Question

10. If a person expressed mutated genes or lost the enzymes used for rearrangement of heavy chain and light chain genes what might happen to that person? What cells would be affected? How would the person be affected as a whole? (2pts)

11. What is the purpose and function of MHC I and MHC II molecules? (2pts)

12. One of the characteristic features of the MHC receptors is the large number of different alleles at each gene locus encoding for the receptor.

a. Where are most of the polymorphic amino acid residues located in MHC molecules? What is the significance of this location? (2pts)

b. What are some of the mechanisms that result in the MHC polymorphism we see in individuals? (2pts)

13. What is the purpose of class I MHC molecules? What cells display these molecules? Where do the antigens they display come from? (3pts)

14. What is the purpose of class II MHC molecules? What cells display these molecules? Where do the antigens they display come from? (3pts)

15. What kind of proteins are considered class III MHC molecules? What role in immunity do they play? (2pts)

16. What are professional APCs? Name some examples of professional APCs. (2pts)

17. Give an example of a nonprofessional APC. When can these cells function in antigen presentation? (2pts)

18. A process called antigen cross-presentation happens in dendritic cells only. Explain what cross-presentation is (4pts)

19. Molecules of the CD1 family have been shown to present non-peptide antigens. What types of antigens do they present? (2pts)

Answer 1

10.

• Heavy and light chain rearrangement is a defining moment in the maturation of T and B immune cells.
• Defect in the rearrangement would mean that person will not be able to launch an adaptive immune response to pathogens.
• Both T and B cells of the adaptive immune system will be affected.
• A person as a whole will be immunologically compromised; However, the innate immunity will be working, the person will not launch a successful attack on microbes and eliminate them from the blood.

11.

• The purpose of the MHC molecule is to bind peptide fragments derived from pathogens and display them on the cell surface for recognition by the T cells.
• MHC is highly polymorphic means multiple variants of each gene are present within a population. No two individuals except identical twins will have the same MHC.
• MHC class 1 is found on the surface of all nucleated cells and platelets. This helps in self-no self-recognition. It presents antigens to CD8+ T cells.
• MHC class 2 is expressed on the surface of antigen-presenting cells(APC) - dendritic cells, macrophages, and B lymphocytes. They present the antigens to CD4+ T cells.

12.

a. Polymorphic amino acids are located in the alpha-helices flanking the peptide-binding cleft. This cleft is exposed outside the cell. It is the most critical part of antigen detection. This region should be able to detect a wide range of pathogenic peptides. Hence it must be polymorphic.

b. Several mechanisms contribute to MHC polymorphism. Some new alleles result from point mutations, some by a combination of sequences by genetic recombination or by gene conversion.

13.

• Purpose pf MHC class 1 is to present cytoplasmic antigens to CD8+ T cells.
• It helps detect self cells from foreign cells.
• The antigens they display come from the peptide fragments derived from intracellular proteins like housekeeping proteins.

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