EVALUATIVE EXAM (SEROLOGY) Flashcards

1
Q

Color Plate 21B depicts a monomeric
immunoglobulin molecule. The portion of
the molecule indicated by the dotted red
circle and the red arrow is called the
A. Fab fragment
B. Fc fragment
C. Heavy chain
D. Hinge region

A

A. The basic structure of all immunoglobulins
is two light chains joined to two heavy chains
by disulfide bonds. The amino terminus of both
the heavy and light chains, together, constitutes
the Fab fragment (fragment of antigen binding).
The carboxy-terminus of the heavy chains constitutes the Fc fragment. The hinge region is the
area at the center of the “Y,” near the carboxyterminus of the light chains.

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2
Q

A hapten is
A. Half of an immunoglobulin molecule
B. A earner molecule for an antigen that
is not antigenic alone
C. An immunoglobulin functional only in
the presence of complement
D. A determinant capable of stimulating
an immune response only when bound
to a carrier

A

D. Haptens are substances that are not immunogenic by themselves. These molecules are not
large or complex enough to stimulate the immune
system. When bound to a carrier, they are capable
of stimulating a specific immune response

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3
Q

Which of the following is characteristic of
B cells?
A. Phagocytic
B. Participate in antibody-dependent
cellular cytotoxicity (ADCC) reactions
C. Contain surface immunoglobulins
D. Secrete the C5 component of
complement

A

C. B cells carry surface immunoglobulins that
react to a specific antigen. The antigen can then be
internalized processed and presented to an appropriate T helper cell. B cells are not phagocytic,
nor do they participate in antibody-dependant cellular cytotoxicity (ADCC) reactions. Complement proteins are secreted by hepatocytes.

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4
Q

A lymphokine is
A. A soluble mediator produced by
granulocytes and affecting lymphocytes
B. A soluble mediator produced by
lymphocytes
C. A soluble mediator produced by
plasma cells
D. An antibody that reacts with
lymphocytes

A

B. Lymphokines are soluble mediators of
immune reactions. They are produced most often
by T lymphocytes. Antibodies are produced by plasma cells.

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5
Q

Monocytes and macrophages play a major
role in the mononuclear phagocytic
system. For an antibody-coated antigen to
be phagocytized, what part of the antibody
molecule fits into a receptor on the
phagocytic cell?
A. Fc region
B. Fab region
C. Hinge region
D. Variable region

A

A. The Fc region of an IgG molecule fits into an
Fc receptor (FcR) on macrophages and monocytes. The Fc receptor binds to specific amino acid residues in the Fc region of the immunoglobulin. The variable region of immunoglobulin
binds to the antigen

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6
Q

Cell-mediated immunity is primarily
mediated by
A. B cells
B. T helper cells
C. Plasma cells
D. Dendritic cells

A

B. T helper cells are the primary mediators of
cell-mediated immunity (CMI). They secrete
several different lymphokines that stimulate a
number of other cells, such as cytotoxic T lymphocytes and monocytes. B cells differentiate
into plasma cells during a humoral-mediated
immune response. Dendritic cells are important
antigen presenting cells, but they are not the primary mediators of a CMI response.

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7
Q

The HLA complex is located primarily on
A. Chromosomes
B. Chromosome 6
C. Chromosome 9
D. Chromosome 17

A

B. The HLA system is part of a larger region
known as the major histocompatibility complex.
It is located on chromosome 6. The region is
located on the short arm of the chromosome.
Chromosome 15 contains one HLA gene, B2M

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8
Q

HLA antigens are found on
A. All nucleated cells
B. Red blood cells only
C. Solid tissue only
D. White blood cells only

A

A. Human leukocyte antigens (HLAs) are a
group of antigens originally described on human
white cells. It is now known that they are found
on all nucleated cells of the body, including solid
tissue cells. HLAs are not found on red blood
cells.

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9
Q

Which of the following is more likely to
be diagnostic of an acute infection?
A. A total acute antibody titer of 2
followed by a convalescent titer of 16
B. A total acute antibody titer of 80
followed by a convalescent titer of 40
C. A total antibody titer of 80
D. An IgG antibody titer of 80

A

A. The most significant indicator of acute or
recent infection is the presence of a rising antibody liter. A fourfold or greater rise in titer, from
2 to 16, is significant. Even relatively high antibody liters of IgG may indicate past infection.
IgM is produced first following infections, so a
high IgM titer is also suggestive of an acute
infection

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10
Q

A young woman shows increased
susceptibility to pyogenic infections.
Upon assay, she shows a low level of C3.
Which of the following statements is
probably true?
A. She has an autoimmune disease with
continual antigen-antibody activity
causing consumption of C3.
B. She has DiGeorge syndrome.
C. She has decreased production of C3.
D. She may produce an inactive form of
C2, a precursor of C3.

A

C. C3 may be decreased due to a genetic defecl
lhat causes deficient production. In certain
autoimmune disorders, such as systemic lupus
erylhematosus, continual complemenl activation
leads lo low levels; however, susceptibility to
pyogenic infections is not a feature of autoimmune diseases. DiGeorge syndrome is a deficiency in T cells, and complement protein C2 is
not a precursor of C3

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11
Q

What is the predominant type of antibody
found in the serum of neonates born after
full-term gestation?
A. Infant IgA
B. Infant IgG
C. Infant IgM
D. Maternal IgG

A

D. Antibody production is immunogen induced.
Because the fetus develops in a sequestered site, it
makes very little immunoglobulin. Maternal IgG
crosses the placenta and is the primary antibody
found in infant’s circulation.

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12
Q

An important part of the nonspecific
immune response is(are)
A. B cells
B. Basophils
C. Complement cascade
D. Cytotoxic T lymphocytes

A

C. Important parts of an animal’s nonspecific
immune response include phagocytosis, inflammation, and complement activation. In a nonspecific immune response, the animal responds in
much Ihe same way to all invaders. B cells and
cytoloxic T lymphocytes responded to specific
antigens and are, therefore, involved in the specific immune response. Basophils are involved
in type I hypersensitivily reactions.

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13
Q

The major class of immunoglobulin found
in adult human serum is
A. IgA
B. IgE
C. IgG
D. IgM

A

C. Immunoglobulin G is Ihe predominant class
of immunoglobulin found in serum. It accounts
for approximately 80% of the lolal serum
immunoglobulin. The normal range is 800-1600
mg/dL.

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14
Q

Which class of immunoglobulin possesses
delta heavy chains?
A. IgA
B. IgD
C. IgE
D. IgG

A

B. The heavy chains divide human immunoglobulin molecules into separate classes and subclasses. The della (A) heavy chain corresponds to
IgD. The remaining classes IgA, IgE, IgG, and
IgM correspond to a, e, y, and JJL, respectively.

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15
Q

Which class of immunoglobulin possesses
10 antigenic binding sites?
A. IgA
B. IgD
C. IgG
D. IgM

A

D. The IgM molecule is a penlamer that contains 10 binding sites. However, the actual
valence falls to 5 with larger antigen molecules,
probably because of steric restrictions. IgA, IgG,
IgD, and IgE monomers each have two antigenic
binding sites.

