Loss of expression of claudin-1 in psoriasis is associated with proliferative state of keratinocytes

Background: Psoriasis is a chronic remitting and relapsing inflammatory disease, with a prevalence of 0.44%–2.5% and is characterized by T-cell-mediated rapid turnover of epithelial cells. Claudin-1 protein is an integral part of the keratinocyte tight junction and has a role in proliferation, differentiation, and cell adhesion. Aim: The aim of the study was to investigate the role of claudin-1 expression in relation to keratinocyte proliferation in psoriasis. Materials and Methods: Fifty cases of psoriasis were included in the study. Skin biopsies were subjected to claudin-1 and Ki67 immunohistochemistry. Claudin-1 expression in the basal and spinous layers was scored. Ki67 proliferation index was assessed. Seven cases of normal skin biopsies were also included as controls. Fisher's exact test was applied for statistical analysis. Results: The cases had a wide age range (14–78 years), with a mean of 46 years with a male preponderance (4:1). The basal cell layer showed a complete loss of expression for claudin-1 in 82% (n = 42). The spinous layer showed a decrescendo pattern of loss of claudin-1 expression in 96% (n = 48). The association of loss of expression of claudin-1 between the basal layer and spinous layer was statistically significant (P = 0.0229). The association of loss of expression of claudin-1 and high Ki67 proliferative index was also statistically significant (P < 0.00001). Conclusion: Our study showed consistent loss of expression of claudin-1 in the lower layers of the epidermis in psoriasis, which is also the site of intense proliferative activity. The cytokine soup released by the T-cells may be responsible for downregulation of claudin-1, which is one of the triggers for proliferation.