Document Type : Original Article


1 Molecular Immunology Research Center, Tehran University of Medical Sciences, Tehran, Iran.

2 Hammurabi College of Medicine, University of Babylon, Hillah-Babel, Iraq.

3 Rheumatology Research Center, Imam Khomeini Hospital, Tehran University of Medical Sciences, Tehran, Iran.

4 Research Center for Immunodeficiencies, Children Medical Center, Tehran University of Medical Sciences, Tehran, Iran.

5 Department of Immunology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.


Background: Ankylosing spondylitis (AS) is a chronic autoimmune disorder characterized by the fusion of vertebral joints and axial arthritis. The programmed death-1 (PD-1) inhibitory receptor has a pivotal role in controlling T cell function and may have a significant impact on the pathogenesis of autoimmune diseases such as AS pathogenesis.
Objective: To investigate PD-1 gene expression and its epigenetic regulation by detecting methylated CpG islands in the regulatory sites of the gene. This will provide insight into the mechanisms involved in the disease.
Methods: 30 AS patients and 30 healthy individuals were examined to detect the 16 CpG islands in intron 1 using bisulfite conversion and methylation-specific PCR technique. In addition, RNA samples were isolated from fresh peripheral blood mononuclear cells (PBMCs), and after complementary DNA (cDNA) synthesis, the expression level of the PD-1 gene was evaluated using Real-Time PCR.
Results: The CpG islands located in the intronic zone of the PD-1 gene were hyper-methylated in both the patients with AS and the healthy controls. The gene expression of PD-1 was significantly downregulated in AS patients compared with the controls (p=0.017). A negative correlation between the Bath Ankylosing Spondylitis Disease Activity Index and PD-1 gene expression was also revealed.
Conclusion: The low level of PD-1 gene expression is implicated in the pathogenesis of AS. However, in both groups, the methylation level of the intron 1 CpG islands of the PD-1 gene suggests that other regulatory mechanisms are more relevant to PD-1 gene expression than methylation in the intron.