To solve this problem, we need to understand the consequences of the immune system losing its ability to distinguish between self-cells and non-self cells.$\newline$In higher vertebrates, the immune system is responsible for identifying and attacking foreign invaders like bacteria and viruses.$\newline$However, if this system malfunctions due to a genetic abnormality, it may start attacking the body's own cells.$\newline$This condition is known as an auto-immune disease.$\newline \bullet$Option 1: Allergic response - This is an exaggerated immune response to a foreign substance, not related to attacking self-cells.$\newline \bullet$Option 2: Graft rejection - This occurs when the immune system attacks transplanted tissue, not self-cells.$\newline \bullet$Option 3: Auto-immune disease - This is the correct answer, as it involves the immune system attacking the body's own cells.$\newline \bullet$Option 4: Active immunity - This refers to immunity developed after exposure to an antigen, not related to attacking self-cells.$\newline$Therefore, the correct answer is Option 3: Auto-immune disease.