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16
Q

Color Plate 22 * represents a dimeric IgA
molecule. The structure printed in red and
indicated by the red arrow is called the
A. J-piece
B. Hinge region
C. Heavy chain
D. Light chain

A

A. IgA is found in mucous secretions as a dimer
stabilized by the J-piece. IgA is synthesized
locally by plasma cells and dimerized intracellularly. IgM is also held together by a J-piece, but
il exists as a pentamer.

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17
Q

Which class of immunoglobulin binds to
basophils and mast cells to mediate
immediate hypersensitivity reactions?
A. IgA
B. IgD
C. IgE
D. IgG

A

C. Mast cells and basophils have surface receptors (FceRI) for the Fc portion of IgE. When IgE
molecules, attached to the surface of mast cells
and basophils, bind the allergen they are specific
for, this triggers the cells to degranulate, producing the symptoms of immediate type I hypersensitivity. The main function of IgE appears to
be the ability to trigger an immune response,
thereby recruiting plasma factors and effector
cells to areas of trauma or parasite infection

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18
Q

Type I hypersensitivity is
A. Associated with complementmediated cell lysis
B. Due to immune complex deposition
C. Mediated by activated macrophages
D. An immediate allergic reaction

A

D. Type I hypersensitivity reactions occur
immediately after second exposure to an allergen. On the first, or primary, exposure, IgE specific to the allergen is produced. The IgE binds
to Fc receptors on the surface of basophils and
mast cells. Immune complexes and complement
are not involved in the response

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19
Q

When performing the enzyme-multiplied
immunoassay technique (EMIT), how is
the ligand in the patient’s serum detected?
A. Agglutinates by binding to antibodycoated latex beads
B. Binds to enzyme-labeled antibody
C. Competes with enzyme-labeled
antigen for binding to a specific
antibody
D. Forms antibody-antigen complex and
precipitates

A

C. In the EMIT, a ligand (antigen) in a sample
competes with an enzyme-labeled ligand for
binding to a specific antibody. The labeled ligand is designed so that following antibody binding, the enzyme is inactive. As the ligand
concentration in the test sample increases, more
enzyme-labeled ligand remains unbound, resulting in greater enzyme activity.

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20
Q

Severe combined immunodeficiency
(SCID) is an
A. Immunodeficiency with decreased B
cells and neutrophils
B. Immunodeficiency with lymphocytopenia and eosinophilia
C. Immunodeficiency with decreased or
dysfunctional T and B cells
D. Immunodeficiency with decreased
lymphocytes and decreased complement concentration

A

C. SCID is defined as a condition in which
adaptive immune responses (i.e., cell-mediated
and humoral-mediated immune responses) do
not occur because of a lack of T and B cell activity. A number of genetic defects can lead to this
condition. Children born with SCID need to live
in a sterile environment, and they have a short
life expectancy

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21
Q

An example of immune injury due to the
deposition of antigen-antibody complexes is
A. Acute glomerulonephritis
B. Bee-sting allergy
C. Contact dermatitis
D. Penicillin allergy

A

A. Acute glomerulonephritis is caused by the
presence of a soluble circulating antigen (Ag) that
provokes and combines with antibody (Ab). As
these Ag-Ab complexes reach a critical size, they
are deposited in the glomerular membranes of the
kidney. Upon deposition, an acute inflammatory
reaction occurs because of complement activation.
Bee-sting and penicillin allergies are examples of
IgE-mediated anaphylactic reactions. Contact dermatitis is mediated by T cells, not antibody.

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22
Q

The serologically detectable antibody
produced in rheumatoid arthritis (RA) is
primarily of the class
A. IgA
B. IgE
C. IgG
D. IgM

A

D. Rheumatoid factor (RF) is an immunoglobulin
that reacts with antigenic determinants on an IgG
molecule. Although they may be of several types,
the one that is easily serologically detectable is
IgM. This is because of the agglutination activity
of the molecule. RF tests are commonly used in
the diagnosis of rheumatoid arthritis.

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23
Q

In bone marrow transplantation, immunocompetent cells in the donor marrow may
recognize antigens in the recipient and
respond to those antigens. This phenomenon is an example of
A. Acute rejection
B. Chronic rejection
C. Graft versus host disease
D. Hyperacute rejection

A

C. Bone marrow transplants by their nature contain immunologically competent cells: B cells
and T cells in particular. Unless the transplanted
marrow is HLA-matched perfectly to the donor,
the immunocompetent cells in the transplant will
recognize and react against the nonself HLAs of
the recipient’s tissues. This phenomenon is known
as graft-versus-host disease, because the graft
attempts to reject its host. Acute rejection, chronic
rejection, and hyperacute rejection are examples
of mechanisms a recipient’s immune system uses
to reject a graft.

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24
Q

Multiple myeloma is a
A. Lymphoproliferative disease of T cells
B. Cancer of plasma cells characterized
by increased antibody concentration
C. Lymphoproliferative disease resulting
in a decrease in antibody production
D. Cancer of monocytes characterized by
increased kappa and lambda chain
synthesis

A

B. Plasma cells are normally end-stage cells; they
live a few days and die. During multiple myeloma,
plasma cells become cancerous and continue to
secrete antibody. The cells also secrete excess
light chains that can be found in the urine; these
proteins are called Bence Jones proteins.

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25
Q

Which one of the following describes a
direct immunofluorescence assay?
A. Conjugated reagent antigen reacts with
antibodies to form antigen-antibody
complexes
B. Antigens react with unlabeled
antibody forming antigen-antibody
complexes that attach to labeled
antibodies
C. A dye is attached to a molecule and it
reacts with an immune complex to
produce a color
D. Conjugated reagent antibody reacts
with antigen to form antigen-antibody
complexes

A

D. In a direct imrnunofluorescence assay, a fluorescent molecule is linked to an antibody. This
complex is often called a conjugate. Clinical material is fixed onto a microscope slide, and the conjugate is added. After a wash step, the slide is
examined with a microscope using UV light. If
antigen specific to antibody was present in the
clinical specimen, fluorescence will be seen

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26
Q

In individuals allergic to pollen, hyposensitization protocols may be initiated.
These individuals receive injections of
A. Allergen
B. Pooled human antisera
C. Monoclonal antibody directed against
human T cells
D. Monoclonal antibody directed against
human B cells

A

A. Hyponsensitization, allergy injections, involves
the administration of gradually increasing concentrations of an allergen. The goal is for the
patient to become tolerant of the allergen and no
longer exhibit an allergic response to the allergen. It is hypothesized that patients will ultimately develop high concentrations of IgG to the
allergen, blocking IgE from binding and thereby
preventing the allergic reaction

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27
Q

After exposure to antigen, the first
antibodies that can be detected belong to
the class
A. IgA
B. IgE
C. IgG
D. IgM

A

D. The first B cells to respond to antigen differentiate into plasma cells that produce IgM antibody. Later in the immune response, stimulated
B cells undergo a phenomenon called “class
switching” and begin to produce antibodies of
the IgG, IgA, and IgE classes. High concentration of IgM in patient serum is indicative of a
recent infection

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28
Q

Corneal tissue may be transplanted
successfully from one patient to another
because
A. The cornea is nonantigenic
B. Cornea! antigens do not activate T cells
C. Anticorneal antibodies are easily
suppressed
D. The cornea occupies a privileged site
not usually seen by the immune system

A

D. Corneas are readily transplanted from one
individual to another. This is because the cornea
is nonvascularized and is a sequestered site.
Thus the immune system of the host does not
“see” the cornea and recognize it as foreign.

