TLR3 and viral infectious disease: Thus, although PAR2 and TLR3 synergize to up-regulate NF-κB-responsive genes, in the context of a response to viral infection in which TLR3 senses viral RNA, PAR2 stimulation of cultured lung A549 epithelial cells causes a reduced expression of TLR3-, and interferon-response-factor-3 (IRF-3)-driven genes, and a suppression of TLR3-inducible STAT1 activation [188].