Chapter 8
Answers
1
QUICK-CHECK questions
What is meant by the terms ‘self’ and ‘non-self’?
The term ‘self’ refers to proteins that are produced within a person’s body. Proteins
that are not produced within a person’s body are referred to as ‘non-self’.
2
Indicate one way in which a non-specific immune response differs from a
specific response.
A non-specific response acts equally against any infective agent; for example, one line
of defence is intact skin that acts as a barrier against entry by many infective agents.
A specific response acts only against a specific infective agent; for example, a specific
antibody acts against one particular protein of an infective agent.
3
Give an example of the first line of defence of the body against infection.
Intact skin is an important first line of defence against infection. Others components of
the first line of defence include tears, saliva and the mucus secreted by lining of the
respiratory tract.
4
List two kinds of cells that form part of the second line of defence of the body.
The second line of defence of the body includes white blood cells such as neutrophils
and monocytes.
5
What is complement protein? How does it act as part of the second line of
defence?
Complement proteins are certain blood proteins, formed in the liver, which play roles in
the second line of defence of the body. Some complement proteins attach to infective
agents that then become identifiable to phagocytes. Some attract phagocytes to a site
of infection.
6
What is interferon? How does it act as part of the second line of defence?
Interferons are proteins secreted by some cells when they become infected by virus
particles. Interferons have many actions including causing the production of dozens of
antiviral proteins, some of which make other cells more resistant to the viral infection.
7
What roles do cytokines play in the immune system?
Cytokines are protein molecules that act as messengers between cells of the immune
system.
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Chapter 8: QUICK-CHECK answers
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What are the two main groups of cells involved in specific immunity and where
do they mature?
The two main groups of cells involved in specific immunity are B cells and T cells. B
cells drive from a B cell progenitor and mature in the bone marrow. T cells derive from
a T cell progenitor and mature in the thymus.
9
What role do protein markers on foreign cells play in the immune response?
Protein markers on foreign cells can be identified as non-self cells by an organism.
This identification initiates an immune response by the organism against the non-self
cells.
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What is an immunoglobulin? Where would you find one?
Immunoglobulin is the general term applied to any antibody molecules, whether found
in body fluids and or on the surface of B cells.
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What cells are produced by the cloning of B cells? What is their function?
When the presence of an antigen activates a B cell, the B cell replicates many times.
Many of these cells produced by this cloning differentiate into plasma cells whose
function is to produce large numbers of antibodies that act specifically against the
antigen that initiated the cloning response by the B cell. Other cells produced by the
cloning differentiate into memory cells that are long lasting and respond immediately to
a future invasion by the same antigen.
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Why is cloning of B cells important in the immune response?
Cloning of B cells is important to ensure that large amounts of antibodies can be
produced to prevent the development of disease caused by the invading organism (the
antigen) or reduce the severity of the disease.
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What are the main features of the primary antibody response?
The primary antigen response occurs after an initial infection. This includes clonal
expansion of B cells and the production of antibodies. After the disease has cleared,
the level of antibodies declines.
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In what ways does the secondary antibody response differ from the primary
antibody response?
A secondary antibody response after a second infection is much more rapid than the
primary antibody response occurring after the first infection. The response is more
rapid because memory cells are in existence from the prior infection, and these cells
immediately produce increased levels of antibodies without the need for clonal
expansion.
15
Are all maternal antibodies equally important for a fetus? Explain.
Different types of antibodies have different characteristics and functions. Of the five
different kinds of antibodies, only one — IgG — is able to cross the placenta and so is
most important for a fetus. These IgG antibodies can act against viruses and some
bacteria.
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Chapter 8: QUICK-CHECK answers
16
Explain why immunity involving T cells is called cellular immunity.
Unlike B cells, T cells do not form antibodies. T cells act directly with other cells in the
immune response, hence the name cellular immunity.
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What is the function of cytotoxic cells?
Cytotoxic cells are a special kind of T cell, called Tc. These Tc cells kill body cells that
have been infected by a virus.
18
What does lymph contain?
Lymph is tissue fluid that circulates in lymphatic vessels. This tissue fluid also contains
memory B cells and T cells that can act should an infection occur.
19
Name three lymphoid tissues or organs.
Lymphoid tissues include:
 spleen
 lymph nodes in various locations in the body, such as in the groin or associated
with the gut
 bone marrow.
20
A child develops the disease tuberculosis and later recovers. Explain whether
the child is likely to have immunity to the disease five years later.
