The book tells how our body protects itself against bacteria and viruses that cause different diseases. You will learn how four small, still very young lymphocytes set off on a risky journey through the human body, wanting to learn its secrets and solve its riddles, but by accident ended up at war. They know almost nothing about the world around them because they haven’t had time to grow up yet. They know only that they must protect this world from enemies, since they are special “white blood” cells—defenders—yet they don’t know how to do it or what these enemies look like. They were afraid; various dangers lurked around them everywhere. But it was precisely they who were destined to play the decisive role in defeating the enemy—the influenza virus. They had to learn a lot and overcome many difficulties, but they managed to survive and win. And all because even blood cells can have what we call friendship. Friendship is when one for all and all for one. That is the main rule of immunity.