Induction of C‐C motif chemokine ligand 2 through Toll‐like receptor 3 signaling in human cerebral microvascular endothelial cell/D3 cells: possible regulation by nuclear factor‐κB

Objective C‐C motif chemokine ligand 2 (CCL2) is a potent chemokine that plays an important role in host defense and inflammatory diseases in the central nervous system. Toll‐like receptor 3 (TLR3) is a pattern recognition receptor that recognizes viral double‐stranded RNAs. In the present study, we examined whether a TLR3 agonist induces CCL2 expression in brain microvascular endothelial cells, and investigated the mechanism underlying upregulation of CCL2 expression through TLR3 signaling. Methods A human brain microvascular endothelial cell line, human cerebral microvascular endothelial cell (hCMEC)/D3 was treated with a TLR3 agonist, polyinosinic‐polycytidylic acid (poly IC). The mRNA and protein expression of CCL2 were evaluated using real‐time reverse transcription polymerase chain reaction and enzyme‐linked immunosorbent assay, respectively. The role of TLR3 and nuclear factor‐κB (NF‐κB) were examined with RNA interference. We also examined the effect of pretreatment with an NF‐κB inhibitor, SN50, an interferon regulatory factor 3 inhibitor MR67307 and human type I interferon neutralizing antibody mixture on poly IC‐induced CCL2 expression. Results Expression of CCL2 was induced by poly IC. Poly IC‐induced CCL2 expression was decreased by knockdown of TLR3 or NF‐κB p65 and by pretreatment with SN50. Neither MR67307 nor human type I interferon neutralizing antibody mixture affected the CCL2 expression induced by poly IC. Conclusions CCL2 expression was induced by poly IC through TLR3 signaling, and NF‐κB is involved in this reaction. CCL2 produced by human brain endothelial cells might induce the infiltration of monocytes followed by immune and inflammatory reactions in the brain, and could be involved in the pathogenesis of viral encephalitis. CCL2 is induced via TLR3 signaling in hCMED/D3 cells. NF‐kB regulates this reaction.