TLR4 and pulmonary arterial hypertension: Figures 6A and 6B show that distal PAECs from pulmonary hypertensive calves (PH-ECs) exhibited higher levels of MCP-1, TLR2 and TLR4 than control ECs. We also observed that TLR2 expression was upregulated in vivo in the endothelium of human patients with IPAH (Figure 6C); as we could not locate bovine TLR antibodies that specifically worked for immunofluorescence.