Your immune system works hard to keep you healthy. Its job is to keep germs out of your body, destroy them or limit the extent of their harm if they get in.
When your immune system is working properly: When your immune system is working properly, it can tell which cells are yours and which substances are foreign to your body. It activates, mobilizes, attacks and kills foreign invader germs that can cause you harm. Your immune system learns about germs after you’ve been exposed to them too. Your body develops antibodies to protect you from those specific germs. An example of this concept occurs when you get a vaccine. Your immune system builds up antibodies to foreign cells in the vaccine and will quickly remember these foreign cells and destroy them if you are exposed to them in the future. Sometimes doctors can prescribe antibiotics to help your immune system if you get sick. But antibiotics only kill certain bacteria. They don’t kill viruses.
When your immune system is not working properly: When your immune system can’t mount a winning attack against an invader, a problem, such as an infection, develops. Also, sometimes your immune system mounts an attack when there is no invader or doesn’t stop an attack after the invader has been killed. These activities result in such problems as autoimmune diseases and allergic reactions.