entry of bacteria into the body would be one of the
earlier events in this sequence
The correct answer is c—Helper T cells are activated
C. Answer c is correct. Helper T-cell activation relies on the presentation of antigen
and the release of interleukin-1, events that would occur after the other choices
listed.
The correct answer is c—
D. Answer d is incorrect. It is the engulfment of pathogens that allows the
macrophage to serve as an antigen-presenting cell which is required for helper Tcell activation.
12. If you wanted to cure allergies by bioengineering an antibody that would bind and
disable the antibody responsible for allergic reactions, which of the following
would you target?
a. IgG
b. IgA
c. IgE
d. IgD
The correct answer is c—
A. Answer a is incorrect. IgG is involved in the secondary response to a pathogen
and is not specific to the immune response.
The correct answer is c—
B. Answer b is incorrect. IgA is the prevalent antibody found in the body secretions
and is not specific to the immune response.
The correct answer is c—IgE
C. Answer c is correct. IgE is responsible for causing allergic release of histamine
and would be an appropriate target for your project.
The correct answer is c—
D. Answer d is incorrect. IgD molecules serve as B-cell receptors and are not
specific to the allergic response.
13. Why don’t we become immune to influenza viruses?
a. Because they attack only the helper T cells, thereby suppressing the
immune system
b. Because they alter their surface proteins and thus avoid recognition
c. Because they don’t actually generate an immune response, the “flu” is
actually an inflammatory response
d. Because they are too small to serve as antigens
The correct answer is b—
A. Answer a is incorrect. The target cells of influenza viruses are not helper T cells.
HIV targets the CD4 receptors of helper T cells.
The correct answer is b—Because they alter their surface proteins and thus avoid
recognition
B. Answer b is correct. By altering their surface proteins, these viruses force a new
immune response each time you are exposed, therefore no immunity arises.
The correct answer is b—
C. Answer c is incorrect. The symptoms of the “flu” are a response by the specific
defenses.
The correct answer is b—
D. Answer d is incorrect. Even though viruses are small they can still serve as
antigens and generate an immune response.
14. Suppose that a new disease is discovered that suppresses the immune system.
Which of the following would indicate that the disease specifically affects the B
cells rather than the helper or cytotoxic T cells?
a. A decrease in the production of interleukin-2
b. A decrease in interferon production
c. A decrease in the number of plasma cells
d. A decrease in the production of interleukin-1
The correct answer is c—
A. Answer a is incorrect. Interleukin-2 is produced by helper T cells and therefore
changes in its production could not be directly linked to B lymphocytes.
The correct answer is c—
B. Answer b is incorrect. Interferon is a local signal and has no direct relationship to
B lymphocytes
The correct answer is c—A decrease in the number of plasma cells
C. Answer c is correct. B cells, when activated, produce plasma cells which in turn
produce antibodies.
The correct answer is c—
D. Answer d is incorrect. Interleukin-1 is not produced by B cells and so would not
be an indicator of disease among these cells.
15. If you wanted to design an artificial cell that could safely carry drugs inside the
body. Which of the following molecules would you need to mimic to deter the
immune system?
a. MHC-1
b. Interleukin-1
c. Antigen
d. Complement
The correct answer is a—MHC-1
A. Answer a is correct. The MHC-1 complex identifies a cell as belonging to the
body in questions and so would allow safe passage of the artificial cell through
the bloodstream.
The correct answer is a—
B. Answer b is incorrect. Mimicking interleukin-1 would not prevent an immune
response, instead it would aggravate it.
The correct answer is a—
C. Answer c is incorrect. Antigens cause immune responses; mimicking one would
cause the destruction of the artificial cell.
The correct answer is a—
D. Answer d is incorrect. Complement proteins respond to infection by creating
holes in cell membranes. The presence of these on the artificial cell membrane
would not help the cell move through the bloodstream.
Challenge Questions
1. Suppose you take a job in the marketing department of a cosmetic company.
Always seeking a competitive advantage, the vice president of marketing has
decided to advertise the new skin lotion as having immune-enhancing effects.
The lotion is produced from secretions of a plant that releases extremely watery,
alkaline fluid. Explain how you will market this product as an immune-enhancer.
Answer—It would be difficult to advertise this lotion as immune-enhancing. The skin
serves as a barrier to infection because it is oily and acidic. Applying a lotion that is
watery and alkaline will dilute the protective effects of the skin secretions, thereby
inhibiting the immune functions. Perhaps it is time to look for another job.
2. Your new kitten scratches your roommate. Her skin is reddened and feels warm
and sore to the touch; she thinks she has contracted some kind of fatal infection.
In order to deflect her anger (she is definitely not a cat person!), you try telling
her about the activities of the nonspecific defense system. Explain what is actually
happening to her skin.
Answer—The scratch has caused an inflammatory response. Although it is very likely
that some pathogens entered her body through the broken skin, the response is actually
generated by the injury to her tissue. The redness is a result of the increased dilation of
blood vessels caused by the release of histamine. This also increases the temperature of
the skin by bringing warm blood closer to the surface. Leakage of fluid from the vessels
causes swelling in the area of the injury, which can cause pressure on the pain sensors in
the skin. All of these serve to draw defensive cells and molecules to the injury site,
thereby helping to defend her against infection.
3. Some people claim that they never catch colds. How could you show that this is
due to a difference in receptors on their respective cell surfaces?
Answer—There are a number of ways that this could be done. However, one method
would be to show that viral genetic material never appears within the cells of those who
claim immunity. Another method would involve testing for the presence of interferon,
which is released by cells in response to viral infection.