Deck 5: Antigen Recognition by T Lymphocytes

Question 1

Which of the following is not a characteristic of immunoproteasomes?

A)They make up about 1% of cellular protein.
B)They consist of four rings of seven polypeptide subunits that exist in alternative forms.
C)They are produced in response to IFN-γ produced during innate immune responses.
D)They produce a higher proportion of peptides containing acidic amino acids at the carboxy terminus compared with constitutive proteasomes.
E)They contain 20S proteasome-activation complexes on the caps.

Answer 1

D

Question 2

viewing the three-dimensional structure of a T-cell receptor from the side,with the T-cell membrane at the bottom and the receptor pointing upwards,which of the following is inconsistent with experimental data?

A)The highly variable CDR loops are located across the top surface.
B)The membrane-proximal domains consist of C_α and C_β.
C)The portion that makes physical contact with the ligand comprises V_β and C_β,the domains farthest from the T-cell membrane.
D)The transmembrane regions span the plasma membrane of the T cell.
E)The cytoplasmic tails of the T-cell receptor α and β chains are very short.

Answer 2

C

Question 3

cells recognize antigen when the antigen

A)forms a complex with membrane-bound MHC molecules on another host-derived cell
B)is internalized by T cells via phagocytosis and subsequently binds to T-cell receptors in the endoplasmic reticulum
C)is presented on the surface of a B cell on membrane-bound immunoglobulins
D)forms a complex with membrane-bound MHC molecules on the T cell
E)bears epitopes derived from proteins,carbohydrates,and lipids.

Answer 3

A

Question 4

Unlike B cells,T cells do not engage in any of the following processes except

A)alternative splicing to produce a secreted form of the T-cell receptor
B)alternative splicing to produce different isoforms of the T-cell receptor
C)isotype switching
D)somatic hypermutation
E)somatic recombination

Question 5

describing the various components of the vesicular system,which of the following is not included?

A)nucleus
B)Golgi apparatus
C)endoplasmic reticulum
D)exocytic vesicles
E)lysosomes.

Question 6

Explain how mycobacteria avoid immune recognition by T cells during infection.

Question 7

T-cell receptors structurally resemble

A)the Fc portion of immunoglobulins
B)MHC class I molecules
C)secreted antibodies
D)a single Fab of immunoglobulins
E)CD3 ε chains.

Question 8

Identify which of the following statements is true regarding the transporter associated with antigen processing (TAP).

A)TAP is a homodimer composed of two identical subunits.
B)TAP transports proteasome-derived peptides from the cytosol directly to the lumen of the Golgi apparatus.
C)TAP is an ATP-dependent,membrane-bound transporter.
D)Peptides transported by TAP bind preferentially to MHC class II molecules.
E)TAP deficiency causes a type of bare lymphocytes syndrome resulting in severely depleted levels of MHC class II molecules on the surface of antigen-presenting cells.

Question 9

degradation of pathogen proteins into smaller fragments called peptides is a process commonly referred to as

A)endocytosis
B)promiscuous processing
C)antigen processing
D)antigen presentation
E)peptide loading.

Question 10

primary reason for transplant rejections is due to differences in _____ between donor and recipient.

A)CD3
B)MHC molecules
C)T-cell receptor α chains
D)γ:δ T cells
E)β₂-microblobulin.

Question 11

During T-cell receptor _____-gene rearrangement,two D segments may be used in the final rearranged gene sequence,thereby increasing overall variability of this chain.

A)α
B)β
C)γ
D)δ
E)ε.

Question 12

Which of the following best describes the function of tapasin?

A)Tapasin is an antagonist of HLA-DM and causes more significant increases in MHC class I than MHC class II on the cell surface.
B)Tapasin is a lectin that binds to sugar residues on MHC class I molecules,T-cell receptors,and immunoglobulins and retains them in the ER until their subunits have adopted the correct conformation.
C)Tapasin is a thiol-reductase that protects the disulfide bonds of MHC class I molecules.
D)Tapasin participates in peptide editing by trimming the amino terminus of peptides to ensure that the fit between peptide and MHC class II molecules is appropriate.
E)Tapasin is a bridging protein that binds to both TAP and MHC class I molecules and facilitates the selection of peptides that bind tightly to MHC class I molecules.

