Classes of Major Histocompatibility Complex (MHC) Molecules Recognized by the TCR of T Cells
The TCR recognizes peptide bound to a MHC molecule expressed on the cell surface. There are two classes of MHC molecules, called MHC class I and MHC class II.
1. MHC class I
Expressed on the surface of all nucleated cell types
Recognized by the TCR of CD8 cytotoxic T cells (Tc cells)
CD8 binds to the class I MHC-peptide complex
Source of peptides is the cytosol
2. MHC class II
Expressed on the surface of a small number of nucleated cell types, referred to as antigen presenting cells (APC), the most important ones being macrophages, B cells, and dendritic cells (Langerhans cells)
Recognized by the TCR of CD4 helper T cells (Th cells)
CD4 binds to class II MHC-peptide complexes
Source of peptides is the vesicular compartment
NOTE: The fragmentation of proteins and association of peptides with each of the two classes of MHC molecules undergo different pathways that are referred to collectively as antigen processing and presentation.
The TCR recognizes peptide bound to a MHC molecule expressed on the cell surface. There are two classes of MHC molecules, called MHC class I and MHC class II.
1. MHC class I
Expressed on the surface of all nucleated cell types
Recognized by the TCR of CD8 cytotoxic T cells (Tc cells)
CD8 binds to the class I MHC-peptide complex
Source of peptides is the cytosol
2. MHC class II
Expressed on the surface of a small number of nucleated cell types, referred to as antigen presenting cells (APC), the most important ones being macrophages, B cells, and dendritic cells (Langerhans cells)
Recognized by the TCR of CD4 helper T cells (Th cells)
CD4 binds to class II MHC-peptide complexes
Source of peptides is the vesicular compartment
NOTE: The fragmentation of proteins and association of peptides with each of the two classes of MHC molecules undergo different pathways that are referred to collectively as antigen processing and presentation.
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