Right now, your body is under attack. You currently have billions (yes, billions) of microorganisms on and in your body. Most of them are just hanging out, doing no harm, but many of them would love to make you sick by turning you into a microorganism-producing factory. Luckily for us, we have a built-in army that helps protect us from these harmful invaders. In this unit, you will have the privilege of discovering how your immune system works, what tools we have to assists our immune system and what happens when our immune system makes a mistake. To start off this unit, there will be a quick review of homeostasis and an overview of your body systems before delving into the microscopic battle between human and pathogen.