Question 13

of the following are included in the peptide-loading complex except

A)tapasin
B)calnexin
C)calreticulin
D)ERp57
E)β₂-microglobulin.

Question 14

Explain the importance of promiscuous binding specificity exhibited by MHC class I and class II molecules.

Question 15

mechanisms contributing to peptide editing include which of the following? (Select all that apply.)

A)removal of amino acids from the amino-terminal end by endoplasmic reticulum aminopeptidase (ERAP)
B)cathepsin S-mediated cleavage of invariant chain
C)the participation of tapasin in finding a 'good fit' for class I heterodimers
D)recycling an MHC class I heterodimer if the peptide falls out of its peptide-binding groove
E)upregulation of HLA-DM by interferon-γ.

Question 16

of the following are primarily associated with CD4 T-cell function except

A)improve phagocytic mechanisms of tissue macrophages
B)assist B cells in the production of high-affinity antibodies
C)kill virus-infected cells
D)facilitate responses of other immune-system cells during infection
E)assist macrophages in sustaining adaptive immune responses through their secretion of cytokines and chemokines.

Question 17

Identify the three functions of the invariant chain.

Question 18

Identify which features of the RAG genes have similarity to the transposase gene of transposons.
B.Explain how the mechanisms for immunoglobulin and T-cell receptor rearrangement may have evolved in humans.

Question 19

terms of V,D,and J segment arrangement,the T-cell receptor α-chain locus resembles the immunoglobulin _______ locus,whereas the T-cell receptor β-chain locus resembles the immunoglobulin _______ locus:

A)λ light chain; κ light chain
B)heavy chain; λ light chain
C)κ light chain; heavy chain
D)λ light chain; heavy chain
E)κ light chain; λ light chain.

Question 20

Which of the following characteristics is common to both T-cell receptors and immunoglobulins?

A)Somatic recombination of V,D,and J segments is responsible for the diversity of antigen-binding sites.
B)Somatic hypermutation changes the affinity of antigen-binding sites and contributes to further diversification.
C)Class switching enables a change in effector function.
D)The antigen receptor is composed of two identical heavy chains and two identical light chains.
E)Carbohydrate,lipid,and protein antigens are recognized and stimulate a response.

Question 22

Which of the following statements regarding CD8 T cells is incorrect?

A)When activated,CD8 T cells in turn activate B cells.
B)CD8 is also known as the CD8 T-cell co-receptor.
C)CD8 binds to MHC molecules at a site distinct from that bound by the T-cell receptor.
D)CD8 T cells kill pathogen-infected cells by inducing apoptosis.
E)CD8 T cells are MHC class I-restricted.

Question 23

Explain how professional antigen-presenting cells optimize antigen presentation to T cells despite the relatively limited capacity of any particular MHC molecule to bind different pathogen-derived peptides.

Question 24

class II molecules are made up of two chains called _______,whose function is to bind peptides and present them to _______ T cells:

A)alpha (α)and beta (β); CD4
B)alpha (α)and beta₂-microglobulin (β₂m); CD4
C)alpha (α)and beta (β); CD8
D)alpha (α)and beta₂-microglobulin β₂m); CD8
E)alpha (α)and beta (β); γ:δ T cells.

Question 25

B cells,transport of immunoglobulin to the membrane is dependent on association with two invariant proteins,Igα and Igβ.Which of the following invariant proteins provide this function for the T-cell receptor in T cells?

A)CD3γ
B)CD3δ
C)CD3ε
D)ζ
E)All of the above.

Question 26

Which of the following statements regarding T-cell receptor recognition of antigen is correct?

