CXCL9 and systemic sclerosis: Moreover, in patients with iPAH levels of tumor growth factor-β (TGF-β), IL-10, and CXCL9 were increased (Koudstaal et al., 2021), whereas in patients with systemic sclerosis (SSc)-associated PAH plasma levels of TNF-α, that is mainly released by macrophages, was elevated compared to those patients who suffered from SSc but did not develop PAH (Kylhammar et al., 2018), revealing varying characteristic of increased chemokine release that might depend on the underlying PH subtype.