title: Viral activation of macrophages through TLR-dependent and -independent pathways.
abstract: Induction of cytokine production is important for activation of an efficient host defense response. Macrophages constitute an important source of cytokines. In this study we have investigated the virus-cell interactions triggering induction of cytokine expression in macrophages during viral infections. We found that viral entry and viral gene products produced inside the cell are responsible for activation of induction pathways leading to IFN-alphabeta expression, indicating that virus-cell interactions on the cell surface are not enough. Moreover, by the use of cell lines expressing dominant negative versions of TLR-associated adaptor proteins we demonstrate that Toll/IL-1 receptor domain-containing adaptor inducing IFN-beta is dispensable for all virus-induced cytokine expression examined. However, a cell line expressing dominant negative MyD88 revealed the existence of distinct induction pathways because virus-induced expression of RANTES and TNF-alpha was totally blocked in this cell line whereas IFN-alphabeta expression was much less affected in the absence of signaling via MyD88. In support of this, we also found that inhibitory CpG motifs, which block TLR9 signaling inhibited early HSV-2-induced TNF-alpha and RANTES expression dramatically whereas IFN-alphabeta induction was only slightly affected. This suggests that virus activates macrophages through distinct pathways, of which some are dependent on TLRs signaling through MyD88, whereas others seem to be independent of TLR signaling. Finally we demonstrate that IFN-alphabeta induction in HSV-2-infected macrophages requires a functional dsRNA-activated protein kinase molecule because cells expressing a dsRNA-dependent protein kinase version unable to bind dsRNA do not express IFN-alphabeta on infection.
authors.affiliation: Department of Medical Microbiology and Immunology, University of Aarhus, Aarhus, Denmark. lm@microbiology.au.dk
authors.forename: Lene
authors.initials: L
authors.lastname: Malmgaard
authors.forename: Jesper
authors.initials: J
authors.lastname: Melchjorsen
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Bowie
authors.forename: Søren C
authors.initials: SC
authors.lastname: Mogensen
authors.forename: Søren R
authors.initials: SR
authors.lastname: Paludan
mesh_terms: D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000502:physiology; D005260:Female; D017781:Genes, Immediate-Early / Q000528:radiation effects; D018259:Herpesvirus 1, Human / Q000235:genetics / Q000276:immunology* / Q000528:radiation effects; D018258:Herpesvirus 2, Human / Q000235:genetics / Q000276:immunology* / Q000528:radiation effects; D050838:Interferon Regulatory Factor-3; D016898:Interferon-alpha / Q000096:biosynthesis / Q000528:radiation effects; D016899:Interferon-beta / Q000096:biosynthesis / Q000528:radiation effects; D007700:Kinetics; D008262:Macrophage Activation / Q000276:immunology* / Q000528:radiation effects; D017737:Macrophages, Peritoneal / Q000276:immunology / Q000378:metabolism / Q000528:radiation effects / Q000821:virology; D008562:Membrane Glycoproteins / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D016328:NF-kappa B / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism / Q000528:radiation effects; D012367:RNA, Viral / Q000378:metabolism / Q000528:radiation effects; D011956:Receptors, Cell Surface / Q000502:physiology*; D015398:Signal Transduction / Q000276:immunology*; D051217:Toll-Like Receptor 9; D051193:Toll-Like Receptors; D014157:Transcription Factors / Q000502:physiology; D014466:Ultraviolet Rays; D014759:Viral Envelope Proteins / Q000276:immunology; D019892:eIF-2 Kinase / Q000502:physiology
chemical_list: D004268:DNA-Binding Proteins; D050838:Interferon Regulatory Factor-3; D016898:Interferon-alpha; C494233:Irf3 protein, mouse; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D012333:RNA, Messenger; D012367:RNA, Viral; D011956:Receptors, Cell Surface; C495370:Tlr9 protein, mouse; D051217:Toll-Like Receptor 9; D051193:Toll-Like Receptors; D014157:Transcription Factors; D014759:Viral Envelope Proteins; C039447:glycoprotein D, Human herpesvirus 1; C077407:glycoprotein L, Human herpesvirus 1; D016899:Interferon-beta; D019892:eIF-2 Kinase