Skin immune sentinels in health and disease

Abstract
Human skin and the immune cells that it contains provide essential protection of the human body from injury and infection. Keratinocytes are a first line of defence and sense danger through alert systems such as the inflammasome and Toll-like receptors. They mediate an inflammatory response by secreting pro-inflammatory cytokines. A subpopulation of CD103+ dendritic cells is strategically positioned for cross-presentation of skin-tropic pathogens. Recent data have highlighted a key role of tissue-resident rather than circulating T cells in skin homeostasis and pathology. Important lessons for human skin immunology have been learnt from immunologically targeted therapies in inflammatory skin disorders such as psoriasis.