MHC Class II Flashcards
What is the function of MHC Class II molecules?
To present exogenous antigens to CD4 plus helper T cells
What types of antigens are presented by MHC Class II molecules?
Exogenous antigens derived from extracellular sources such as bacteria and parasites
Where are MHC Class II molecules expressed?
On antigen-presenting cells such as dendritic cells macrophages and B cells
What is the structure of MHC Class II molecules?
It consists of two chains alpha and beta each with two domains alpha 1 beta 1 and alpha 2 beta 2
What is the source of antigens for MHC Class II presentation?
Antigens are captured from the extracellular environment through processes like endocytosis and phagocytosis
What happens to antigens after they are internalized by antigen-presenting cells?
They are degraded into peptides within acidic endosomal and lysosomal compartments
What enzymes are involved in antigen degradation for MHC Class II presentation?
Lysosomal proteases such as cathepsins asparaginyl endopeptidase and exopeptidases
What is the role of the invariant chain Ii in MHC Class II biogenesis?
It prevents premature peptide binding and guides MHC Class II molecules to endosomal compartments
What is CLIP in the context of MHC Class II?
Class II-associated invariant chain peptide, a fragment of the invariant chain that temporarily occupies the peptide-binding groove
What is the role of HLA-DM in MHC Class II presentation?
It removes CLIP from the peptide-binding groove and facilitates the loading of antigenic peptides
What is the peptide-binding groove of MHC Class II molecules?
The region where peptides of 12 to 24 amino acids are bound for presentation to T cells
What types of cells interact with MHC Class II molecules?
CD4 plus helper T cells
What is the role of CD4 in MHC Class II recognition?
CD4 stabilizes the interaction between the T cell receptor and the MHC Class II molecule
What cytokines are produced by Th1 cells and what are their effects?
Th1 cells produce IL2 and IFN gamma which enhance cellular immunity and activate CTLs
What cytokines are produced by Th2 cells and what are their effects?
Th2 cells produce IL4 and IL5 which enhance humoral responses and antibody production
What is the role of dendritic cells in MHC Class II presentation?
They capture antigens in peripheral tissues process them and present them to CD4 plus T cells in lymph nodes
What are Langerhans cells?
A subset of dendritic cells that capture antigens in the skin and migrate to lymph nodes for T cell activation
What is the immunological synapse?
The interface between an antigen-presenting cell and a T cell involving MHC TCR interactions and co-stimulatory signals
What is the role of co-stimulatory molecules in T cell activation?
Molecules like B7.1 and B7.2 bind to CD28 on T cells to enhance activation
What is the role of ICAM-1 and LFA-1 in the immunological synapse?
They facilitate adhesion between antigen-presenting cells and T cells during antigen presentation
What happens to MHC Class II peptide complexes after assembly?
They are transported to the cell surface for presentation to CD4 plus T cells
What is the importance of antigen presentation by MHC Class II molecules?
It activates CD4 plus T helper cells which regulate and coordinate immune responses
How do macrophages contribute to MHC Class II presentation?
They phagocytose pathogens process antigens and present them to T helper cells
How do B cells contribute to MHC Class II presentation?
They capture specific antigens through their surface immunoglobulin process them and present them to T helper cells
What is the order of the MHC Class II pathway?
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
