TLR3 and pulmonary arterial hypertension: This then leads to upregulation of various inflammatory cytokines and interferons such as IL-6, CXC chemokine ligand 8 (CXCL8), and CC chemokine ligand 2 (CCL2) (44, 45) We have previously shown that expression of TLR3, an endosomal RNA receptor, is reduced in ECs and lung tissue of patients with PAH and that TLR3−/− mice exhibit more severe pulmonary hypertension (42).