The effect of ultraviolet radiation exposure on the prevalence of mast cells in human skin

Background Dermal mast cells have been implicated as important effector cells in innate immunity, hypersensitivity responses and ultraviolet (UV)B-induced suppression of cell-mediated immune responses to contact allergens. Humans, like mouse strains, display variations in dermal mast cell prevalence. The factors determining these differences are yet to be fully elucidated. In mice, expression of the receptor for stem cell factor, c-kit , on dermal mast cells correlates with prevalence. Objectives To evaluate dermal mast cell prevalence and mast cell c-kit expression in non-sun-exposed and sun-exposed skin in the same donor. Methods In 14 subjects, biopsies of skin (4 mm) were sampled from the skin sites of buttock, inner arm, shoulder and back of hand skin and dermal mast cell prevalence quantified. Non-sun-exposed buttock and chronically sun-exposed hand skin were evaluated for mast cell expression of c-kit and elastin content, a feature of photoageing and surrogate marker of UV exposure. Results The prevalence of dermal mast cells was significantly higher in hand skin than in the three other anatomically different skin sites. Significant correlations were observed in hand but not buttock skin between increasing dermal mast cell densities, extent of elastin content in the papillary dermis and age of the subject. Cellular expression of c-kit correlated with mast cell prevalence in hand skin. However, no relationship was observed in hand skin between c-kit expression, elastin content and age. Conclusions The prevalence of mast cells in human skin is altered by factors that are intrinsic (mechanisms regulating c-kit expression) and extrinsic (chronic sun exposure), and the fact that the associations of mast cell prevalence with age is explained by the latter being a correlate of cumulative sun exposure.