7/22 Discussion

T cells and B cells always recognize the same types of antigen.

• True

• False

T cells and B cells require MHC molecules for the recognition of peptide antigens.

• True

• 
  False

T-cell receptors structurally resemble

• the Fc portion of immunoglobulins.

• MHC class I molecules.

• secreted antibodies.

• a single Fab of immunoglobulins.

• CD3 ε chains.

All of the following are primarily associated with CD4 T-cell function EXCEPT that it

• improves phagocytic mechanisms of tissue macrophages.

• assists B cells in the production of high-affinity antibodies.

• kills virus-infected cells.

• facilitates responses of other immune-system cells during infection.

• assists macrophages in sustaining adaptive immune responses through their secretion of cytokines and chemokines.

Which of the following best describes the function of tapasin?

• Tapasin is an antagonist of HLA-DM and causes more significant increases in MHC class I than MHC class II on the cell surface.

• 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.

• Tapasin is a thiol-reductase that protects the disulfide bonds of MHC class I molecules.

• 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.

• 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.

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

• Somatic recombination of V, J, and/or D segments is responsible for the diversity of antigen-binding sites.

• Somatic hypermutation changes the affinity of antigen-binding sites and contributes to further diversification.

• Class switching enables a change in effector function.

• The antigen receptor is composed of two identical heavy chains and two identical light chains.

• • Carbohydrate, lipid, and protein antigens are recognized and stimulate a response.

Which of the following statements regarding CD8 T cells is NOT correct?

• When activated, CD8 T cells will activate B cells.

• CD8 is also known as the CD8 T-cell co-receptor.

• CD8 T cells kill pathogen-infected cells by inducing apoptosis.

• • CD8 T cells are MHC class I-restricted.

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

• 
  α:β T-cell receptors recognize antigen only as a peptide bound to an MHC molecule.

• αβ T-cell receptors recognize antigens in their native form.

• α:β T-cell receptors, like B-cell immunoglobulins, can recognize carbohydrate, lipid, and protein antigens.

• Antigen processing occurs in extracellular spaces.

• Like α:β T cells, γ:δ T cells are restricted to the recognition of antigens presented by MHC molecules.

MHC molecules have promiscuous binding specificity. This means that

• a particular MHC molecule has the potential to bind to different peptides.

• when MHC molecules bind to peptides, they are degraded.

• peptides bind with low affinity to MHC molecules.

• 
  many alleles of MHC genes exist in the population.

• None of these answers describes promiscuous binding specificity.

Cross-presentation occurs when

• viral antigens are presented by MHC class I molecules on the surface of a cell that is not actually infected by that particular virus.

• cytosol-derived peptides enter the endoplasmic reticulum and bind to MHC class II molecules.

• phagolysosome-derived peptides bind to MHC class II molecules.

• viral antigens are presented by MHC class I molecules on the surface of a virally-infected cell.

• one peptide is able to bind to multiple distinct MHC isoforms on a cell.