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29
Q

A kidney transplant from one identical
twin to another is an example of a(n)
A. Allograft
B. Autograft
C. Isograft
D. Xenograft

A

C. Identical twins have the same genetic makeup.
Grafts between them would be isografts or
syngeneic grafts. Autografts are transplantations from one site to another in the same individual.
Xenograft refers to transplantation between different species. Transplantation between two nonidentical individuals of the same species is called an
allograft.

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30
Q

In Bruton disease, measurement of serum
immunoglobulins would show
A. Elevated levels of IgE
B. Elevated levels of IgG
C. Normal levels of IgG and IgM but
reduced levels of IgA
D. The absence of all immunoglobulins

A

D. Bruton disease is a congenital form of agammaglobulinemia. It is a sex-linked phenomenon
that affects males. Because B cells are not produced, affected males have levels of IgA, IgD,
IgE, and IgM undetectable by routine assays.
IgG may be absent or present at very low levels.

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31
Q

Diagnosis of group A streptococci
(Streptococcus pyogenes) infection is
indicated by the presence of
A. Anti-protein A
B. Anti-DNaseB
C. Anti-beta-toxin
D. C-reactive protein

A

B. The serological diagnosis of group A streptococcal infection can be made by demonstrating anti-DNase B. The antistreptolysin O (ASO)
assay can also be used; however, ASO response
is poor in skin infections. C-reactive protein is
an acute-phase protein indicating inflammation.

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32
Q

A molecule found in human serum
sometimes used as a tumor marker is
A. a-Fetoprotein
B. HBsAg
C. Biotin
D. CDI

A

A. a-Fetoprotein (AFP) and carcinoembryonic
antigen (CEA) are oncofetal antigens that
become expressed after malignant transformation. Approximately 70% of patients with primary hepatoma have elevated levels of AFP.
However, the major use of determining AFP
levels is in monitoring patients undergoing
cancer treatment.

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33
Q

Which cell is the principal source of
interleukin 2?
A. Bcell
B. Tcell
C. Monocyte
D. Plasma cell

A

B. Interleukin 2 (IL-2) is a lymphokine produced
by activated T helper cells. IL-2 principally affects
T cells, including the cell that released IL-2, acting
on its target cells via the IL-2 receptor. This receptor is not present on resting cells.

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34
Q

Diagnostic reagents useful for detecting
antigen by the coagglutination reaction
may be prepared by binding antibody to
killed staphylococcal cells via the Fc
receptor of staphylococcal protein A. The
class of antibody bound by this protein is
A. IgA
B. IgD
C. IgG
D. IgM

A

C. Staphylococcal protein A binds only the IgG
class (subclasses IgGl, IgG2, and IgG4) of
immunoglobulin. Binding occurs via the Fc portion of the antibody molecule, leaving the Fab
portion available to bind antigen in an immunologic assay. Binding of the Fab portion to test
antigen causes agglutination of the staphylococcal cells (coagglutination).

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35
Q

A major advantage of passive immunization
compared to active immunization is that
A. Antibody is available more quickly
B. Antibody persists for the life of the
recipient
C. IgM is the predominant antibody class
provided
D. Oral administration can be used

A

A. In passive immunization, preformed antibody
is delivered to the recipient, making the antibody
available immediately. In active immunization, a
period of days is required before antibody production occurs. Passive immunity is short-lived,
in contrast to the possibly lifelong persistence of
actively induced antibody. Because passive
immunization involves the transfer of antibodies,
the oral route cannot be used—antibodies are
digested in the gastrointestinal tract. The antibodies administered by passive immunization consist
largely of the IgG class

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36
Q

The strength with which a multivalent
antibody binds a multivalent antigen is
termed the
A. Affinity
B. Avidity
C. Reactivity
D. Valence

A

B. “Avidity” is used to describe the strength of
binding between a multivalent antibody and multivalent antigen. “Affinity” describes the bond
between a single antigenic determinant and an
individual combining site. “Valence” refers to the
number of antigenic determinants on an antigen

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37
Q

How does the secondary humoral immune
response differ from the primary
response?
A. The lag phase (the time between
exposure to immunogen and production of antibody) is longer in the
secondary immune response.
B. IgM is the predominant antibody class
produced in the secondary immune
response.
C. The antibody levels produced are
higher in the secondary immune
response.
D. Cytotoxic T lymphocytes play an
important role in the secondary
response

A

C. The secondary immune response is characterized by the predominance of IgG over IgM. In
addition, because of the formation of memory
cells following the primary response, the secondary response occurs much more quickly and
strongly. This is the basis for immunization as a
protection against various infectious diseases.
Cytotoxic T lymphocytes are not involved in
humoral immunity.

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38
Q

After activation of the complement
system, leukocytes and macrophages are
attracted to the site of complement
activation by
A. Cl
B. C5a
C. C8
D. IgM

A

B. The complement-activation product C5a is
chemotactic for neutrophils and macrophages.
Neither Cl nor C8 (which occur in the plasma
before complement activation) possesses such
chemotactic properties. IgM antibody, although
capable of activating complement by the classical pathway, is not a chemotactic factor for
phagocytic cells.

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39
Q

The type of immunity that follows the
injection of an immunogen is termed
A. Artificial active
B. Natural active
C. Artificial passive
D. Innate

A

A. Active immunity follows exposure to an
antigen that stimulates the recipient to develop
his or her own immune response. Vaccines are
an example of artificial immunity in that the animal was exposed to the immunogen by the
actions of a healthcare provider (unnatural). Surviving infections can result in natural active
immunity. Protection is due to the formation of
memory cells

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40
Q

The type of immunity that follows the
injection of antibodies synthesized by
another individual or animal is termed
A. Artificial active
B. Natural adaptive
C. Artificial passive
D. Natural passive

A

C. Artificial passive immunity results following
the injection of antibody synthesized by another
individual or animal. This type of immunity is
only temporary but may be very important in
providing “instant” protection from an infectious agent before the recipient would have time
to actively synthesize antibody. The injected
antibodies are treated as foreign proteins and are
eventually cleared from the body

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41
Q

Innate immunity includes
A. Anamnestic response
B. Antibody production
C. Cytotoxic T cell activity
D. Phagocytosis by polymorphonuclear
cells

A

D. Innate, or nonspecific, immunity refers to
host defenses that are in general present at birth
and do not require immunogen stimulation.
Phagocytosis of bacteria by polymorphonuclear
cells is an example. Cytotoxic T cell activity is
part of the adaptive cell-mediated immune
response, and antibody production is the mechanism of protection in the adaptive humoral mediated immune response

