Our body has a personal army of dedicated soldiers ready to defend us all the time—our immune system. Its combatants can fend off simple infections like a common cold or a sore throat, as well as life-threatening intruders like Mycobacterium tuberculosis, the bacteria which causes tuberculosis, or the virus that causes hepatitis. However, sometimes, the cells in our immune system go berserk and find an enemy within—they start attacking cells in our body!