9 General Introduction keratinocytes, healthy skin is inhabited mainly by lymphocytes and antigen presenting cells (dendritic cells, Langerhans cells and macrophages) that survey the skin and react to foreign structures and danger signals [17,18,22]. The immune response plays a central role during wound healing. It is essential for a proper host defense against invading microbes and coordinates healing processes during the different stages of skin regeneration [23]. The inflammatory response starts immediately after trauma. Injured skin will release damage associated molecular patterns (DAMPs) that emerge from ruptured cells [24,25]. DAMPs such as HMGB1, IL-1α or DNA are structures that act as danger signals and stimulate pattern PRRs on surrounding cells and skin-resident immune cells [26–28]. These cells respond to PRR stimulation by secreting effector molecules such as cytokines and chemokines that attract and navigate immune cells towards the wound site [29]. Immune cells that are active during tissue damage and regeneration include neutrophils, eosinophils, mast cells, monocytes, macrophages, T cells, B cells and NK cells (Figure 1). 1
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