Role of the Mast Cell Product Histamine in Ultraviolet Radiation Induced Systemic Immunomodulation

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The harmful effects of ultraviolet radiation on skin, as exemplified by sun exposure, are well recognised: sunburn, premature ageing of skin, and induction of skin cancer. Indeed, skin cancers are the most common cancers in Australia. Increasingly recognised now is that UV radiation can alter the immune system. This is of particular relevance to the development of skin cancer: alteration of the immune system is critical to outgrowth of UV-induced cancers. The intact immune system is otherwise able to reject the great majority of UV-induced skin cancers. This effect of UV radiation on the immune system may be relevant to other diseases. It may alter the course of some infections, change the way the body responds to vaccination, and may also have a role in some immune-related diseases such as multiple sclerosis. How it is that these wavelengths just beyond visible light can affect the immune system is the subject of this project. We know that UV radiation can penetrate only a short way into the skin, yet can have widespread effects on the immune system. Our research to now has shown that a particular cell type sitting just below the surface of skin, the dermal mast cell, is essential. We've also demonstrated some of the complexity of the early response to UV exposure - both a chemical (cis-urocanic acid) in the very outermost layer of skin, and nerves in the skin, have roles. Importantly, anti-histamines can inhibit UV effects on immune responses. Additional lines of evidence also point to histamine, a product of mast cells, as playing a pivotal role in the immune alterations following UV exposure. Our research aims to characterise the effects of histamine on cells central to the development of immune responses, known as dendritic cells, and define the mechanisms of the effect in experimental models. In collaboration with researchers in the UK, we will further characterise the role of mast cells in UV alterations to immunity in humans.