How does your body fight a virus? Take a look inside your cells to witness how they produce antibodies and fight to keep you healthy. -- All living things are made of cells. In the human body, these highly efficient units are protected by layer upon layer of defense against icky invaders like the cold virus. Shannon Stiles takes a journey into the cell, introducing the microscopic arsenal of weapons and warriors that play a role in the battle for your health. Lesson by Shannon Stiles, animation by Igor Coric.