9781422280300

Chapter One

Meet the Immune System Y ou may not know it, but every day you are under siege by would- be invaders. Too tiny to see, these hordes of microscopic creatures surround you. Some of these microbes are harmless to you. Some of them actually help your body accomplish certain tasks. But other microbes can make you sick. Called pathogens , these bacteria, viruses, fungi, and parasites want to colonize new territories—inside you. If they succeed, your body provides them with food, shelter, and a place to raise the next generation of pathogens. In return, they make you sick. The air around you teems with these invisible armies. You inhale them with every breath, swallow them with your food and drink. They settle on your skin by the billions, looking for ways to get inside you. But you hardly ever even notice they exist. Why? Because your body has its own army, and that army protects you. An Army of You Your army is called the immune system . Like any army, it has soldiers, bases, fortifications, and battle plans. It has transport systems to bring more troops to the

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