42
Q

The agglutination pattern shown in Color
Plate 23 * was observed while performing
an antibody titration. This agglutination
pattern is an example of
A. A prezone reaction
B. A prozone reaction
C. A postzone reaction
D. Incomplete complement inactivation

A

B. Prozone occurs when an extremely high titer
of antibody is present. In the first tubes of the
titration, not enough antigen is present to allow
for cross-linking and lattice formation. The antibody effectively blocks all the antigen sites present, so agglutination does not occur. Complement
is not involved in antibody titration

43
Q

The antibody most frequently present in
systemic lupus erythematosus is directed
against
A. Surface antigens of bone marrow
stem cells
B. Surface antigens of renal cells
C. Nuclear antigen
D. Myelin

A

C. Antinuclear antibody (ANA) is the most
consistent feature of systemic lupus erythematosus (SLE). Although renal or nerve pathology
may occur, that pathology is secondary to deposition of antigen-antibody complexes and subsequent activation of complement proteins. Bone
marrow stems cells are not involved in the
pathology of SLE

44
Q

The rapid plasma reagin assay for syphilis
does not need to be read microscopically
because the antigen is
A. Cardiolipin
B. Complexed with latex
C. Complexed with charcoal
D. Inactivated bacterial cells

A

C. The rapid plasma reagin (RPR) and Venereal
Disease Research Laboratory (VDRL) tests use
a cardiolipin antigen. However, in the RPR test,
charcoal particles are included with the antigen.
When antibody in the patient sample combines
with the antigen, the charcoal is trapped in the
immune complex, allowing the reaction to be
read macroscopically.

45
Q

The Venereal Disease Research Laboratory
(VDRL) test for syphilis is classified as a(n)
A. Agglutination reaction
B. Flocculation reaction
C. Hemagglutination reaction
D. Precipitation reaction

A

B. The cardiolipin antigen is particulate, not soluble, in the VDRL test. However, the particles are
too small to make macroscopic agglutinates when
combined with antibody. This type of reaction is
called a flocculation reaction and needs to be read
with low-power microscopy

46
Q

One cause of a false-positive VDRL test is
A. Brucellosis
B. Treponema pallidum infection
C. Rocky Mountain spotted fever
D. Systemic lupus erythematosus

A

D. Patients with connective tissue disorders
such as systemic lupus erythematosus may show
a false positive reaction in the VDRL test. Other
causes of false positives include rheumatic fever, infectious mononucleosis, malaria, and pregnancy. Treponema pallidum subsp. pallidum is
the causative agent of syphilis

47
Q

The portion of an antigen that binds to an
antibody or T cell receptor is called a(n)
A. Allergin
B. Avidin
C. Epitope
D. Valence

A

C. Antigens can have multiple epitopes. Each
epitope can be unique, binding an antibody with
a different idiotype. “Valence” refers to the number of epitopes on an antigen.

48
Q

Identical antibodies produced from a
single clone of plasma cells describes
A. Reagin
B. Cold agglutinins
C. Heterophile antibodies
D. Monoclonal antibodies

A

D. Monoclonal antibodies are derived from a
single clone of plasma cells. Plasma cells are
fused with a cancerous myeloma cell. Reagin
has two meanings: it can refer to the antibody
produced during syphilis or it can refer to IgE.
Cold agglutinins are antibodies that agglutinate
in cold temperatures (e.g., 4°C). Heterophile
antibodies are antibodies produced following
exposure to an immunogen that are able to bind
a similar but different molecule.

49
Q

IgM antibodies react well in complement
fixation (CF) tests. Because of this, CF
tests for antibodies should
A. Be positive early in the course of the
disease
B. Be useful in identifying antibodies
responsible for a delayed hypersensitivity reaction
C. Be useful in identifying antibodies
responsible for anaphylactic reactions
D. Detect transplacental antibodies

A

A. In most infections, IgM antibodies will
develop first followed by IgG, which develop
higher titers and are longer lasting. Anaphylactic
reactions are caused by IgE antibody. Delayed
hypersensitivity reactions are caused by T cells.
Transplacental antibodies belong to the IgG
class. IgG antibodies, although they can be
detected by complement fixation (CF), do not fix
complement efficiently

50
Q

Which of the following serologic tests is
commonly performed by an immunofluorescence method?
A. Anti-HBs
B. Antinuclear antibody (ANA)
C. Antistreptolysin O (ASO)
D. C-reactive protein (CRP)

A

B. Testing for antinuclear antibodies (ANAs) is
commonly performed by the immunofluorescence method—using fluorescein-conjugated
antihuman antibody to detect patient antibody
bound to nuclear components of test cells. Antistreptolysin O tests are performed with red cells
or, more recently, by latex agglutination. AntiHBs assays are generally performed by ELISA,
and C-reactive protein assays are generally performed by latex agglutination, turbidimetry, or
nephelometry

51
Q

The Fab portion of an antibody
A. Binds T cell receptor
B. Consists of two light chains only
C. Consists of two heavy chains only
D. Contains the hypervariable reagion

A

D. The Fab portion of an antibody contains the
hypervariable region. This portion of the molecule has a variable sequence of amino acids that
affects the three-dimensional structure of the
molecule and, therefore, determines the specificity (idiotype) of the antibody. This region contains the amino terminal portion of the two light
chains and the two heavy chains.

52
Q

In the enzyme-linked immunosorbent
assay (ELISA), the visible reaction is due
to a reaction between
A. Enzyme and antibody
B. Enzyme and substrate
C. Fluorescent dye and antigen
D. Latex particles and antibody

A

B. The indicator system in an ELISA test consists of an enzyme and its substrate. If the
enzyme-labeled antibody has complexed with
the immobilized antigen, the addition of substrate will produce a colored end product. Alkaline phosphatase is an enzyme frequently used in
ELISA tests. Latex particles, fluorescent dyes,
and red blood cells are not used in ELISA tests
but in other test methodologies

53
Q

Elevated IgE levels are typically found in
A. Type I hypersensitivity reactions
B. Type II hypersensitivity reactions
C. Type III hypersensitivity reactions
D. Type IV hypersensitivity reactions

A

A. Elevated IgE levels are found in type I
hypersensitivity reactions. The antibody binds
via the Fc portion of the molecule to Fc receptors on mast cells and basophils. When the
attached antibody binds its specific allergen, the
cell degranulates.

54
Q

Loss of self-tolerance results in
A. Autoimmune disease
B. Graft-versus-host disease
C. Immunodeficiency
D. Tumors

A

A. The immune system recognizes host cells as
self and is tolerant to antigens on those cells. The
loss of tolerance will result in an autoimmune
disease in which the immune system mounts an
immune response against self cells. Graft-versus-host disease occurs when a bone marrow
graft is incompatible with the host tissue and
attacks the host.

55
Q

A human cell with CDS on its surface is
most likely a
A. Bcell
B. Monocyte
C. T helper cell
D. Cytotoxic T cell

A

D. The CDS molecule is found primarily on
cytotoxic T lymphocytes. T helper cells possess
CD4 on their surface, as do several other cell
types. CD3 is a marker found on most T cells.

