Overexpression of PD-1 on Peripheral Blood Lymphocytes in Patients with Idiopathic Pulmonary Arterial Hypertension and Its Association with High Viral Loads of Epstein-Barr Virus and Poor Clinical Parameters

Idiopathic pulmonary arterial hypertension (IPAH) is a rare but severe disease with the elevated blood pressure in the pulmonary arteries without a known trigger of vascular remodelling. It leads to the right heart failure with reduced survival. Changes in the immunological landscape of the lungs and the periphery are common in IPAH patients, suggesting an immune system dysfunction. A cohort of 25 IPAH patients was enrolled in our study to investigate a link between the patient’s clinical status, immune parameters of the blood, and the Epstein–Barr virus (EBV) infection. We found significant alterations of the patients’ peripheral blood parameters. Therein, T lymphocytes and NK cell counts were decreased in the IPAH patients’ blood, while the proportion of regulatory T cells was increased. Additionally, levels of proinflammatory cytokines interleukin-6 (IL-6), IL-2, and interferon-gamma (IFN-γ) were elevated. We identified a weak correlation between EBV loads and IPAH patients’ clinical state (r = 0.54) and between EBV loads and overexpression of PD-1 on helper T cells (r = 0.56). We speculate that a significant dysregulation of the immune system homeostasis observed in IPAH patients may contribute to increased susceptibility of those patients to EBV infection, yet further longitudinal studies are required to characterize this relation in detail.