Localization of Mycobacterium leprae to endothelial cells of epineurial and perineurial blood vessels and lymphatics

Infection of peripheral nerve by Mycobacterium leprae, the histopathologica l hallmark of leprosy, is a major factor in this disease, but the route and mechanisms by which bacilli localize to peripheral nerve are unknown. Expe rimentally infected armadillos have recently been recognized as a model of lepromatous neuritis; the major site of early accumulation of M. leprae is epineurial, To determine the epineurial cells involved, 1-cm segments of 44 nerves from armadillos were screened for acid-fast bacilli, and thin secti ons were examined ultrastructurally. Of 596 blocks containing nerve, 36% co ntained acid-fast bacilli. Overall, M. leprae were found in endothelial cel ls in 40% of epineurial blood vessels and 75% of lymphatics, and in 25% of vessels intraneurally. Comparison of epineurial and endoneurial findings su ggested that colonization of epineurial vessels preceded endoneurial infect ion, Such colonization of epineurial nutrient vessels may greatly increase the risk of endoneurial M, leprae bacteremia, and also enhance the risk of ischemia following even mild increases in inflammation or mechanical stress . These findings also raise the possibility that early, specific mechanisms in the localization of M. leprae to peripheral nerve may involve adhesion events between M. leprae (or M, leprae-parasitized macrophages) and the end othelial cells of the vasa nervorum.