USMLE Immunology - Part 2

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USMLE Immunology - Part 2 - Quiz

Questions and Answers
  • 1. 

    Patients sharing similar clinical symptoms and disease pathology may nevertheless present differently based upon age at disease onset. Adultonset rheumatoid arthritis (RA) and juvenile rheumatoid arthritis (JRA) are both the result of infl ammatory processes. How does the presentation of JRA differ from the presentation of adult-onset RA?

    • A.

      JRA is simply the presence of RA that begins before the age of 21 years

    • B.

      Patients with JRA are less likely to have systemic symptoms, but the likelihood of high levels of serum rheumatoid factor is the same

    • C.

      Patients with JRA are more likely to have large joint involvement, but the likelihood of concurrent systemic symptoms is the same

    • D.

      Patients with JRA are more likely to have systemic symptoms and high levels of serum rheumatoid factor

    • E.

      Patients with JRA are more likely to have systemic symptoms and large joint involvement

    Correct Answer
    E. Patients with JRA are more likely to have systemic symptoms and large joint involvement
    Explanation
    The correct answer is E. JRA may appear with
    a different presentation than adult-onset RA.
    By defi nition, JRA begins before age 16 years
    and must include arthritis in at least one joint
    for at least 6 weeks. Additionally, the morphologic
    joint pathology is similar to that of adultonset
    RA. However, there are several signs and
    symptoms that occur more commonly in JRA
    than in adult-onset RA; these include increased
    likelihood of systemic onset (with symptoms
    including high fevers, lymphadenopathy, and
    hepatomegaly), increased likelihood of large
    joint involvement, and increased likelihood of
    antinuclear antibody seropositivity. Furthermore,
    JRA patients are less likely to have rheumatoid
    nodules and rheumatoid factor.
    Answer A is incorrect. There are several signs
    and symptoms that occur more commonly in
    JRA than in adult-onset RA, including increased
    likelihood of systemic onset, increased likelihood
    of large joint involvement, and increased
    likelihood of antinuclear antibody seropositivity.
    Answer B is incorrect. Systemic symptoms are
    more likely, but high levels of serum rheumatoid
    factor are less likely, in patients with JRA.
    Answer C is incorrect. Both systemic symptoms
    and large joint involvement are more
    likely in patients with JRA.
    Answer D is incorrect. Systemic symptoms are
    more likely, but high levels of serum rheumatoid
    factor are less likely, in patients with JRA.

    Rate this question:

  • 2. 

    A 37-year-old man comes to the physician with recurrent viral infections. Blood studies show normal levels of circulating lymphocytes and neutrophils. A defi ciency in which of the following cytokines would most likely lead to this man’s condition?

    • A.

      Interleukin-2

    • B.

      Interleukin-3

    • C.

      Interleukin-4

    • D.

      Interleukin-5

    • E.

      Interleukin-8

    Correct Answer
    A. Interleukin-2
    Explanation
    The correct answer is A. Recurrent viral infections
    are a sign of T lymphocyte dysfunction.
    Particularly important in the response to viral
    infections are cytotoxic (CD8) T lymphocytes.
    IL-2 is a cytokine secreted by helper T lymphocytes
    that stimulates the growth of helper and
    cytotoxic T lymphocytes. Therefore, even
    though this patient may have an adequate
    number of T lymphocytes, a defi ciency in IL-2
    could lead to impaired cytotoxic T lymphocyte
    differentiation and activation. This would result
    in an increased susceptibility to viral infections.
    Answer B is incorrect. IL-3 is secreted by activated
    T lymphocytes and has functions similar
    to granulocyte macrophage colony-stimulating
    factor.
    Answer C is incorrect. IL-4 is secreted by
    helper T lymphocytes and promotes the growth
    of B lymphocytes.
    Answer D is incorrect. IL-5 is secreted by
    helper T lymphocytes and promotes the differentiation
    of B lymphocytes.
    Answer E is incorrect. IL-8 is the major
    chemotactic factor for neutrophils.

    Rate this question:

  • 3. 

