Andrea Sant

The defining feature of the immune system is its ability to distinguish self from non-self. The major component of the immune system responsible for this self / non-self discrimination is the diverse repertoire of antigen-specific T lymphocytes. T cell receptors can only recognize antigens derived from pathogens or transformed cells if these antigens in the derived peptide fragments of pathogenic protieins combine with Major Histocompatibility Complex (MHC) molecules.