The observed increase of CCR6+ T cells and modulation of the IFNγ and IL-17 production capacity of circulating CD4+ T cells at diagnosis and 1-year follow-up – together with the presence of CCR6+ T cells in vascular lesions - support the involvement of the Th17-associated CCR6+ T cell subset in CTEPH. The gene discussed is IL17A; the disease is chronic thromboembolic pulmonary hypertension.