    Cluster of differentiation (CD) antigens are glycoproteins present on the cell surface of many cell types involved in the immune system. They are recognized by monoclonal antibodies and aid in the identifi cation of various cell types. Which of the following glycoproteins is present on the cell surface of all thymocytes: helper T-cells, cytotoxic T-cells, and natural killer cells?

    • A.

      B7

    • B.

      CD2

    • C.

      CD3

    • D.

      CD4

    • E.

      CD19

    • F.

      T-cell receptor

    Correct Answer
    B. CD2
    Explanation
    The correct answer is B. CD2 is a marker
    present in all lymphocytes of thymic origin,
    and is in the Ig superfamily of adhesion molecules.
    In T lymphocytes, it precedes either
    CD4 or CD8 expression and is present
    throughout the cell’s life. It is also expressed by
    natural killer cells.
    Answer A is incorrect. B7 is a protein complex
    consisting of CD80 and CD86 glycoproteins
    that is present on antigen presenting cells, including
    B lymphocytes. CD80/86 serves as a ligand
    for the costimulatory receptor CD28 present
    on T lymphocytes; a dual CD28-TCR
    signal is a potent activator of T lymphocytes.
    Answer C is incorrect. CD3 is a pan-T-lymphocyte
    marker that complexes with T-cell receptor
    and CD4 or CD8 to convey activation
    signals to the T lymphocytes. CD3 is not present
    on natural killer cells.
    Answer D is incorrect. CD4 is present on the
    surfaces of helper (rather than cytotoxic) T
    lymphocytes, while CD8 is present on the surfaces
    of cytotoxic (rather than helper) T lymphocytes.
    Answer E is incorrect. CD19 is present on B
    lymphocytes, CD8 is present on cytotoxic
    T lymphocytes, and CD4 is present on helper
    T lymphocytes.
    Answer F is incorrect. T-cell receptor (TCR)
    is an α/β heterodimer encoded by genes undergoing
    V(D)J recombination. Each clone of
    T lymphocytes therefore binds a wide range of
    antigens owing to the specifi city of this receptor.
    Natural killer cells do not express TCR.

    Rate this question:

  • 4. 

    A 2-year-old girl with a lifelong history of malabsorptive and foul-smelling diarrhea, weakness, and general failure to thrive has just undergone a small intestine biopsy (see image). Her parents believe her problems began at 6 months of age, when she started eating solid foods, but have signifi cantly worsened over the past few months. The only recent change in her diet is that she eats a bowl of cereal every morning with her parents before they go to work. She tried a dairy-free diet a month ago, but it did not improve her symptoms. Which of the following is the most likely diagnosis?

    • A.

      Abetalipoproteinemia

    • B.

      Celiac sprue

    • C.

      Lactase defi ciency

    • D.

      Viral enteritis

    • E.

      Whipple’s disease

    Correct Answer
    B. Celiac sprue
    Explanation
    The correct answer is B. Celiac sprue is also
    known as gluten-sensitive enteropathy, nontropical
    sprue, and celiac disease. It is due to a
    sensitivity to gluten, which is found in wheat,
    grains, and many cereals. Biopsy shows marked
    atrophy, total loss, or fl attening of the villi of
    the small bowel.
    Answer A is incorrect. Abetalipoproteinemia is
    an autosomal recessive disease that causes a defect
    in the synthesis and export of lipids by mucosal
    cells because of the inability to synthesize
    apolipoprotein B. These patients usually have
    acanthocytes (or spur cells, RBCs that have
    spiny projections) and do not have any characteristic
    features of the intestine found in celiac
    disease.
    Answer C is incorrect. Lactase defi ciency
    causes osmotic diarrhea from the inability to
    break down lactose into glucose and galactose.
    Answer D is incorrect. Viral enteritis, usually
    caused by a rotavirus, is common in children
    and can cause diarrhea. However, the clinical
    time course, suggested gluten sensitivity, and
    fi ndings on biopsy make viral enteritis unlikely.
    Answer E is incorrect. Whipple’s disease usually
    presents in middle-aged men who have
    malabsorptive diarrhea, and the hallmark is the
    presence of periodic acid-Schiff-positive macrophages
    in the intestinal mucosa. Rod-shaped
    bacilli of the causal agent, Tropheryma whippelii,
    are found on electron microscopy.

