Plasmacytoid Dendritic Cells and Type I Interferon Signature in Lichen Striatus

Background/Objectives: In addition to several infectious and neoplastic cutaneous entities, plasmacytoid dendritic cells ( pDCs) have been shown to be involved in the pathogenesis of multiple cutaneous inflammatory and autoimmune disorders, including those characterized histologically by an "interface dermatitis" pattern such as lupus or lichen planus ( LP), but their role in lichen striatus ( LS), which is also known to have this histologic inflammatory pattern, has never been studied. The objective of the study was to investigate the role of pDCs in LS. Methods: Fifteen LS patients were found in our database and were immunohistochemically tested for pDC occurrence and activity using anti-blood-derived dendritic cell antigen-2 and anti-myxovirus resistance protein A ( MxA) antibodies, respectively. These individuals were also compared with 15 individuals with LP. Results: pDCs were present in all individuals with LS and LP, but they were less abundant in those with LS, although MxA ( surrogate marker of local type I interferon production and thus an indirect assessment of pDC activity) was similarly intense and diffuse in all individuals with LS and LP. In addition to being part of the upper dermal inflammatory bandlike infiltrate as in LP, LS cases, unlike LP, also showed perieccrine pDCs. Conclusions: pDCs constitute a central component of the inflammatory infiltrate in LS, suggesting a significant role in its pathogenesis. pDC distribution ( perieccrine distribution) could also help in microscopically differentiating LS from LP.