Pityriasis rosea (Gibert): abnormal distribution pattern of antigen presenting cells in situ.

Pityriasis rosea is a skin disease which is obscure in its etiology and pathogenesis. We studied its immunopathology by immunophenotyping the inflammatory cells in situ using monoclonal antibodies that define leukocyte subsets. Findings as to T-cells and their major subsets did not reveal disease-specific data. Monocytes stained only rarely. Neither natural killer cells, B-cells nor plasma cells were ever found. An unexpected finding was the presence within the infiltrates and rarely within the epidermis of cells having the immunophenotype of interdigitating cells (RFD1+). Intense and dendritic staining with anti-T6 and anti-HLA-DR indicated Langerhans cells to be present in the dermal infiltrates, in between these infiltrates in the papillary dermis, and focally within the parakeratotic horny layer. This Langerhans' cell pattern provides evidence for dermal Langerhans cell compartmentalization and transepidermal Langerhans' cell elimination. Such a distribution indicates a change in Langerhans' cell migration processes in pityriasis rosea pathogenesis.