Lecture 15: Mechanisms of Antigen Presentation

Question 1

Recall the timeline of the adaptive immune response.

Answer 1

Question 2

Recall the type of intracellular parasites.

Answer 2

• Protozoans (Leishmania)
• Bacteria (Salmonella, Mycobacterium)
• Viruses

Question 3

Recall the structure of MHC Class I Proteins.

Answer 3

Question 4

Recall the structure of MHC I Peptide-binding site

Answer 4

Question 5

The antigenic determinants recognized by T cells include residues from _____________and the ____________

Answer 5

antigenic peptide and the MHC molecule

(This is the structural basis for MHC restriction - TCR doesn’t interact only with the peptide)

Question 6

Recall the difference in antigen presentation to T and B cells.

Answer 6

Question 7

Mention the steps in MHC Class I Antigen presentation.

Answer 7

Question 8

Antigen presentation happens _______________. In the absence of pathogens, MHC I molecules present __________________.

Answer 8

constitutively

self-components

Question 9

Recall the process of MHC Class II Antigen Presentation

Answer 9

Question 10

Recall the process at which endocytosed proteins are denatured.

Answer 10

Question 11

Describe the characteristics of Cathepsins.

Answer 11

In early endosomes of neutral pH, endosomal proteases are inactive. Acidification of vesicles activates proteases to degrade antigen into peptide fragments

Question 12

Recall the comparison between MHC Class I and II

Answer 12

Question 13

Recall the process of MHC Class II assembly and transport to the endocytic route.

Answer 13

Question 14

Describe mechanisms that prevent premature binding of non-endosomal peptides to the MHC Class II.

Answer 14

The endoplasmic reticulum is full of unfolded and partly folded polypeptide chains, and premature peptide binding is prevented by the assembly of newly synthesized MHC class II molecules with a MHC class II-associated invariant chain (Ii, CD74).

Ii is a type II membrane glycoprotein; its amino terminus resides in the cytosol and its transmembrane region spans the membrane of the endoplasmic reticulum. The remainder resides within the endoplasmic reticulum.

Ii has a unique cylindrical domain that mediates formation of stable Ii trimers. Near this domain, Ii contains a peptide sequence, the class II-associated invariant chain peptide (CLIP), with which each Ii subunit of the trimer binds noncovalently to an MHC class II α:β heterodimer. Each Ii subunit binds to an MHC class II molecule with CLIP lying within the peptide-binding groove, thus blocking the groove and preventing the binding of either peptides or partly folded proteins.

Question 15

Recall the mechanism of substituting antigenic peptides for CLIP in endosomes.

Answer 15

Question 16

Much cytosolic protein degradation is carried out by a large, multicatalytic protease complex called the ___________

Answer 16

Much cytosolic protein degradation is carried out by a large, multicatalytic protease complex called the proteasome.

Question 17

What is the function of TAP?

Answer 17

It delivers cytosolic peptides into the endoplasmic reticulum (ER), where they bind to nascent MHC class I molecules.

Question 18

Newly synthesized MHC class I molecules are retained in the endoplasmic reticulum until _____________.

Answer 18

Newly synthesized MHC class I molecules are retained in the endoplasmic reticulum until they bind a peptide.

(Note: The folding and assembly of a complete MHC class I molecule depends on the association of the MHC class I α chain first with β2-microglobulin and then with peptide.)