Immunology Exam 2

T-cell receptors structurally resemble ______.

a. the Fc portion of immunoglobulins
b. MHC class 1 molecules
c. secreted antibodies
d. a single Fab of immunoglobulins
e. CD3 ε chains

When comparing the T-cell receptor α-chain locus with the immunoglobulin heavy-chain locus, all of the following are correct except:

a. the T-cell receptor α locus differs because it has embedded within its sequence another locus that encodes a different type of T-cell receptor chain
b. both are encoded on chromosome 14
c. the T-cell receptor α-chain locus does not contain D segments
d. the T-cell receptor α-chain locus contains more V and J regions
e. the T-cell receptor α-chain locus contains more C regions

Unlike the C regions of immunoglobulin heavy-chain loci, the C regions of the T-cell receptor β-chain loci ______..

a. are functionally similar
b. do not contain D segments
c. are more numerous
d. are encoded on a different chromosome from the variable β-chain gene segments of the T-cell receptor
e. do not encode a transmembrane region

All of the following statements regarding γ:δ T cells are correct except:

a. activation is not always dependent on recognition of a peptide:MHC molecule complex
b. they are more abundant in tissue than in the circulation
c. expression on the cell surface is not dependent on the CD3 complex
d. they share some properties with NK cells
e. the δ chain is the counterpart to the β chain in α:β T-cell receptors because it contains V, D, and J
segments in the variable region

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

a. endocytosis
b. antigen processing
c. promiscuous processing
d. antigen presentation
e. peptide loading

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

a. kill virus-infected cells
b. assist macrophages in sustaining adaptive immune responses through their secretion of cytokines and chemokines
c. improve phagocytic mechanisms of tissue macrophages
d. assist B cells in the production of high-affinity antibodies
e. facilitate responses of other immune-system cells during infection

Which of the statements below is false regarding MHC molecule:

a. MHC molecules have promiscuous binding specificity, which means that one MHC molecule is able
to bind a wide range of peptides with different sequences.
b. The consequence of MHC promiscuity is that humans need only encode a relatively small number of
MHC molecules in their genome if they are to bind to the huge number of pathogen-derived
peptides encountered during a lifetime of infections.
c. MHC molecules are coexpressed on the cell surface. This also ensures that an appropriate density of
MHC molecules populates the cell surface to ensure efficient T-cell engagement and subsequent
activation.
d. Each MHC molecule can bind only to a very restricted number of peptides. This is why we need to expressed so many MHC molecules per cell
e. MHC I molecule are found is most nucleated cells, whereas MHC II are expressed almost exclusively by antigen-presenting cells (APCs), such as B cells, dendritic cells and macrophages.

Which of the following is not a characteristic of immunoproteasomes?

a. They produce a higher proportion of peptides containing acidic amino acids at the carboxy terminus compared with constitutive proteasomes.
b. They contain 205 proteasome-activation complexes on the caps.
c. They consist of four rings of seven polypeptide subunits that exist in alternative forms.
d. They make up about 1% of cellular protein.
e. They are produced in response to IFN-γ
produced during innate immune responses.

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

a. TAP is an ATP-dependent, membrane-bound transporter
b. TAP is a homodimer composed of two identical subunits
c. TAP transports proteasome-derived peptides from the cytosol directly to the lumen of the Golgi apparatus
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.

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

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

Which of the following statements is false regarding MHC class I:

a. The complete MHC class I molecule is a heterodimer made up of one α chain and a smaller chain

called β-microglobulin. The α chain consists of three extracellular domains α1, α2, and α3—a transmembrane region and a cytoplasmic tail.

b. β2-Microglobulin is a single-domain protein covalently associated with the extracellular portion of the α chain, providing support and stability.

c. The polymorphic class I molecules in humans are called HLA-A, HLA-B, and HLA-C. The α chain is encoded in the MHC region by an MHC class I gene. The gene for β2-microglobulin is elsewhere in the genome.

d. The antigen-binding site is formed by the α1 and α2 domains, the ones farthest from the membrane, which create a peptide-binding groove. The region of the MHC molecule that binds to the T-cell receptor encompasses the α helices of the α1 and α2 domains that make up the outer surfaces of the peptide-binding groove. The α3 domain binds to the T-cell co-receptor CD8.

e. The most polymorphic parts of the α chain are the regions of the α1 and α2 domains that bind antigen and the T-cell receptor. β2-Microglobulin is invariant; that is, it is the same in all individuals.