    Rate this question:

  • 5. 

    A pediatrician becomes concerned after learning the family and medical history of an infant who is currently suffering from pneumonia, with a presumed diagnosis of Streptococcus pneumoniae infection. Over the past year, the patient has suffered from erysipelas as well as a previous bout of pneumococcal pneumonia; both were treated successfully with antibiotics. The patient’s mother says that her son’s maternal uncle also suffered from repeated bacterial infections and was successfully treated with antibiotics. On physical examination, it appears that the patient does not have tonsils. His mother denies a previous tonsillectomy. Analysis of the boy’s serum would most likely yield which of the following results?

    • A.

      Absence of T lymphocytes

    • B.

    • C.

      IgA, IgG, and IgM levels normal

    • D.

      IgG and IgM levels markedly decreased, no IgA

    • E.

      IgG and IgM levels normal, IgA markedly decreased

    Correct Answer
    D. IgG and IgM levels markedly decreased, no IgA
    Explanation
    The correct answer is D. The infant’s family
    history is suggestive of a trait with X-linked inheritance,
    and the preponderance of bacterial
    infections suggests a defect in the humoral (antibody-
    mediated) immune response. These two
    clues are most suggestive of a diagnosis of Bruton’s
    X-linked agammaglobulinemia. The molecular
    defect occurs in a signaling molecule
    named Btk (Bruton’s tyrosine kinase), leading
    to maturing arrest of developing B cells at the
    pre-B-cell stage. Arrest at the pre-B-cell stage
    would result in an inability to produce immunoglobulins,
    and thus the patient would have
    very low levels of all immunoglobulins in his
    serum. Indeed, it should be noted that these
    patients are particularly susceptible to extracellular
    pyogenic bacterial infections with organisms
    such as Haemophilus infl uenzae, Streptococcus
    pyogenes, Staphylococcus aureus, and
    Streptococcus pneumoniae.
    Answer A is incorrect. Absence of T lymphocytes
    would result in a defect in cell-mediated
    immunity, and the patient would be more
    highly susceptible to viral and intracellular
    bacterial pathogens.
    Answer B is incorrect. A CD4+ T-lymphocyte
    count

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  • 6. 

    A 25-year-old man presents to his doctor with a 2-day history of blood in his urine. A kidney biopsy is obtained. When the tissue is stained with fl uorescent anti-IgG antibodies, the staining reveals a linear pattern. Which of the following is the most likely diagnosis?

    • A.

      Acute poststreptococcal glomerulonephritis

    • B.

      Alport’s syndrome

    • C.

      Goodpasture’s syndrome

    • D.

      IgA nephropathy

    • E.

      Membranous glomerulonephritis

    Correct Answer
    C. Goodpasture’s syndrome
    Explanation
    The correct answer is C. Goodpasture’s syndrome
    is characterized by autoantibodies forming
    against the glomerular basement membrane.
    Forming against a tissue, as opposed to
    something in the blood, constitutes a type II
    sensitivity reaction. This produces linear immunofl
    uorescent staining. Renal involvement
    in Goodpasture’s syndrome leads to hematuria,
    anemia, and crescentic glomerulonephritis.
    Along with the kidney, this syndrome may include
    pulmonary involvement, leading to hemoptysis.
    Answer A is incorrect. Acute poststreptococcal
    glomerulonephritis occurs 1–4 weeks after a β-
    hemolytic streptococci infection; it is classifi ed
    as a type III sensitivity reaction in which deposits
    of IgG, IgM, and C3 form in the mesangium
    along the basement membrane. On immunofl
    uorescent staining, a granular pattern is
    seen, rather than a linear one.
    Answer B is incorrect. Alport’s syndrome is not
    an immune reaction against the glomerular
    basement membrane. It is an X-linked disorder
    characterized by absent or mutated collagen
    IV, affecting kidney, nerve, and ocular function.
    Answer D is incorrect. IgA nephropathy, also
    known as Berger’s disease, produces mesangial
    deposits of IgA antibodies. It does not produce
    a linear pattern, and the staining will require
    anti-IgA antibodies rather than IgG.
    Answer E is incorrect. Membranous glomerulonephritis
    is an immune-mediated kidney disease
    that leads to sub-epithelial deposits of IgG
    and complement. With immunofl uorescent
    staining, it produces a granular pattern along
    the glomerular basement membrane.

