Skin represents the first line of defense against various stresses including pathogens and injuries. Within skin, cutaneous homeostasis is maintained by permanent cross-talk between skin cells, epidermal keratinocytes in particular, and cells of the immune system residing in the skin or recruited through the local production of cytokines and chemokines (see Figure 1).
The antigen-presenting cells—dendritic cells (DC) or Langerhans cells (LC)—are major early actors in the inflammatory or allergic response.1, 2 Recruitment and activation of immune or blood cells, such as T lymphocytes (TL), polymorphonuclear leukocytes (PMN) or others, leads to keratinocyte stimulation and the installation of an inflammatory loop. This inflammatory loop represents the innate defense of the skin but its deregulation may lead to more or less severe skin symptoms.
