Question 1

Which one of the following statements about T cell tolerance to self proteins is accurate?

Accepted Answer

A) Self proteins are not presented by the class I pathway because only microbial proteins,and not self proteins,are ubiquinated in the cytosol. 
B) Peptides derived from self proteins are not presented by the class I or class II pathways because MHC molecules are expressed only in response to infections. 
C) Self proteins are not presented by the class II pathway because endosomal acidic proteases digest microbial proteins but not eukaryotic proteins. 
D) Self peptide/self MHC complexes are formed and displayed by antigen-presenting cells in both class I and class II MHC pathways,but T cells that recognize these complexes usually are not present or are functionally inactive. 
E) Peptides derived from self proteins are not displayed by MHC molecules because they usually are displaced by the more abundant microbial peptides. D

Question 2

A young adult is exposed to a virus that infects and replicates in mucosal epithelial cells of the upper respiratory tract.One component of the protective immune response to this viral infection is mediated by CD8+ cytolytic T lymphocytes (CTLs),which recognize and kill virus-infected cells.The CTLs can recognize and kill the infected cells because:

Accepted Answer

A) In response to interferon-$\gamma$secreted during the innate immune response to the virus,the mucosal epithelial cells express class II MHC,with bound viral peptides,on their cell surfaces. 
B) Mucosal epithelial cells,like all nucleated cells,express class I MHC molecules and are able to process cytoplasmic viral proteins and display complexes of class I MHC and bound viral peptides on their cell surfaces. 
C) Antibodies specific for viral antigens bind to these antigens on infected cell surfaces and engage Ig Fc receptors on the CTL,thereby targeting the CTL to the infected cells. 
D) Virus-infected mucosal epithelial cells migrate to draining lymphoid tissues,where they present viral peptide antigens to naive CD8+ T cells. 
E) Viral infection of the mucosal epithelial cells stimulates them to express E-selectin,which promotes CD8+ T cell adhesion. B

Question 3

A child who suffers from a persistent viral infection is found to have a deficiency in lymphocyte production and very few T and B cells.Other bone marrow-derived cells are produced in normal numbers,and MHC molecule expression on cells appears normal.Transfusion of mature T cells from an unrelated donor who had recovered from a previous infection by the same virus would not be expected to help the child clear his infection.Which one of the following is a reasonable explanation for why this therapeutic approach would fail?

Accepted Answer

A) Viral infections are cleared by antibodies,not T cells. 
B) The patient's own immune system would destroy the transfused T cells before they could respond to the viral infection. 
C) T cells recognize peptides,not viral particles. 
D) Donor T cell viral antigen recognition is restricted by MHC molecules not expressed in the patient. 
E) In responding to the previous infection,the donor would have used up all his T cells specific for that virus. D

Question 4

A helper T cell response to a protein antigen requires the participation of antigen-presenting cells that express which of the following types of molecules?

Accepted Answer

A) Class II MHC and costimulators 
B) Class I MHC and CD4 
C) Class II MHC and CD8 
D) CD4 and costimulators 
E) Class II MHC and CD4

Question 5

Maturing dendritic cells that migrate to a lymph node from peripheral tissues end up mainly in:

Accepted Answer

A) Follicles 
B) High endothelial venules 
C) The medullary sinus 
D) T cell zones 
E) Efferent arterioles

Question 6

In the class I MHC pathway of antigen presentation,peptides generated in the cytosol are translocated into the endoplasmic reticulum in which of the following ways?

Accepted Answer

A) By ATP-dependent transport via the transporter associated with antigen-processing (TAP)1/2 pump 
B) By passive diffusion 
C) By receptor-mediated endocytosis 
D) Through membrane pores 
E) Via the proteasome

Question 7

In a clinical trial of a new antiviral vaccine composed of a recombinant viral peptide and adjuvant,4% of the healthy recipients did not show evidence of response to the immunization.Further investigation revealed that all the nonresponders expressed the same,single allelic variant of HLA-DR but all the responders were heterozygous for HLA-DR alleles.Which of the following is the most likely explanation for this finding?

Accepted Answer

A) Response to the vaccine requires T cell recognition of complexes of the viral peptide with HLA-DR,but the peptide cannot bind to the allelic variant of HLA-DR found in the nonresponders. 
B) The nonresponders could not express class II MHC proteins. 
C) The viral peptide is not an immunodominant epitope. 
D) The nonresponders underwent determinant selection of another viral epitope. 
E) Because of technical errors,the nonresponders had not received adequate doses of the vaccinE.

Question 8

Many vaccines now in development will include highly purified,recombinant,or synthetic peptide antigens.These vaccine antigens are expected to stimulate highly specific immune responses,but they are less immunogenic than vaccines containing intact killed or live microbes.Adjuvants are substances added to such vaccines to enhance their ability to elicit T cell immune responses.Which of the following statements about adjuvants is NOT correct?

