Increased caspase-3 and altered expression of apoptosis-associated proteins, Bcl-2 and Bax in lichen planus

Lichen planus (LP) is a chronic inflammatory disease of probable immune-based aetiology. The pathogenesis of LP is unclear, but apoptotic changes in epidermal (epithelial) cells have been reported. To evaluate apoptosis in LP through studying caspase-3 expression and to determine whether the apoptosis-associated proteins Bcl-2 and Bax are significantly involved in the pathogenesis of LP. In total, 25 lesional biopsy specimens [15 cutaneous LP (CLP) and 10 oral LP (OLP)] and 10 control specimens [5 normal skin and 5 normal oral mucosa] were studied using immunochemical methods for the expression of caspase-3, Bcl-2 and Bax proteins. Compared with controls, a significant increase in caspase-3 and Bax protein expressions were found in LP lesions. Basal cell expression of caspase-3 was positive in 14 cases (56%), and 12 cases (48%) showed mild expression. Caspase-3 expression in inflammatory infiltrate was positive in 13 cases (52%). Of these, 12 cases (48%) showed mild positivity. Bax was localized mostly to the upper prickle layer. Basal cell expression of Bcl-2 was negative in 18 (72%) cases, with no significant difference between patients with LP and controls. Bcl-2 was expressed in the inflammatory infiltrate in 15 cases of LP (60%), showing mild expression in 12 cases (48%). Compared with CLP, there was a significant increase in caspase-3 expression in OLP, despite the nonsignificant difference in Bcl-2 and Bax protein expressions by the epithelial cells. Increased caspase-3 and altered expression of Bcl-2 and Bax were found in LP, indicating the possible involvement of these proteins in the pathogenesis of the disease. The observed increase in apoptosis in OLP compared with CLP might explain the difference in clinical behaviour that distinguishes these LP variants.