CD99 Is Strongly Expressed in Basal Cells of the Normal Adult Epidermis and Some Subpopulations of Appendages: Comparison with Developing Fetal Skin

This study examined CD99 expression in normal adult and fetal skin using 75 adult and 8 fetal skin samples. CD99 was strongly expressed in the basal keratinocytes of the epidermis, hair follicle bulges, outer root sheaths, and eccrine sweat glands in adult skin. In fetal skin, CD99 expression began around 19 weeks of gestation and became similar to adult skin after 20 weeks. CD99 and CD34 were co-expressed in hair follicle outer root sheaths. This research provided a foundational understanding of CD99's role in skin, suggesting it as a potential target for treating dermatologic conditions.