The inflammatory infiltrate in oral LP is primarily composed of CD8+ T cells. A potential pathway for CD8+ T cell-mediated cytotoxicity in oral LP is described as follows:Antigens presented on MHC 1 molecules activates CD8+ T cells on keratinocytes or by encounters with activated CD4+ helper T cells or cytokines produced by activated CD4+ helper T cells
Activated CD8+ T cells induce keratinocyte apoptosis through various mechanisms such as secretion of tumor necrosis factor (TNF)-alpha, secretion of granzyme B, or Fas-Fas ligand interactions. Chemokines are produced by activated CD8+ T cells that attract additional inflammatory cells, thereby promoting continued inflammation. Other mechanisms that have been proposed include:

upregulation of matrix metalloproteinases that disrupt the epithelial basement membrane zone and allow entry of immune cells into the epidermis,
the release of proinflammatory mediators and proteases by mast cells, and
perturbations in the innate immune response that may involve toll-like receptors.Oral LP may also be caused by genetic factor which influence the immune function. A separate study performed in China found an association between a polymorphism in the TNF-alpha gene and risk for oral LP in a subset of patients. An Italian study found a significant increase in a genetic polymorphism of the first intron of the interferon (IFN)-gamma promoter in patients with oral LP compared with controls. Diagnosis
Skin
Patient history and clinical presentation need to be taken to diagnose lichen planus. Patients with suspected cutaneous lichen planus need to be evaluated clinically through patient interviews and physical examinations.
Oral lichen planus (OLP) tends to present bilaterally as mostly white lesions on the inner cheek, although any mucosal site in the mouth may be involved. Other sites, in decreasing order of frequency, may include the tongue, lips, gingivae, floor of the mouth, and very rarely, the palate.Generally, oral lichen planus tends not to cause any discomfort or pain, although some people may experience soreness when eating or drinking acidic or spicy foodstuffs or beverages. When symptoms arise, they are most commonly associated with the atrophic and ulcerative subtypes. These symptoms can include a burning sensation to severe pain. They may also experience mucosal bleeding in response to mild trauma, such as toothbrushing. Additionally, the Koebner phenomenon (the development of new lesions at sites of trauma) is not only present in cutaneous lichen planus (CLP) but can also occur in the setting of OLP. Residual postinflammatory hyperpigmentation has been reported in association with OLP, manifesting as brown to black pigmentation on the oral mucosa and may most likely occur in dark-skinned individuals.OLP may occur as a sole manifestation of the disease or in conjunction with other clinical manifestations of LP, including cutaneous LP, genital LP, nail LP, and lichen planopilaris (scalp LP). Causes
Cutaneous LP is a self-limiting condition. It usually resolves within 6 to 12 months. Oral LP is a non infectious, chronic inflammatory condition that involves the oral mucosa and may be accompanied by skin lesions.