    Rate this question:

  • 7. 

    A clinician is concerned that an Rh-negative mother may be pregnant with an Rh-positive fetus. The potential pathology that the clinician is concerned about is classifi ed as which of the following immune reactions?

    • A.

      Graft-versus-host disease

    • B.

      Type I hypersensitivity

    • C.

      Type II hypersensitivity

    • D.

      Type III hypersensitivity

    • E.

      Type IV hypersensitivity

    Correct Answer
    C. Type II hypersensitivity
    Explanation
    The correct answer is C. This clinician is concerned
    that the fetus may have erythroblastosis
    fetalis (hemolytic disease of the newborn). This
    disease is mediated by maternally derived IgG
    anti-Rh antibodies developed in Rh-negative
    mothers that are directed at the Rh antigen
    present on the fetal RBCs of a Rh-positive fetus
    in a previous pregnancy. If the mother possesses
    the antibodies developed from a previous
    exposure to an Rh-positive fetus, they may cross
    the placenta (antibodies of the IgG isotype
    readily cross the placenta) and coat the fetal
    RBCs of a Rh-positive fetus if the mother is
    now pregnant with another Rh-positive child.
    Antibody coating of the RBCs leads to phagocytosis
    of RBCs (via Fc receptors) and/or destruction
    of the RBCs by the complement system
    and potentially fatal anemia. This
    antibody-mediated cytotoxic reaction is an example
    of a type II hypersensitivity reaction.
    Answer A is incorrect. GVHD is a potentially
    lethal side effect of bone marrow transplantation.
    Answer B is incorrect. Type I hypersensitivity
    reactions are antibody-mediated but require
    antigen binding to IgE, which is prebound to
    the surface of mast cells. Mast cell degranulation
    then ensues. Examples include anaphylaxis,
    asthma, hives, and local wheal and fl are.
    Answer D is incorrect. Type III hypersensitivity
    reactions are immune complex-mediated.
    Examples include polyarteritis nodosa, glomerulonephritis,
    rheumatoid arthritis, and systemic
    lupus erythematosus.
    Answer E is incorrect. Type IV hypersensitivity
    reactions are a group of T-cell-mediated pathologies.
    Examples include the tuberculin
    skin test, transplant rejection, and contact dermatitis.

    Rate this question:

  • 8. 

    A 14-year-old boy presents to the physician with recurrent pyogenic infections. Physical examination shows that the boy has pruritic papulovesicular dermatitis. Blood is drawn and sent for laboratory evaluation of platelets and immunoglobulin levels. The results show a markedly low platelet count, a low serum IgM level, and an elevated IgA level. This patient most likely has which of the following conditions?

    • A.

      Bruton’s agammaglobulinemia

    • B.

      Chédiak-Higashi disease

    • C.

      Job’s syndrome

    • D.

      Thymic aplasia

    • E.

      Wiskott-Aldrich syndrome

    Correct Answer
    E. Wiskott-Aldrich syndrome
    Explanation
    The correct answer is E. Wiskott-Aldrich syndrome
    is an X-linked defect associated with elevated
    IgA levels, elevated IgE levels, normal
    IgG levels, and low IgM levels. It involves a defect
    in the body’s ability to mount an IgM response
    to bacteria. Recurrent pyogenic infections,
    eczema, and thrombocytopenia are the
    typical triad of symptoms. It does not present
    with any specifi c enzyme abnormality.
    Answer A is incorrect. Bruton’s agammaglobulinemia
    is an X-linked defi cit and therefore
    presents in males. It is a defect in a tyrosine kinase
    associated with low levels of all classes of
    immunoglobulins. After 6 months of age, when
    the levels of maternal antibodies have declined,
    patients with the disease tend to present
    with recurrent bacterial infections.
    Answer B is incorrect. Chédiak-Higashi disease
    is an autosomal recessive disease that presents
    with recurrent streptococcal and staphylococcal
    infections. A defect in lysosomal
    emptying of phagocytic cells due to microtubular
    dysfunction is the underlying cause of
    the disease.
    Answer C is incorrect. Job’s syndrome involves
    the failure of helper T lymphocytes to produce
    IFN-γ. Since IFN-γ is a potent activator of
    phagocytic cells, a decrease in its production
    leads to a failure of neutrophils to respond to
    chemotactic stimuli.
    Answer D is incorrect. The third and fourth
    pharyngeal pouches, and thus the thymus and
    parathyroid glands, fail to develop in patients
    with thymic aplasia (DiGeorge’s syndrome).
    The disease often presents with congenital defects
    such as cardiac abnormalities, cleft palate,
    and abnormal facies. Thymic aplasia can also
    present with tetany due to hypocalcemia.

