IL-7 upregulates T cell receptor/CD3 expression by cultured dendritic epidermal T cells

Dendritic epidermal T Cells (DETC) in adult mice express uniformly the phenotype of Thy-1⁺, T cell receptor (TCR)-Vγ3/Vδ1⁺, CD3⁺, CD4^- and CD8^-. In newborn mice, however, the epidermis contains smaller numbers of Thy-1⁺ cells and they rarely express TCR or CD3, suggesting that a phenotypic maturation and/or a rapid expansion of TCR⁺/CD3⁺ cells must occur within the epidermis soon after birth. We have observed previously that keratinocytes produce biologically relevant amounts of IL-7 and that this cytokine promotes the survival and growth of DETC in vitro. Here we report that IL-7 also promotes CD3/TCR expression by DETC. When the long-term cultured DETC line, 7-17, was incubated with IL-7, surface expression was upregulated in time- and dose-dependent fashions, as assessed with antibodies against γδ TCR, Vγ3 TCR or CD3ε. Among 10 other cytokines tested, only IL-2 was effective. IL-7-dependent upregulation also occurred at the levels of mRNA expression (Northern blot) and protein synthesis (immunoprecipitation). We propose that keratinocyte-derived IL-7 promotes not only the growth, but also the phenotypic maturation of DETC, thereby supporting the intraepidermal development of a DETC network during the neonatal period.