MHC Molecules

MHC Molecules play a key role in the presentation of antigens.  The foreign protein must be processed into a peptide before it can be presented by MHC. This processing occurs in the proteasome of the cell. There are 2 types of MHC Molecule; Class 1 MHC & Class 2 MHC. 

MHC Class 1

MHC  Class 1 molecules are expressed in all nucleated cells. These are involved in the presentation of endogenous antigens (those found intracellularly).  Presentation of these endogenous antigens is recognised by Cytotoxic T cells that destroy the antigen via a mechanism involving the use of Granzyme and Perfornin.

MHC Class 2

MHC Class 2 are expressed in professional antigen presenting cells such as macrophages and B Cells.  They present exogenous antigens (those made outside the cell).  They bind peptides 18-20 amino acids long.