Immunocytochemical localization of a protein in tonofilaments as a morphologic marker for epidermal differentiation.

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Abstract
The localization of antibodies to a purified fibrous epidermal protein, with a high leucine content and a MW of 58,000, was demonstrated in the newborn rat epidermis using 3 immunocytochemical procedures: fluoroisothiocyanate and horseradish peroxidase-labeled antibodies, and the unlabeled antibody, or peroxidase antiperoxidase method. The immunocytochemistry reactions were done on picric acid-formalin fixed and nonfixed tissue strips before tissue embedding. Light microscopy of the fluoroisothiocyanate and peroxidase labeled tissue embedding. Light microscopy of the fluoroisothiocyanate and peroxidase labeled tissues revealed the presence of label in the epidermis but not in the dermis. EM examination of tissues labeled by both peroxidase procedures reveals that the peroxidase staining is localized over the 50-80 .ANG. thick filaments in all cell layers of the differentiating epidermis with no detectable label in the dermis. The unfixed tissue preparations allowed greater peroxidase staining and deeper tissue penetration, but the ultrastructural preservation was less desirable. The picric acid-formalin fixed tissues showed good ultrastructural detail and good immunocytochemical staining by the peroxidase antiperoxidase and peroxidase conjugated goat anti-rabbit methods. The results of this study show that the isolated fibrous protein to which antibodies were made is a component of the tonofilaments in each layer of the epidermis and suggest that this protein is conserved throughout the differentiation process.