A)α:β T-cell receptors recognize antigen only as a peptide bound to an MHC molecule.
B)αβ T-cell receptors recognize antigens in their native form.
C)α:β T-cell receptors,like B-cell immunoglobulins,can recognize carbohydrate,lipid,and protein antigens.
D)Antigen processing occurs in extracellular spaces.
E)Like α:β T cells,γ:δ T cells are also restricted to the recognition of antigens presented by MHC molecules.

Question 27

many complementarity-determining regions contribute to the antigen-binding site in an intact T-cell receptor?

A)2
B)3
C)4
D)6
E)12.

Question 28

Discuss how T-cell receptors differ from immunoglobulins in the way that they recognize antigen.Use the following terms in your

Question 29

contrast to immunoglobulins,α:β T-cell receptors recognize epitopes present on _______ antigens:

A)carbohydrate
B)lipid
C)protein
D)carbohydrate and lipid
E)carbohydrate,lipid,and protein.

Question 30

antigen-recognition site of T-cell receptors is formed by the association of which of the following domains?

A)V_α and C_α
B)V_β and C_β
C)C_α and C_β
D)V_α and C_β
E)V_α and V_β.

Question 31

Antigen processing involves the breakdown of protein antigens and the subsequent association of peptide fragments on the surface of antigen-presenting cells with

A)immunoglobulins
B)T-cell receptors
C)complement proteins
D)MHC class I or class II molecules
E)CD4.

Question 32

Pathogens that infect the human body replicate either inside cells (such as viruses)or extracellularly,in the blood or in the extracellular spaces in tissues.
A.Identify (i)the class of T cells that are stimulated by intracellular pathogens,(ii)their co-receptor,(iii)the MHC molecule used for recognition of antigen and (iv)the T-cell effector function.
B.Repeat this for the classes of T cells that are stimulated by extracellular pathogens.For the purposes of this question,count those pathogens (such as mycobacteria)that can survive and live inside intracellular vesicles after being taken up by macrophages as extracellular pathogens.

Question 33

Explain specifically how interferon-γ produced during an infection enhances (A)antigen processing in the MHC class I pathway,and (B)antigen presentation in the MHC class II pathway.

Question 34

possesses _______ binding sites for antigen,and the T-cell receptor possesses _______ binding sites for antigen:

A)1; 1
B)2; 1
C)1; 2
D)2; 2
E)2; 4.

Question 35

Which of the following describes a ligand for an α:β T-cell receptor?

A)carbohydrate:MHC complex
B)lipid:MHC complex
C)peptide:MHC complex
D)all of the above
E)none of the above.

Question 36

Which of the following is not a characteristic of native antigen recognized by T cells?

A)peptides ranging between 8 and 25 amino acids in length
B)not requiring degradation for recognition
C)amino acid sequences not found in host proteins
D)primary,and not secondary,structure of protein
E)binding to major histocompatibility complex molecules on the surface of antigen-presenting cells.

Question 37

most variable parts of the T-cell receptor are

A)V_α and C_α
B)V_β and C_β
C)C_α and C_β
D)V_α and C_β
E)V_α and V_β.

Question 38

Owing to the location of the δ-chain locus of the T-cell receptor on chromosome 14,if the _______-chain locus rearranges by somatic recombination,then the δ-chain locus is _______:

A)α; also rearranged
B)α; deleted
C)α; transcribed
D)β; deleted
E)γ; also rearranged.

Question 39

Cross-priming of the immune response occurs when _____.(Select all that apply.)
a.viral antigens are presented by MHC class I molecules on the surface of a cell that is not actually infected by that particular virus
b.cytosol-derived peptides enter the endoplasmic reticulum and bind to MHC class II molecules
c.phagolysosome-derived peptides bind to MHC class II molecules
d.peptides of nuclear or cytosolic proteins are presented by MHC class II molecules.

