An immunohistochemical and immunoelectron microscopic study of the ontogeny of rat Langerhans cell lineage with anti-macrophage and anti-Ia monoclonal antibodies.

An immunohistochemical study with anti-macrophage and anti-Ia monoclonal antibodies was performed to clarify the relationship between Langerhans cells (LC) and indeterminate cells (IC) in rat epidermis both in adulthood and in the fetal stage. On immunoelectron microscopy, a mouse anti-rat macrophage monoclonal antibody, TRPM-1, recently produced by us, reacted with IC and some LC in adult rat skin. Ontogenic study revealed that TRPM-1-positive cells first appeared in the epidermis of fetal rat heads on Day 17 of gestation and then spread caudally along the anterior-posterior axis. On Day 20 of gestation, when the distribution of the TRPM-1-positive cells over body surface became even, Ia-positive cells appeared in the epidermis and began to increase in number. Ia-positive cells with Birbeck granules were found on Day 21 of gestation. These results indicate that. TRPM-1-positive IC matured into Ia-expressing LC after being exposed to microenvironmental change during the perinatal period. The number of Ia-positive cells exceeded that of TRPM-1-positive cells at around 5 d after birth. Afterwards, there were more dendritic Ia-positive cells found in the interfollicular areas than TRPM-1-positive ones. However, local concentrations of the TRPM-1-positive IC in the follicular infundibula were frequently found in the fetal stage and occasionally in adulthood. These TRPM-1-positive cells in the follicular infundibula were thought to be a precursor pool in the epidermis for LC.