Deck 5: Antigen Recognition in the Adaptive Immune System

Question 1

CD8 is a protein that functions as a coreceptor for a subset of T cells and plays a significant role in all of the following EXCEPT:

A)Recognition of peptide antigen bound to class I MHC molecules
B)Maturation of MHC class I-restricted T cells
C)Infection of T cells by human immunodeficiency virus (HIV)
D)Signaling via Lck tyrosine kinase to initiate T cell activation
E)Strengthening the binding of T cells to antigen-presenting cells,albeit with low affinity

Answer 1

Infection of T cells by human immunodeficiency virus (HIV)

Question 2

CD44 expressed on the surface of T cells is critical for the binding of activated T cells to endothelium at sites of inflammation,and for the retention of T cells in extravascular tissues at sites of infection.CD44 does this by binding to which one of the following molecules?

A)VCAM-1
B)Hyaluronate
C)ICAM-1
D)Fibronectin
E)E-selectin

Answer 2

Hyaluronate

Question 3

The T cell receptor (TCR)complex differs from an immunoglobulin molecule in which one of the following ways?

A)On average,a TCR binds antigen with much lower affinity than does an Ig molecule.
B)The TCR can serve as a lymphocyte antigen receptor,but an Ig molecule cannot.
C)Only the TCR can bind soluble antigen directly.
D)The TCRs expressed by one clone of T cells can undergo changes in constant region structure after cellular activation,whereas Ig molecules expressed by one clone of B cells do not.
E)The TCR polypeptide chains have short cytoplasmic tails and rely on associated proteins for signaling functions,whereas membrane Ig receptors are competent signaling molecules on their own.

Answer 3

On average,a TCR binds antigen with much lower affinity than does an Ig molecule.

Question 4

Selectins differ from integrins in which one of the following ways?

A)Selectins are expressed only on endothelial cells and integrins are expressed only on leukocytes.
B)Selectins are important mediators of leukocyte adhesion to endothelium,but integrins are not.
C)Selectins bind carbohydrate ligands,but integrins do not.
D)Selectins mediate rolling of leukocytes on endothelium,but integrins do not.
E)Selectins are a family of homologous molecules,but integrins are not.

Question 5

CD1-restricted T cells differ from other T cells restricted to class I or class II MHC molecules in which one of the following ways?

A)CD-1 restricted T cells cannot rapidly secrete cytokines.
B)CD-1 restricted T cells recognize non-peptide antigens,such as lipids.
C)CD-1 restricted T cells bind both cell-associated and soluble antigens.
D)CD-1 restricted T cells express both CD4 and CD8 coreceptors.
E)CD-1 restricted T cells are actually natural killer (NK)cells.

Question 6

A healthy 45-year-old child-care worker becomes infected with a virus and develops a sore throat,cough,and fever.Infected cells in the bronchial mucosa of this patient process virus-encoded proteins through an intracellular pathway and display peptides derived from the protein on the cell surface bound to class I MHC molecules.CD8⁺ T cells migrate to the mucosa and recognize these peptide-MHC complexes.Which of the following components of the TCR actually bind to the viral peptide-MHC complex?

A)Hypermutated regions: 1 in the $\alpha$ chain,2 in the $\beta$ chain
B)Complementarity-determining regions: 3 in the $\alpha$ chain,3 in the $\beta$ chain
C)Hypervariable regions: 2 in the $\alpha$ chain,2 in the $\beta$ chain
D)Congenic regions: 1 in the $\alpha$ chain,1 in the $\beta$ chain
E)One peptide-binding groove formed by the $\alpha$ chain and the $\beta$ ₂-microglobulin chain

Question 7

After 2 years of hard work,a graduate student finally succeeds in creating a gene knockout mouse lacking CD4.The student is particularly careful to keep this mouse line in a microbe-free animal facility because these mice are expected to show:

A)No ability to produce IgM antibodies
B)Impaired ability to produce antibodies and activate macrophages
C)No ability to activate naive class I-restricted T cells
D)Complete absence of cytotoxic T lymphocyte (CTL)responses to viral infections
E)Failure to produce neutrophils

Question 8

The T cell receptor (TCR)complex contains:

A)A highly variable antigen coreceptor
B)CD28
C)Three homologous CD3 chains,each covalently linked to the TCR $\alpha$$\beta$ heterodimer
D)Invariable $\alpha$$\beta$ chains noncovalently linked to the TCR $\alpha$$\beta$ heterodimer
E)Ig $\beta$

Question 9

A 15-year-old girl develops malaise,headache,and low-grade fever,followed by pharyngitis and cervical lymph node enlargement as a result of infectious mononucleosis caused by Epstein-Barr virus (EBV).Her acute symptoms resolve within 2 weeks,and the fatigue improves within 3 months.Following the primary infection described in this patient,the patient's subsequent exposure to Epstein-Barr virus (EBV)will trigger clonal expansion of EBV-specific T cells expressing which one of the following surface molecules?

A)CD62L^high
B)CD44^low
C)CD45RA^high
D)CD45RO^high
E)CD21^high

Question 10

Both CD28 and CTLA-4 are receptors on T cells that are critical for regulating T cell activation.In which one of the following ways does CD28 differ from CTLA-4?

A)Only CD28 binds the costimulatory ligands B7-1 and B7-2 expressed on professional antigen-presenting cells.
B)CD28 counteracts positive,pro-proliferative T cell signals delivered by CTLA-4.
C)CD28 is constitutively expressed on naive T cells,whereas CTLA-4 is expressed on activated T cells.
D)CD28 binds its ligand with 10-fold greater affinity than does CTLA-4.
E)CD28 is important for delivering "signal 1" for T cell activation,whereas CTLA-4 is important for delivering "signal 2."

