So this is the system by which these white blood cells are continually trying to find these abnormal cells of our bodies, such as cancer cells, as well as our infected cells that might be infected by some type of outside pathogen. So the major difference between our natural killer cell and our cytotoxic T cell is the cytotoxic T cell only binds to the MHC class One complex, while our natural killer cell can bind to a cell that doesn't have that MHC class One complex. And that's very important because sometimes these infected or cancer cells lose the ability to create these complexes that hold the antigens. And so we've won't find any of these complexes on our membrane. And they will become virtually invisible to all cells of our body, including these cytotoxic T cells. But the exception is the natural killer cells.