Dendritic cells are unique in their ability to present antigen to naive T cells, and therefore play a central role in the initiation of immune responses. The protein encoded by this gene is a transmembrane molecule that is preferentially expressed by dendritic cells. Its expression is down-regulated by ligation of the CD40 molecule. Several alternatively spliced transcript variants of this gene have been described, but the full-length nature of some of these variants has not been determined.