[Lichen planus: etiopathogenesis].

Lichen planus could result from a succession of immunological events: stimulation of Langerhans cells and keratinocytes by foreign antigen--production of interleukin 1 (IL 1)--activation, attraction and multiplication of helper T lymphocytes--production of interferon gamma--appearance of intercellular adhesion molecule-1 (ICAM 1) and HLA DR Antigen on keratinocytes membranes, allowing adhesion of T lymphocytes to keratinocytes and subsequent destruction of the latter.