The human immune system is a wondrous thing. In fact, it’s the most complex biological system after the human brain. But most of us have no idea how the immune system really works.

Our immune systems make hundreds of billions of fresh cells every single day to try to protect us from all kinds of things that can go haywire.

Watch the fascinating video above to find out what’s really going on inside our bodies. And follow Kurzgesagt on YouTube to keep up with their great videos.