Langerhans cells in the developing mucosal epithelium of mice.

The presence of Langerhans cells in the developing mucosal epithelium of mice was investigated by ATPase histochemistry and by electron microscopy. In the stratified squamous epithelium of the tongue and forestomach, a few ATPase-positive Langerhans cells could be recognized at 1 or 2 weeks after birth. They increased in number by 3 weeks of age, but the density was lower than that in the epidermis. The ATPase-positive cells in the mucosal epithelium had longer (18-22 microns) dendritic processes; each cell thus occupied a large space. The mucosal Langerhans cell with elongated dendritic processes may well be responsible for the surveillance of a wide area in the defense system of the mucous membrane. The cells had a clear cytoplasm among keratinocytes in the basal cell layer and, under the electron microscope, showed characteristics similar to those of the epidermal Langerhans cells; Birbeck granules were also recognizable in the cytoplasm.