Among the T cell subtypes, increased expression of CD4-naive T cells, exhausted T cells, and central memory T cells was observed in the IPAH group compared with the normal controls, whereas the expression of other T cells, such as cytotoxic T cells, type 17 T helper cells, effector memory T cells, NKT, gamma-delta T cells, and CD8 T cells was lower in the lungs of IPAH patients. This evidence concerns the gene CD4 and idiopathic pulmonary arterial hypertension.