MHC Class II

Question 1

What is the function of MHC Class II molecules?

Answer 1

To present exogenous antigens to CD4 plus helper T cells

Question 2

What types of antigens are presented by MHC Class II molecules?

Answer 2

Exogenous antigens derived from extracellular sources such as bacteria and parasites

Question 3

Where are MHC Class II molecules expressed?

Answer 3

On antigen-presenting cells such as dendritic cells macrophages and B cells

Question 4

What is the structure of MHC Class II molecules?

Answer 4

It consists of two chains alpha and beta each with two domains alpha 1 beta 1 and alpha 2 beta 2

Question 5

What is the source of antigens for MHC Class II presentation?

Answer 5

Antigens are captured from the extracellular environment through processes like endocytosis and phagocytosis

Question 6

What happens to antigens after they are internalized by antigen-presenting cells?

Answer 6

They are degraded into peptides within acidic endosomal and lysosomal compartments

Question 7

What enzymes are involved in antigen degradation for MHC Class II presentation?

Answer 7

Lysosomal proteases such as cathepsins asparaginyl endopeptidase and exopeptidases

Question 8

What is the role of the invariant chain Ii in MHC Class II biogenesis?

Answer 8

It prevents premature peptide binding and guides MHC Class II molecules to endosomal compartments

Question 9

What is CLIP in the context of MHC Class II?

Answer 9

Class II-associated invariant chain peptide, a fragment of the invariant chain that temporarily occupies the peptide-binding groove

Question 10

What is the role of HLA-DM in MHC Class II presentation?

Answer 10

It removes CLIP from the peptide-binding groove and facilitates the loading of antigenic peptides

Question 11

What is the peptide-binding groove of MHC Class II molecules?

Answer 11

The region where peptides of 12 to 24 amino acids are bound for presentation to T cells

Question 12

What types of cells interact with MHC Class II molecules?

Answer 12

CD4 plus helper T cells

Question 13

What is the role of CD4 in MHC Class II recognition?

Answer 13

CD4 stabilizes the interaction between the T cell receptor and the MHC Class II molecule

Question 14

What cytokines are produced by Th1 cells and what are their effects?

Answer 14

Th1 cells produce IL2 and IFN gamma which enhance cellular immunity and activate CTLs

Question 15

What cytokines are produced by Th2 cells and what are their effects?

Answer 15

Th2 cells produce IL4 and IL5 which enhance humoral responses and antibody production

Question 16

What is the role of dendritic cells in MHC Class II presentation?

Answer 16

They capture antigens in peripheral tissues process them and present them to CD4 plus T cells in lymph nodes

Question 17

What are Langerhans cells?

Answer 17

A subset of dendritic cells that capture antigens in the skin and migrate to lymph nodes for T cell activation

Question 18

What is the immunological synapse?

Answer 18

The interface between an antigen-presenting cell and a T cell involving MHC TCR interactions and co-stimulatory signals

Question 19

What is the role of co-stimulatory molecules in T cell activation?

Answer 19

Molecules like B7.1 and B7.2 bind to CD28 on T cells to enhance activation

Question 20

What is the role of ICAM-1 and LFA-1 in the immunological synapse?

Answer 20

They facilitate adhesion between antigen-presenting cells and T cells during antigen presentation

Question 21

What happens to MHC Class II peptide complexes after assembly?

Answer 21

They are transported to the cell surface for presentation to CD4 plus T cells

Question 22

What is the importance of antigen presentation by MHC Class II molecules?

Answer 22

It activates CD4 plus T helper cells which regulate and coordinate immune responses

Question 23

How do macrophages contribute to MHC Class II presentation?

Answer 23

They phagocytose pathogens process antigens and present them to T helper cells

Question 24

How do B cells contribute to MHC Class II presentation?

Answer 24

They capture specific antigens through their surface immunoglobulin process them and present them to T helper cells

Question 25

What is the order of the MHC Class II pathway?

Answer 25

1- Uptake of Exogenous Antigens
2- Degradation of Antigens
3- Synthesis of MHC Class II Molecules
4- Targeting to Endosomes
5- Invariant Chain Processing
6- Peptide Loading
7- Transport to the Cell Surface
8- Presentation to CD4+ T Cells