RESUMO
The genome of vertebrates contains endogenous retroviruses (ERVs) that are largely nonfunctional relicts of ancestral germline infection by exogenous retroviruses. However, in some mouse strains ERVs are actively involved in disease. Here we report that nucleic acid-recognizing Toll-like receptors 3, 7, and 9 (TLR 3, TLR7, and TLR9) are essential for the control of ERVs. Loss of TLR7 function caused spontaneous retroviral viremia that coincided with the absence of ERV-specific antibodies. Importantly, additional TLR3 and TLR9 deficiency led to acute T cell lymphoblastic leukemia, underscoring a prominent role for TLR3 and TLR9 in surveillance of ERV-induced tumors. Experimental ERV infection induced a TLR3-, TLR7-, and TLR9-dependent group of "acute-phase" genes previously described in HIV and SIV infections. Our study suggests that in addition to their role in innate immunity against exogenous pathogens, nucleic acid-recognizing TLRs contribute to the immune control of activated ERVs and ERV-induced tumors.
Assuntos
Retrovirus Endógenos/genética , Ácidos Nucleicos/genética , Leucemia-Linfoma Linfoblástico de Células T Precursoras/genética , Receptores Toll-Like/genética , Receptores Toll-Like/metabolismo , Viremia/genética , Animais , Anticorpos Antivirais/genética , Anticorpos Antivirais/imunologia , Linhagem Celular , Retrovirus Endógenos/imunologia , Retrovirus Endógenos/metabolismo , Imunidade Inata/genética , Imunidade Inata/imunologia , Células Matadoras Naturais/imunologia , Células Matadoras Naturais/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Ácidos Nucleicos/imunologia , Ácidos Nucleicos/metabolismo , Oncogenes/genética , Oncogenes/imunologia , Leucemia-Linfoma Linfoblástico de Células T Precursoras/imunologia , Leucemia-Linfoma Linfoblástico de Células T Precursoras/metabolismo , Receptores Toll-Like/imunologia , Viremia/imunologia , Viremia/metabolismoRESUMO
Infection of monocytes and macrophages by influenza A virus leads to proinflammatory and chemotactic cytokine production. The signalling pathways linking innate immune virus recognition to cytokine expression are little understood. Here, we report that blocking of CD14 on human monocytes by specific antibody or use of CD14-deficient murine macrophages abolished influenza A virus-induced cytokine production. Toll-like receptor (TLR) 2 and 4-deficient murine macrophages remained fully responsive. These results suggest that CD14, together with a TLR other than TLR2 or 4, is an essential coreceptor of the influenza A virus sensing recognition system.
Assuntos
Quimiocinas/metabolismo , Citocinas/metabolismo , Vírus da Influenza A/imunologia , Receptores de Lipopolissacarídeos/metabolismo , Glicoproteínas de Membrana/metabolismo , Receptores de Superfície Celular/metabolismo , Animais , Células Cultivadas , Humanos , Macrófagos/metabolismo , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Endogâmicos C57BL , Camundongos Knockout , Monócitos/metabolismo , Receptor 2 Toll-Like , Receptores Toll-LikeRESUMO
Foreign RNA serves as pathogen-associated molecular pattern (PAMP) and is a potent immune stimulator for innate immune receptors. However, the role of single bacterial RNA species in immune activation has not been characterized in detail. We analyzed the immunostimulatory potential of transfer RNA (tRNA) from different bacteria. Interestingly, bacterial tRNA induced type I interferon (IFN) and inflammatory cytokines in mouse dendritic cells (DCs) and human peripheral blood mononuclear cells (PBMCs). Cytokine production was TLR7 dependent because TLR7-deficient mouse DCs did not respond and TLR7 inhibitory oligonucleotides inhibited tRNA-mediated activation. However, not all bacterial tRNA induced IFN-α because tRNA from Escherichia coli Nissle 1917 and Thermus thermophilus were non-immunostimulatory. Of note, tRNA from an E. coli knockout strain for tRNA (Gm18)-2'-O-methyltransferase (trmH) regained immunostimulatory potential. Additionally, in vitro methylation of this immunostimulatory Gm18-negative tRNA with recombinant trmH from T. thermophilus abolished its IFN-α inducing potential. More importantly, Gm18-modified tRNA acted as TLR7 antagonist and blocked IFN-α induction of influenza A virus-infected PBMCs.
Assuntos
Bactérias/genética , Guanosina/metabolismo , Imunidade Inata/imunologia , Glicoproteínas de Membrana/imunologia , RNA de Transferência/imunologia , Receptor 7 Toll-Like/imunologia , tRNA Metiltransferases/metabolismo , Animais , Bactérias/imunologia , Cromatografia Líquida de Alta Pressão , Células Dendríticas/imunologia , Humanos , Imunização , Interferon-alfa/metabolismo , Leucócitos Mononucleares/imunologia , Glicoproteínas de Membrana/antagonistas & inibidores , Glicoproteínas de Membrana/genética , Camundongos , Camundongos Knockout , Oligonucleotídeos , RNA de Transferência/farmacologia , Receptor 7 Toll-Like/antagonistas & inibidores , Receptor 7 Toll-Like/genética , tRNA Metiltransferases/genéticaRESUMO
Bronchiolar epithelial cells are the prime targets for influenza A virus infection. It still remains to be clarified which signals are generated from these cells to initiate an immune response. Among chemokines, viral infection of primary lung epithelial cells triggered exclusively the release of CXCL8/interleukin-8 (IL-8), which contrasts with our previous observation that influenza A virus induced in monocytes the expression of mononuclear-leukocyte-attracting chemokines and even suppressed the production of neutrophil-attracting chemokines. Therefore, we speculated that it may be advantageous for respiratory epithelial cells to release primarily neutrophil-attracting CXCL8/IL-8 since neutrophils rapidly remove necrotic debris and are the first line of defense against bacterial superinfections. This concept has also been supported by our finding that influenza A virus infection led to necrosis of lung epithelial cells. This is in striking contrast to previous studies where influenza A virus infection induced apoptosis in monocytes and epithelial cells from origins other than the lung. Thus, the cell type instead of the virus determines which death pathway will be followed. In addition to the release of CXCL8/IL-8, we obtained a massive release of macrophage migration inhibitory factor (MIF) from virus-infected lung cells. However, whereas the CXCL8/IL-8 secretion was accompanied by induced gene activation, the transcription rate of MIF remained unchanged during the infection course and the virus-induced MIF release was predominantly a discharge from intracellular stores, suggesting that MIF is passively released upon cell death. Despite virus induced necrosis, the passively liberated MIF remained bioactive. Considering the well-established immunostimulatory effects of MIF on different leukocyte subsets, is its very likely that enhanced levels of MIF may contribute to the host immune response during the acute phase of influenza A virus infection in humans.