1. All the following are characteristics of both MHC class I and class II molecules except:
   
   A) They are expressed codominantly.
   B) They are expressed constitutively on all nucleated cells.
   C) They are glycosylated polypeptides with domain structure.
   D) They are involved in presentation of antigen fragments to T cells.
   E) They are expressed on the surface membrane of B cells.

2. MHC class I molecules are important for which of the following?
   
   A) binding to CD8 molecules on T cells
   B) presenting exogenous antigen (e.g., bacterial protein) to B cells
   C) presenting viral protein to antigen-presenting cells such as macrophages
   D) binding to CD4 molecules on T cells
   E) binding to Ig on B cells

3. Which of the following is incorrect concerning MHC class II molecules?
   
   A) B cells may express different MHC class II molecules on their surface.
   B) MHC class II molecules are synthesized in the endoplasmic reticulum of many cell types.
   C) Genetically different individuals express different MHC class II alleles.
   D) MHC class II molecules are associated with b2-microglobulin on the cell surface.
   E) A peptide that does not bind to an MHC class II molecule will not trigger a CD4⁺ T cell response.

4. Products of TAP-1 and -2 genes
   
   A) bind b2-microglobulin.
   B) prevent peptide binding to MHC molecules.
   C) are part of the proteasome.
   D) transport peptides into the endoplasmic reticulum for binding to MHC class I.
   E) transport peptides into the endoplasmic reticulum for binding to MHC class II.

5. Which of the following is incorrect concerning the processing of an antigen, such as a bacterial protein, in the acid compartments of the cell?
   
   A) It results in production of potentially immunogenic peptides that associate with MHC class II molecules.
   B) Predominantly exogenous antigens are processed by this pathway.
   C) It may lead to activation of CD4⁺ T cells.
   D) It may lead to the activation of CD8⁺ T cells.
   E) Bacterially derived peptides displace a fragment of the invariant chain from the MHC class II binding groove.

6. Which of the following statements about the MHC is incorrect?
   
   A) It codes for complement components.
   B) It codes for both chains of the MHC class I molecule.
   C) It codes for both chains of the MHC class II molecule.
   D) It is associated with susceptibility and resistance to different diseases.
   E) The total set of MHC alleles on the chromosome is known as the MHC haplotype.

   Online Only Review Questions

7. When the sequences of different MHC class I molecules are compared, the variation between molecules is concentrated within which of the following?
   
   A) Areas of the molecule that bind CD4
   B) Areas of the molecule that bind to the T cell receptor and to the antigenic peptide
   C) b-2 microglobulin
   D) the transmembrane domain of the a chain
   E) the b1 domain (the N terminal domain of the b chain)

Answers to Review Questions

1. B MHC class I molecules are expressed on nearly all nucleated cells, but the constitutive expression of MHC class II molecules is more limited (B cells, dendritic cells, and thymic epithelial cells). MHC class II expression can be induced on other cell types (such as macrophages, endothelial cells, and human T cells) by cytokines.

2. A As described further in Chapters 9 and 10, the interaction of CD8 on the T cell and an invariant region of MHC class I molecule is crucial in the triggering of CD8⁺ T cells.

3 D The MHC class I molecule, not the MHC class II molecule, associates with b2- microglobulin.

4. D The products of the TAP-1 and -2 genes selectively transport peptides 8—9 amino acids in length from the cytoplasm into the ER where they bind to MHC class I molecules.

5. D CD8⁺ T cells are generally not activated by processing in acid compartments; exogenous antigen processing in acid compartments results in the generation of peptides, some of which can displace the CLIP fragment of the invariant chain from the MHC class II binding groove. The peptide—MHC class II complexes move to the cell surface and can interact with a CD4⁺ T cell with the appropriate receptor.

6. B The b2-microglobulin gene is located outside the MHC, on a different chromosome.