Which of the following statements is false regarding MHC class II:

a. MHC class II molecules are heterodimers made up of an α chain and a β chain. The α chain consists

of α1 and α2 extracellular domains, a transmembrane region, and a cytoplasmic tail. The β chain

contains β1 and β2 extracellular domains, a transmembrane region, and a cytoplasmic tail.

b. In humans there are three polymorphic MHC class II molecules called HLA-DP, HLA-DQ, and HLA-DR.

c. Both chains of an MHC class II molecule are encoded by genes in the MHC region.

d. Antigen binds in the peptide-binding groove formed by the α2 and β2 domains. The α helices of the

α2 and β2 domains interact with the T-cell receptor. The β1 domain binds to the T-cell co-receptor

CD4.

e. With the exception of HLA-DRα, which is dimorphic, both the α and β chains of MHC class II molecules are highly polymorphic. Polymorphism is concentrated around the regions that bind antigen and the T-cell receptor in the α1 and β1 domains.

Identify which of the following statements is false regarding T-cell receptors.

a. The antigen-recognition site of T-cell receptors is formed by the association of which of the Vα and
Vβ domains.
b. Six complementarity-determining regions contribute to the antigen-binding site in an intact T-cell
receptor
c. In B cells, transport of immunoglobulin to the membrane (B-cell receptor) is dependent on
association with two invariant proteins, Igα and Igβ. This function for the T-cell receptor in T cells is
provided by the invariant proteins CD3γ, CD3δ, CD3ε, and ζ.
d. α:β T-cell receptors recognize antigen only as a peptide bound to an MHC molecule.
e. Like α:β T cells, γ:δ T cells are also restricted to the recognition of peptides presented by MHC
molecules.

Cross-priming of the immune response occurs when _____.

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, or peptides of nuclear or cytosolic proteins are presented by MHC class II molecules.
b. phagolysosome-derived peptides bind to MHC class III molecules
c. viral antigens are presented by MHC class II molecules on the surface of a cell that is not actually
infected by that particular virus or peptides of nuclear or cytosolic proteins are presented by MHC
class I molecules.
d. cytosol-derived peptides enter the endoplasmic reticulum and bind to MHC class II molecules
e. phagolysosome-derived peptides bind to MHC class II molecules

Identify which of the following statements is false in regard to the binding of peptides to the groove of MHC I and MH II molecules.

a. For all MHC molecules, only a few of the amino acids in the antigen peptide are critical for binding to amino acids in the peptide-binding groove.
b. The critical amino acids in the peptide are called anchor residues; they are the different in all peptides that bind to a given MHC molecule. The other amino acid residues in the peptides must be similar.
c. The pattern of anchor residues that binds to a given MHC molecule is called the peptide-binding motif. Hence, a very large number of discrete peptides can bind to each MHC isoform, the only constraint being the possession of the correct anchor residues at the appropriate positions in the peptide.
d. MHC class I molecules bind peptides that are 8-10 (mostly 9) amino acids long.
e. MHC class II molecules bind longer peptides with a range of lengths, usually from 13 to 25 amino
acids long.

Identify which of the following statements is false regarding the diversity and polymorphism of human leukocyte antigen (HLA) and MHC molecules.

a. The diversity of MHC class I and II genes is due to the existence of many similar genes encoding MHC molecules in the genome and extensive polymorphism at many of the alleles.
b. The combination of all HLA class I and class II allotypes that an individual expresses is referred to as their HLA type.
c. Interallelic conversion is a recombination between homologous alleles of the same gene. Gene conversion is a recombination between non-homologous alleles of different genes.
d. MHC polymorphisms are non-randomly localized, predominantly to the region of the molecule that makes contact with peptide and T-cell receptors. Random DNA mutations, in contrast, would be scattered through the gene, giving rise to amino acid changes throughout MHC molecules and not just in those areas important for peptide binding and presentation.
e. Directional selection is best described as all polymorphic alleles preserved in a population.