    Rate this question:

  • 9. 

    A 32-year-old woman comes to the emergency department complaining of sudden blindness. On obtaining a thorough history, it is learned that the patient’s right leg has “given out” from time to time, causing the patient to have episodes of weakness and falling. Periventricular white matter plaques are found on MRI. Which of the following cells are primarily damaged in this disease?

    • A.

      Astrocytes

    • B.

      Ependymal cells

    • C.

      Oligodendrocytes

    • D.

      Schwann cells

    • E.

      T cells

    Correct Answer
    C. Oligodendrocytes
    Explanation
    The correct answer is C. Multiple sclerosis is
    a central nervous system (CNS) demyelinating
    disorder characterized by lesions that are separated
    by both time and anatomic location in
    the CNS. The exact etiology is unknown, but
    there is evidence supporting a role of autoimmune
    antibody attack to the CNS myelinsecreting
    oligodendrocytes. Oligodendrocytes,
    which are found in the CNS, are involved in
    myelination of axons.
    Answer A is incorrect. Astrocytes are found in
    the central nervous system and are involved in
    regulating the metabolic and structural environment
    of neurons, including repair and scar
    formation. Astrocytes are not the primary cells
    affected in multiple sclerosis, but they may proliferate
    in areas of multiple sclerosis lesions in
    an effort to repair infl ammatory damage.
    Answer B is incorrect. Ependymal cells line the
    ventricles. Disruptions in this cell barrier can
    cause proliferation of astrocytes nearby, but is
    not thought to be related to multiple sclerosis.
    Answer D is incorrect. Schwann cells are
    found in the peripheral nervous system and are
    involved in myelination of axons. Schwann
    cells are not the primary cells affected in multiple
    sclerosis. The morphologic changes in
    this disease are limited to the central nervous
    system.
    Answer E is incorrect. T cells are the primary
    cells responsible for cellular immunity. It is
    likely that they are involved in the putative autoimmune
    attack on the central nervous system
    in multiple sclerosis, but they are not the cells
    primarily damaged in this disease.

    Rate this question:

  • 10. 

    Women have about a 2.7 times greater lifetime risk of developing at least one autoimmune disease than men. Which of the following statements, if true, would support the higher rate of systemic lupus erythematosus in women than in men?

    • A.

      Androgens such as testosterone have an inhibitory role in the process of clearing immune complexes

    • B.

      Both estrogens and androgens have the same potency in inhibiting the clearing of immune complexes

    • C.

      Estrogen has an inhibitory role in the process of antibody production of B cells

    • D.

      Estrogen has an inhibitory role in the process of clearing immune complexes

    • E.

