CD4+ T Cells and Antitumor Immunity - MHC Class I and Class II Pathways

MHC Class I and Class II Pathways

The down regulation of the invariant chain (Ii) becomes important when considering the two pathways by which antigens are presented by cells. Most recognized tumor antigens are endogenously produced, altered gene products of mutated cells. These antigens, however, are normally only presented by MHC class I molecules, to CD8+ T cells, and not expressed on the cell surface bound to MHC class II molecules, which is required for presentation to CD4+ T cells. Research has shown that the two pathways by which antigens are presented cross over in the endoplasmic reticulum of the cell, in which MHC class I, MHC class II and endogenously synthesized antigenic proteins are all present. These antigen proteins are prevented from binding to MHC class II molecules by a protein known as the invariant chain or Ii, which, in a normal cell, remains bound to the MHC class II molecule until leaving the ER. Down regulation of this Ii, using antisense technology, has yielded promising results in allowing MHC class I tumor antigens to be expressed on MHC class II molecules at the cell surface. (Qui, 1999)