Antigen Presentation by Langerhans/Dendritic Cells

Langerhans cells (LC) intersperse the epidermis forming a thin meshwork of sentinel cells. LC are members of the heterogeneous family of dendritic cells which are recognized to perform an exquisite immunosurveillance function. Distributed throughout the body and localized in nonlymphoid and lymphoid tissues, cells of this category are uniquely equipped to trigger a primary immune response (for review see ref. 1). Notably, processes related to the sentinel function such as antigen uptake and its degradation, and those involving antigen presentation with subsequent T cell priming are separated spatially and by time. Dendritic cells in distinct developmental stages perform these totally different functions. Thus, sentinel dendritic cells such as LC which reside in peripheral nonlymphoid sites are developmentally immature. They carry phenotypic markers of juvenile dendritic cells, i.e., submaximal levels of major histocompatibility complex (MHC) class I, class II and other markers.1