56
Q

Which of the following statements about
immunoglobulin light chains is true ?
A. Each immunoglobulin monomer has
either one kappa or one lambda chain.
B. There are two types: kappa and
lambda.
C. They consist of constant regions only.
D. They form part of the Fc fragment.

A

B. Light chains are of two distinct types: kappa
and lambda. Either type may combine with any
of the heavy chains, but in any one molecule,
only one type is found. Each immunoglobulin
monomer contains two light chains, either kappa
or lambda. They extend into the Fab, or antigenbinding, site. This half of the chain is highly
variable, whereas the carboxy-terminal portion
of the molecule is a constant region.

57
Q

Which of the following statements applies
to the Fc fragment of an immunoglobulin
molecule?
A. It consists of the entire heavy chain.
B. It contains the variable region of the
heavy chain.
C. It contains the antigen binding sites of
the molecule.
D. It is the region of the molecule that
binds to receptors on various white
blood cells.

A

D. The Fc (crystalline) fragment of an immunoglobulin is produced by papain digestion of an
immunoglobulin monomer. The Fc portion of
antibodies binds to specific Fc receptors on the
surface of some white blood cells. Only part of
the heavy chain is found in the Fc fragment. The
Fab fragment contains the antigen-combining
sites of both the heavy chains and the light
chains.

58
Q

Monoclonal antibodies are produced by
A. Cultured T cells
B. Human plasma cells
C. Mouse plasma cells
D. Hybridomas

A

D. A monoclonal antibody is produced by a
single cell or clone. Plasma cells obtained from an
immunized animal and subsequently fused with
myeloma cells result in a hybrid myeloma or
hybridoma that will indefinitely secrete a specific
antibody. Hybridomas have been prepared from
mouse and human plasma cells fused with
myeloma cells. T cells do not produce antibodies

59
Q

Antibodies that bind to the same epitope
are of the same
A. Allotype
B. Autotype
C. Idiotype
D. Isotype

A

C. Idiotype of an antibody refers to the antigen
specificity of the molecule. The isotype is the different classes and subclasses of antibodies (e.g.,
IgG, IgM, etc.). “Allotype” refers to different alleles of the same isotype. Genetically different individuals will produce antibodies of the same
isotype, but they would have a different allotype

60
Q

Skin testing is a useful diagnostic tool in a
number of disorders, such as tuberculosis.
Which of the following statements about
skin testing is true?
A. A positive test depends on preformed
antibody.
B. Reactivity to a particular antigen may
be transferred from one individual to
another by sensitized lymphocytes.
C. The intensity of the response correlates directly with the clinical activity
of the disease.
D. The maximum response will occur
immediately.

A

B. Skin testing is based upon the presence of T
cells sensitized to antigen. Their activation produces a delayed hypersensitivity reaction, which
reaches its peak in about 48 hours. There is no
correlation of the amount of the reaction with
clinical disease. If the sensitized T cells are
transferred from one individual to another, the
recipient individual will manifest the same
delayed hypersensitivity as the donor

61
Q

The activity of natural killer (NK) cells
A. Does not require previous exposure to
an antigen
B. Involves phagocytosis and killing of
bacteria
C. Requires interaction with cytotoxic
T cells
D. Requires interaction with B cells

A

A. The natural killer (NK) cells destroy target
cells through an extracellular nonphagocytic
mechanism. NK cells are part of the host’s innate
resistance and, therefore, do not need previous
exposure to an antigen to be active. They also do
not need interaction with B or cytotoxic T cells

62
Q

Interaction between B and T helper cells
involves
A. MHC II molecule on B cell binding to
MHCI molecule on the T cell
B. MHC II molecule on B cell binding to
CDS on the T cell
C. Foreign antigen on B cell binding to
T cell receptor
D. CDS molecule on B cell binding to
T cell receptor

A

C. B cells have the ability to present antigen
(immunogen) to T helper cells. This interaction
involves several surface molecules. The antigen is complexed with MHC II on the surface of the
B cell. CD4 on the T cell interacts with MHC II,
whereas the T cell receptor binds the antigen

63
Q

Which of the following is a characteristic
of T cells?
A. Synthesize antibody
B. Mature in the thymus
C. Able to bind unprocessed antigen
D. Primarily protect against extracellular
parasites

A

B. T cells are produced in the bone marrow and
mature in the thymus. Plasma cells, not T cells,
produce antibody, and T cells can only react to
antigen processed by an antigen-presenting cell.
The cell-mediated immune response, which
requires the activity of T cells, is primarily helpful in fighting against intracellular parasites.

64
Q

The primary mechanism responsible
for pathology in systemic lupus
erythematosus is
A. Allergic reaction to foreign molecules
B. Antibodies directed against self
antigens
C. Polyclonal activation of cytotoxic
T cells
D. Lack of intracellular killing after
neutrophil phagocytosis of bacteria

A

B. Antibodies directed against self antigens form
immune complexes and activate complement.
Circulating immune complexes, composed of
nuclear antigen and antinuclear antibody, deposit
in various organ systems, activate complement,
and produce organ pathology. T cells are not
directly involved in this process. Allergens,
phagocytosis, and killing of ingested bacteria by
neutrophils do not play a role in the pathogenic
process.

65
Q

Which complement protein is present in
the greatest concentration in human
serum?
A. Cl
B. C2
C. C3
D. C4

A

C. Complement protein C3 has a serum concentration of about 1300 (xg/mL, which makes it the
complement protein present in the greatest concentration. The second highest concentration of
complement protein is C4 (600 |xg/mL). C3 is
cleaved into fragments: C3a and C3b.

66
Q

An autoimmune disease causing destruction of pancreatic cells can result in
A. Hashimoto disease
B. Multiple sclerosis
C. My asthenia gravis
D. Type 1 diabetes

A

D. Destruction of the beta cells in the pancreas
results in type 1 diabetes. An autoimmune
response destroys the insulin-producing cells.
The immune response is probably due to molecular mimicry. Cytotoxic T cells and antibodies
directed against an infectious agent cross react
to the beta cells.

67
Q

An Ouchterlony gel diffusion plate is
depicted in Color Plate 24B. The center
well contains antibody, and the peripheral
wells contain antigens labeled 1 through 4.
What is the relationship between the
antigens in wells 2 and 3?
A. 2 is part of 3.
B. 3 is part of 2.
C. They are identical.
D. They are unrelated

A

D. The two antigens are not related. There are
two different antibodies that are able to react
with the two antigens, forming precipitin lines
that cross. If the antigens were identical, a
smooth curve precipitation line would have
formed.

68
Q

An Ouchterlony gel diffusion plate is
depicted in Color Plate 24B. The center well
contains antibody, and the peripheral wells
contain antigens labeled 1 through 4. What
is the relationship between the antigens in
wells 2 and 4?
A. Cannot be determined.
B. They are identical.
C. They are unrelated.
D. They react incompletely with the
antibody.

A

B. When two antigens are identical, a smooth
curved line of precipitation is formed between
them. In the diagram, the antigen in well 2 is
identical to one of two antigens in well 1. The
same antigen in well 1 is identical to antigen in
well 4. Therefore, it follows that antigens 2 and 4
are identical.

