6. Antigens and the Major Histocompatibility Complex

Question 1

Name 3 host factors that can influence an immune response.

Answer 1

• overall health (affected by nutrition, stress, sleep, etc.)
• age
• genetics

Question 2

What are the major characteristics of the most immunogenic antigens?

Answer 2

• foreignness
• size
• chemical complexity and epitopes
• dose and route of administration
• combination with adjuvants
• ability to interact with MHC molecules

Question 3

Why can’t a hapten stimulate the immune system by itself?

Answer 3

• too small of molecular weight

- not complex enough

Question 4

What is a heteroantigen? When are heteroantigens considered to be cross-reacting?

Answer 4

• antigen from other species

- if the Ag is similar to another Ag in structure and is capable of reacting with the same antibody

Question 5

What class of MHC antigens is found on almost all cell types?

Answer 5

• Class I MCH is expressed on all nucleated cells

Question 6

What class of MHC antigens is found only on antigen presenting cells?

Answer 6

• Class II MCH

Question 7

What types of antigens are processed by the MHC Class I and Class II antigens, and which types of T cells are they presented to in the immune response?

Answer 7

MHC Class I

• presents antigens that have been synthesized inside the cell
• presents them to cytotoxic T cells

MHC Class II

• presents antigens that have been synthesized outside the cell and taken into the cell
• presents them to helped T cells

Question 8

The HLA system is highly polymorphic. What does this mean? What advantage does polymorphism have for the human population?

Answer 8

• highly polymorphic = alternative forms with slight variations exist in the population
• leads to variation in immune response (one person may have a stronger immune response to a certain antigen than another).
• also play a role in graft rejection and the development of autoimmune diseases