The human immune system is responsible for fighting off germs and viruses that can attack our body at any time. We encounter any number of these microscopic invaders as we go about our daily lives, from the person sitting next to us on the bus to the door handles that we have to touch to get to our offices, and through our errands and on our telephones. They are on the computer keyboard that we keep meaning to disinfect – germs are everywhere. In most cases, you touch these germs and transfer them from the surface to your hand. You touch your face, especially your nose or mouth, and they are now inside of you. If you have a healthy and strong immune system, a number of different cells will be launched to kill off the invader.