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

a. bind to antigen associated with MHC molecules
b. bind to MHC molecules
c. bind to CD4 or CD8 molecules
d. transduce signals to the interior of the T cell
e. facilitate antigen processing of antigens that bind to the surface of T cells

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. endoplasmic reticulum →proteasome →MHC class I →TAP1/2 →plasma membrane
b. plasma membrane →TAP1/2 →proteasome →MHC class I →endoplasmic reticulum
c. proteasome →TAP1/2 →MHC class I →endoplasmic reticulum →plasma membrane
d. TAP1/2 →proteasome →MHC class I →endoplasmic reticulum→plasma membrane
e. proteasome →TAP1/2 →endoplasmic reticulum →MHC class I →plasma membrane

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. plasma membrane →endocytosis →protease activity →removal of CLIP from MHC class II →binding of peptide to MHC class II
b. protease activity →removal of CLIP from MHC class II →binding of peptide to MHC class II →endocytosis →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. endocytosis →protease activity →removal of CLIP from MHC class II →binding of peptide to MHC class II →plasma membrane

Identify which of the following statements is false regarding inheritance of MHC/HLA genes.

a. Allotype is any of the genetically determined variants in the constant region of a given subclass of a
protein that is detectable as an antigen by members of the same species having a different constant
region.
b. Haplotype is one complete set of MHC genes, which is inherited from either one’s mother or one’s
father.
c. Mice and humans are diploid organisms, and therefore have two complete sets of chromosomes
(one maternally-inherited and one paternally-inherited). Therefore, each cell of a human or a mouse
actually possesses two MHC haplotypes - a maternal haplotype and a paternal haplotype.
d. Inbred mouse strains, however, are homozygous at all genetic loci, thus we typically only state the
MHC haplotype once, since both haplotypes are identical.
e. Human populations must maintain a homogenous, less diverse population of HLA class I and II allotypes to increase the chances of surviving many epidemics of infectious disease.

Regarding the distinct phases of B-cell development, which of the statements below is incorrect?

a. Repertoire assembly: Bone marrow expression of diverse B-cell receptors.
b. Negative selection: Modification, elimination or inactivation of autoreactive B cells.
c. Positive selection: Selection of a small subset of immature B cells to become mature B cells in the
bone marrow.
d. Searching for infection: Patrolling for infectious material by recirculating continuously between lymph, blood and secondary lymphoid organ compartments.
e. Finding infection: B cells become activated by antigen in secondary lymphoid tissues and then undergo clonal expansion. Attacking infection: B cells differentiate into plasma cells and memory cells in secondary lymphoid tissues.

Which of the following is characteristic of a large pre-B cell?

a. V is rearranging to DJ at the heavy-chain locus.
b. V–J is rearranging at the light-chain locus.
c. μ (mu) heavy chain and lambda or kappa light chain is made.
d. VDJ is successfully rearranged and mu heavy chain is made.
e. D–J is rearranging at the heavy-chain locus

Which of the following statements is correct?

a. The κ light-chain genes rearrange before the λ light-chain genes.
b. The κ light-chain genes rearrange before the heavy-chain genes.
c. The μ heavy-chain genes rearrange first and then the λ light-chain genes rearrange
d. The λ light-chain genes rearrange before the heavy-chain genes.
e. The λ light-chain genes rearrange before the κ light-chain genes.

Which of the following statements is false regarding B cell development:

a. Immature B cells develop into B cells in the secondary lymphoid organs
b. The latest stages of late pro-B-cell development are recognized by the association of a surrogate
light chain with a μ (mu) chain. The surrogate light chain is composed of VpreB and λ5.
c. Large pre-B-cell stage constitutively express RAG-1 and RAG-2 proteins.
d. A developing B cell unable to generate a productive rearrangement on any of the four light-chain loci will undergo allelic exclusion.
e. After the production of a functional μ chain as a pre-B-cell receptor: i) RAG proteins are degraded; ii) the chromatin structure of the heavy-chain locus is reorganized to prevent gene rearrangement; iii) transcription of the RAG1 and RAG2 genes ceases; and iv) there is allelic exclusion of a second mu chain.

