Objective To investigate the significance of cytokine interleukin-12p40（IL-12p40） and interferon-γ （IFN-γ） in tissues formation and development of human oral lichen planus（OLP）. Methods The tissues of 11 cases of normal oral epithelium and 43 cases of OLP were investigated for the expression of IL-12p40 and IFN-γ proteins by using Envision two-step immunohistochemistry. The correlations between the expressions of these two cytokines, and their clinical and pathological significance in OLP were analyzed. Results 1）IL-12p40 and IFN-γ proteins were up-regulated in OLP comparing with that in normal oral mucosa and there was statistical significance between their difference（P
