Consistent with our finding of the greatly decreased IL-7 concentrations in the systemic and pulmonary circulation of children with PAH (Figure 1), others had demonstrated reduced expression of IL-7 receptor (IL-7R) in circulating PBMC and CD4+ T-cells from adult scleroderma (SSc) patients with PAH vs. those without PAH (17). Here, CD4 is linked to systemic sclerosis.