Development, differentiation, and proliferation of epidermal Langerhans cells in rat ontogeny studied by a novel monoclonal antibody against epidermal Langerhans cells, RED-1.

An antirat monoclonal antibody (mAb) against nonlymphoid dendritic cells, RED-1, was produced using epidermal Langerhans cells (LCs) as the immunogen. This mAb reacted mainly with the LCs and indeterminate dendritic cells (ICs), interdigitating cells in the T cell areas of lymphoid tissues, and monocyte/macrophages in various organs and tissues of adult rats. In the epidermal sheets prepared from adult rats, it specifically recognized the cell surface antigen(s) present on LCs and ICs. In the fetal rat skin, primitive or fetal macrophages migrated into the epidermis and expressed RED-1 at fetal day 17. With advance of gestation, RED-1-positive cells increased, started expressing Ia antigens at fetal day 18, and subsequently differentiated into dendritic cells. Most of them showed Ia expression by fetal day 20 and differentiated into LCs within a few days after birth. The labeling index of 5-bromo-2'-deoxyuridine in RED-1-positive cells was 18% at fetal day 17 and decreased to 5 to 6% in the postnatal period. These results imply that proliferative capacity of RED-1-positive cells is important for the formation and expansion of the IC population in the fetal stage and for the survival of LCs in the postnatal period.