Immunohistopathology of light-induced skin lesions in lupus erythematosus.

Recently we have been able to induce pathological skin reactions with UVB, UVA and visible light in patients with lupus erythematosus (LE). The pathological skin reactions had the appearance of spontaneously developed LE lesions. In the present study, using patients with polymorphic light eruption as controls, we subsequently investigated what types of immunohistochemical abnormalities were found in these lesions. It was shown that in the induced skin lesions, phenotypically similar inflammatory cells were found as in spontaneously evolved lesions. Granular deposits of immunoreactants, as found in most spontaneously evolved LE lesions, occurred in 12 out of 16 LE patients 7-10 days after onset of the artificial irradiation. The dermal infiltrates in light-induced LE lesions differed mainly from those in polymorphic light eruption, by the amounts of CD1+ cells (Langerhans' cells). In polymorphic light eruption, the relatively large amount of these cells suggests an active migration of antigen-presenting cells, a mechanism apparently not operative in LE. Our results underline the importance of the pathogenic action of light in LE.