Endocrine Abstracts

Introduction: Programmed death-1 (PD-1) is one of the most important inhibitory co-receptors. Studies show that the PD-1/PD-L1 pathway regulates the induction and maintenance of peripheral tolerance and protects tissues from autoimmune attack in physiological conditions. Several studies have shown association of PD-1/PD-L1 pathway with several autoimmune diseases although, to date, no such studies have been performed for Graves’ disease (GD).

Aims: The aim of this study was to describe the frequencies of T and B lymphocytes expressing PD-1 and PD-L1 molecules in patients with GD. The relationships between PD-1+ and PD-L1+ cells, and selected clinical parameters were also assessed.

Material and methods: The expression of PD-1 and PD-L1 was analyzed using flow cytometry on T and B lymphocytes collected from 45 adult patients with newly diagnosed, untreated GD. The control group consisted of 20 healthy subjects.

Results: We observed high expression of PD-1 and PD-L1 on analyzed lymphocytes subpopulations of GD patients. Among T cells, the expression of PD-1 on protein level was higher on CD4+ cells in GD patients (mean: 31.54±13.74%) than in healthy controls (mean: 5.35±1.54%, P<0.001). Moreover, higher frequencies of PD-1+/CD8+ cells and PD-1+/CD19+ cells in the study group than in healthy volunteers were observed (mean: 18.71±10.37% vs 3.6±1.45%, P=0.015 and 12.07±4.34% vs 1.67±0.84%, P=0.017, respectively). There was a positive correlation of PD-1 and PD-L1 expressions on CD19+B cells (r=0.43, P=0.026) in patients with GD, and a positive correlation of the frequencies of PD-1+/CD4+ cells and the serum concentration of anti-TPO antibodies (r=0.61, P=0.014). Interestingly, there was also a positive correlation between the frequencies of PD-1+/CD19+ cells and the serum concentration of anti-TR antibodies (r=0.53, P=0.019).

Conclusion: High expression of PD-1 and PD-L1 on T and B cells could represent the hallmark of immune system reaction to chronic antigenic exposition in patients with GD.