T‐cell infiltrate in Lichen Planus. Demonstration of activated lymphocytes using monoclonal antibodies

Double layer immunocytochemical procedures were performed on fresh frozen serial sections of lichen planus (LP), using three monoclonal antibodies: OKT3 (T-cells) and two anti Ia-like antigens, monoclonal antibodies. Lymphocytes in dermal LP infiltrates were OKT3 positive and Ia-like positive; lymphocytes in the paracortical area of human normal lymph-node were OKT3 positive and Ia-like negative. Unstimulated peripheral blood-OKT3 positive, E-rosette forming cells of normal donors were Ia-like negative, while the same T-cells, when mitogen-stimulated, became Ia-like positive. Therefore, in dermal infiltrates of LP, T-lymphocytes are Ia-like positive cells, representing an antigen-stimulated T-cell population. The in situ presence of activated T-lymphocytes seems to support the hypothesis of an immunological nature of LP.