Migratory properties and functional capacities of human skin dendritic cells.

The different cell types which migrated 'spontaneously' out of human skin explants during different periods of culture were characterized. Before culture, CD1a+ dendritic cells were observed not only in the epidermis but also in the dermis, whereas CD1b+ dendritic cells were present exclusively in the dermis. The populations of migrating cells were harvested and phenotyped on 3 successive days of culture. They always contained high percentages of CD1a+ cells. The other cells that migrated were T cells and macrophages. A relatively high proportion of the CD1a+ cells that migrated during the first 24 h culture period was also CD1b+. The number of cells which were positive for both CD1a and CD1b decreased in the following 2 days of culture. However, the purified CD1a+ cell populations isolated on the 3 consecutive days did not show any difference in their capacity to stimulate allogeneic T cells. The CD1a+ cells possess potent allo-activating capacities that are independent of whether or not they are positive for CD1b+. Three days after culture about half of the CD1a+ cells were still present in the epidermis and dermis, but no CD1b+ cells could be detected in the dermis. This suggests that the CD1b+ cells represent a population of active migrating cells.