Why Is Peripheral Tolerance Critical to Barrier Immunity

Why is peripheral tolerance critical to barrier immunity?

A) Because it counters inappropriate activation.
B) Because overactivation can lead to chronic inflammation and disease.
C) Because microbes that colonize areas like the skin and intestines are not harmful.
D) Because it both counters inappropriate activation, and overactivation can lead to chronic inflammation and disease.
E) None of the answers explains why peripheral tolerance is critical to barrier immunity.