CCL2 and pulmonary arterial hypertension: To verify the results obtained in our ex-vivo model system and to confirm that the expression of TLRs and MCP-1 in pulmonary arterial endothelial changes with hypoxia-induced pulmonary hypertension characterized by proximal vascular stiffening [17], we analyzed protein levels in fresh cell lysates of PAECs derived from normal and hypertensive calves using western blotting.