      Estrogen has a stimulatory role in the process of clearing immune complexes

    Correct Answer
    D. Estrogen has an inhibitory role in the process of clearing immune complexes
    Explanation
    The correct answer is D. This statement supports
    the notion that there is a higher occurrence
    of systemic lupus erythematosus (SLE)
    among women than among men. SLE is a type
    III hypersensitivity disease. Autoantibodies bind
    to self-antigens to form immune complexes
    that activate complement, leading to the activation
    of neutrophils. Since estrogen plays an
    inhibitory role on the process of clearing immune
    complexes, women have a higher risk
    than men of developing pathologically high
    levels of immune complexes, a number of
    which can lead to autoimmune diseases such
    as SLE.
    Answer A is incorrect. If this statement were
    true, then men, who have higher levels of androgens
    than women, would be at an increased
    risk of developing pathologically high levels of
    immune complexes (see the explanation of the
    correct answer). Note that androgens actually
    accelerate the clearance of circulating immune
    complexes.
    Answer B is incorrect. This statement does not
    support the epidemiologic phenomenon that
    women have a higher occurrence of SLE than
    men.
    Answer C is incorrect. This statement does
    not support the higher occurrence of SLE in
    women than in men. As stated in the explanation
    of the correct answer choice, antibodies
    (particularly certain antibodies against self-antigens)
    are needed to form immune complexes.
    Estrogen actually stimulates the process of antibody
    production by B cells, which contributes
    to the higher risk of developing SLE
    among women than among men.
    Answer E is incorrect. This statement is the
    exact opposite of the correct answer choice.

    Rate this question:

  • 11. 

    A 2-year-old boy is brought to the physician by his parents because of recurrent sinus infections. The parents also state that the boy has had multiple lung infections. Which of the following results would most likely be found on further testing?

    • A.

      A defi cit in IgA level

    • B.

      A low IgM level, with increased IgA

    • C.

      A negative nitroblue tetrazolium dye test

    • D.

      An increase in IgE level

    • E.

      A normal Ig level for all isotypes

    Correct Answer
    A. A defi cit in IgA level
    Explanation
    The correct answer is A. Selective immunoglobulin
    defi ciency is a defi cit in a specifi c
    class of immunoglobulins. IgA defi ciency is the
    most common of these diseases. Since IgA is
    the most prominent immunoglobulin found in
    mucous membranes, patients suffering from a
    defi ciency of it can present with sinus and lung
    infections.
    Answer B is incorrect. A low IgM level with
    an elevated IgA level and a normal IgG level is
    characteristic of Wiskott-Aldrich syndrome.
    Wiskott-Aldrich syndrome involves a defect in
    the body’s ability to mount an IgM response to
    encapsulated bacteria. The triad of symptoms
    consists of recurrent pyogenic infections, eczema,
    and thrombocytopenia.
    Answer C is incorrect. Normal immunoglobulin
    levels and a negative nitroblue tetrazolium
    dye reduction test indicate a diagnosis of
    chronic granulomatous disease. Chronic granulomatous
    disease involves a defect in the
    phagocytic ability of neutrophils and does not
    present with low levels of immunoglobulins.
    The defi nitive test for this disorder is a negative
    nitroblue tetrazolium dye reduction test.
    Answer D is incorrect. A very high IgE level
    and normal levels of all immunoglobulins are
    characteristics of Job syndrome. Job syndrome
    is a disorder of the immune system that involves
    the failure of helper T lymphocytes to
    produce INF-γ. It presents with multiple
    “cold,” or non-infl amed, skin lesions and high
    IgE levels.
    Answer E is incorrect. Normal immunoglobulin
    levels can be seen in thymic aplasia (Di-
    George’s syndrome). Thymic aplasia presents
    with recurrent viral and fungal infections. It results
    from a congenital problem with the migration
    of the pharyngeal pouches that form
    the thymus and parathyroid glands. It results in
    a total lack of T lymphocytes and tetany due to
    hypocalcemia. It often presents with disorders
    of the great vessels and heart.

    Rate this question:

  • 12. 

    A 50-year-old man presents to his clinician because of bilateral itching, burning, and redness of the lower extremities. He states that he wore shorts while gardening outside his house recently and could have come in contact with poison ivy. Which of the following statements regarding this patient’s immune response is most correct?

    • A.

      Goodpasture’s syndrome is a disease with a similar reaction pathogenesis

    • B.

      Histamine is the primary mediator leading to this type of reaction

    • C.

      The pathogenesis implicates previously sensitized B lymphocytes

    • D.

      The patient has never been exposed to poison ivy

    • E.

      The patient is suffering from a type I hypersensitivity reaction

    • F.