Question 40

Provide an explanation of why it is believed that MHC class I genes are the evolutionary ancestors of MHC class II genes.

Question 41

of the following are oligomorphic except

A)HLA-G α chain
B)HLA-DO β chain
C)HLA-DQ β chain
D)HLA-A α chain
E)HLA-DR α chain.

Question 42

molecules have promiscuous binding specificity.This means that

A)a particular MHC molecule has the potential to bind to different peptides
B)when MHC molecules bind to peptides,they are degraded
C)peptides bind with low affinity to MHC molecules
D)none of the above describes promiscuous binding specificity.

Question 43

reference to the interaction between T-cell receptors and their corresponding ligands,which of the following statements is correct?

A)The organization of the T-cell receptor antigen-binding site is distinct from the antigen-binding site of immunoglobulins.
B)The orientation between T-cell receptors and MHC class I molecules is different from that of MHC class II molecules.
C)The CDR3 loops of the T-cell receptor α and β chains form the periphery of the binding site making contact with the α helices of the MHC molecule.
D)The most variable part of the T-cell receptor is composed of the CD3 loops of both the α and β chains.
E)All of the above statements are correct.

Question 44

T-cell receptors interact not only with peptide anchored in the peptide-binding groove of MHC molecules,but also with

A)anchor residues
B)peptide-binding motif
C)variable amino acid residues on α helices of the MHC molecule
D)β₂-microglobulin
E)invariant chain.

Question 45

Describe (A)five ways in which T-cell receptors are similar to immunoglobulins,and (B)five ways in which they are different (other than the way in which they recognize antigen).

Question 46

of the following are highly polymorphic except

A)HLA-A α chain
B)HLA-DO α chain
C)HLA-B α chain
D)HLA-DR β chain
E)HLA-C α chain.

Question 47

which domain of MHC class I does CD8 bind?

A)α₁
B)β₁
C)α₂
D)β₂
E)α₃.

Question 48

Directional selection is best described as

A)all polymorphic alleles preserved in a population
B)T-cell receptor interaction with peptide:MHC complexes directed to a planar interface
C)a mechanism in T cells that is analogous to affinity maturation of immunoglobulins
D)selected alleles increase in frequency in a population
E)selection of most appropriate transplant donor directed at the identification of identical or similar combinations of HLA alleles compared with the transplant recipient.

Question 49

_____ refers to the complete set of HLA alleles that a person possesses on a particular chromosome 6.

A)isoform
B)isotype
C)oligomorph
D)allotype
E)haplotype.

Question 50

combination of all HLA class I and class II allotypes that an individual expresses is referred to as their

A)haplotype
B)allotype
C)isotype
D)autotype
E)HLA type.

Question 51

peptide-binding groove of MHC class I molecules is composed of the following extracellular domains:

A)α₁:β₁
B)β₁:β₂
C)α₂:β₂
D)α₂:α₃
E)α₁:α₂.

Question 52

CDR3 loops of the T-cell receptor contact the _______:

A)side chains of amino acids in the middle of the peptide
B)co-receptors CD4 or CD8
C)membrane-proximal domains of the MHC molecule
D)constant regions of antibody molecules
E)α helices of the MHC molecule.

Question 53

the following HLA α-chain loci,which one exhibits the highest degree of polymorphism?

A)HLA-A
B)HLA-B
C)HLA-C
D)HLA-DP
E)HLA-DR.

Question 54

which domain of MHC class II does CD4 bind?

A)α₁
B)β₁
C)α₂
D)β₂
E)α₃.

Question 55

Peptides that bind to a particular MHC isoform usually have either the same or chemically similar amino acids at two to three key positions that hold the peptide tightly in the peptide-binding groove of the MHC molecule.These amino acids are called _____ and the combination of these key residues is known as its _____.

A)alleles; allotypes
B)anchor residues; peptide-binding motif
C)allotype; haplotypes
D)invariant chains; haplotypes
E)restriction residues; MHC allotype.

