The occurrence ofMycobacterium leprae within axons of peripheral nerves

Summary

• 1. Mycobacterium leprae were found within axons of peripheral nerves in patients with lepromatous leprosy and in mice with leprosy.

• 2. In the human radial and superficial peroneal nerve biopsies examined, intra-axonal (IA) bacilli were found in 1 to 5% of the myelinated axons. The bacilli usually occurred in groups situated near the core of the axon, but single organisms were sometimes located more peripherally.

• 3. In mouse sciatic nerves, IA bacilli were predominantly found in unmyelinated axons, and the organisms occurred singly. The number of IA bacilli per unit area of the nerve was positively correlated with the number of bacilli occurring in Schwann cells of unmyelinated axons.

• 4. Some IA bacilli in both man and mice occurred free in the axoplasm, some were invested by a phagosomal membrane, whereas others were surrounded by an electron-transparent zone and by a phagosomal membrane.

• 5. Morphologically, the IA bacilli in mice and in one patient appeared to be viable. In other patients, however, half of the IA bacilli were fragmented (non-viable) and these were found within lysosome-like structures.

• 6. There was no histological evidence that IA bacilli were causing pathological changes in the axoplasm.