Why Is Leprosy Confined to the PNS

Why is leprosy confined to the PNS?

A) Cooler body temperatures of 30- 35°C are necessary for M. leprae's growth.
B) The immune system is able to hold its ground and protect the CNS.
C) Cells of the CNS lack the necessary receptor for M. leprae to gain access.
D) M. leprae are aerobic and therefore prefer having the access oxygen that living just under the tattered epidermis can provide.
E) It's not, but because it grows slowly and takes decades to reach the CNS, many believe that is where it is confined.