      The patient must have been exposed to a poison ivy plant prior to this instance

    Correct Answer
    F. The patient must have been exposed to a poison ivy plant prior to this instance
    Explanation
    The correct answer is F. The contact dermatitis
    that erupts following re-exposure to a poison
    ivy plant is a type IV hypersensitivity reaction,
    also known as delayed-type hypersensitivity.
    This reaction can only occur if an individual
    has had a prior exposure to the antigen, which
    triggers the differentiation of CD4+ T lymphocytes
    into T-helper type 1 lymphocytes. When
    these differentiated cells are reexposed to that
    antigen, they are quickly activated to secrete
    cytokines, which mediate the local infl ammatory
    response that takes place in the skin.
    Answer A is incorrect. Goodpasture’s syndrome
    is a type II hypersensitivity reaction and
    usually affects the lungs and kidneys.
    Answer B is incorrect. Histamine is one of the
    primary mediators released, together with leukotriene
    and prostaglandin, during a type I hypersensitivity
    reaction.
    Answer C is incorrect. Type IV hypersensitivity
    reactions are mediated by previously sensitized
    T lymphocytes, not B lymphocytes.
    Answer D is incorrect. The patient must have
    been previously exposed in order to activate
    the cytokines to mediate the dermatitis.
    Answer E is incorrect. Contact dermatitis is a
    type IV hypersensitivity reaction, not a type I
    hypersensitivity reaction.

    Rate this question:

  • 13. 

    Antibodies are one of the major players in the adaptive immune response. All antibody molecules consist of two heavy chains and two light chains, and the specifi c type of heavy and light chain will determine the antigen binding site. In all antibodies, the two heavy chains and the two light chains are identical. Like most proteins, much of their functional capabilities and antigen binding characteristics stem from their three-dimensional structure. Which of the following holds the heavy and light chains together to make the three-dimensional structure of the antibody?

    • A.

      Disulfide bonds

    • B.

      Hydrogen bonds

    • C.

      Ionic bonds

    • D.

      Triple covalent bonds

    • E.

      Van der Waals forces

    Correct Answer
    A. Disulfide bonds
    Explanation
    The correct answer is A. Antibody molecules
    consist of two heavy chains and two light
    chains. Interchain disulfi de bonds connect
    both the heavy chains and the light chains.
    Answer B is incorrect. Hydrogen bonds are
    weaker than disulfi de bonds and do not connect
    the antibody chains.
    Answer C is incorrect. Ionic bonds are found
    in chemicals such as sodium chloride but are
    not responsible for holding antibody chains together.
    Answer D is incorrect. Triple covalent bonds
    are seen between some atoms, such as nitrogen,
    but are not responsible for holding the
    chains of antibody molecules together.
    Answer E is incorrect. Van der Waals forces
    are weak attraction forces and do not hold antibody
    chains together.

    Rate this question:

  • 14. 

    A 23-year-old woman comes to the physician for a routine checkup. She has generally been well over the past year, although she notes that she has “had a few falls lately.” On physical examination, the lesion shown in the image is found on her skin. Blood is drawn for laboratory evaluation. The results show that the woman has very low levels of IgA. Based on her presentation, this patient will most likely also present with which of the following symptoms?

    • A.

      Cerebellar problems

    • B.

      Granulomas

    • C.

      Low levels of all other immunoglobulin isotypes

    • D.

      Tetany

    • E.

      Visual hallucinations

    Correct Answer
    A. Cerebellar problems
    Explanation
    The correct answer is A. Ataxia-telangiectasia
    involves a defect in DNA repair enzymes. The
    image shows spider angiomas, which are a
    common symptom in patients with this condition.
    Ataxia-telangiectasia is associated with an
    IgA defi ciency and cerebellar problems leading
    to ataxia and, in this case, multiple falls.
    Answer B is incorrect. Granulomas are collections
    of cells seen in (among other things)
    chronic granulomatous disease. This disease is
    caused by an inability of neutrophils to kill
    bacteria once they have phagocytosed them.
    Answer C is incorrect. Bruton’s agammaglobulinemia
    is an X-linked defi cit and therefore
    presents in males. It is a defect in a tyrosine kinase
    associated with low levels of all classes of
    immunoglobulins. After 6 months of age, when
    the levels of maternal antibodies have declined,
    patients with the disease tend to present
    with recurrent bacterial infections. Patients
    also presents with uniformly low antibody titers
    of all classes.
    Answer D is incorrect. The third and fourth
    pharyngeal pouches, and thus the thymus and
    parathyroid glands, fail to develop in patients
    with thymic aplasia (DiGeorge’s syndrome).
    The disease often presents with many congenital
    defects such as, cardiac abnormalities, cleft
    palate, and abnormal facies. Thymic aplasia
    can also present with tetany due to hypocalcemia.
    Answer E is incorrect. Visual hallucinations
    are not a symptom of any of the known immune
    defi ciencies.

