sentence2_structure: The immune system<>typically recognizes<>$$$The immune system<>destroys<>foreign cells or substances that may cause disease$$$foreign cells or substances<>may cause<>disease
sentence1: Finally, it has been proposed that the initial polio infection causes an autoimmune reaction, in which the body's immune system attacks normal cells as if they were foreign substances.
sentence2: The immune system typically recognizes, attacks, and destroys foreign cells or substances that may cause disease.
question: Which body system typically recognizes, attacks, and destroys foreign cells or substances that may cause disease?