Plane warts under spontaneous regression. Immunopathologic study on cellular constituents leading to the inflammatory reaction.

Immunohistologically, cellular infiltrates in regressing plane warts were mainly composed of lymphocytes and mononuclear phagocytes. There were many infiltrating T lymphocytes. Immunoelectron microscopic observation demonstrated that both helper/inducer and suppressor/cytotoxic phenotypes of T lymphocytes infiltrated in the lesions. OKT6-positive cells were observed in the dermis as well as in the epidermis. Moreover, as noted in allergic contact dermatitis, the apposition of T lymphocytes to Langerhans' cell-like cells could be seen. Lymphocytes and a small number of mononuclear phagocytes were found adjacent to damaged keratinocytes in the epidermis, the picture of which has been described as satellite cell necrosis, a hallmark of cytotoxic reaction by aggressors. These findings suggest that specific cell-mediated immunity against virus-infected keratinocytes takes place in the process of regressing plane warts.