CD4 and pulmonary arterial hypertension: To investigate the relationships between immune cells and the three biomarkers in PAH, an immune infiltration analysis in Group I PAH was conducted As a result, the expression of seven immune cell gene sets (natural killer T cell, activated CD8 T cell, effector memory CD4 T cell, central memory CD4 T cell, T follicular helper cell, natural killer cell, and monocyte) were significantly different between controls and PAH patients (Figure 6A).