An important advantage of having two gene loci (kappa and lambda) for the light chain is .

a. that immunoglobulins are homogeneous and not heterogeneous in mature B cells
b. that different effector functions are conferred by the two different light-chain loci
c. that surrogate light-chain transcription cannot compete with kappa and lambda transcription and
enables B-cell development
d. that the likelihood of a successful rearrangement of light-chain genes increases
e. that the likelihood of a unsuccessful rearrangement of light-chain genes increases

The consequence of allelic exclusion at the immunoglobulin loci ensures that _.

a. all functional copies of a gene are expressed
b. B-cell receptors have a low-avidity binding
c. hybrid immunoglobulins are formed
d. heterogeneous B-cell receptors bind more effectively to antigen
e. B cells express antigen receptors of a single specificity and homogeneous B-cell receptors bind more effectively to antigen

Negative selection of developing B cells ensures that ___.

a. B-cell receptors that bind to normal constituents of the body do not emerge
b. only antigen-activated B cells leave the bone marrow
c. there is not an overabundance of circulating B cells that would compete with other important cell
types in the circulation
d. clonal expansion of B cells does not occur in the absence of infection
e. B cells do not leave secondary lymphoid tissues

Which of the statements below is false regarding the two checkpoints of B-cell development?

a. Checkpoint 1 is marked by the formation of a complex of a μ heavy chain complexed with the
surrogate light chain VpreBλ, Igα, and Igβ.
b. Checkpoint 2 occurs when a complete B-cell receptor, comprising μ heavy chains, κ or λ light chains,
and Igα and Igβ chains, is expressed on the B-cell surface.
c. At checkpoint 1, if the V(D)J rearrangement gives rise to a nonfunctional pre-B-cell receptor the late pro-B cell will be permitted to survive and undergo clonal proliferation. If V(D)J rearrangement produces a functional heavy chain and no pre-B-cell receptor is assembled, the pro-B cell undergoes apoptosis and dies.
d. At checkpoint 2, production of a functional light chain results in the assembly of a functional surface immunoglobulin and the survival and maturation of the B cell. Nonproduction of a light chain results eventually in apoptosis.
e. Checkpoint 1 delivers an important signal to the cell, verifying that a functional heavy chain has been made. This triggers the cessation of heavy-chain gene rearrangement followed by the inactivation of surrogate light-chain synthesis.

Receptor editing occurs _.

a. in the bone marrow to establish self-tolerance of the B-cell repertoire
b. after encounter with foreign antigen in secondary lymphoid organs
c. in mature B cells
d. to establish self-reactivity of the B-cell repertoire
e. to express an excess of IgM over IgD on the surface of mature B cells

All of the following are associated with the development of Burkitt’s lymphoma except:

a. Cell division restraints on mutated B cells are lifted.
b. The expression of Myc protein is perturbed.
c. A chromosomal translocation involving a proto-oncogene and an immunoglobulin gene occurs.
d. In addition to a chromosomal translocation event, mutations elsewhere in the genome are usually
involved.
e. Overproduction of the Bcl-2 protein prolongs the lifetime of B-lineage cells

Which of the following is a characteristic of B-2 cells?

a. They are located primarily in secondary lymphoid organs.
b. They are sometimes referred to as CD5 B cells.
c. They are not dependent on T helper cells for activation.
d. They comprise only 5% of the B-cell repertoire.
e. In adults, they are renewed by cell division in the peripheral circulation.

