Ch 6 Book Questions Flashcards
Which of the following is the nonpolymorphic molecule that is structurally homologous to the class I MHC α chain, associates with β2-microglobulin, and displays lipid antigens for recognition by NKT cells?
a. CD1
b. CD2
c. CD3
d. CD4
e. CD8
a. CD1
CD1 is encoded outside the MHC, but is structurally homologous to class I MHC molecules. Some subsets of T cells, all with relatively invariant T cell receptors, recognize lipid or glycolipid antigens bound to CD1 on antigen-presenting cells. CD2, CD3, CD4, and CD8 are all present on T cells. Although they are members of the Ig superfamily, like class I MHC, they are not otherwise homologous to class I MHC and do not bind and display antigens for T cell recognition.
Which one of the following statements about peptide binding to MHC molecules is true?
a. MHC molecules preferentially bind peptides derived from foreign (e.g., microbial) proteins and not peptides derived from self proteins.
b. Each type of MHC molecule and each allelic variant of each type have a narrow specificity for a single peptide with a particular amino acid sequence.
c. The affinity of peptide binding to MHC molecules is higher, on average, after chemokine stimulation of a cell.
d. An MHC molecule has only one peptide-binding site, which accommodates only a single peptide at a time.
e. Peptide binding to class I MHC molecules involves noncovalent interactions, whereas peptide binding to class II MHC molecules is covalent.
d. An MHC molecule has only one peptide-binding site, which accommodates only a single peptide at a time.
There is only one peptide-binding site in both class I and class II MHC molecules that can fit only a single peptide at one time. MHC molecules do not distinguish foreign from self proteins; self-nonself discrimination is achieved by T cells. Each MHC molecule has a broad specificity for large numbers of peptides with varying sequences, although there are some structural constraints that result in each type of MHC molecule binding a different subset of peptides. The affinity of peptide-MHC interactions is not altered by chemokines. Peptide binding to both class I and class II MHC molecules involves only noncovalent interactions.
Which of the following is a human class I MHC molecule?
a. HLA-DR
b. HLA-DP
c. HLA-B
d. I-A
e. CD8
c. HLA-B
The human class I MHC molecules are HLA-A, HLA-B, and HLA-C. The human class II MHC molecules are HLA-DP, HLA-DQ, and HLA-DR. I-A is a mouse class II MHC molecule. CD8 is not an MHC molecule, but it binds to class I MHC molecules.
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?
a. By ATP-dependent transport via TAP
b. By passive diffusion
c. By receptor-mediated endocytosis
d. Through membrane pores
e. Via the proteasome
a. By ATP-dependent transport via TAP
The TAP1/TAP2 heterodimer is an ATP-dependent pump that delivers peptides generated by the proteasome into the endoplasmic reticulum.
In the class I MHC pathway of antigen presentation, cytoplasmic proteins are tagged for proteolytic processing by covalent linkage with which of the following molecules?
a. Calreticulin
b. Nuclear factor (NF)-κB
c. Tapasin
d. Ubiquitin
e. Calnexin
d. Ubiquitin
In the class I pathway, proteins are tagged for proteasomal processing by covalent addition of several copies of the polypeptide ubiquitin. Ubiquitin-dependent proteasomal proteolysis is also important in many other cellular processes besides antigen presentation. For example, NF-κB is a transcription factor whose activation is dependent on ubiquitination and proteasomal degradation of an inhibitor (called IκB). Calreticulin, tapasin, and calnexin regulate the assembly of class I MHC proteins within the endoplasmic reticulum.
MHC genes are the most polymorphic of any in the human genome. Which of the following statements about MHC polymorphism is true?
a. HLA-A, HLA-B, and HLA-C represent three different alleles of the same gene.
b. Many unrelated people have identical MHC alleles
c. Only class I MHC genes are polymorphic; class II MHC genes are not.
d. Most of the polymorphic residues in any MHC protein are located in the peptide binding groove.
e. MHC polymorphism is a result of somatic recombination of inherited nonpolymorphic MHC gene segments.
d. Most of the polymorphic residues in any MHC protein are located in the peptide binding groove.
MHC polymorphism are concentrated in the peptide binding groove, resulting in differences in the range of peptides that can bind to each allelic form on each type of class I or class II MHC molecules. HLA-A,-B, and –C are different types of class I MHC molecules, encoded by three different genes, each one of which has many different alleles in the population. It is very rare for two individuals to have identical HLA alleles, unless they are identical twins. Both class I and class II MHC genes are polymorphic, although class I MHC genes are more polymorphic. MHC genes are not somatically rearranged, but rather the allelic variations are encoded in the germline and are inherited.
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:
a. One
b. All the MHC molecules on the cell must be complexed with the peptide
c. About 0.1% of the total number of class II MHC molecules on the cell surface
d. Greater than 106
e. Zero
c. About 0.1% of the total number of class II MHC molecules
As few as 100 complexes of a particular peptide and a particular class II MHC molecule are needed to activate naive T cells specific for that complex and thereby initiate a detectable T cell response. This represents less than 0.1% of the total class II MHC molecules on a typical antigen-presenting cell surface.
Which of the following statements about microbial antigen presentation is correct?
a. Class I MHC molecules display peptides derived mainly from cytosolic microbial proteins for recognition by CD8+ T cells
b. Class I MHC molecules display peptides derived mainly from cytosolic microbial proteins for recognition by CD4+ T cells
c. Class II MHC molecules display peptides derived mainly from cytosolic microbial proteins for recognition by CD4+ T cells
d. Class II MHC molecules display peptides derived mainly from extracellular microbial proteins for recognition by CD8+ T cells
e. Class II MHC molecules display peptides derived mainly from extracellular microbial proteins for recognition by B cells
a. Class I MHC molecules display peptides derived mainly from cytosolic microbial proteins for recognition by CD8+ T cells
CD8+ T cells are class I MHC restricted, and most peptides that are displayed by class I MHC are derived from proteasomal processing of cytosolic proteins.
