<prompt> Answer this question truthfullyWhat is the number of MHC class I expressed on a single cell?  <response>: <reason> A single cell expresses six different classes of MHC class I molecules. MHC class I molecules are cell surface proteins that present peptides derived from intracellular proteins to CD8 T cells. These peptides are generated by the cells own proteasome and are transported into the endoplasmic reticulum, where they bind to MHC class I molecules. The MHC class I-peptide complex is then transported to the cell surface, where it is recognized by CD8 T cells. The diversity of MHC class I molecules allows a cell to present a wide range of peptides to CD8 T cells, enabling the immune system to detect and eliminate infected or abnormal cells. 