Plasma cells have all of the properties listed except .

a. they secrete antibody and they are terminally differentiated B cells
b. they no longer express MHC class II molecules
c. they cease expressing membrane-bound immunoglobulin
d. they rapidly proliferate in secondary lymphoid follicles
e. differentiation into plasma cells occurs after migration from germinal centers to other sites in lymphoid tissue and bone marrow

All of the following events occur within germinal centers except:

a. centroblasts arise from activated B cells
b. production of memory B cells
c. isotype switching
d. affinity maturation
e. B cells are activated by CD4 helper T cells

Immunological tolerance in the B-cell repertoire is called tolerance when it develops in primary lymphoid organs, and tolerance when it is induced outside the bone marrow.

a. central; peripheral
b. primary; secondary
c. receptor-mediated; systemic
d. apoptotic; anergic
e. stromal; follicular

The proto-oncogene _ is associated with the development of Burkitt’s lymphoma.

a. CD5
b. BCL-2
c. CD19
d. BTK
e. Myc

What is the fate of an immature B cell that encounters and has specificity for self-antigen?

a. If further heavy-chain and light-chain gene rearrangements are possible, it undergoes apoptosis.
b. Somatic hypermutation.
c. Continued rearrangement of light-chain genes.
d. Decrease in production of IgD.
e. Continued rearrangement of heavy-chain genes.

The circulatory route through a lymphoid tissue for both immature B cells and mature B cells that do not encounter specific antigen is:

a. bloodstream --> HEV of lymphoid cortex --> primary lymphoid follicle --> efferent lymphatic vessel
b. afferent lymphatic vessel --> primary lymphoid follicle --> HEV of lymphoid cortex --> efferent
lymphatic vessel
c. afferent lymphatic vessel --> medullary cords --> primary lymphoid follicle --> efferent lymphatic
vessel
d. primary lymphoid follicle --> HEV of lymphoid cortex --> afferent lymphatic vessel --> efferent
lymphatic vessel
e. bloodstream --> afferent lymphatic vessel --> HEV of lymphoid cortex --> efferent lymphatic
vessel.

Regarding the role of primary lymphoid follicles in eliminating B cells that have antigen receptors specific for soluble self antigen, which statement below is incorrect?

a. To survive, circulating B cells must enter primary follicles where survival signals are delivered by cells in the follicles, including follicular dendritic cells, which are the stromal cells of primary lymphoid follicles.
b. Circulating B cells that fail to enter follicles in secondary lymphoid tissues will die in the peripheral circulation with a half-life of about 3 days.
c. B cells with antigen receptors specific for soluble self antigen are generally rendered anergic in the bone marrow or the circulation.
d. Anergic B cells that enter secondary lymphoid organs are held in the T-cell areas adjacent to primary follicles and are not permitted to penetrate the follicle.
e. Anergic B cells receive the necessary stimulatory signal for survival and remain circulating in the body for many years.

As to memory B cells, which of the following statements is incorrect?

a. Memory enables faster, more efficient recall responses when antigen is encountered subsequently. This enables the body to get rid of a pathogen before it has time to cause disease.
b. Immunoglobulin produced during a primary immune response is mainly IgM, in low concentration (titer) and of low affinity for the antigen.
c. Immunoglobulin expressed during a secondary immune response has undergone isotype switching and is often of the IgG isotype.
d. IgG produced during the secondary immune response has a higher titer and, through the process of somatic hypermutation, will have a higher affinity for its corresponding antigen.
e. All of the answers are correct

As to B-1 and B-2 cells, which of the following statements is incorrect?

a. Unlike conventional B-2 cells, B-1 cells arise early in embryonic development, express the cell-
surface protein CD5, possess few N nucleotides at VDJ junctions, and have a restricted range of
antigen specificities.
b. B-1 cells are also characterized by little or no IgD on the surface and a distinctive repertoire of
antigen receptors.
c. Unlike B-2 cells, B-1 cells produce IgM antibodies of low affinity and respond mainly to carbohydrate, rather than protein, epitopes.
d. Individual B-1 cells are polyspecific for antigen; that is, their immunoglobulins bind several different antigens.
e. B-1 cells are probably best associated with adaptive immune responses because of their rapid response to antigen, their limited diversity, their polyspecificity, and no need of T-cell help.

