CD4 and pulmonary arterial hypertension: Nonetheless, other studies have shown an increase in Treg levels in the peripheral blood of PAH patients.[19] This could be due to immune biomarkers, with the ratio of regulatory T cells within CD4 (+) T cells being notably higher in the PAH group compared to the non-PAH group.[20] Additionally, as per research by Tomohiko Ishibash and colleagues, the IL-6/gp130 signal within CD4 + T cells plays a crucial role in the development of PAH.