The interaction of T cells with MHC molecules. Class I and class II MHC molecules display peptide fragments of antigens to cytotoxic T cells and helper T cells, respectively. In each case, the T cell receptor binds with an MHC molecule-peptide antigen complex. Class I MHC molecules are made by most nucleated cells, whereas class II MHC molecules are made primarily by antigen-presenting cells (macrophages, dendritic cells, and B cells).