Immunofluorescence localization of the epidermolytic toxin target in mouse epidermal cells and tissue.

An epidermolytic toxin target was observed in keratohyalin granules of sectioned epidermis by a 'direct' fluorescence procedure using FTC-toxin, but not by an 'indirect' procedure using sequential reaction with toxin, anti-toxin and FTC-secondary antibody. The investigation of the two procedures was extended to keratinocytes. A dispase digestion procedure yielded three fractions which corresponded to basal, spinous and granular cells according to biochemical and morphological criteria. It was shown that the 'direct' and 'indirect' procedures both detected the toxin target in the keratohyalin granules of granular cells, but that the 'indirect' procedure was very insensitive. In control experiments, the profilaggrin of keratohyalin granules was detected readily in cells by a 'direct' procedure using FTC-antiprofilaggrin but only weakly by an 'indirect' double antibody procedure. Insensitivity to 'indirect' procedures thus appears to be a particular property of the keratohyalin granule site. It was shown that the toxin target was readily accessible in permeable (trypsin-isolated) granular cells but inaccessible in impermeable (dispase-isolated) cells.