Question 56

diversity of MHC class I and II genes is due to _____.(Select all that apply.)
a.gene rearrangements similar to those observed in T-cell receptor genes
b.the existence of many similar genes encoding MHC molecules in the genome
c.somatic hypermutation
d.extensive polymorphism at many of the alleles
e.isotype switching.

Question 57

complementarity-determining region (CDR)1 and CDR2 loops of the T-cell receptor contact the _______:

A)side chains of amino acids in the middle of the peptide
B)co-receptors CD4 or CD8
C)membrane-proximal domains of the MHC molecule
D)constant regions of antibody molecules
E)α helices of the MHC molecule.

Question 58

Which of the following describes the sequence of events involved in the processing of peptides that will be presented as antigen with MHC class II?

A)protease activity →removal of CLIP from MHC class II →binding of peptide to MHC class II →endocytosis →plasma membrane
B)endocytosis →protease activity →removal of CLIP from MHC class II →binding of peptide to MHC class II →plasma membrane
C)removal of CLIP from MHC class II →binding of peptide to MHC class II →protease activity →endocytosis →plasma membrane
D)binding of peptide to MHC class II →endocytosis →removal of CLIP from MHC class II →protease activity →plasma membrane
E)plasma membrane →endocytosis →protease activity →removal of CLIP from MHC class II →binding of peptide to MHC class II.

Question 59

Which of the following accurately completes this statement: "The function of _______ T cells is to make contact with _______ and _______"? (Select all that apply.)

A)CD8; virus-infected cells; kill virus-infected cells
B)CD8; B cells; stimulate B cells to differentiate into plasma cells
C)CD4; macrophages; enhance microbicidal powers of macrophages
D)CD4; B cells; stimulate B cells to differentiate into plasma cells
E)All of the above are accurate.

Question 60

type of bare lymphocyte syndrome is caused by a genetic defect in MHC class II transactivator (CIITA),which results in the inability to synthesize MHC class II and display it on the cell surface.The consequence of this would be that

A)B cells are unable to develop
B)CD8 T cells cannot function
C)CD4 T cells cannot function
D)intracellular infections cannot be eradicated
E)peptides cannot be loaded onto MHC molecules in the lumen of the endoplasmic reticulum.

Question 61

is meant by the terms (A)antigen processing and (B)antigen presentation? (C)Why are these processes required before T cells can be activated?

Question 62

immunological consequence of severe combined immunodeficiency disease (SCID)caused by a genetic defect in either RAG-1 or RAG-2 genes is

A)lack of somatic recombination in T-cell receptor and immunoglobulin gene loci
B)lack of somatic recombination in T-cell receptor loci
C)lack of somatic recombination in immunoglobulin loci
D)lack of somatic hypermutation in T-cell receptor and immunoglobulin loci
E)lack of somatic hypermutation in T-cell receptor loci.

Question 63

Which of the following describes the sequence of events involved in processing of peptides that will be presented as antigen with MHC class I?

A)plasma membrane →TAP1/2 →proteasome →MHC class I →endoplasmic reticulum
B)TAP1/2 →proteasome →MHC class I →endoplasmic reticulum→plasma membrane
C)proteasome →TAP1/2 →MHC class I →endoplasmic reticulum →plasma membrane
D)proteasome →TAP1/2 →endoplasmic reticulum →MHC class I →plasma membrane
E)endoplasmic reticulum →proteasome →MHC class I →TAP1/2 →plasma membrane.

Question 64

Which of the following removes CLIP from MHC class II molecules?

A)HLA-DM
B)HLA-DO
C)HLA-DP
D)HLA-DQ
E)HLA-DR.

Question 65

role of the CD3 proteins and ζ chain on the surface of the cell is to

A)transduce signals to the interior of the T cell
B)bind to antigen associated with MHC molecules
C)bind to MHC molecules
D)bind to CD4 or CD8 molecules
E)facilitate antigen processing of antigens that bind to the surface of T cells.

