Lichen planus (LP) is a chronic inflammatory disease of unknown aetiology, affecting the skin and mucous membranes, characterised by a CD8+ cytotoxic T-cell infiltrate, associated with epithelial cell death and disruption of the basement membrane zone. In previous work, T cell antigen receptor (TCR) repertoire studies were performed. In all patients tested, whether with erosive or non-erosive LP, unique nucleotide sequences, called clonotypes, have been identified. They appear during the process of TCR gene rearrangement. These clonotypes are specific for human papillomavirus (HPV) in blood and lesions, suggesting antigenic stimulation of these clonotypes by a viral epitope of HPV, which crosses with an epitope on keratinocytes. The diagnosis of LP is made on the basis of clinical and histological criteria, but in some patients and in some anatomical locations, the diagnosis is difficult to make and LP may be confused with other skin conditions.

Lichen planus (LP) is a chronic inflammatory disease of unknown aetiology, affecting the skin and mucous membranes, characterised by a CD8+ cytotoxic T-cell infiltrate, associated with epithelial cell death and disruption of the basement membrane zone. Several triggers have been proposed for LP, including viral antigens. In previous work, T cell antigen receptor (TCR) repertoire studies were performed, i.e. investigating the diversity of TCRs expressed on the surface of an individual's lymphocyte population. In all patients tested, whether with erosive or non-erosive LP, unique nucleotide sequences, called clonotypes, have been identified. They appear during the process of TCR gene rearrangement. These clonotypes are specific for human papillomavirus (HPV) in blood and lesions, suggesting antigenic stimulation of these clonotypes by a viral epitope of HPV, which crosses with an epitope on keratinocytes. The diagnosis of LP is made on the basis of clinical and histological criteria, but in some patients and in some anatomical locations, the diagnosis is difficult to make and LP may be confused with other skin conditions.

Inclusion Criteria:

• Subject coming at the time of diagnosis of the disease before any systemic treatment, or at the time of a progressive episode of the disease, without systemic treatment or after cessation of immunomodulatory or immunosuppressive treatment
• Ability to give their consent in writing
• Must understand spoken and written French
• Affiliated to the French social security or assimilated regimes

Exclusion Criteria:

• Dermatosis exclusively localised in the skin folds or on the face (risk of scarring from biopsies)