Accepted Answer

A) Adjuvants induce local inflammation,thereby increasing the number of antigen-presenting cells (APCs)at the site of immunization. 
B) Adjuvants stimulate the expression of costimulators on local APCs. 
C) Adjuvants enhance local production of cytokines that promote T cell activation. 
D) Adjuvants prolong the expression of peptide-MHC complexes on the surface of APCs. 
E) Adjuvants bind to T cell antigen receptors and promote their proliferation.

Question 9

Which of the following is the main criterion that determines whether a protein is processed and presented via the class I MHC pathway in an antigen-presenting cell (APC)?

Accepted Answer

A) Encoded by a viral gene 
B) Present in an acidic vesicular compartment of the APC 
C) Present in the cytosol of the APC 
D) Internalized into the cell from the extracellular space 
E) Small in size

Question 10

Naive CD8+ T cells require signals in addition to T cell receptor recognition of peptide-MHC to become activated and differentiate into cytolytic T cells.These signals are called costimulatory signals and are provided by professional antigen-presenting cells (APCs),such as dendritic cells.If a virus infects epithelial cells in the respiratory tract but does not infect professional APCs,what process ensures that naive T cells specific for viral antigens will become activated?

Accepted Answer

A) Cross-reactivity,whereby the naive CD8+ T cell recognizes a self antigen that is structurally similar to a viral antigen presented by dendritic cells 
B) Crossover,whereby part of the viral genome is exchanged with part of one chromosome of the host 
C) Crosstalk,whereby signals generated by the virus binding to class I MHC molecules intersect with T cell receptor signaling pathways 
D) Cross-presentation,whereby infected epithelial cells are captured by dendritic cells,and the viral proteins originally synthesized in the epithelial cells are processed and presented in association with class I MHC molecules on the dendritic cell 
E) Cross-dressing,whereby viral infection of the epithelial cell stimulates the expression of surface molecules that are typically found only on dendritic cells

Question 11

In the class I MHC pathway of antigen presentation,cytoplasmic proteins are tagged for proteolytic degradation by covalent linkage with which of the following molecules?

Accepted Answer

A) Calreticulin 
B) Nuclear factor (NF)-$\kappa$B 
C) Tapasin 
D) Ubiquitin 
E) Calnexin

Question 12

Which one of the following molecules does NOT play an important role in the class II MHC pathway of antigen presentation?

Accepted Answer

A) ($\beta$2)-Microglobulin 
B) Cathepsin 
C) Invariant chain 
D) HLA-DM 
E) Calnexin

Question 13

Antigen-presenting cells (APCs)perform which of the following functions in adaptive immune responses?

Accepted Answer

A) Display major histocompatibility complex (MH
C) -associated peptides on their cell surfaces for surveillance by B lymphocytes 
B) Initiate T cell responses by specifically recognizing and responding to foreign protein antigens 
C) Display MHC-associated peptides on their cell surfaces for surveillance by T lymphocytes 
D) Display polysaccharide antigens on their cell surfaces for surveillance by B lymphocytes 
E) Secrete peptides derived from protein antigens for binding to T cell antigen receptors

Question 14

Which one of the following statements about dendritic cells is true?

Accepted Answer

A) Immature dendritic cells are ubiquitously present in skin and mucosal tissues. 
B) Dendritic cell maturation occurs after migration to lymph nodes in response to signals derived from activated T cells. 
C) Class II MHC and T cell costimulators are highly expressed on immature dendritic cells and are down-regulated during maturation. 
D) Dendritic cells that enter lymph nodes through draining lymphatics migrate to the B cell-rich follicles in response to chemokines. 
E) The principal function of mature dendritic cells is antigen capturE.

Question 15

Which type of antigen-presenting cell is most important for activating naive T cells?

Accepted Answer

A) Macrophage 
B) Dendritic cell 
C) Endothelial cell 
D) B lymphocyte 
E) Epithelial cell

Question 16

Which of the following statements about the antigen-presenting function of macrophages is NOT correct?

Accepted Answer

A) Macrophages are particularly important at presenting peptides derived from particulate or opsonized antigens that are internalized by phagocytosis. 
B) Macrophages become activated by the helper T cells to which they present microbial peptides,and as a result of this activation they become efficient at killing the microbes. 
C) Resting macrophages express low levels of class II MHC molecules,but higher class II MHC expression is induced on activation by the T cells to which they present antigen. 
D) Macrophages express highly variable,high-affinity receptors for many different antigens,and these receptors facilitate the internalization of the antigens for processing and presentation. 
E) Macrophages present antigen to T cells in lymphoid organs and many nonlymphoid organs.

Question 17

The required number of complexes of a microbial peptide and a particular class II MHC allele on the surface of an antigen-presenting cell to initiate a T cell response specific for the viral peptide is:

Accepted Answer

A) At least equal to the number of complexes of self peptides with class II MHC on the cell surface 
B) Greater than 103 
C) Less than or equal to 0.1% of the total number of class II MHC molecules on the cell surface 
D) Greater than 106 
E) Zero

Exam 4: Antigen Capture and Presentation to Lymphocytes