Immunocompetent cells of fixed drug eruption.

The positive provocation test reactions of the skin of six patients with fixed drug eruption (FDE) were studied from timed skin biopsies taken between 2 hours and 9 days after the appearance of FDE. Monoclonal antibodies to the following immunocompetent cell surface epitopes were used: T3, T4, T6, T8, T9, M1, Ia1, Drc, Leu7 and B cell. The dermal infiltrate comprised 60-80% of T lymphocytes at all the times studied. Cells with T4 and T8 epitopes were displayed in similar numbers. A transient decrease in the number of T6+ cells of the epidermis could be detected with a simultaneous and also transient increase of the T6+ cells in the dermis, which suggests a possible traffic of Langerhans' cells from the epidermis to the dermis. The epidermal Ia1+ cells showed changes similar to but less marked than the T6+ cells. The number of the dermal Ia1+ cells increased continuously. In the late biopsies these Ia1+ cells comprised up to 90% of the infiltrating cells. Except for the finding of a reduction of T6+ and Ia1+ epidermal cells, the cellular kinetics of FDE are similar to those seen in both cutaneous immunological and irritant reactions.