Dendritic cells can be self sustaining

Langerhans cells (LCs) are antigen-presenting cells that explore the skin for signs of infection. Whether or not they find an infection, LCs are continually replaced. Miriam Merad (Stanford University School of Medicine, Stanford, CA), Edgar Engleman, and colleagues show that LCs maintain their numbers through two sources: a local supply for normal upkeep, and an emergency store in the blood.

LCs are the first example of a dendritic cell type that is maintained locally. Merad and colleagues examined LCs in mice that had received a bone marrow transplant. Although LCs in the bloodstream were replaced by cells from the donor, LCs in the skin remained of host origin. “Langerhans were thought to be constantly reproduced by the bone marrow,” says Merad. “But LCs in skin are replacing themselves...