The presence of Langerhans cell 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 epidermis. The ATPase-positive cell in the mucosal epithelium had longer (18-22μm) 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 cell has a clear cytoplasm among keratinocytes in the basal cell layer and, under electron microscopy, showed characteristics similar to those of the epidermal Langerhans cells. Birbeck granules were also recognizable in the cytoplasm.
