Figure 1. Cutaneous Photoimmunological Events.

A number of early/immediate immune modulating events (middle panel) occur in the skin following exposure to UV including: (A) isomerization of trans-urocanic acid (UCA) to the immune suppressive cis-UCA isoform (De Fabo and Noonan, 1983; Gibbs et al., 2008), (B) production of the biologically active lipid mediator, PAF (Alappatt et al., 2000; Travers et al., 2010) which contributes to skin cancer development (Sreevidya et al., 2008) by suppressing both adaptive immunity (Walterscheid et al., 2002) and DNA repair (Sreevidya et al., 2010), and (C) recruitment of immune modulating mast cells into the dermis peaking at 6h post UV (Byrne et al., 2008). These early events precipitate a number of later photoimmunological events (bottom panel) including: (D) The production of immune modulating IL-33 in keratinocytes and dermal fibroblasts (Byrne et al., 2011), (E) the migration of epidermal Langerhan’s Cells (Streilein et al., 1980), dermal dendritic cells (dDC) (Fukunaga et al., 2010) and (F) CXCR4+ dermal mast cells to the local draining lymph nodes (DLN) (Byrne et al., 2008) (G) Activation of complement components in the skin (including those associated with the alternative pathway; Factor B and Properdin (Stapelberg et al., 2009) also contributes to UV-induced immune suppression (Hammerberg et al., 1998; Yoshida et al., 1998).