69
Q

Which of the following complement
proteins is part of the membrane attack
complex?
A. Cl
B. C3
C. C4
D. C5

A

D. The membrane attack complex forms following the binding of C5 to a biologic membrane. The complex is formed by the sequential
addition of C6, C7, C8, and C9. When C5-C8
complex with C9, a tubule is formed that bridges
the cell membrane.

70
Q

Which of the following is characteristic of
contact hypersensitivity reactions?
A. Caused by preformed IgE antibody
B. Characterized by infiltration of
neutrophils into the area of reaction
C. The primary symptoms often occur in
the respiratory tract.
D. Usually due to a hapten

A

D. Contact dermatitis is a cell-mediated hypersensitivity reaction. The offending substance is
typically a hapten that combines with a carrier
molecule on the skin surface. The hapten-carrier
complex is recognized by T cells. IgE mediates
immediate hyper sensitivity reactions such as
hay fever and some forms of asthma

71
Q

Which of the following statements about the
test for C-reactive protein (CRP) is true?
A. It correlates with neutrophil phagocytic function.
B. It is an indicator of ongoing inflammation.
C. It is diagnostic for rheumatic fever.
D. Levels decrease during heart disease.

A

B. CRP is an acute-phase reactant. Although it
is elevated in inflammation, its presence is not
diagnostic for any one disease, such as rheumatic fever. It does not correlate with antibody
levels or with neutrophil phagocytic function.
CRP levels are sometimes elevated during heart
disease.

72
Q

In the classical pathway of complement
activation,
A. C3 is activated by binding C-reactive
protein
B. The sequence of activation is Cl, C2,
C3,C4
C. Clq is activated by the presence of
a single Fab region
D. Activation by antibody requires one
IgM or two IgG molecules

A

D. Complement attaches to the Fc portion of the
antibody molecule. At least two Fc binding sites
are required for Clq to attach. Therefore, activation requires two IgG molecules or a single
molecule of IgM, which is a pentamer. The C
proteins were named in order of discovery. The
correct reaction sequence is Cl, C4, C2, C3. As the last step of this reaction sequence, C3 is split into C3a and C3b.

73
Q

The alternative complement pathway
A. Can be activated by bacterial capsule
polysaccharides
B. Uses C5b as a C3 convertase
C. Bypasses steps C3 through C5
D. Is inactivated by properdin

A

A. The alternative pathway for complement activation is a more nonspecific defense mechanism,
in that it does not require the presence of antibody
for activation. It can be activated by a variety of
substances, including complex polysaccharides
found in bacterial capsules and cell walls. These
materials activate C3 directly. Properdin protein
stabilizes some of the active complement proteins, and C4b2a is a C3 convertase

74
Q

A cut on a person’s finger becomes
contaminated with the bacterium
Staphylococcus aureus. The first
response by the immune system
consists of activity of
A. B cells
B. Monocytes
C. Neutrophils
D. T cells

A

C. The first response to invading bacteria is
mounted by the innate immune system. The
innate immune system, although it lacks the
specificity of the adaptive immune system, is
nonetheless effective at handling many invading
bacteria. The first response by the innate
immune system consists of an influx of neutrophils into the tissue invaded by bacteria.
Monocytes and macrophages, although they are
phagocytic cells and part of the innate immune
system, play only a minor role in the initial
response to bacterial invasion.

75
Q

Incompatible blood transfusions are
examples of
A. Type I hypersensitivity reactions
B. Type II hypersensitivity reactions
C. Type III hypersensitivity reactions
D. Type IV hypersensitivity reactions

A

B. Incompatible blood transfusions are
examples of a type II hypersensitivity reaction.
These reactions are characterized as the antigen
being a part of a cell. Antibody binds to the antigen, complement is activated, and the red blood cells are lysed.

76
Q

A soluble antigen and soluble antibody
reacting to form an insoluble product
describes
A. Agglutination reactions
B. Heterophile reactions
C. Labeled reactions
D. Precipitation reactions

A

D. Precipitation reactions involve both soluble
antigens and antibodies. These reactions are typically detected in agarose gels. With agglutination reactions, one of the reactants is soluble and
the other is insoluble. A reactant is made insoluble by combining with a carrier particle such as
latex beads.

77
Q

Which of the following is an example of a
treponemal antigen test used for the
diagnosis of syphilis?
A. CRP
B. RPR
C. VDRL
D. FTA-ABS

A

D. The fluorescent treponemal antibody
absorbance (FTA-ABS) test is often used as a confirmatory test for syphilis. Treponema pallidum
subsp. pallidum, the causative agent of syphilis, is
the source of the antigen. The rapid plasma reagin
(RPR) and Venereal Disease Research Laboratory
(VDRL) are diagnostic tests for syphilis that use
nontreponemal antigen. C-reactive protein (CRP)
is not involved in syphilis testing.

78
Q

A serum sample is positive for HBsAg.
This result indicates that the person from
whom the serum was taken
A. Had a hepatitis B infection in the past
but overcame the infection
B. Has either active or chronic hepatitis B
infection
C. Was immunized recently against the
hepatitis B virus
D. Is not infectious for the hepatitis B
virus

A

B. Hepatitis B surface antigen (HBsAg) is a
marker for active or chronic infection by the hepatitis B virus; it indicates ongoing viral replication.
A person positive for this marker is infectious. If
the person had overcome a past infection, he or
she would have antibody to the surface antigen
(anti-HBs) but not the surface antigen. Immunization causes formation of anti-HBs antibody, and
the surface antigen would not be present in serum.

79
Q

What is the indicator system used in the
complement fixation test?
A. Sensitized sheep red blood cells
B. Fluorescent-labeled antihuman
globulin
C. Enzyme-labeled antihuman globulin
D. Guinea pig complement

A

A. The first step in the complement fixation test,
the test system, involves the reaction of antibody
in the patient’s serum to the corresponding antigen in the presence of guinea pig complement. If
antibody-antigen binding occurs, complement
will bind to the immune complexes. The second
step is the addition of sensitized sheep red blood cells (the indicator system). If complement
bound to the immune complexes in the first step, it is not available to lyse the sensitized red blood cells. If antibody was not present in the patient sample, complement will not bind to the immune
complexes, and it will be free to lyse the sensitized cells.

80
Q

The isotype of an immunoglobulin
antibody
A. Is defined by the heavy chain
B. Is defined as different alleles of the
same antibody type (e.g., IgG)
C. Is constant for all immunoglobulins of
an individual
D. Is the variation within the variable
region

A

A. The isotype of an antibody is determined
by which heavy chain is present. The term
“idiotype” refers to the variable region of an
immunoglobulin molecule. The variable region is the portion of immunoglobulin that binds antigen. Every immunoglobulin with a given antigenie specificity has a unique idiotype.

81
Q

A patient report states the presence of
serum antibodies to OspC. What disease
does the patient most likely have?
A. Syphilis
B. Strep throat
C. Lyme disease
D. Rubella

A

C. IgM antibody to OspC is an important early
marker in the diagnosis of Lyme disease. This
antibody, along with several others, is often
detected by Western blot. Antibodies to p35,
p39, and the flagellin subunits p37 and p41 are
also useful in diagnosing this disease.

