Is maturation required for Langerhans cell migration?

Key papers in scientific literature sometimes bring a definitive resolution to a long-awaited issue. Others may be far less decisive but importantly implore us to question the fitness of prevailing models. So it is that a paper in this issue by F. Geissmann and colleagues, albeit subject to some variety of interpretation, nevertheless compels us to reexamine the widely accepted idea that migration of Langerhans cells in response to inflammatory stimuli is necessarily coupled to and follows from their maturation. It is well established that in the steady-state Langerhans cells turn over very slowly, but they can be mobilized en masse by inflammatory or antigenic stimuli. In vitro and in vivo, these inflammatory mediators have also been observed to promote maturation, and Langerhans cells that migrate from skin explants in culture usually display a mature phenotype. In further agreement with the idea that migration is linked with maturation is evidence that molecules associated with migration, particularly CCR7, are induced during Langerhans cell maturation.