Effect of oral methoxsalen photochemotherapy on human Langerhans cell number. Dose-response and time-sequence studies.

In human adult volunteers, oral 8-methoxypsoralen and UVA (PUVA) caused an almost linear dose-response effect in depleting adenosine 1--5 J/cm2 were used. A higher dose did not appreciably augment the LC depleting effect although the intensity of the PUVA-induced skin inflammation increased. After a single PUVA dose of 5 J/cm2, a nadir in LC density was achieved on day 8 after irradiation, with a decrease from the starting mean count of 704 +/- 58 cells/mm2 to 195 +/- 173 cells/mm2. On day 15 after irradiation, the LC count was still low (261 +/- 249 cells/mm2). In comparison, a single erythematogenic irradiation with a medium-pressure mercury lamp emitting mainly UVB caused an LC depletion which was less intensive, peaked earlier and was almost completely restored by day 15. With both modalities morphological changes were induced in the LC, manifested initially as a shortening of the dendritic processes and later as cell enlargement and dendrite elongation.