82
Q

Patient serum is mixed with a suspension
of guinea pig antigen. When the sample is
then mixed with horse red blood cells,
agglutination occurs. This is suggestive
of an infection caused by
A. Borrelia burgdorferi
B. Hepatitis B virus
C. Hepatitis C virus
D. Epstein-Barr virus

A

D. The Davidsohn differential test can be used to detect heterophile antibodies produced during
infectious mononucleosis. These antibodies are not
adsorbed by guinea pig antigens. Therefore,
the antibodies are available to agglutinate horse
red blood cells. Forssman heterophile antibodies
are absorbed by guinea pig antigens and would
not agglutinate the horse red blood cells.

83
Q

Hashimoto disease is an autoimmune
disease primarily involving the
A. Kidneys
B. Liver
C. Lungs
D. Thyroid gland

A

D. Hashimoto disease is a type of thyroiditis
due to an autoimmune disease. Patients produce
autoantibodies and T cells that respond to thyroid antigens. This results in inflammation and swelling of the thyroid gland (goiter). The
autoantibody blocks the uptake of iodine, which
results in a decrease in the production of thyroid
hormones (hypothyroidism).

84
Q

Rheumatic fever sometimes occurs after
group A streptococcal infections. In this
condition, an autoimmune response
attacks the tissue of the heart valves. This
phenomenon is an example of
A. Epitope spreading
B. Molecular mimicry
C. Polyclonal B cell activation
D. Preferential activation of T helper cells

A

B. Group A streptococci contain antigenic
determinants that are similar to antigenic determinants found on heart valve tissue in some
individuals. The immune response occurring
during the course of a group A streptococcal
infection may be extensive enough to include an
immune-mediated attack on the heart valves—
rheumatic heart disease. “Molecular mimicry” is
the term given to this phenomenon, whereby an
immune response directed against one antigen
may be extended to include activity against
closely related antigens

85
Q

“Superantigens” are toxins produced by
some strains of Staphylococcus aureus
and group A streptococci and cause
damage by
A. Molecular mimicry
B. Polyclonal T cell activation
C. Lysing white blood cells and platelets
D. Lysing red blood cells

A

B. Some strains of Staphylococcus aureus and group A streptococci produce toxins that have
the properties of “superantigens.” Superantigens react with T cells directly without processing by an antigen presenting cell. These toxins can stimulate many T cells, rather than only those T-cells bearing T cell receptors specific for the bacterial toxins. The result is a massive T cell response, leading to the release of cytokines and resulting in disease entities known as toxic
shock syndrome (in the case of S. aureus infection) and toxic shock-like syndrome in the case of group A streptococci.

86
Q

The first serologic marker to appear in
patients with acute hepatitis B virus
infection is
A. Anti-HB
B. Anti-HBc
C. Anti-HBe
D. HBsAg

A

D. HBsAg is the first serologic marker occurring in patients with hepatitis B virus infection. The antigen appears about 3-5 weeks before symptoms appear. About 2—4 weeks later, anti-HBc, primarily of the IgM class, begins to appear

87
Q

A living donor is being sought for a child
who requires a kidney transplant. The best
odds of finding an MHC-compatible
donor occur between the child and
A. A sibling (brother or sister)
B. An unrelated individual
C. The child’s father
D. The child’s mother

A

A. Because the human leukocyte antigen (HLA)
system is extremely polymorphic, the odds are greatly against finding an HLA-compatible donor
in unrelated individuals. The genes coding for
HLA antigens are inherited from one’s parents and are expressed co-dominantly. Between an offspring and either parent, there is, statistically, a 25% chance of an HLA match. Between siblings, there is a 50% chance of an HLA match.

88
Q

Cells that can act as antigen-presenting
cells for exogenous antigens include
A. All nucleated cells
B. Endothelial cells
C. B lymphocytes
D. T lymphocytes

A

C. Exogenous antigens are nonself antigens
derived from infectious agents or immunizing
preparations. Exogenous antigens are processed
for presentation to specific T cells by specialized cells collectively referred to as antigen-presenting
cells (APCs). APCs for exogenous antigens
include B cells, macrophages, monocytes, and
dendritic cells

89
Q

In patients with human immunodeficiency
virus infection, immune status can be
monitored by measuring the ratio of
A. CD3+ cells to CD8+ cells
B. CD4+ cells to CD8+ cells
C. Lymphocytes to monocytes
D. T cells to B cells

A

B. Human immunodeficiency virus preferentially infects T helper cells, which are positive for the surface marker CD4. As the infection progresses, the number of CD4+ cells in the peripheral bloodstream decreases. CDS is a marker found on another subset of T cells, cytotoxic T cells. The reference ratio of CD4:CD8 cells is 2:1. A decrease in the ratio indicates a decline in immune function.

90
Q

Why does vaccination against hepatitis B
virus (HBV) also prevent hepatitis D virus
(HDV) infections?
A. An immunogen from HBV in the
vaccine is also associated with HDV.
B. The HBV vaccine induces formation
of heterophile antibodies that cross
react with HDV.
C. The HBV vaccine stimulates liver cells
to produce antiviral molecules active
against all hepatitis viruses.
D. HDV requires the host to be concurrently infected with HBV

A

D. HDV requires HBsAg produced by BV infected cells. HDV, therefore, requires the host to be concurrently infected with HBV. The HBV vaccine prevents HBV infection and also HDV
infection.

91
Q

B lymphocytes and T lymphocytes are
derived from
A. Hematopoietic stem cells
B. Macrophages or monocytes
C. Mucosa-associated lymphoid tissue
D. The fetal liver

A

A. The stem cells of the bone marrow give rise to
both T and B cells, as well as other cells in the
bloodstream. Macrophages and monocytes also
arise from hematopoietic stem cells, but they do
not differentiate into lymphocytes. Mucosa-associated lymphoid tissue contains mature lymphocytes, particularly B cells, but is not the source of
lymphocytes. The fetal liver is a maturation site
for B lymphocytes during fetal life but is not the
source of those lymphocytes.

92
Q

Contact dermatitis is mediated by
A. B lymphocytes
B. T lymphocytes
C. Macrophages
D. Polymorphonuclear cells

A

B. Contact dermatitis is a delayed-type hypersensitivity reaction mediated by T cells. Antibody
is not involved in this type of hypersensitivity, so B cells play no role in it. Neither macrophages
nor neutrophils are involved in this type of hypersensitivity

93
Q

In a competitive radioimnumosorbent test
(RIST), what does a high signal suggest?
A. The patient sample has a low
concentration of IgE.
B. The patient sample has a low
concentration of IgM.
C. The patient sample has a high
concentration of IgE.
D. The patient sample has a high
concentration of total antibody.

