Immunopathologic studies in pityriasis lichenoides.

Skin biopsy specimens from five patients with pityriasis lichenoides et varioliformis acuta and from six patients with pityriasis lichenoides chronica were studied by direct immunofluorescence and by an immunoperoxidase technique using a panel of monoclonal antibodies. The dermal inflammatory infiltrate was composed of T cells, macrophages, and a small proportion of CD1a+ cells, mostly perivascular. CD8+ cells (cytotoxic/suppressor phenotype) predominated in the epidermis according to the degree of epidermal necroses, whereas CD4+ cells (helper/inducer phenotype) were superior in number among dermal T cells. A few B cells and Leu7+ cells were detected in only a small proportion of lesions. The results obtained confirm that the two conditions are variants of a single disease process and suggest that cell-mediated immune mechanisms may be important in the pathogenesis of the epidermal and vascular damage. Endothelial cells (HLA-DR+ and HLA-DQ+) and CD1a+ cells (epidermal and possibly dermal) could be primarily involved, acting as antigen-presenting cells.