Major Histocompatibility Complex

Question 1

What is the MHC?

Answer 1

The Major Histocompatibility Complex (MHC) is a set of closely linked genetic loci (genes of the MHC) that have been found to be overwhelmingly important in determining the fate of engrafted tissue. This set of linked loci is highly polymorphic and plays a central role in control of the cellular interactions responsible for physiological immune responsiveness.

Question 2

What is the function of the MHC?

Answer 2

Their physiological function is to present peptides to T lymphocytes.

Question 3

What are HLAs?

Answer 3

Human Leukocyte Antigens.

Question 4

What are the Class I loci?

Answer 4

They include HLA A-C.

These molecules are present on virtually all nucleated cells and present antigen to CD8+ T lymphocytes.

Question 5

What are the Class II loci?

Answer 5

It includes HLA D

These molecules are found on dendritic cells, B-lymphocytes, and macrophages and present antigen to CD4+ lymphocytes.

Question 6

What are the Class III loci?

Answer 6

These are genes that happen to reside in the MHC region but do not present antigen to T lymphocytes.

Question 7

What forms the platform for the bound protein on the MHCs?

Answer 7

Antiparallel beta pleated sheets

Question 8

What do Class I MHCs bind?

Answer 8

Short peptides around 9 AAs in length

Question 9

What do Class II MHCs bind?

Answer 9

Long polypeptides 13-17 AAs in length

Question 10

What is the crucial part of the peptides that bind to the MHCs?

Answer 10

There are anchor proteins that are highly conserved and need a specific AA. (Ex: Tyrosine)

Question 11

What is the expression of MHC receptors?

Answer 11

Codominant

Question 12

Why is transplant of male organs into females usually avoided?

Answer 12

Males code for proteins that usually aren’t found in females.

Question 13

What does T cell response to antigen depend on?

Answer 13

A specific T cell response to antigen (Ag) on cell surfaces depends not on recognition of the Ag alone but on recognition of an antigenic peptide in the groove of an MHC molecule on the cell surface.

Question 14

What is MHC restriction?

Answer 14

The dependence of the T cells specific reactivity on foreign Ag plus MHC products rather than on foreign Ag alone is called
MHC Restriction.

Question 15

What do CD4 and CD8 bind?

Answer 15

CD4 and CD8 bind non-polymorphic regions of the MHC receptor

Question 16

What is the structure of the Class I MHC receptor?

Answer 16

α2 - α1

α3 - β2

Question 17

What is the structure of the Class II MHC receptor?

Answer 17

β1 - α1

β2 - α2

Question 18

Are Class I and II α and β chains encoded by the same genes?

Answer 18

No. MHC class I a chains and MHC class II a chain and ß chains are encoded by separate genes of the MHC locus.

Question 19

How many Class I and Class II MHCs are expressed in individuals?

Answer 19

Each individual expresses 3 maternal and 3 paternal class I molecular types, as well as 3 maternal and 3 paternal class II molecular types.

Question 20

Does recognition occur when the antigen matches and the MHC matches?

Answer 20

Yes

Question 21

Does recognition occur when the antigen does not match and the MHC matches?

Answer 21

No

Question 22

Does recognition occur when the antigen matches and the MHC does not match?

Answer 22

No