CD4 and idiopathic pulmonary arterial hypertension: We have shown that statistically significantly higher percentages of CD4+CTLA-4+ (p ≤ 0.01, Figure 5) and CD8+ CTLA-4+ (p ≤ 0.001, Figure 6) T cells, measured at the time of IPAH diagnosis, were found in patients who died within 5 years of the diagnosis, which allows us to consider both of the above lymphocyte subpopulations as a negative prognostic/predictive factor in iPAH.