Alterations in circulating naïve and activated Tregs in idiopathic pulmonary arterial hypertension
Immunological mechanisms (English)High pulmonary arterial pressure, characteristic for pulmonary arterial hypertension (PAH), leads to hypertrophy of the right ventricle (RV) and PAH patients often die due to RV failure. PAH can develop in patients with an autoimmune connective tissue disease (CTD). However, the most common form of PAH is idiopathic PAH (IPAH) for which until date no identified risk factor has been found. Increasing evidence implies a role for immune dysfunction in IPAH. Tertiary lymphoid structures are present around pulmonary arterioles in IPAH patients, which are formed during chronic inflammation. Regulatory T-cells (Tregs) are important to maintain/regain immune homeostasis. In IPAH, total Tregs are increased, and appear less functional. We therefore wanted to perform a detailed characterization of the Treg population in IPAH patients.
To investigate this, we combined cytokine and transcription factor staining on peripheral blood mononuclear cells (PBMCs) from IPAH patients, CTD-PAH patients and healthy controls (HC) using 14-color flow cytometry. Before staining, PBMCs were stimulated with PMA/ionomycin in the presence of brefeldin A for 4 hours.
The proportion of naïve Tregs (nTregs) was decreased in IPAH patients compared to CTD-PAH patients and HCs, whereas activated Tregs (aTregs) were increased. nTregs had an increased expression of activation marker CD25 in IPAH patients and CTD-PAH patients compared to HCs. Activated IPAH Tregs presented with a diminished expression of the transcription factors T-bet and RORγT as well as cytokines interleukin (IL)-6 and IL-17 compared to CTD-PAH and HC Tregs. The expression of inhibitory molecule CTLA-4 on nTregs and aTregs was similar between PAH patients and HCs.
In conclusion, the increased CD25 expression on nTregs might indicate a more activated state. This might facilitate easy transition towards aTregs, contributing to an increase in aTregs and a decrease in nTregs in peripheral blood of IPAH and CTD-PAH patients. Activated IPAH Tregs do not have a T regulatory (Tr) 17 or Tr1 phenotype, as they express lower levels of T-bet, RORγT, IL-6 and IL-17. IPAH Tregs might be differentiated into other distinct Tr subsets such as Tr2 or follicular Tregs. Tregs of IPAH and CTD-PAH patients seem functional, as they harbor a normal CTLA-4 expression. The increase in activated Tregs suggest a need for functional aTregs to suppress the immune response in IPAH patients. Whether these aTregs suppress a distinct Th subset needs to be determined.