A

A. The competitive RIST assay is used to determine the concentration of total IgE. Patient sample containing IgE is mixed with labeled
IgE. Both labeled and unlabeled IgE are captured by antihuman IgE. After a wash step, the
signal from the label is detected. A high signal
indicates a low concentration of unlabeled IgE from the patient sample

94
Q

An antibody titration is depicted in Color
Plate 25 *. In this titration, a 0.2 mL aliquot
of a patient’s serum sample was added to
0.8 mL of saline, and this mixture was
placed into tube #1. A 0.5 mL sample was
removed from tube #1 and placed into
tube #2, containing 0.5 mL of saline. This
procedure was repeated through tube #10.
The dilutions were assayed for antibody to
an infectious agent. How should the
antibody titer be reported?
A. 256
B. 512
C. 640
D. 1280

A

C. The titer of this assay is the reciprocal of the
highest dilution demonstrating the desired result, in this case tube #8. The dilution is determined as shown below. Dilution for tube #1: 0.2 mL serum in a total volume of 1.0 mL =1:5 dilution.
Dilutions in succeeding tubes: 0.5 mL diluted
serum in a total volume of 1.0 mL = 1:2 dilution.
The dilutions in the series of tubes are as follows:
Tube #1, 1:5; tube #2, 1:10; tube #3, 1:20;
tube #4,1:40; tube #5,1:80; tube #6,1:160;
tube #7, 1:320; tube #8, 1:640; tube #9,
1:1280; tube #10, 1:2560
The reciprocal of the dilution in tube #8 (1:640)
is 640.

95
Q

In a chemiluminescent immunologic
assay, what is the signal detected?
A. Light
B. An electric signal
C. A purple-colored compound
D. A yellow-colored compound

A

A. In chemiluminiscent assays, light is the end
product. These assays require special instruments to measure the light emitted in the reaction. Chemicals used to generate light include
luminol and luciferase

96
Q

A 28-year-old female complains to her
family physician of abdominal pain, loss
of appetite, and low-grade fever. Physical
examination reveals abdominal tenderness
and a low-grade fever. Her physician
orders a hepatitis profile and obtains the
results below

Anti-HAV = nonreactive
Anti-HBc = reactive
Anti-HBs = nonreactive
HBsAg = reactive
HBeAg = reactive
Anti-HCV = nonreactive

Which of the following is the most likely
conclusion?

A. Acute HAV infection
B. Acute HBV infection
C. Chronic HBV infection
D. Immunity to HBV due to past infection

A

C. The presence of HBsAg indicates viral replication and that the patient is infectious; this
marker can be seen in both acute and chronic
infections. The lack of anti-HBs indicates that
the patient is not immune to the infection. The
presence of anti-HBc and HBeAg with HBsAg
indicates a chronic infection.

97
Q

An 11-year-old female presents with fever,
sore throat, lethargy, and tender cervical
lymphadenopathy. Relevant findings include
splenomegaly and lymphocytosis, with
many large reactive (atypical) lymphocytes.
A heterophile antibody test was negative.
Further laboratory results were as follows:

Cytomegalovirus
(CMV) = IgG - 20; IgM Titer - 0

Epstein-Barr
virus (EBV) VGA = IgG - 0; IgM Titer - 80

Mono spot = IgG and IgM Titer - 0

What conclusion can be made concerning
the diagnosis?
A. Acute CMV infection
B. Acute EBV infection
C. Chronic CMV infection
D. Chronic EBV infection

A

B. The symptoms of fever of unknown origin,
lymphocytosis, and lymphadenopathy suggest EBV or CMV infection and lymphoma or leukemia. Heterophile antibodies become positive later than antibodies to viral core antigen (VGA) of EBV. In addition, only about 50% of children less than 12 years of age form heterophile antibodies following EBV infection. The IgM titer of 80 for EBV is consistent with acute EBV infection

98
Q

A male infant had been well until about 5
months of age, at which time he was
diagnosed as having otitis media and
bronchitis caused by Haemophilus
influenzae. Over the next several months he
presented with streptococcal pneumonia
several times. At 10 months of age a serum
protein electrophoresis showed a virtual lack
of gamma globulins. Quantitative serum
levels were as follows: 75 mg/dL IgG and
undetectable levels of IgM, IgA, and IgE.
There were a normal number of T cells, and
they exhibited normal mitogen stimulation.
What disease does this child most likely
suffer from?
A. Combined immunodeficiency
B. DiGeorge syndrome
C. latrogenic immunodeficiency
D. X-linked agammaglobulinemia

A

D. The case history is typical of a child with
X-linked agammaglobulinemia. He presented with chronic and recurrent infections beginning at 5 months of age, when transplacentally acquired
IgG had declined. Normal IgG serum level is about 800-1200 mg/dL. The infant had normal T-cell function, which rules out combined immunodeficiency and DiGeorge syndrome. “latrogenic immunodeficiency” refers to an immunodeficiency
following therapy prescribed by a physician

99
Q

A 25-year-old male presents to his family
physician complaining of fatigue, diarrhea,
and weight loss of a few months duration.
On physical examination the patient is
found to have a fever and abdominal
discomfort. Laboratory results indicate a
white blood cell count of 14.3 X 109/L
(reference range 4.8-10.8 X 109/L).
Assays for HBSAg and anti-HCV are
negative. An ELISA test for antibodies to
the human immunodeficiency virus (HIV)
performed on the patient’s serum is found to
be reactive. What step should be taken next?
A. Call the physician with the HIV result.
B. Repeat the HIV ELISA test on the
sample.
C. Test the patient’s serum for anti-HBs.
D. Contact the patient to collect a second
sample.

A

B. When a standard screening test for human
immunodeficiency virus infection, such as an
ELISA, is positive, it is recommended that the
sample be repeated in duplicate. If one or both of the repeated tests is reactive, the sample is considered to be repeatedly reactive and needs to be confirmed by a confirmatory test (e.g., Western blot or immunofluorescent antibody). If this test
is positive, the sample can be reported as positive. If the confirmatory test is negative, an additional confirmatory test should be performed if the patient has risk factors for HIV infection. If
the repeated ELISA tests are both negative, the
sample is reported as negative.

100
Q

A 38-year-old woman visited her
physician because of fatigue, fever, and
joint pain (proximal interphalangeal,
wrist, and knee joints). She also noticed
sensitivity to the sun and reported having a
rash following recent exposure. The
physician noted a rash over her nose and
cheeks. Laboratory results included white
blood cell count 5.5 X 109/L (reference
range 4.8-10.8 X 109/L) and red blood
cell count 4.5 X 1012/L (reference range
4.0-5.4 X 1012/L). Urinalysis results
were within reference ranges, except for
4+ protein and 1+ RBCs, 0-3 hyaline
casts/lpf and 0-1 RBC cast/lpf on
microscopic examination. Which of the
following tests would be most helpful in
diagnosing this patient’s condition?

A. Anti-nuclear antibody
B. a-Fetoprotein
C. Anti-streptolysin O
D. Hepatitis profile

A

A. The presence of arthritis is suggestive of a
number of autoimmune diseases. Protein, RBCs,
and casts in the urine are indicative of kidney
inflammation. These signs and symptoms along with the rash on the face are characteristic of systemic lupus erythematosus (SLE). A commonly used sensitive screening test for SLE is the antinuclear antibody (ANA) test. The ANA, however, is not specific for SLE. If the ANA were positive, additional autoantibody tests specific for SLE
(e.g., anti-Smith) should be performed.