Deck 9: Effector Mechanisms of Humoral Immunity

Question 1

Most effective vaccines that are currently in widespread use are specific for pathogenic viruses,and the immunity induced by the vaccines is mediated largely by antibodies.Which of the following statements accurately describes the major mechanism by which these vaccine-dependent antibody responses function?

A)The antibodies bind extracellular viral particles and prevent them from infecting cells.
B)The antibodies bind to viral antigens on the surface of infected cells and promote phagocytosis of the cells.
C)The antibodies bind to viral antigens on the surface of infected cells and promote complement-mediated lysis of the cells.
D)The antibodies bind to extracellular viral particles and target Fc receptor-expressing cytolytic T lymphocytes to kill the viruses.
E)The antibodies bind to viral envelope proteins and induce signals that inhibit viral replication.

Answer 1

The antibodies bind to viral antigens on the surface of infected cells and promote phagocytosis of the cells.

Question 2

Which of the following is NOT a property of the classical pathway C3 convertase?

A)Composed of proteolytic fragments of C4 and C2
B)Has protease activity specific for C3 to form C3b
C)Inhibited by decay acceleration factor (DAF)
D)Stabilized by C4 binding protein (C4bp)
E)Same substrate specificity as the alternative pathway C3 convertase

Answer 2

Stabilized by C4 binding protein (C4bp)

Question 3

Which of the following events initiates activation of the alternative complement pathway?

A)C1q binding to a microbial surface
B)Mannose-binding lectin (MBL)binding to a microbial surface
C)Complement receptor 1 (CR1)binding of C3b
D)Factor I cleavage of C3
E)Spontaneous cleavage of C3 to C3b

Answer 3

Spontaneous cleavage of C3 to C3b

Question 4

An 8-month-old boy infant with a 3-month history of recurrent upper and lower respiratory tract infections is admitted to the hospital.The physicians consider the possibility of a hereditary immune disorder and run several tests,eventually determining that the patient has undetectable levels of serum IgA.The infant is treated with strong antibiotics and recovers.Which of the following is NOT a medical problem likely to occur in this patient as he gets older?

A)Anaphylactic reactions to blood transfusions
B)Chronic gastrointestinal infections
C)Lactose and wheat gluten intolerance
D)Inflammatory skin disease
E)Recurrent nasal sinus congestion

Question 5

Which of the following statements about C3 is NOT correct?

A)C3 contains an internal thioester bond that participates in covalent linkage to cell surfaces.
B)C3 is the most abundant complement protein in the serum.
C)A proteolytic fragment of C3 is part of both the C3 and C5 convertases.
D)Activated C3 is a serine protease that cleaves C4.
E)C3 in the plasma is spontaneously cleaved into C3b.

Question 6

A 17-year-old boy is taken to the emergency department because of severe abdominal and lumbar pain.Physical examination reveals splenomegaly,and laboratory studies reveal hemoglobinemia and thrombocytopenia.A urine sample is remarkable for gross hemoglobinuria.The patient reports a history of bloody urine on multiple occasions in the past.Flow cytometric analysis of the patient's red blood cells (RBC)will most likely indicate reduced or absent expression of which pair of molecules that is normally present on RBC membranes?

A)Complement receptor 1 (CR1)and CR2
B)C1 inhibitor (C1 INH)and membrane cofactor protein (MCP,CD46)
C)Decay accelerating factor (DAF,CD55)and CD59
D)C4 binding protein (C4bp)and factor H
E)Complement receptor 3(CR3)and complement receptor 4(CR4)

Question 7

Treatment of antibodies with the enzyme papain under conditions of limited proteolysis results in hinge-region cleavage,yielding monovalent antigen-binding Fab fragments that lack a constant region.Which effector function of antibodies would Fab fragments be able to perform?

A)Complement pathway activation
B)Antibody-dependent cell-mediated cytotoxicity
C)Opsonization
D)Antigen cross-linking and precipitation
E)Microbe neutralization

Question 8

A 15-year-old girl is brought to a pediatric clinic with severe abdominal pain,nausea,and vomiting.She does not have a fever,peritoneal signs,or an elevated white blood cell count.The symptoms resolve in 48 hours.She has a history of multiple transient episodes of facial edema without pruritus.Laboratory examination is most likely to reveal which of the following abnormalities in this patient?

A)C4 deficiency
B)Reduced levels of C1 inhibitor (C1 INH)
C)Absence of C3
D)Presence of C3 nephritic factor
E)Deficiency of factor I

Question 9

Up to half of the IgG found in the serum of a normal individual is produced by which of the following cells?

A)Naive B cells in lymph nodes
B)Activated B cells in the spleen
C)B cells in germinal centers of lymph nodes
D)B lymphocytes in the gastrointestinal tract
E)Long-lived plasma cells in the bone marrow

Question 10

All of the following are accurate statements about neonatal immunity EXCEPT:

A)Transfer of maternal IgG across the placenta is mediated by an Fc receptor structurally similar to class I MHC.
B)IgA is absorbed in the gut from breast milk and re-secreted by the infant into the bronchial mucosa.
C)IgA secretion into breast milk involves transport through breast epithelial cells,and is dependent on the poly-Ig receptor.
D)Transport of IgG across the neonatal intestinal epithelium is mediated by an Fc receptor structurally similar to class I MHC.
E)Loss of maternal antibodies is partly responsible for increased frequency of infections in infants at about 6 months of agE.

Question 11

Which of the following statements about Ig Fc receptors is NOT true?

A)Some Fc receptors or Fc receptor-associated signaling chains contain ITAMs in their cytoplasmic tails.
B)Some Fc receptors are linked to signal transduction pathways that cause granule exocytosis.
C)There are Fc receptors specific for all common Ig isotypes.
D)Some Fc receptors with ITIMs in their cytoplasmic tails transduce inhibitory signals.
E)Fc receptor signaling may enhance generation of reactive oxygen intermediates in phagocytes.

Question 12

In 1890,Emil von Behring and Shibasaburo Kitasato demonstrated the efficacy of serum transfer at conferring infection resistance-a process now known as "passive immunity." The researchers isolated serum from animals that had recovered from infection with the diphtheria bacilli and subsequently injected the serum into other healthy animals.This procedure conferred specific resistance against the pathologic effects of diphtheria infection in the recipient animals.Which of the following immune phenomena were primarily responsible for these effects?

A)Pathogen-specific B and T cells from the original infected animals triggered a robust immune response after re-exposure to diphtheria antigens in the recipient animal.
B)Inflammatory cytokines in the transferred serum increased the strength and efficacy of innate immune system activity.
C)Diphtheria-specific antibodies in the transferred serum neutralized bacillus toxins and promoted bacterial elimination by innate effector cells.
D)Serum complement proteins in the transfer directly promoted bacterial cell lysis and phagocytosis.
E)The recipient animal's immune response to the foreign serum further activated host immune system function,allowing greater response to the bacillus infection.

Question 13

Which of the following anatomic regions is normally protected from pathogens only by humoral immune responses and not by cell-mediated immune responses?

A)Skin
B)Intestinal lumen
C)Intestinal epithelium
D)Central nervous system
E)Spleen