Peripheral blood leucocyte phenotype in IPAH and CTEPH

Introduction: There is increasing evidence of the role immune dysregulation in idiopathic pulmonary arterial hypertension (IPAH). Whether there are shared immunological mechanisms in chronic thromboembolic pulmonary hypertension (CTEPH) remains uncertain. We have previously identified abnormalities in leucocyte subpopulations in IPAH, compared to healthy age and sex matched controls and sought to determine whether these abnormalities are also present in CTEPH. Objective: To compare peripheral blood leucocyte phenotypes in IPAH patients and healthy controls to CTEPH patients. Methods: Fresh peripheral blood samples were analysed using a standardised flow cytometry panel for cell surface markers of leucocyte subpopulations, adapted from the Human Immunology Project 2. (Maecker HT et al. Nat.Rev.Immunol. 2012). Results: In contrast to both healthy controls and CTEPH, IPAH patients demonstrated significantly increased populations of regulatory T cells, implicated in the immune response to loss of self-tolerance [figure 1a]. Additionally, in IPAH there was a significant increase in T follicular helper (Tfh) cells [figure 1b] and CD8 + PD1 + T cells associated with T cell exhaustion. Conclusions: We found distinct differences in peripheral blood immune cell profiles in IPAH compared to both healthy controls and CTEPH. This suggests that the abnormalities detected are a reflection of IPAH disease pathobiology, rather than secondary to heart failure or the presence of pulmonary hypertension.