Most T Cells in Human Neonatal Skin are Not Naive

T cells present in human skin are involved in cutaneous immune surveillance but can also contribute actively to inflammatory skin diseases. In healthy human adult skin, T cells mainly belong to the CD45RO+ memory population. In contrast, human fetal skin contains predominantly CD45RA+ naive T cells. In this study, we elucidated the T cell composition in human skin samples after birth to unravel whether the change of the microenvironment influences the cutaneous T cell repertoire. Double-immunofluorescence staining on skin cryostat sections revealed that the majority of CD3+ T cells in human neonatal epidermis as well as dermis displayed a memory phenotype and that their numbers progressively increased with age. While naive T cells were observed in neonatal dermis, these cells were not present in neonatal epidermis. Some rare naive T cells appeared in infant epidermis. Taken together our results show that the composition of T cells in human neonatal skin is comparable in some aspects to adult as well as fetal skin and shows that the change of the microenvironment is accompanied by an altered T cell arrangement of the skin