Question 11

The strength of integrin-dependent binding of T cells to antigen-presenting cells (APCs)may be rapidly increased by which one of the following mechanisms?

A)Integrin clustering and increased integrin affinity are induced by chemokines and antigen recognition.
B)Integrins stored in cytoplasmic organelles are mobilized to the T cell surface in response to TCR-mediated signals.
C)Integrin gene transcription is enhanced by chemokine-generated signals.
D)The affinity of integrin ligands on APCs is increased in response to chemokines.
E)Integrin ligands stored in cytoplasmic granules in the APCs are mobilized to the cell surface in response to CD40-CD40 ligand interaction.

Question 12

Neonates,elderly persons,and otherwise immunocompromised patients are particularly susceptible to infections with Listeria monocytogenes.These patients typically have fever and chills,often progressing to hypotension and septic shock.In healthy individuals,however,such intracellular microbes are usually effectively phagocytosed and killed by macrophages,which become activated via:

A)CD40L-CD40 interactions between activated T helper cells and macrophages
B)CD28-B7 interactions between activated T cells and macrophages
C)Fas ligand-Fas interactions between activated cytotoxic T lymphocytes and macrophages
D)TCR-MHC class II interactions between activated T helper cells and macrophages
E)LFA-1-ICAM-1 interactions between activated T cells and macrophages

Question 13

A 4-year-old boy suffers from an immunodeficiency disease characterized by impaired T cell activation.The disease is caused by genetic deficiency of a membrane protein whose cytoplasmic tail is involved in intracellular signaling in response to T cell receptor (TCR)recognition of antigen.Which one of the following proteins does NOT fit this description?

A)TCR $\alpha$
B)CD3 $\gamma$
C)( $\zeta$ )
D)CD4
E)CD3?

Question 14

A 2-year-old boy suffers from recurrent bacterial infection of his ears,sinuses,lungs,and skin;laboratory studies indicate absence of sialylated Lewis X on his leukocytes.He is diagnosed with leukocyte adhesion deficiency type 2 (LAD-2).Which type of adhesive interaction required for leukocyte migration is defective in this boy?

A)E-selectin ligand binding to E-selectin
B)CD4 binding to class II MHC
C)VLA-4 binding to VCAM-1
D)Ig Fc receptor binding to Ig-coated cells
E)LFA-1 binding to ICAM-1

Question 15

LFA-1 is an integrin that promotes T cell activation by which one of the following mechanisms?

A)Binds to the $\alpha$ 3 domain of class I MHC molecules,mediating high avidity between T cells and antigen-presenting cells (APCs)
B)Binds to B7-1 or B7-2 on the surface of APCs,mediating "signal 2"
C)Binds to GlyCAM-1 on high endothelial venules of lymph nodes,mediating rolling of T cells on endothelium
D)Binds to ICAM-1 on the surface of a variety of cells,mediating firm adhesion between T cells and APCs or endothelial cells
E)Binds to VCAM-1 on the surface of cytokine-activated endothelial cells,mediating homing of T cells to peripheral sites of inflammation

Question 16

Most T lymphocytes have a dual specificity for which one of the following pairs of molecules?

A)A particular allelic form of a major histocompatibility complex (MHC)molecule and a peptide bound to the MHC molecule
B)Both MHC class I and class II molecules
C)Both peptide and glycolipid antigens
D)Both soluble peptides and peptide-MHC complexes
E)MHC molecules and CD4 or CD8

Question 17

A 15-year-old girl develops malaise,headache,and low-grade fever,followed by pharyngitis and cervical lymph node enlargement as a result of infectious mononucleosis caused by Epstein-Barr virus (EBV).Her acute symptoms resolve within 2 weeks,and the fatigue improves within 3 months.All of the following are required for CD8⁺ cytotoxic T lymphocyte (CTL)recognition and killing of EBV-infected cells EXCEPT:

A)( $\beta$ ₂)-Microglobulin
B)HLA-A,-B or -C
C)CD28
D)LFA-1 (leukocyte function-associated antigen-1)
E)TAP (transporter associated with antigen processing)

Question 18

$\gamma$ $\sigma$ T cells may be important for recognition of common antigens at epithelial boundaries between the host and the external environment.The $\gamma$ $\sigma$ T cells differ from the $\alpha$$\beta$ T cells in which one of the following ways?

A)( $\gamma$ $\sigma$ ) T cells recognize only nonprotein antigens.
B)( $\gamma$ $\sigma$ ) T cells are not MHC-restricted and do not recognize MHC-associated antigens.
C)The $\gamma$ $\sigma$ TCR complex contains CD3 $\gamma$ or CD3 $\sigma$ but not CD3? .
D)Most mature $\gamma$ $\sigma$ T cells express either CD4 or CD8 but not both.
E)( $\gamma$ $\sigma$ ) T cells lack key biologic activities,including the ability to lyse target cells.

Question 19

Which of the following is NOT a property shared by both CD4 and CD8?

A)Binds to nonpolymorphic regions of MHC molecules
B)Cytoplasmic tail associates with the Src family kinase Lck
C)Is a member of the Ig superfamily
D)Functions as a coreceptor for $\alpha$$\beta$ TCRs
E)Is expressed on the majority of mature blood T cells