Psoriasis and lichen planus: an immunohistochemical study of Trophoblast cell-surface antigen 2 expression in skin biopsies

: Chronic plaque psoriasis (CPS) and lichen planus (LP) are two chronic, immune-mediated inflammatory skin conditions that often spontaneously heal, even if recurrence is common. In both diseases, the immune system mistakenly targets skin cells, leading to inflammation and visible cutaneous lesions. Although the pathogenesis of LP is not fully understood, it is thought to involve an alteration of epidermal self-antigens, which activates T cells lymphocytes causing a persistent chronic inflammation at the dermal-epidermal junction. In psoriasis (PSO), an involvement of not properly considered immune cells, such as dendritic cells, monocytes, macrophages, neutrophils, keratinocytes and natural killer (NK) cells is present. Trophoblast surface antigen 2 (Trop2) is a type I transmembrane glycoprotein belonging to the epithelial cell adhesion molecule (EpCAM) family involved in cell adhesion. We conducted a retrospective study on 30 patients with the following diagnoses: 10 cases of Lichen planus (LP), 10 cases of chronic plaque psoriasis (CPS) and 10 healthy skin samples (HS). In all these samples, we performed an immunohistochemical analysis of Trop2 expression. LP and CPS samples showed a significant decrease in Trop2 expression compared to HS. Contrarily to LP, basal and supra-basal layers of CPS samples were completely negative, while the medium layers were highly positive for Trop2. The sub-corneal layers were negative for Trop2 in both LP and CPS. Our findings suggest that Trop2 may play a protective or regulatory role in maintaining skin homeostasis, particularly in the setting of immune-mediated inflammation.