Toll-Like Receptor 3 Has No Critical Role During Early Immune Response of Human Monocyte-Derived Dendritic Cells After Infection with the Human Cytomegalovirus Strain TB40E

Toll-like receptors (TLRs) recognize an increasingly broad range of pathogens, thus demonstrating the importance of these pattern-recognition receptors (PRRs) in host defense. Here, the role of TLR3 in the interaction of monocyte-derived dendritic cells (moDCs) with human cytomegalovirus (HCMV) was investigated by using the TB40E strain, which actively replicates in moDCs. Microarray analysis and quantitative real-time PCR revealed that TB40E infection of moDCs led to changes in the gene expression pattern. A variety of proinflammatory cytokines and chemokines (CXCL10, CXCL11, and CCL5), TLR3, and genes whose products function downstream of the TLR3 signaling pathway (e.g., IFN-alpha and IFN-beta) were significantly upregulated. By silencing TLR3 expression with short interfering RNA (siRNA), and subsequent stimulation with TLR3 ligand poly I:C, expression of IFN-alpha was markedly reduced compared to cells transfected with a non-silencing control siRNA. However, expression of IFN-beta induced by HCMV was not diminished when TLR3 was silenced first. Thus the early HCMV-triggered immune response of human moDCs appears to be independent of TLR3 signaling.