So natural killer cells are specialized lymphocytes and they have granules that carry digestive enzymes as we'll see in just a moment. And these granules, these vesicles play an important role in destroying those cancer cells. Now let's recall the important points. So the majority of the white blood cells in our immune system are able to differentiate normal cells from abnormal cells as well as communicate with one another. As a result of these special protein complexes found on the immune cells and our normal cells of our body known as the major histocompatibility complex MHC. And we have several classes.