Purification of functional active epidermal Langerhans cells: a simple and efficient new technique.

Our knowledge of the functional activity of the epidermal Langerhans cell has been severely hampered by the lack of an easy method of purification of these cells that is both efficient and reproducible. In the present study we have used immunomagnetic beads directly conjugated to an IgM class mouse anti-human human leukocyte antigen DR monoclonal antibody to positively select human Langerhans cells from an epidermal cell suspension. Cells were then treated with a high-affinity polyclonal anti-mouse immunoglobulin that detached the beads by competing with the antigen for the antigen-binding site on the monoclonal antibody. This procedure allowed removal of the immunomagnetic beads, leaving Langerhans cells free from bound antibody. Recovery of Langerhans cells ranged from 40 to 80% of the starting number of Langerhans cells. The resulting cells were up to 99% CD1a positive and showed potent functional activity in the allogeneic mixed epidermal cell - lymphocyte reaction. Keratinocytes were shown to exert a profound inhibitory effect on Langerhans cell function that could not be prevented by indomethacin. This method is technically simple and allows good recovery of a highly purified population of Langerhans cells that are functionally active.