    Rate this question:

  • 15. 

    A 50-year-old man comes to the physician with hemoptysis and diffuse joint pain. He states that both his father and cousin had similar symptoms and were diagnosed with microscopic polyangiitis, a disease affecting mediumto small-sized arteries that is believed to have an autoimmune component to its pathogenesis. Which of the following autoantibodies might be present in this patient?

    • A.

      Anticentromere antibodies

    • B.

      Antineutrophil cytoplasmic autoantibodies

    • C.

      Anti-Smith antibodies

    • D.

      Anti-SS-A (Ro) antibody

    • E.

      Anti-SS-B (La) antibody

    Correct Answer
    B. Antineutrophil cytoplasmic autoantibodies
    Explanation
    The correct answer is B. Microscopic polyangiitis
    is one of the trio of diseases (with Wegener’s
    granulomatosis and Churg-Strauss syndrome)
    that are referred to as the ANCA
    (antineutrophil cytoplasmic antibody)-associated
    vasculitides. Over 80% of patients with
    this disease have ANCA, usually the perinuclear
    pattern of staining (P-ANCA) type. Infl ammation of the pulmonary capillaries,
    which can lead to hemoptysis, is common in
    these patients, and 90% of patients have necrotizing
    glomerulonephritis (leading to hematuria).
    Other common symptoms include intestinal
    pain/bleeding, muscle pain, and weakness.
    The pathologic lesions are similar to those
    found in classic polyarteritis nodosa (PAN), but
    unlike PAN, large and muscular arteries as well
    as those in the pulmonary circulation are
    spared. The term “classic” is now often added
    to the term PAN to differentiate classic polyarteritis
    nodosa from other small-vessel vasculitides
    (such as microscopic polyangiitis), which
    are now thought to represent distinct entities.
    Classic polyarteritis nodosa has little association
    with ANCA.
    Answer A is incorrect. Anticentromere antibodies,
    which are found in 90% of patients
    with the CREST variant of scleroderma, are
    not particularly associated with microscopic
    polyangiitis. Anticentromere antibodies are
    more specifi c for the CREST variant of scleroderma.
    Answer C is incorrect. Anti-Smith antibodies
    are found in 20%–30% of patients with systemic
    lupus erythematosus and are not particularly
    associated with microscopic polyangiitis.
    “Smith antigen” describes certain core proteins
    of small nuclear ribonucleoprotein particles.
    Nonspecifi c antinuclear antibodies and/or
    rheumatoid factor may be found in patients
    with microscopic polyangiitis, but anti-Smith
    antibodies are more specifi c for systemic lupus
    erythematosus.
    Answer D is incorrect. Anti-ribonucleoprotein
    (anti-RNP) antibody SS-A (Ro), which is present
    in 70%–95% of patients with Sjögren’s syndrome,
    is not particularly associated with microscopic
    polyangiitis. Anti-RNP SS-A is more
    specifi c for Sjögren’s syndrome.
    Answer E is incorrect. Anti-ribonucleoprotein
    (anti-RNP) antibody SS-B (La), which is present
    in 60%–90% of patients with Sjögren’s syndrome,
    is not particularly associated with microscopic
    polyangiitis. Anti-RNP SS-B is more
    specifi c for Sjögren’s syndrome.

    Rate this question:

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  • Current Version
  • Mar 20, 2023
    Quiz Edited by
    ProProfs Editorial Team
  • Aug 11, 2012
    Quiz Created by
    Chachelly
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