Skin(2TM): An in vitro model to assess cutaneous immunotoxicity

The skin serves as a complex barrier protecting the internal environment against external factors (e.g. bacteria, viruses, environmental toxins and UV light). For the epidermis to produce the most effective toxicological, immunological and biochemical barrier, the major cell types of the epidermis (i.e. keratinocytes) and in the dermis (i.e. fibroblasts) must function together in a dynamic integrated fashion. Furthermore, epidermal-dermal intercellular biochemical signals such as interleukins (IL), cytokines and other growth factors provide the skin with local homoeostatic signals to ensure the skin's immune integrity in response to a variety of environmental insults. Other investigators have shown that exposure of the skin to long-wave ultraviolet light (UVA) and mid-range ultraviolet light (UVB) can alter epidermal immune functions, including epidermal cytokine (e.g. IL-1, IL-6, TNF-alpha, IL-10 and GM-CSF) levels. The studies reported here use a co-culture system of dermal fibroblasts and well differentiated epidermal layers with an attached stratum corneum to form an in vitro human skin analogue. Baseline endogenous levels of IL-1alpha and tumour necrosis factor-alpha (TNF-alpha) were detected by using commercially available ELISA kits. The tissue substrates were exposed to UVA/UVB light (280-400 nm). The UV light was administered by a Dermsol 3 mercury halide solar simulator configured with filters to remove energy levels below 280 nm and above 410 nm. Skin tissue irradiated at 4J/cm(2) revealed a significant increase in IL-1alpha and TNF-alpha in comparison with non-UV irradiated tissue. Additional experiments revealed that the topical administration of indomethacin (0.1 to 10mg/ml) to the skin tissue ameliorated the up-regulation of these immune cytokines following UV irradiation. The use of such an in vitro co-culture system may provide researchers with a unique method to quantify mechanistically immunotoxicological events in the skin after exposure to ultraviolet light.