Toll-like receptors expression and function of human metapnemnovirus infected human lung epithelial cells
Objective To investigate the expression changes of Toll-like receptors(TLR) and the signaling pathway function on airway epithelial cells infected with human metapneumovirus(hMPV), and to explore the mechanisms of hMPV-induced airway inflammation. Methods A549 cells were infected with hMPV live or co-cultured with UV-inactivated hMPV in vitro. Growth curve of the virus in A549 cells was established and mRNA expression of TLR were detected by RT-PCR assay and real-time PCR assay at 3, 6, 9, 12, 24 h post infection. IFN-α and TNF-α in the culture supernatants were detected by ELISA. Results hMPV was able to replicate in A549 cell, growing to peak titer of 10~(5.2) TCID_(50)/ml at 3 d after infection. Most of TLR mRNA levels were up-regulated by hMPV infection but not UV-inactivated viruses via RT-PCR assay (P<0.05) after 6 h of stimulation. Real-time PCR assay showed that TLR3-4, TLR7-9 mRNA increased after being infected by hMPV in a time-dependent manner. The expression of IFN-α and TNF-α in the cul-ture supernatants were significantly up-regulated after 24 h infected by hMPV. Conclusion hMPV infection up-regulates the expression of TLR in lung epithelial cells. The inflammatory response to hMPV may associ-ate with part of TLR signal transduction pathway. 
 
Key words: 
Human metapneumovirus;  Toll like receptors;  A549 cells;  IFN-α;  TNF-α