Are skin cells guards or go-betweens?

Accounting for 15 percent of our body weight, and with an average surface area of 20 square feet, the skin is the body’s largest organ. In addition to providing a rugged protective sheath, the skin is studded with immune system cells. Langerhans cells (LCs) in the epidermis have long been thought to spur the immune system into action when we encounter pathogens, and overactive LCs have been implicated in autoimmune diseases of the skin.

But an unexpected result reported on the cover of the December 15 issue of Immunity by Daniel H. Kaplan, M.D., Ph.D., assistant professor of dermatology, and Mark J. Shlomchik, M.D., Ph.D., professor of laboratory medicine and immunobiology, may force a rethinking of these ideas.

When the researchers engineered mice that lacked LCs at birth, they expected the animals to be resistant to allergic skin reactions. Instead, these mice have skin that is far more sensitive than normal mice.

“We now view these cells not just as sentinels or stimulators of immune reactions, but as peacekeepers with the environment,” says Shlomchik. “Failure of this mechanism could result in chronic inflammatory skin conditions like lupus and psoriasis.”