When the first cells appeared on Earth approximately 3.8 billion years ago, viruses were already here to greet them. Ever since, viruses have been devising ways to infect cells, and cells have been responding by evolving ways to stop these infections. This evolutionary dance eventually led to the development of your immune system.
A key aspect of your immune system is to distinguish “self” from “nonself” so it can destroy and remove foreign materials from your body. While this immune reaction protects you from viruses, it also has implications for how well foreign materials such as medications work.
