Activation of Toll-like receptor-3 induces interferon-λ expression in human neuronal cells

We examined the gene expression and regulation of type III human interferon (IFN), IFN-λ, in human neuronal cells. Human neuronal cells expressed endogenous IFN-λ1 but not IFN-λ2/3. Upon the activation of Toll-like receptor (TLR)-3 expressed in the neuronal cells by polyriboinosinic polyribocytidylic acid (PolyI:C), both IFN-λ1 and IFN-λ2/3 expression was significantly induced. The activation of TLR-3 also exhibited antiviral activity against pseudotyped human immunodeficiency virus (HIV)-1 infection of the neuronal cells. Human neuronal cells also expressed functional IFN-λ receptor complex, interleukin-28 receptor α subunit (IL-28Rα) and IL-10Rβ, as evidenced by the observations that exogenous IFN-λ treatment inhibited pseudotyped HIV-1 infection of the neuronal cells and induced the expression of apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like (APOBEC)3G/3F, the newly identified anti-HIV-1 cellular factors. These data provide direct and compelling evidence that there is intracellular expression and regulation of IFN-λ in human neuronal cells, which may have an important role in the innate neuronal protection against viral infections in the CNS.