Ultrastructural Localization of S100A3, a Cysteine-Rich, Calcium Binding Protein, in Human Scalp Hair Shafts Revealed by Rapid-Freezing Immunocytochemistry

The study investigated the localization of the S100A3 protein in human scalp hair shafts using rapid-freezing immunocytochemistry. S100A3 was primarily found in the endocuticle and the intermacrofibrillar matrix of cortex cells, suggesting its role in maintaining hair shaft structural integrity. It was highly expressed in hair cells but absent in other skin structures, indicating a specific association with hair. The study provided the first ultrastructural evidence of S100 protein localization in specific hair cell subcompartments and suggested that S100A3 might contribute to hair structure through its cysteine-rich composition, potentially forming disulfide bridges during hair maturation.