Interleukin 9 in Oral Lichen Planus: an immunohistochemical study before and after treatment by intralesional steroid injection.

Oral Lichen Planus (OLP) is a chronic inflammatory mucocutaneous disorder of the oral mucosa. Th9 cells secrete IL9, which induces elevated levels of MMP9, exacerbating OLP disease severity. IL9 also increases Th17 levels in OLP lesions.