Yes, if the immune system is strong, it is capable of fight off an illness with the help of the white blood cells (leukocytes). They act as the "soldiers" of the body because they are the first ones to try and kill whatever illness affects the body. Unless the person has a weak immune system, which can be a cause from poor health.
The main job of the innate immune system is to fight harmful substances and germs that enter the body, for instance through the skin or digestive system. The adaptive (specific) immune system makes antibodies and uses them to specifically fight certain germs that the body has previously come into contact with.