In which of the following ways does the developmental pathway of alpha:beta T cells differ from that of B cells?

a. When the first chain of the antigen receptor is produced it combines with a surrogate chain.
b. MHC molecules are required to facilitate progression through the developmental pathway and T cells do not rearrange their antigen-receptor genes in the bone marrow.
c. Their antigen receptors are derived from gene rearrangement processes.
d. Cells bearing self-reactive antigen receptors undergo apoptosis.
e. T cells rearrange their antigen-receptor genes in the bone marrow.

Which of the following processes is not dependent on an interaction involving MHC class I or class II molecules?

a. peripheral activation of mature naive T cells
b. intracellular signaling by pre-T-cell receptors and positive selection of gamma:delta T cells
c. positive selection of alpha:beta T cells
d. negative selection of alpha:beta T cells
e. None of the above.

If a double-negative thymocyte has just completed a productive beta-chain gene rearrangement, which of the following describes the immediate next step in the development of this thymocyte?

a. This cell will inevitably differentiate into a committed gamma:delta T cell.
b. Rearrangement of gamma- and delta-chain genes commences.
c. Expression levels of RAG-1 and RAG-2 are elevated.
d. The linked delta-chain genes are eliminated.
e. A pre-T-cell receptor is assembled as a superdimer.

_ is a T-cell-specific adhesion molecule expressed before the expression of a functional T-cell receptor while the thymocytes are still in their double-negative stage of development.

a. CD25
b. CD4
c. CD2
d. CD8
e. CD3

Which of the following statements about Notch 1 is incorrect?

a. Notch1 is a membrane-bound receptor found on thymocytes that participates in the regulation of
early T-cell development. Its ligand (Notch ligand) is a membrane-bound protein on the surface of
thymic epithelial cells.
b. Notch 1 is to T-cell development as Pax-5 is to B-cell development. In the absence of Notch 1
expression, T cells cannot complete their differentiation.
c. After binding of the intracellular domain of Notch1 to the intracellular portion of Notch ligand, the extracellular domain of Notch1 is released by proteolysis and subsequently translocates to the nucleus.
d. In the thymocyte nucleus, this domain forms a transcription factor complex that displaces repressor proteins from genes involved in T-cell development and initiates transcription of these genes by recruiting transcription activator proteins.
e. The extracellular domain of Notch 1 must interact with a ligand on thymic epithelium to initiate cleavage and separation of the Notch 1 extracellular and intracellular domains.

Which of the following is the first stage of T-cell receptor gene rearrangement in alpha:beta T cells?

a. V-alpha --> D-alpha
b. D-beta --> J-beta
c. D-alpha --> J-alpha
d. V-beta --> D-beta
e. V-alpha --> J-alpha

There are many parallels between the development of B cells and T cells. Identify the incorrectly matched counterpart in B cells (left) versus T cells (right).

a. multiple kappa and lambda light-chain gene rearrangements: multiple alpha-chain gene rearrangements.
b. VpreBlambda5: pTalpha
c. Igalpha/Igbeta:CD3
d. Pax-5: FoxP3
e. Pax-5: CD3

Which of the following statements is false of a T cell that expresses two α chains (and thus two different T-cell receptors) as a result of ineffective allelic exclusion of the α chain during rearrangement?

a. Engaging either of the T-cell receptors on MHC molecules of the thymic epithelium will result in positive selection.
b. One of the T-cell receptors will be functional while the other will most probably be non-functional.
c. If either T-cell receptor binds strongly to self-peptides presented by self-MHC molecules, the
thymocyte will be negatively selected.
d. One of the T-cell receptors may be autoreactive but escape negative selection because its peptide
antigen is present in tissues other than the thymus.
e. Subsequent gene rearrangements may give rise to a gamma:delta T-cell receptor.

Once a thymocyte has productively rearranged a beta-chain gene, which of these events cannot occur subsequently?

a. Expression of CD34 and CD2 gives rise to double-positive thymocytes.
b. Rearrangement of beta-, gamma- and delta-chain genes ceases as a result of the suppression of expression of RAG-1 and RAG-2.
c. The pre-T cell proliferates and produces a clone of cells all expressing an identical beta chain.
d. beta binds to pTalpha and is expressed on the cell surface with the CD3 complex and zeta chain.
e. Alpha-, gamma-, delta-chain loci rearrange simultaneously.

