Blood Levels of Programmed Cell Death Protein 1 and its ligand (PD-L1) as Predictors of Systemic Sclerosis Severity

Background: Programmed cell death protein 1 (PD-1) and PD-1 ligand (PD-L1), are key regulators of immune tolerance and are implicated in the pathogenesis of various autoimmune diseases. Systemic sclerosis (SSC) is a complex autoimmune condition characterized by widespread skin fibrosis, involvement of internal organs, and immune dysregulation leading to the production of autoantibodies. Objectives: The aim of this study was to evaluate the expression levels of PD-1 and PD-L1 on CD19+ B lymphocytes and CD3+CD8+ T lymphocytes in patients with SSC. We also aimed to assess the relationship between PD-1/PD-L1 expression and clinical parameters, laboratory findings, and the extent of skin sclerosis in SSC patients. Methodology: 45 patients diagnosed with SSC and 45 healthy controls were enrolled in this study. The expression of PD-1 and PD-L1 on CD19+ B cells and CD3+CD8+ T cells was evaluated using flow cytometry on peripheral blood samples. Results: The expression levels of PD-1 and PD-L1 were significantly elevated in both CD19+ B cells and CD3+CD8+ T cells in the SSC group in comparison to the control group (P = 0.001 for all comparisons). Additionally, strong positive correlations were observed between the expression of PD-1 and PD-L1 on both cell types and disease activity in the SCC group. Conclusions: The findings of this study suggest that PD-1 and PD-L1 may contribute to the modulation of disease severity in patients with SSC, highlighting their potential as biomarkers for disease activity.