MHC molecules (also known as major histocompatibility complex molecules) assist in the presentation of antigens to T cells in order to eradicate foreign pathogens. These molecules are highly polymorphic, meaning that they exist in multiple variants in order to avoid pathogens evading their activation of the immune response. MHC Class I molecules in particular deliver cytosolic peptides to the cell surface so that they can continue on through the cytosol and ultimately the endoplasmic reticulum (ER).
