T cells and the skin: from protective immunity to inflammatory skin disorders.

Skin is our primary interface with the environment, and T cells are crucial for orchestrating host immune responses against pathogenic microorganisms at this site. Effective skin immune responses require the generation of antigen-specific effector T cells, which home to cutaneous sites of injury or infection. Long-lasting immunity against future immune challenges is mediated by memory T cells. Among the memory T cells found in skin are both recirculating cells that transit between skin and blood and tissue-resident memory T (TRM) cells, which remain in skin for long periods of time and mediate durable protective immunity. These TRM cells also appear to drive many inflammatory diseases of skin. Here, we consider how a better understanding of cutaneous T cell responses can aid in the development of effective new therapies for immune-mediated cutaneous diseases.