Histopathologic study of lichen planus shows:
Mixed cellular inflammatory infiltrate
Presence of T-Lymphocytes predominantly
Antiepithelial antibodies
Scattered infiltrate with ill-defined lower border
Histologic features of lichen planus include: 

Saw, tooth appearance of retepegs
Liquefaction degeneration of basal layer which is replaced by thin band of eosinophilic coagulum
Presence of civatte bodies
Characteristic band Like subepithelial mononuclear infiltrate consisting of T- lymphocytes and histiocytes sharply limited to papillary and most superficial portion of the reticular layers of connective tissue
Hyperparakeratosis or hyperorthokeratosis
Thickening of granular layer