The influence of photochemical treatment on immunogenicity and epidermal Langerhans cells of murine skin grafts.

The combined treatment of murine skin grafts with 8-methoxypsoralen and longwave ultraviolet radiation (PUVA) leads to a prolonged survival after transplantation on allogeneic recipients. This may be due to inactivation of intragraft antigen presenting cells like epidermal Langerhans cells. In this study the effects of PUVA or middle range ultraviolet radiation (UVB) on ATPase positive Langerhans cells and immunogenicity of murine skin grafts were compared. Graft immunogenicity is reduced immediately after PUVA treatment, whereas the number of ATPase positive Langerhans cells decreases later, reaching its minimum three days after irradiation. UVB light reduces the number of ATPase positive Langerhans cells to a similar degree but skin graft survival is prolonged only marginally. Obviously, the effects of photochemotherapy on the ATPase activity of Langerhans cells reflect only partially the alterations of skin graft immunogenicity. Other antigen presenting cells like dendritic cells in the dermis may be of importance. Because these cells are located deeper in the graft they are better reached by stronger penetrating longwave ultraviolet radiation (PUVA) than by UVB.