CCL21 and chronic thromboembolic pulmonary hypertension: Chemokine CXC ligand 13 (CXCL13), which plays an analogous role as CCL19/CCL21-CCR7 for B-cell homing, was elevated in patients with idiopathic PAH and chronic thromboembolic pulmonary hypertension (CTEPH), but there was only a weak association between serum CXCL13 and markers of disease severity and outcome [49].