Immunohistochemical Expression of Programmed death-ligand 1 (PD-L1) in Lesional Psoriatic Skin: A Study of Its Role in Psoriasis Pathogenesis

Psoriasis is a chronic, immune-mediated inflammatory disorder in which persistent T-cell activation by antigen-presenting cells (APCs) and defects in immune tolerance contribute to disease development, similar to other autoimmune conditions. Programmed death-1 (PD-1) is an inhibitory co-receptor that regulates inflammation and supports peripheral immune tolerance. Dysfunction of the PD-1/PD-L1 pathway is thought to play a significant role in the pathogenesis of various immune-mediated diseases. The objective of this study was to investigate the expression of Programmed death-ligand 1 (PD-L1) in psoriasis through its immunohistochemical (IHC) expression in involved skin in psoriatic cases. This prospective case control study was conducted on 30 skin biopsies of patients with plaque psoriasis and 20 biopsies of sex and age matched individuals as control group. Immunohistochemical staining using monoclonal mouse antibody against PDL-1(22C3) was applied on skin biopsy specimens obtained from both patient and control groups. There was a high statistically significant difference (p-value < 0.001) between both groups as regard PDL1 expression. In patient’s group, 30% of specimens were with low expression and 70% of specimens with high expression (80% low expression & 20% high expression in control group). A statistically significant and strong inverse correlation was observed between the number of PD-L1(+) immune cells and PASI scores (P < 0.001, r = − 0.77). Furthermore, the number of PD-L1(+) immune cells demonstrated a statistically significant negative correlation with disease duration (P = 0.02, r = − 0.42). In conclusion, PD-L1 expression in immune cells was significantly higher compared to healthy controls, indicating a potential role of PD-L1 in the disease pathogenesis.