A healthy immune system can defeat invading pathogens, but it is exactly that: an entire synergistic and working system, not a single entity. In order for people to optimize immune function, balance and harmony from a holistic viewpoint and approach is required.
The most obvious part of the immune system is what you can see. For example, the largest and first basic defense system to our immunity is our skin, since it acts as the primary boundary between germs and your body. Skin is tough and generally impermeable to bacteria and viruses.