Effects of UV Irradiation on CAMs

In the past decade, many researchers have studied the effect of UV irradiation on adhesion molecule expression, with possible clinical implications for photosensitive disorders such as CLE.A nuclear factor (NFkB) has been implicated by DNA sequencing as potential transcriptional activator for ICAM-1 (Muller et al. 1995), and it has been shown in vitro that UVB activates the NFkB in the cytosol of epidermal cells (Simon et al. 1994). A direct effect of UVA on transcription of the ICAM-1 gene has been shown via a singlet-oxygen-dependent mechanism (Grether-Beck et al. 1996). After UVB irradiation of cultured keratinocytes, a biphasic effect is seen on ICAM-1 expression, with suppression in the first 24h and then up-regulation (Norris 1995). DNA photoproducts such as pyrimidine-dimers are directly involved in the UV-induced suppression of IFN-y-induced ICAM-1 expression on keratinocytes (Krut-mann et al. 1994).

In vitro studies have shown direct induction of ICAM-1 but not of VCAM-1 or E-selectin by UVB irradiation of cultured human dermal endothelial cells (Cornelius et al. 1994, Rhodes et al. 1996). Anti-double-stranded DNA has been shown to induce ICAM-1 and VCAM-1 but not E-selectin on cultured human umbilical vein endothe-lial cells, and increased levels of soluble ICAM-1 and VCAM-1 were also found in supernatants from the cell cultures (Lai et al. 1996).

PA Norris and coworkers reported in vivo sequential expression of CAMs in UVB-induced erythema compared with intracutaneous injection of purified protein derivative (PPD). E-selectin expression on endothelial cells was seen after 6h in both reactions, with a prolonged expression (1 week) in the PPD reaction. PPD but not UVB induced basal keratinocyte ICAM-1 expression and VCAM-1 expression on stellate-shaped cells in the upper dermis, first seen at 24 h (Norris et al. 1991). In PLE, similar findings regarding CAM expression were found as after PPD injection, but keratinocyte ICAM-1 expression was strong already after 5 h, and VCAM-1 was expressed on perivascular cells (Norris et al. 1992). UVA irradiation in vivo on healthy skin increased endothelial ICAM-1 after 24 h, whereas ICAM-1 expression on cultured keratinocytes decreased after UVA but increased on cultured fibroblasts 6-48 h after irradiation. These authors also reported constitutive keratinocyte ICAM-1 expression (Treina et al. 1996), whereas most authors claim that keratinocytes nor mally do not express ICAM-1 in vivo (Trefzer and Krutmann 1995). In another study, both UVA and UVB induced endothelial ICAM-1 and E-selectin expression in vivo, but only UVA induced these molecules on cultured human dermal endothelial cells. The induction was dose dependent, peaking at 20 J/cm2 for both molecules, and time dependent, peaking at 6h for E-selectin and 24h for ICAM-1 (Heckmann et al. 1994).

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