Do You Understand Concept 31.1?
List the differences between innate and adaptive immunity.
Answer:
Innate immunity is nonspecific. It may be present all the
time or activated in response to an injury or invasion. Innate systems include
the skin and toxic molecules, which provide a rapid first line of defense, and
phagocytic cells that ingest foreign particles. Adaptive immunity is specific
and distinguishes between substances as self or nonself. Found only in
vertebrates, adaptive immunity is slow to develop and involves proteins such as
antibodies and T cell receptors that can recognize and destroy foreign
particles.
Rarely, a person is born with a genetic disease and has no
lymphocytes. What would be the consequences of this situation for the immune
system? Explain why such a person would have to be very careful about going
outdoors.
Answer:
Lymphocytes include both B cells and T cells and are involved
in adaptive immunity. A person without them would not develop immunity over
time to pathogens in the environment, and thus would be at risk for infections
when going outdoors. The immune system would have to rely on less-specific
innate responses, which might not be as effective.
Do You Understand Concept 31.2?
Outline the sequence of innate defenses encountered by a
pathogenic bacterial cell if it is ingested in food. Similarly, outline the
defenses encountered by a bacterial cell that lands in the nose.
Answer:
A bacterial cell
that is ingested in food will encounter mucus in the body cavities, which may
trap it. In the stomach it will also be exposed to gastric juices containing
hydrochloric acid and proteases. A bacterial cell that lands in the nose will
encounter mucus, lysozymes that can cleave bacterial cell walls, and defensins.
Defensins can insert themselves into the bacterial membrane and increase its
permeability to water and all solutes.
Antihistamines are used to treat the symptom of sneezing due
to inflammation caused by irritants in the airways. How do you think
antihistamines might work?
Answer:
Antihistamines block the action of histamine, a substance
that increases permeability of blood vessels to white blood cells and other
molecules and allows these to move into tissues that are challenged. If these
cells and molecules are blocked they will not be able to initiate the responses
of inflammation and sneezing.
A massive inflammation due to a food allergy can be treated
with an injection of epinephrine. Refer to the description of epinephrine’s
effects in Concept 30.2. How do you think this hormone relieves the
inflammation symptoms?
Answer:
Epinephrine is involved in the fight-or-flight response. Some
of its effects include increased heart rate and blood flow, and increases in
fuel in the blood. These responses can combat the inflammation caused by a food
allergy. Epinephrine also constricts blood vessels. This results in less flow
in the capillaries and a reduction of inflammation.
Do You Understand Concept 31.3?
Make a table describing the four key features of the adaptive
immune system.
Answer:
|
Specific
|
Focuses
responses on pathogens that are actually present
|
|
Diverse
|
Responds
to novel pathogens
|
|
Distinguishes self from non-self
|
Doesn't
destroy self-cells
|
|
Has immunological memory
|
Responds
effectively to the same pathogen in later exposures
|
Answer:
The immune system
remembers a pathogen after an earlier exposure through the adaptive immune
response. Older people who had been exposed to that pathogen in the first
epidemic and survived would have mounted a stronger and more rapid immune
response to the subsequent exposure.
Insulin-dependent diabetes (Type 1) results from a
destruction of the cells in the pancreas that make the hormone insulin (see
Concept 39.4). One hypothesis for this disease is that it is caused by an autoimmune
reaction. Explain how this might happen and how you would investigate your
hypothesis.
Answer:
During
development, B cells that fail to recognize self-cells usually undergo
apoptosis, called clonal deletion. If clonal deletion doesn't occur, it can
lead to an autoimmune disease, in this case destruction of the pancreatic cells
that make insulin. One way to test this would be using molecular mimicry to see
if exposure to an antigen very similar to the suspected self antigen, the
pancreatic cells, would lead to an immune response.
Do You Understand Concept 31.4?
Sketch an IgG antibody, identifying the variable and constant
regions, light and heavy chains, and antigen-binding sites.
