Epidermal T cell subsets-Effect of age and antigen exposure in humans and mice

Epidermal T cells play a central role in immune surveillance and in inflammatory skin diseases. Major differences in the epidermal T cell composition are found between adult humans and antigen-inexperienced laboratory mice. Whether this is due to inborn species differences, to different environmental exposures, or a combination of the two is a matter of debate.

To investigate the role of age and exposure to antigens on epidermal T cell subsets in human and mouse skin.

We isolated T cells from the epidermis from 19 infants and 26 adults, and determined the frequency of CD4⁺ and CD8⁺ αβ T cells and γδ T cells by flow cytometry. In addition, we determined the epidermal T cell composition in antigen-inexperienced and antigen-experienced mice.

We found that humans are born with very few epidermal T cells. The number increases and the composition changes with age. In antigen-inexperienced mice, the epidermal T cell composition is unaffected by age, but it is dramatically affected by antigen exposure.

Taken together, we show that antigen exposure, as opposed to age, is the major factor determining the composition of epidermal T cells, suggesting that the skin of antigen-experienced mice better reflects the immunological conditions in human skin.