EVALUATIVE EXAM (SEROLOGY)

Question 1

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

Answer 1

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.

Question 2

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

Answer 2

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

Question 3

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

Answer 3

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.

Question 4

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

Answer 4

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

Question 5

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

Answer 5

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

Question 6

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

Answer 6

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.

Question 7

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

Answer 7

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

Question 8

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

Answer 8

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.

Question 9

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

Answer 9

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

Question 10

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.

Answer 10

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

Question 11

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

Answer 11

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.

Question 12

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

Answer 12

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.

Question 13

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

Answer 13

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.

Question 14

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

Answer 14

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.

Question 15

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

Answer 15

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.

Question 16

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

Answer 16

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.

Question 17

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

Answer 17

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

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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.

Question 20

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

Answer 20

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

Question 21

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

Answer 21

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.

Question 22

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

Answer 22

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.

Question 23

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

Answer 23

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.

Question 24

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

Answer 24

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.

Question 25

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

Answer 25

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

Question 26

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

Answer 26

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

Question 27

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

Answer 27

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

Question 28

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

Answer 28

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.

Question 29

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

Answer 29

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.

Question 30

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

Answer 30

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.

Question 31

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

Answer 31

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.

Question 32

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

Answer 32

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.

Question 33

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

Answer 33

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.

Question 34

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

Answer 34

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).

Question 35

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

Answer 35

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

Question 36

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

Answer 36

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

Question 37

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

Answer 37

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.

Question 38

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

Answer 38

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.

Question 39

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

Answer 39

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

Question 40

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

Answer 40

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

Question 41

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

Answer 41

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

Question 42

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

Answer 42

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

Question 43

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

Answer 43

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

Question 44

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

Answer 44

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.

Question 45

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

Answer 45

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

Question 46

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

Answer 46

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

Question 47

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

Answer 47

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.

Question 48

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

Answer 48

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.

Question 49

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

Answer 49

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

Question 50

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)

Answer 50

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

Question 51

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

Answer 51

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.

Question 52

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

Answer 52

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

Question 53

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

Answer 53

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.

Question 54

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

Answer 54

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.

Question 55

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

Answer 55

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.

Question 56

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.

Answer 56

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.

Question 57

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.

Answer 57

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.

Question 58

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

Answer 58

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

Question 59

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

Answer 59

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

Question 60

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.

Answer 60

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

Question 61

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

Answer 61

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

Question 62

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

Answer 62

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

Question 63

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

Answer 63

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.

Question 64

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

Answer 64

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.

Question 65

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

Answer 65

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.

Question 66

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

Answer 66

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.

Question 67

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

Answer 67

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.

Question 68

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.

Answer 68

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.

Question 69

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

Answer 69

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.

Question 70

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

Answer 70

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

Question 71

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.

Answer 71

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.

Question 72

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

Answer 72

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.

Question 73

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

Answer 73

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

Question 74

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

Answer 74

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.

Question 75

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

Answer 75

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.

Question 76

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

Answer 76

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.

Question 77

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

Answer 77

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.

Question 78

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

Answer 78

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.

Question 79

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

Answer 79

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.

Question 80

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

Answer 80

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.

Question 81

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

Answer 81

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.

Question 82

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

Answer 82

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.

Question 83

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

Answer 83

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).

Question 84

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

Answer 84

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

Question 85

"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

Answer 85

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.

Question 86

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

Answer 86

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

Question 87

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

Answer 87

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.

Question 88

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

Answer 88

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

Question 89

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

Answer 89

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.

Question 90

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

Answer 90

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.

Question 91

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

Answer 91

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.

Question 92

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

Answer 92

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

Question 93

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.

Answer 93

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

Question 94

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

Answer 94

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.

Question 95

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

Answer 95

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

Question 96

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

Answer 96

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.

Question 97

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

Answer 97

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

Question 98

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

Answer 98

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

Question 99

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.

Answer 99

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.

Question 100

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

Answer 100

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.