Page 541 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com mebooksfree.com 2. Regarding IgG, which one of the following is the most accurate? mebooksfree.com
PART VII Immunology
530
RNA splicing). Note that once a B cell has “class” switched
past a certain H chain gene, it can no longer make that class
(A) Each IgG molecule has one antigen binding site.
(B) It is the most important antigen receptor on the surface of
of H chain because the intervening DNA is excised and
neutrophils.
discarded. Class switching occurs only with heavy chains;
(C) During the primary response, it is made in larger amounts than
light chains do not undergo class switching. “Switch recom-
is IgM.
binase” is the enzyme that catalyzes the rearrangement of
(D) The ability of IgG to fix complement resides on the constant
the VDJ genes during class switching.
region of the light chain.
The control of class switching is dependent on at least
(E) It is the only one of the five immunoglobulins that is trans-
two factors. One is the concentration of various interleu- 3. If a person had a mutation in the gene encoding J (joining)
ferred from mother to fetus in utero.
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mebooksfree.com mebooksfree.com mebooksfree.com 4. Regarding the function of the different classes of antibodies, which mebooksfree.com
kins. For example, interleukin-4 (IL-4) enhances the pro-
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duction of IgE, whereas IL-5 increases IgA (see Table 58–7).
chains, which of the following classes of antibodies could NOT be
The other is the interaction of the CD40 protein on the B
produced?
(A) IgA and IgM
cell with CD40 ligand protein on the helper T cell. In
(B) IgA and IgG
hyper-IgM syndrome, the failure to interact properly
(C) IgG and IgE
results in an inability of the B cell to switch to the produc-
(D) IgD and IgE
tion of IgG, IgA, or IgE. Therefore, only IgM is made (see
(E) IgM and IgE
Chapter 68).
one of the following statements is the most accurate?
ALLELIC EXCLUSION
(B) IgA acts as an antigen receptor on the surface of B cells.
A single B cell expresses only one L chain gene (either κ or λ)
(C) IgD is our most important defense against worm parasites,
such as hookworms.
and one H chain gene. In theory, a B cell could express two (A) IgE blocks the binding of viruses to the gut mucosa.
(D) IgG can activate the alternative pathway of complement, result-
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sets of immunoglobulin genes, a maternal set and a pater-
mebooksfree.com mebooksfree.com mebooksfree.com 5. Regarding the genes that encode antibodies, which one of the fol- mebooksfree.com
ing in the production of C3a that degrades the bacterial cell
nal set. But this is not what happens. Only one set of genes
wall.
is expressed, either maternal or paternal, and the other set
(E) There are receptors for the heavy chain of IgG on the surface of
is silent (i.e., it is excluded). This is called allelic exclusion.
neutrophils that mediate a host defense process called
Each individual contains a mixture of B cells, some express-
opsonization.
ing the paternal genes and others the maternal ones. The
mechanism of this exclusion is unknown.
lowing is most accurate?
(A) Hypervariable regions are encoded by the genes of both the
light and heavy chains.
CATALYTIC ANTIBODY
(B) The genes for the light and heavy chains are linked on the same
chromosome adjacent to the HLA locus.
Antibody can act as an enzyme to catalyze the synthesis of
ozone (O ) that has microbicidal activity. Antibody can
3
acquire the same antigen binding sites by translocation of the
take the singlet oxygen produced by neutrophils and react (C) During the production of IgG, the light and the heavy chains
same variable genes.
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it with water to produce hydrogen peroxide and O . The O
(D) The gene for the constant region of the gamma heavy chain is
3
3
generated can kill Escherichia coli. The catalytic function of
first in the sequence of heavy chain genes, and that is why IgG
antibodies is independent of their antigen specificity and
is made in greatest amounts.
of the requirement to bind to any antigen. The importance
of these observations to our host defenses remains to be
determined.
1. (E)
2. (E)
3. (A)
SELF-ASSESSMENT QUESTIONS
5. (A)
1. It’s time to play “Who am I?” I am the first class of antibody to
appear, so my presence indicates an active infection rather than an 4. (E)
PRACTICE QUESTIONS: USMLE &
infection that occurred in the past. I can fix complement, which
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COURSE EXAMINATIONS
is an important defense against many bacterial infections. I am
found in plasma as a pentamer.
Questions on the topics discussed in this chapter can be found
(A) IgA
(B) IgD
Board) Practice Questions starting on page 733. Also see Part
(C) IgE
XIV: USMLE (National Board) Practice Examination starting
(D) IgG
on page 751.
(E) IgM
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