For example, we have MHC class One and we have MHC class two. Class one is used to differentiate abnormal cells from healthy cells. And class two is used to actually communicate between the white blood cells. So virtually all cells in our body, all white blood cells, require these major histocompatibility complexes to actually interact with one another and to detect these abnormal cells. But the very unique thing about natural killer cells which, by the way, are part of the innate immunity of our immune system, the very unique thing about these natural killer cells is that they don't actually need the major histocompatibility complex to actually find what our abnormal cell actually is. Unlike most other cells of our body, including cytotoxic T cells, the other white blood cell that destroys cancer cells.