CpG and poly(I:C) stimulation of dendritic cells and fibroblasts limits herpes simplex virus type 1 infection in an IFNb-dependent and -independent way Giel R. Gaajetaan, Tanja H. Geelen, Gert E. Grauls, Cathrien A. Bruggeman, Frank R. Stassen ⇑ Department of Medical Microbiology, Maastricht University Medical Centre, P.Debyelaan 25, 6202 AZ, The Netherlands NUTRIM School for Nutrition, Toxicology and Metabolism of Maastricht, The Netherlands article info Article history: Received 31 August 2011 Revised 17 October 2011 Accepted 18 October 2011 Available online 25 October 2011 Keywords: Toll-like receptor Interferon Dendritic cell HSV-1 abstract Viral activation of toll-like receptors (TLRs) on dendritic cells (DCs) leads to production of various cyto- kines, including antiviral type I interferons (IFNs). Synthetic ligands specific for TLRs are also able to induce the production of type I IFNs (IFNa/b) by DCs, suggesting that these ligands have potential as anti- viral drugs. In this in vitro study we extensively investigated the antiviral activity of various TLR ligands. Mouse bone marrow (BM) cells were differentiated into plasmacytoid and conventional DCs (pDCs and cDCs), stimulated with various TLR ligands and tested the antiviral abilities of collected supernatants in an in vitro herpes simplex virus type 1 (HSV-1) infection model. We observed a significant IFNb-, (but not IFNa-) dependent reduction in HSV-1 infection when a mixed pDC/cDC population was stimu- lated with the TLR9 ligand CpG. In the absence of pDCs, TLR stimulation resulted in less pronounced anti- viral effects. The most pronounced antiviral effect was observed when both DC subsets were stimulated with poly(I:C). A similar noticeable antiviral effect was observed when fibroblasts (L929 cells) were stim- ulated directly with poly(I:C). These poly(I:C)-mediated antiviral effects were only partially IFNb- mediated and probably TLR independent. These data demonstrate that TLR ligands are not only able to produce type I IFN but can indeed act as antiviral drugs. In particular poly(I:C), which exerts its antiviral effects even in the absence of DCs, may become a promising drug e.g. to prevent respiratory infections by topical intranasal application. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Type I interferons (IFNs) are the key cytokines produced pre- dominantly by innate immune cells to combat viral infections. After viral recognition the release of IFN induces the expression of so-called interferon stimulated genes (ISGs) which subsequently activate a variety of antiviral processes including amplification of IFN signalling and the activation of adaptive immunity (Borden et al., 2007; Der et al., 1998; Fitzgerald-Bocarsly and Feng, 2007; Sadler and Williams, 2008). This will ultimately result in the induc- tion of a non-virus-specific antiviral state in infected cells, culmi- nating in direct inhibition of viral replication while also enhancing the host’s specific antiviral immune responses through IFN-related immuno-modulatory stimuli. Because of this strong antiviral activity, type I IFNs have also been used in clinical practice. For example, pegylated interferon al- pha (Peg-IFNa) in combination with ribavirin is currently recom- mended as standard-of-care treatment of chronic hepatitis C virus infection. However, depending on the HCV genotype in- volved, success rates of Peg-IFNa/ribavirin treatment vary signifi- cantly. Moreover, in clinical practice approximately 10–15% of patients discontinue this therapy due to adverse effects which im- pacts most, if not all, organ systems (McHutchison et al., 2009; Rustgi, 2010; Sulkowski et al., 2011). Therefore, there is need for alternative therapies. Although a large variety of immune as well as non-immune cells is able to produce type I IFNs, the most important cells in this respect are dendritic cells. In particular plasmacytoid, but also con- ventional dendritic cells are well able to produce significant amounts of type I IFNs (IFNab). The type I interferon response is usually initiated following recognition of viral components by pathogen recognition receptors e.g. toll-like receptors (TLRs) and 0166-3542/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.antiviral.2011.10.015 Abbreviations: BM, bone marrow; BM-DC, BM-derived DC; cDC, conventional dendritic cell; CPE, cytopathogenic effect; DC, dendritic cell; FL, Flt-3L; GM, GM- CSF; HSV, herpes simplex virus; IFN, interferon; LPS, lipopolysaccharide; MCMV, mouse cytomegalovirus; MDA5, melanoma-differentiation-associated gene 5; ODN, oligodeoxynucleotides; pDC, plasmacytoid dendritic cell; PRR, pattern recognition receptor; TLR, toll-like receptor; UNG, uracil-N-glycosylase. ⇑ Corresponding author. Address: Department of Medical Microbiology, Maastricht University Medical Center, P.O. Box 5800, 6202 AZ Maastricht, The Netherlands. Tel.: +31 43 387 6644; fax: +31 43 387 6643. E-mail addresses: giel.gaajetaan@maastrichtuniversity.nl (G.R. Gaajetaan), t.gee len@maastrichtuniversity.nl (T.H. Geelen), g.grauls@maastrichtuniversity.nl (G.E. Grauls), c.bruggeman@mumc.nl (C.A. Bruggeman), f.stassen@maastrichtuni versity.nl (F.R. Stassen). Antiviral Research 93 (2012) 39–47 Contents lists available at SciVerse ScienceDirect Antiviral Research journal homepage: www.elsevier.com/locate/antiviral