Let There Be Hair

The roots of all hairs, their follicles, can be swapped from one person to another without bringing on fierce immune attacks seen with almost every other kind of transplanted tissue, scientists have found. But don't toss out your toupee--the scientists who performed the microtransplant feat, described in tomorrow's Nature, warn that the procedure is unlikely to restore leonine shocks any time soon.

A hair follicle is a complex collection of cells. At its core is the so-called papilla, which "provides the instructions to produce hair," says developmental biologist Colin Jahoda of the University of Durham, United Kingdom. Responding to these signals, epithelial cells crank out each hair, which is cocooned in a dermal sheath until it passes through the skin.

Earlier observations suggested that certain parts of the follicles are somehow beyond the reach of the immune system--an "immune privilege" enjoyed by a few other tissues, including the cornea, joint cartilage, and the brain. Putting this hypothesis to the test, team member Amanda Reynolds suggested transplanting fragments of follicle from Jahoda (her husband) to her.

She then punched out several tiny patches of skin, including hair follicles, from Jahoda's scalp. Under the microscope, the researchers painstakingly dissected individual follicles until they ended up with pinhead-sized samples of pure dermal sheath, the region they wanted to probe for its follicle-inducing properties. Next they planted the sheath into incisions on Reynold's inner, hairless forearm.

After several weeks, hairs darker and thicker than ones elsewhere on her arm began to sprout. The dermal sheaths, they found, had developed into fully fledged follicles all bearing the male Y chromosome in their central papilla. Even after repeated transfers the researchers could not detect any sign of rejection of the grafted cells.

"This is very exciting, and ingenuously simple," says dermatologist Ralf Paus of the University Hospital Eppendorf in Hamburg, Germany. The apparent lack of rejection is surprising, he adds, because it is in fact the hair-producing epithelial cells that are immune privileged and not the dermal sheath cells transplanted by the Jahoda team.

Portable follicles are unlikely to become an antibalding tonic, however: Normal hair loss is usually due to altered hair growth properties and follicle shrinking, not a loss of active hair follicles altogether.