Your immune system helps to protect your body from infections and illnesses. You can imagine your immune system has troops of army (white blood cells) that protect your body from bad guys (harmful bacteria and viruses). The primary protective response of the immune system comes from the white blood cells they work by recognizing the intruders, killing harmful bacteria, and creating antibodies to protect your body against future exposure to some bacteria and viruses. Your immune system works hard to keep you healthy and safe from germs.