Question 66

T-cell subpopulations are specialized to combat _______ pathogens,whereas CD4 T-cell subpopulations are specialized to combat _______ pathogens:

A)bacterial; viral
B)dead; live
C)extracellular; intracellular
D)intracellular; extracellular
E)virulent; attenuated.

Question 67

Describe in chronological order the steps of the antigen-processing and antigen-presentation pathways for extracellular pathogens.
B.What would be the outcome (i)if invariant chain were defective or missing,or (ii)if HLA-DM were not expressed?

Question 68

Compare the organization of T-cell receptor α and β genes (the TCRα and TCRβ loci)with the organization of immunoglobulin heavy-chain and light-chain genes.

Question 69

Which of the following cell types is not considered a professional antigen-presenting cell?

A)macrophage
B)neutrophil
C)B cell
D)dendritic cell
E)all of the above are professional antigen-presenting cells.

Question 70

What is the difference between MHC variation due to multigene families and that due to allelic polymorphism?
B.How does MHC variation due to multigene families and allelic polymorphism influence the antigens that a person's T cells can recognize?

Question 71

T-cell receptors do not undergo isotype switching.Suggest a possible reason for this.

Question 72

evidence supports the proposal that MHC diversity evolved by natural selection caused by infectious pathogens rather than exclusively by random DNA mutations?

Question 73

Describe in chronological order the steps of the antigen-processing and antigen-presentation pathways for intracellular,cytosolic pathogens.
B.(i)What would be the outcome if a mutant MHC class I α chain could not associate with β₂-microglobulin,and (ii)what would happen if the TAP transporter were lacking as a result of mutation? Explain your answers.

Question 74

Which of the following HLA-DRB genotypes is not possible in an individual? (X: X represents diploid genotype.)

A)DRB1: DRB1
B)DRB1,DRB3: DRB1,DRB4
C)DRB1: DRB1,DRB5
D)DRB1,DRB4: DRB1
E)DRB3: DRB1,DRB5.

Question 75

Which of the following cell types does not express MHC class I?

A)erythrocyte
B)hepatocyte
C)lymphocyte
D)dendritic cell
E)neutrophil.

Question 76

(i)Describe the structure of an MHC class I molecule,identifying the different polypeptide chains and domains.(ii)What are the names of the MHC class I molecules produced by humans? Which part of the molecule is encoded within the MHC region of the genome? (iii)Which domains or parts of domains participate in the following: antigen binding; binding the T-cell receptor; and binding the T-cell co-receptor? (iv)Which domains are the most polymorphic?
B.Repeat this for an MHC class II molecule.

Question 77

How many HLA-DR α:β combinations can be made by an individual who is heterozygous at all HLA-DRβ loci,inherits the DRβ haplotype DRB1 from their mother,the DRβ haplotype DRB1,DRB4 from their father,and also inherits different allelic forms of DRA from each parent?
B.Repeat this exercise given the same information except that the maternal DRβ haplotype is DRB1,DRB3.

Question 78

Which of the following is mismatched?

A)peptide-binding motif: combination of anchor residues in a peptide capable of binding a particular MHC haplotype
B)MHC restriction: specificity of T-cell receptor for a particular peptide:MHC molecule complex
C)balancing selection: maintenance of variety of MHC isoforms in a population
D)directional selection: replacement of older MHC isoforms with newer variants
E)interallelic conversion: recombination between two different genes in the same family.

Question 79

the context of MHC isoforms,what is the difference between balancing selection and directional selection?

Question 80

A.What is the maximum number of MHC class I and class II molecules that a heterozygous individual could theoretically express? Explain your answer.(Ignore the possibility of MHC class II molecules composed of chains from different isotypes.)
B.How does this relatively small number of MHC molecules have the potential to bind the huge number of antigenic peptides encountered in the environment,and what features of a peptide determine whether it will be bound by a given MHC molecule?