In armadillos, leprosy expands healthy liver tissue. Could that tell us something about regenerating our own?

The mystery started with some skin samples. Anura Rambukkana was a Ph.D. student in Amsterdam, analyzing biopsies from migrants with Hansen’s disease, or leprosy. The illness could be painful and disfiguring, but in the lab, the infected cells didn’t look sickly. To Rambukkana’s eye, they seemed to be doing great.

He noticed the same thing with nerve cells from mice. When he infected them with Mycobacterium leprae, they didn’t just look OK; they actually looked better than their uninfected counterparts. They were brighter, and proliferating more vigorously, as if the pathogen had somehow made them more youthful. The analogy wasn’t far off: These cells’ molecular profile turned out to be almost embryonic, primordial, resembling the body’s shape-shifting materials before they’ve been assigned a specific role. They looked like stem cells.

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