Which of the following statements regarding positive selection is correct?

a. Positive selection results in the production of T cells bearing T-cell receptors that have the
capacity to interact with all allotypes of MHC class I and class II molecules, and not just those of
the individual.
b. All subsets of developing T cells undergo positive selection before export to the peripheral
circulation.
c. Positive selection ensures that autoreactive T cells are rendered non-responsive.
d. If there is a genetic defect in AIRE, then T-cell development is arrested as positive selection
commences.
e. T-cell receptor editing is linked to the process of positive selection.

Thymocytes that are not positively selected

a. make up about 98% of developing thymocytes and die by apoptosis in the thymic cortex
b. undergo genetic reprogramming and differentiate into a different cell type
c. try out different β chains to acquire reactivity with self-MHC molecules
d. are exported to the periphery, where they are phagocytosed by macrophages
e. are eliminated because of their reactivity with self antigens

Immediately after positive selection __.

a. the thymocyte reaches maturity and is exported to the periphery
b. receptor editing commences to eliminate reactivity against self antigens
c. the developing thymocyte acquires a double-negative phenotype
d. RAG proteins are degraded and are no longer synthesized
e. expression of pTalpha is repressed

Allelic exclusion occurs for all of the following except _.

a. T-cell receptor beta genes
b. B-cell receptor heavy-chain genes
c. T-cell receptor alpha genes
d. B-cell receptor kappa-chain genes
e. B-cell receptor lambda-chain genes

Autoimmune polyendocrinopathy–candidiasis–ectodermal dystrophy (APECED) is caused by a defect in ___.

a. cathepsin L
b. a transcription factor that regulates tissue-specific gene expression in the thymus
c. the production of regulatory CD4 T cells
d. FoxP3
e. T-cell receptor gene rearrangement

Identify which of the following describes how antigen processing and presentation of self antigens by thymic epithelial cells differs from that of antigen-presenting cells in peripheral tissues.

a. Thymic epithelium expresses MHC class I molecules but not MHC class II molecules.
b. Thymic epithelium uses cathepsin L for proteolytic degradation of self proteins.
c. Thymic epithelium expresses MHC class II molecules but not MHC class I molecules.
d. Thymic epithelium expresses transcription repressor protein FoxP3.
e. Thymic epithelium expresses MHC class II molecules but not MHC class I molecules.

All of the following types of protein are processed and presented by macrophages in the thymus except _ proteins.

a. soluble proteins from extracellular fluids
b. ubiquitous proteins
c. proteins made by macrophages
d. tissue-specific
e. proteins derived from other cells that macrophages phagocytose

Healthy individuals have approximately ____ of CD4 T cells compared with CD8 T cells.

a. one quarter the number
b. twice the number
c. half the number
d. equal numbers
e. four times the number

The function of negative selection of thymocytes in the thymus is to eliminate _.

a. single-positive thymocytes
b. double-positive thymocytes
c. alloreactive thymocytes
d. autoreactive thymocytes
e. apoptotic thymocytes

Which of the following statements is correct?

a. In DiGeorge syndrome the bone marrow takes over the function of the thymus and produces
mature peripheral T cells.
b. T cells and B cells are both short-lived cells and require continual replenishment from primary
lymphoid organs.
c. The human thymus is not fully functional until age 30, at which time it begins to shrink and
atrophy.
d. In adults the mature T-cell repertoire is self-renewing and long-lived and does not require a thymus for the provision of new T cells.
e. None of the above statements is correct.

The human thymus begins to degenerate as early as one year after birth. This process is called and is marked by the accumulation of ___ once occupied by thymocytes.

a. thymectomy; dendritic cells
b. differentiation; gamma:delta T cells
c. negative selection; gamma:delta T cells
d. involution; fat
e. involution; thymic stroma