The child is likely to have an ongoing immunity to the disease after an infection of
tuberculosis. Memory cells will exist in the body; they can respond immediately by
producing antibodies if an infection occurs later and so prevent development of the
disease.
21
Not all adults have been vaccinated against tetanus. One such person stands on
a rusty nail and is at risk of developing the disease. The person receives an
injection of antitoxin shortly after the accident. Explain whether the person is
likely to have an immunity to tetanus five years later.
The person is unlikely to have an immunity to tetanus. The antitoxin given to the adult
would have killed the invading organism. This is most likely to have occurred before
the person’s immune system had time to react fully to the invading organism. It is
unlikely that there was sufficient time for memory cells to be produced. In the absence
of memory cells, no immunity exists against the organism responsible for the particular
disease.
22
Explain the main differences between non-specific immunity and specific
immunity.
Non-specific immunity acts equally against any infective agent; for example, intact skin
acts as a barrier against entry by many infective agents. Likewise, tears and saliva that
contain lysozymes, an enzyme that causes bacterial membranes to rupture, are also
part of the non-specific response of the human body to infection. Natural flora on body
surfaces occupy space and reduce the chance of pathogens entering through those
surfaces.
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Chapter 8: QUICK-CHECK answers
Specific immunity acts against one specific infective agent only; for example, the
proliferation of B cells initiated by entry of an infective agent into the body, and the
antibodies produced by these B cells, act only against that specific infective agent.
23
Outline one way in which vaccines or antivenoms are made.
A small ‘dose’ of the infective agent or venom is injected into an animal, such as a
rabbit. Because the dose is small, it does not kill the rabbit but stimulates the
production of antibodies against the infective agent. The animal is given a series of
such injections, with each successive dose being higher than the previous dose. This
means the animal produces higher and higher levels of antibodies able to act against
the specific disease. These antibodies are extracted from the blood of the animal at
regular intervals and incorporated into vaccines.
24
Explain why treatment of transplant patients with the drug cyclosporin reduces
the chance of transplant rejection.
Cyclosporin is a drug that inhibits the normal immune response. It acts specifically on
T cells that normally react with other cells. This reduces the potential of the host’s T
cells reacting with transplanted tissue.
25
Explain why a person suffering from an allergy may be treated with an
antihistamine.
During an allergic response, mast cells accumulate around blood vessels and release
histamine when they rupture. Histamine causes contraction of smooth muscles; for
example, the muscles around tubules into lungs can contract, making breathing
difficult. Antihistamines react with and reduce the effect of histamines.
26
Explain what is meant by an auto-immune disease.
An auto-immune disease is one in which the body fails to identify self material and
makes antibodies against the body’s own tissues.
27
Explain why some women are given an injection of immunoglobulin shortly after
the birth of a baby.
If a Rhesus negative woman has a Rhesus positive baby, some of the baby’s Rh
positive cells may cross the placenta into the mother’s bloodstream. If this occurs, the
mother produces Rh antibodies that may be fatal for a future pregnancy if the second
baby is also Rhesus positive. Such a mother is given an injection of immunoglobulin,
high in Rhesus antibodies after the birth of the first child. The Rh antibodies in the
immunoglobulin react with any Rhesus positive cells that have entered the mother
from the first baby. These cells are destroyed and so the mother’s immune system fails
to be activated to produce Rhesus antibodies.
28
Explain why a person with AIDS is particularly susceptible to a range of
infections.
AIDS, acquired immune deficiency syndrome, is a disease that destroys T helper cells.
As these cells play an important role in the action of the immune system, a person with
AIDS is particularly susceptible to infection because their immune response is
compromised.
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Chapter 8: QUICK-CHECK answers
29
A baby is born with a defective thymus. Comment on the baby’s ability to resist
infection — immediately after birth and at six months of age.
During pregnancy, maternal antibodies pass across the placenta into the developing
baby. Hence, at birth, a baby possesses a range of antibodies similar to those found in
the mother. Also, the baby obtains more of these antibodies for as long as it is breast
fed. These antibodies give the baby protection against infection by some organisms.
However, when breastfeeding ceases (say, at six months), this source of protection is
lost. In a baby with a defective thymus, it is likely that T cells are unable to mature. The
lack of T cells makes the baby increasingly susceptible to infection as the level of
maternal antibodies reduces to zero.
30
Why are galls effective in reducing the spread of infection in some plants?
A gall is produced by some plants when they are infected by insects or other
organisms. When tissue is damaged by the invasion by the infective agent, the
adjacent plant cells release hormones that stimulate growth of the local tissue to
produce gall that limits the spread of the infection.
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