Cathepsin D expression in chronic plaque psoriasis: an immunohistochemical study

Cathepsins are lysosomal cysteine proteases, which are involved in a variety of physiologic processes such as proenzyme activation, antigen presentation, tissue remodeling, bone matrix resorption, and pathologic processes such as facilitating tumor invasion and modulating the process of programmed cell death. This study aimed to evaluate the pattern of cathepsin D (CD) expression in chronic plaque psoriasis in comparison to normal skin by means of immunohistochemistry. The study included 34 patients presenting with chronic plaque psoriasis and 10 age- and sex-matched normal subjects as control group. Sixty percent of normal skin showed granular positivity for CD confined to basal layer. CD is upregulated in psoaritic lesion with 94.1% positivity making a significant difference between psoriasis and normal skin as regards the percentage and distribution of CD expression, where the latter was predominantly diffuse in psoriatic lesion. The eight cases exposed to PUVA therapy showed reduction of CD positivity to 62.5% with a predominance of mild staining and focal expression compared to pretreatment biopsies. CD may have a role in the pathogenesis of psoriasis in view of its high percentage and diffuse expression in psoriatic epidermis. CD degradative capacity may be responsible for disordered differentiation and scale formation characteristic of psoriasis. Reduction of CD expression may be one of the pathways of PUVA mechanism of action.