People have a kind of memory called immune memory. There are very few self-sacrificing cells in human blood, which live for a very short time, and their main function is to destroy as many enemies of the human body as possible. Lymphocytes react quickly to bacteria or simple toxic substances that invade the bloodstream to produce antibodies that stick to harmful substances and prevent them from entering other organs. The task of destroying the enemy falls on the phagocytes in the blood. These cells can easily distinguish foreign cells, remember them and retain memories. Once a person has measles or scarlet fever, he will gain immunity for life.
The main function of phagocytes in human blood is to remember the foreign cells that invade the body is true of the argument in this paragraph.