Ultrastructural Localization of Hair Keratins in Human Scalp Hair Shafts as Revealed by Rapid-Freezing Immunocytochemistry.

Abstract

Although many hair proteins have been investigated biochemically, little information is available on their subcellular distribution in human hair. We report here on the immunoelectron microscopic technique for defining the ultrastructural localization of hair proteins, especially hair keratins, in human scalp hair shafts: a combination of a rapid-freezing, freeze-substitution fixation without chemical fixatives, and subsequent immunocytochemistry (i. e., rapid-freezing immunocytochemistry). The hair shafts were rapid-frozen, freeze-substituted in acetone without chemical fixatives, and then embedded in LR White resin. Subsequently, ultrathin-sectioned samples were stained for hair keratins by an immunogold technique. Rapid-freezing followed by freeze-substitution without chemical fixatives well-preserved not only the fine structure of the hair shafts but also the antigenicity of hair keratins for immunocytochemistry. In the cortex, hair keratins were present mainly on the macrofibrils. In the cuticle, they were also located primarily in the endocuticle, which did not show the fibrous structure like the macrofibrils did. Rapid-freezing immunocytochemistry appears to be the most viable approach for revealing the macromolecular architecture of human hair, which is a completely keratinized tissue and one of the most delicate tissues in preparation for transmission electron microscopy.