Derivation of Langerhans cell granules from cytomembrane

OKT6 monoclonal antibody has been shown to react selectively with Langerhans cell (LC) cytomembrane in human skin. Taking advantage of this property, we examined the stainability of LC granules with OKT6 using immunoperoxidase method at the ultrastructural level. It was found that the delimiting membranes of LC granules, both attached to the cytomembrane and in the cytoplasm, were specifically stained in the epidermal sheet. These findings suggest that LC granules are derived from invagination of LC cytomembrane and retain T6 antigen. We employed two new methods: one is promotion of endocytosis by incubating the epidermal sheet in tissue culture medium with OKT6 at 4 degrees C and further incubation without OKT6 at 37 degrees C, and the other is the use of saponin to facilitate penetration of the secondary antibody through the cytomembrane of LC. In the LC cytoplasm only the delimiting membrane of the granule was stained; other membranous organelles, such as mitochondria and rough endoplasmic reticulum, did not react.