CD4 Expression Controls Epidermal Stem Cell Balance

The study reveals that CD4, commonly known as a marker for immune cells, is also expressed on murine K5⁺ keratinocytes and plays a crucial role in maintaining epidermal stem cell balance. CD4⁺ cells in the epidermis have self-renewal abilities and contribute to epidermal renewal, colonizing the interfollicular epidermis and hair follicles with age. Wound healing studies show that these cells accumulate at wound sites. CD4 knockout mice demonstrate that CD4 is essential for maintaining fast-cycling epidermal stem cells during homeostasis and that its absence reduces the age-related decline in wound repair capacity. The findings underscore the importance of CD4 in the long-term maintenance of epidermal stem cell balance.