CD4 and pulmonary arterial hypertension: We found that a significant difference in immune cell infiltration between PAH and normal control with accumulation of memory resting CD4+ T cells, CD8+ T cells, γδ T cells, M1 macrophages and resting mast cells, but decreased monocytes, neutrophils, naive CD4+ T cells, resting NK cells, and activated mast cells in PAH patients.