It was a cool Saturday morning two years ago. I was browsing through YouTube, trying to find a video that I am interested in. I found a video about space exploration on a channel called Kurzgesagt - In a Nutshell. I found the topic pretty interesting and started watching. The art style and explanation made me want to continue watching other videos. Around November 2021, Kurzgesagt released a video about the immune system. I was very fascinated about the subject and I also saw that they had a whole book on the immune system. I purchased the book, and read through it. Now, in April-May, there is a passion project and I knew what to write about. I chose to write about the immune system, with the book being Immune: A Journey Into the Mysterious System That Keeps You Alive. My question is, "What is the immune system made up of?"