A Study on the Correlation between the Expression of a Cysteine Protease, Cathepsin L, and its Inhibitor, Cystatin A, in Oral Lichen Planus

Cathepsin L (Cat-L), a cysteine protease, and cystatin A (Cys-A), a cysteine protease inhibitor, are known to be involved in Oral Lichen Planus (OLP). The imbalance in expression between these two proteins may favor OLP pathogenesis.

This study aimed to evaluate the correlation between the expression of Cat-L and Cys-A in OLP.

Thirty specimens of OLP and 30 specimens of normal tissue were used for immunohistochemistry. The pattern of cell staining, number of positive cells, and cell staining intensity were recorded. An Immunoreactive Score (IRS) was also assigned.

Cat-L and Cys-A were found in all OLP specimens. In the control group, Cat-L and Cys-A were demonstrated in 83.33% and 96.67% of cases, respectively. Cat-L was primarily seen in the stratum basale in the OLP and control groups. In contrast, Cys-A expression was seen in the whole epithelium in both groups, and the intensity was lowest in the stratum basale. The percentage of positive cells, score of positive cells, staining intensity, and IRS of Cat-L and Cys-A were significantly higher in OLP than in control specimens (p < 0.05). Interestingly, a positive correlation between Cat-L and Cys-A was found in the control group but not in the OLP group.

The expressions of Cat-L and Cys-A were significantly higher in OLP tissues compared to normal tissues. The alterations in expression of the Cat-L cysteine protease and its Cys-A inhibitor in OLP may indicate that these two proteins play a role in the pathogenesis of OLP.