Ultrastructural evidence for the participation of Langerhans cells in cutaneous photoaging processes: a quantitative comparative study.

Langerhans cells were studied comparatively by electron microscopy in order to explore their possible participation in cutaneous photoaging processes in chronically photodamaged preauricular skin and in paired sun-protected postauricular sites of 25 Caucasian women aged 56-76 years. The characteristic ultrastructural features of Langerhans cells in photodamaged skin compared to those in sun-protected skin were as follows: (1) a significant decrease in the density of Langerhans cells and Birbeck granules, and an increase in the number of indeterminate cells, (2) an inversely proportional relationship between intraepidermal density of Langerhans cells and the severity of epidermal photodamage, (3) frequent apposition of Langerhans cells to vacuolar structures of photodamaged keratinocytes, (4) predominant distribution of Langerhans cells in the lower epidermis, (5) degenerative changes suggesting direct cellular damage, without evidence of apoptosis, (6) a strong correlation of the number of degenerated Langerhans cells with the degree of epidermal photodamage, (7) loss of dendritic processes, (8) direct contact of Langerhans cells with melanocytes suggesting interaction between these two types of cells, (9) juxtaposition of Langerhans cells and lymphocytes in the epidermis. These results suggest marked qualitative and quantitative ultrastructural differences in Langerhans cells between photodamaged and intrinsically aged skin and the positive involvement of Langerhans cells in the processes of cutaneous photoaging.