Answer:
Refer to textbook
Figure 31.7A. The bacterium that causes diphtheria (refer to textbook Figure 31.4) synthesizes a toxic protein. You have probably not been exposed to this bacterium or its toxin. At the present time, are you making B cells and antibodies that bind specifically to diphtheria toxin? Explain your answer.
Answer:
There are
millions of naïve B cells in circulation, each one specific to a particular
antigen, even if not previously exposed. A small number of the B cells make an
antibody on their cell surface that binds to the diphtheria toxin. Once a B
cell is activated by antigen-binding (exposure) only then will it begin
antibody production.
When an antigenic protein such as diphtheria toxin (see
above) enters the bloodstream, numerous clones of B cells are activated.
Explain.
Answer:
The original
antigen binding stimulates the B cell to divide and create a clone of cells.
These are genetically identical to the B cell and will all produce or secrete
antibodies with the same specificity as the B cell and will bind to the free
antigen in the bloodstream. Because
an antigen, such as a protein, usually has several groups of atoms that
themselves are antigens (antigenic determinants), there will be numerous B cell
clones activated.
Do You Understand Concept 31.5?
Compare the T cell receptor and B cell receptor in terms of
structure, diversity, and function.
Answer:
T cell and B cell receptors are similar in structure, each
with a variable and a constant region, though the T cell receptors are smaller
and are glycoproteins instead of immunoglobulins. The two types are equally
diverse and specific to a particular antigen. B cells function as part of the
humoral response to produce antibodies. T cells are of two types: TH and TC. TH cells can
bind to an antigen and stimulate other immune cells, including B and TC cells, to
divide. TC cells bind
to and destroy cells that bear the antigen on their surface.
What are the similarities and differences in function between
class I and II MHC proteins?
Answer:
Class I MHC
proteins are present on the surfaces of nucleated mammalian cells. They present
fragments of antigens to TC cells.
Class II MHC proteins are on the surfaces of macrophages, B cells, and
dendritic cells. They ingest antigens and bind fragments for presentation to TH cells.
What are the roles of TH cells in cellular and humoral immunity?
Answer:
TH cells with specific receptors bind to
antigen-presenting cells and then release cytokines, which stimulate B cells to
divide in the humoral immune response and TC cells to divide in the cellular immune
response.
Since MHC proteins are highly variable and almost always
differ between unrelated people, an organ transplant between such people will
generally provoke a cellular immune response, and the organ will be rejected.
Patients receiving organ transplants are treated with cyclosporin, a drug that
inhibits T cell development. How do you think cyclosporin prevents rejection?
What side effects might you expect in treated people?
Answer:
Blocking the
production of T cells would interfere with the immune responses at several
stages immediately following recognition. Without T cell activity, the
transplanted organ would not be treated as an antigen or be subject to
rejection or attack. However, the patient would also not be able to mount an
immune response to real pathogens and so would be susceptible to disease.
Apply the Concept for
Chapter 31
Concept 31.1 The Adaptive Immune
Response Is Specific, p. 629
1.
|
Mother
|
Mother
|
Fetus
|
Fetus
|
Result
|
|
Genotype
|
Phenotype
|
Genotype
|
Phenotype
|
|
|
Dd
|
Rh+
|
Dd
|
Rh+
|
Compatible
|
|
dd
|
Rh–
|
Dd
|
Rh+
|
Incompatible
|
2.
An immune response is mounted in the mother to the Rh+ fetal cells.
But the fetus has been born and so is not affected. After the mother’s
response, immune cells specific for Rh+ remain as memory cells. The
next time a fetus carries the Rh+, there is a massive response by the
mother, only this time the fetus has not yet been born and hemolytic disease
can result.
3.
Antibodies against Rh+, given to the mother, “tie up” antigens that
may pass to the mother, and shield the mother’s immune system, with its memory
cells, from the antigen so an immune response is not mounted.
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