antigen processing and presentation

Question 1

What are the major differences between MHC 1 & MHC 2?

Answer 1

a. MHC1: Present Intracellular pathogens
b. MHC 2: present extracellular pathogens
c. APC: have both MHC 1&2
d. ALL nucleated cells: MHC 1

Question 2

MHC 1 composition?

Answer 2

a. Single polypeptide chain 

b. non MHC protein called the Beta2 microglobulin protein which is coded by
at another genetic location

Question 3

MHC 2 composition?

Answer 3

Two polypeptide chains alpha and beta

Question 4

The MHC gene products in humans are called?

Answer 4

Human Leukocyte Antigen (HLA)

Question 5

Genes are present on?

Answer 5

Chromosome 6

Question 6

The MHC variability is achieved by?

Answer 6

having multiple alleles (alternative genes at each locus), not by somatic
recombination

Question 7

Do MHC undergo somatic recombination?

Answer 7

No They do not

Question 8

Each person has how many copies of each locus?

Answer 8

Two copies for each locus one from mother and one from father, both are
expressed

Question 9

Expression of HLA genes is

Answer 9

co dominant

Question 10

All loci are expressed

Answer 10

in an individual

Question 11

HLA loci being _____ _____ within the human population, it is unlikely
that two individuals will have the same genes for all the alleles

Answer 11

highly polymorphic

Question 12

Members of a family may share _____ common alleles than distant relatives

Answer 12

more

Question 13

In MHC 1 molecules CD8 binds to which domain?

Answer 13

Alpha 3

Question 14

In MHC II molecules CD4 binds to which domain

Answer 14

Beta 2

Question 15

What must a cell do to present peptide to MHC class I

Answer 15

a. Cell must first degrade larger proteins into smaller peptide fragments.
b. This is accomplished through the proteasome. (in cytosol)

Question 16

How are these fragments translocated to lumen of rough ER to be expressed on
MHC

Answer 16

TAP: Transports select peptides from the cytoplasm into the lumen of the
rough ER

Question 17

Deficiency in TAP leads to?

Answer 17

Without TAP the MHC I do not leave ER. No Expression

Question 18

Role of antigen presenting cells?

Answer 18

a. To capture antigen (pathogen)
b. To process antigens for presentation to T- cells

c. To produce signals (cytokines) required for the proliferation and
differentiation of lymphocytes

Question 19

What is the role of invariant chain?

Answer 19

a. The invariant chain is assembled with MHC class II and blocks the 
peptide-binding cleft while in the rough ER. 

b. Once the invariant chain is associated with MHC class II, the complex 
leaves the rough ER within an intracellular vesicle that buds from the membrane of the ER.  

c. The invariant chain is subsequently degraded while in this vesicle, leaving
only a fragment of the invariant chain, called the CLIP, that remains
within the peptide-binding cleft.

d. The vesicle containing MHC class II with CLIP then fuses with the 
endolysosome, forming a specialized compartment called the MHC class 
II compartment (MIIC). 

e. Within the MIIC, a protein known as HLA-DM causes the CLIP to be
released from the peptide-binding groove.

f. The peptides that were degraded in the endolysosome are now free to 
interact with the peptide-binding groove. HLA-DM continues to serve as 
a peptide editor by forcing MHC class II to release any peptides that are 
not bound stably within the peptide-binding groove

Question 20

What happens if exogenous antigen processing leads to peptide leak?

Answer 20

The peptides will be presented as if they are endogenous (hypersensitivity)