If the natural kill knows it's either an infected cell or a cancer cell, it will kill off those cells. So the natural kill cell is a non specific wide blood cell that kills off these pathogens infected cells and cancer cells without worrying about the specific type of antigen that exists on the membrane of those cells. So this is what we call the innate immune system. The innate immune system is nonspecific. It attacks everything that is pathogenic, it creates immediate response and it also is the primary line of defense. Now, unlike the adaptive immune system, which we'll talk about in next lecture, the innate immune system does not actually learn.