Photoageing shows histological features of chronic skin inflammation without clinical and molecular abnormalities

Photodamage is characterized by degradation of collagen and accumulation of abnormal elastin in the superficial dermis. Mast cells and macrophages, which are found in higher numbers in photoaged skin, have been implicated in this process.

To analyse the phenotype of haematopoietic-derived infiltrating cells in photodamaged skin.

Chronically sun-exposed (preauricular) and control sun-protected (postauricular) skin was recovered from eight healthy subjects undergoing cosmetic surgery (facial lifting).

Histological analysis showed that sun-exposed skin harboured more infiltrating mononuclear cells than sun-protected skin. Cellular infiltrates were found at the periphery of areas of elastolysis around hair follicles in sun-exposed sites, whereas they were found in the interfollicular dermis around blood vessels and around hair follicles in sun-protected samples. Immunohistochemical analysis revealed an increased number of mast cells, macrophages and CD4+ CD45RO+ T cells in sun-exposed dermis as well as a higher number of CD1a+ dendritic cells in sun-exposed epidermis, compared with the sun-protected samples. Thus photoageing displays histological features of chronic skin inflammation. However, no molecular sign of inflammation was observed and we even found a decreased expression of interleukin-1beta mRNA in sun-exposed compared with sun-protected sites. Furthermore, the patients' skin looked normal and did not display any clinical inflammation.

Collectively, these data show that chronic ultraviolet irradiation induces alterations of innate immune cells which are recruited in sun-exposed skin without being activated.