Ixodes scapularis transmits the agent of human granulocytic anaplasmosis, among other pathogens. The mechanisms used by the tick to control Anaplasma phagocytophilum are not known. We demonstrate that the I. scapularis Janus kinase (JAK)–signaling transducer activator of transcription (STAT) pathway plays a critical role in A. phagocytophilum infection of ticks. The A. phagocytophilum burden increases in salivary glands and hemolymph when the JAK-STAT pathway is suppressed by RNA interference. The JAK-STAT pathway exerts its anti-Anaplasma activity presumably through STAT-regulated effectors. A salivary gland gene family encoding 5.3-kDa antimicrobial peptides is highly induced upon A. phagocytophilum infection of tick salivary glands. Gene expression and electrophoretic mobility shift assays showed that the 5.3-kDa antimicrobial peptide–encoding genes are regulated by tick STAT. Silencing of these genes increased A. phagocytophilum infection of tick salivary glands and transmission to mammalian host. These data suggest that the JAK-STAT signaling pathway plays a key role in controlling A. phagocytophilum infection in ticks by regulating the expression of antimicrobial peptides.
Caspase-12 has been shown to negatively modulate inflammasome signaling during bacterial infection. Its function in viral immunity, however, has not been characterized. We now report an important role for caspase-12 in controlling viral infection via the pattern-recognition receptor RIG-I. After challenge with West Nile virus (WNV), caspase-12-deficient mice had greater mortality, higher viral burden and defective type I interferon response compared with those of challenged wild-type mice. In vitro studies of primary neurons and mouse embryonic fibroblasts showed that caspase-12 positively modulated the production of type I interferon by regulating E3 ubiquitin ligase TRIM25–mediated ubiquitination of RIG-I, a critical signaling event for the type I interferon response to WNV and other important viral pathogens.
Dengue virus (DENV), the causative agent of human Dengue hemorrhagic fever, is a mosquito-borne virus found in tropical and sub-tropical regions around the world. Vaccines against DENV are currently unavailable. Guanylate-binding protein 1 (GBP1) is one of the Interferon (IFN) stimulated genes (ISGs) and has been shown important for host immune defense against various pathogens. However, the role of GBP1 during DENV infection remains unclarified. In this study, we evaluated the relevance of GBP1 to DENV infection in in vitro model.
Quantitative RT-PCR (qRT-PCR) and Western blot showed that the expression of mouse Gbp1 was dramatically upregulated in DENV-infected RAW264.7 cells. The intracellular DENV loads were significantly higher in Gbp1 silenced cells compared with controls. The expression levels of selective anti-viral cytokines were decreased in Gbp1 siRNA treated cells, while the transcription factor activity of NF-κB was impaired upon GBP1 silencing during infection.
Our data suggested that GBP1 plays an antiviral role during DENV infection.
GBP1; DENV; Antiviral response; NF-κB
The Th17 cytokine, IL-22, regulates host immune responses to extracellular pathogens. Whether IL-22 plays a role in viral infection, however, is poorly understood. We report here that Il22−/− mice were more resistant to lethal West Nile virus (WNV) encephalitis, but had similar viral loads in the periphery compared to wild type (WT) mice. Viral loads, leukocyte infiltrates, proinflammatory cytokines and apoptotic cells in the central nervous system (CNS) of Il22−/− mice were also strikingly reduced. Further examination showed that Cxcr2, a chemokine receptor that plays a non-redundant role in mediating neutrophil migration, was significantly reduced in Il22−/− compared to WT leukocytes. Expression of Cxcr2 ligands, cxcl1 and cxcl5, was lower in Il22−/− brains than wild type mice. Correspondingly, neutrophil migration from the blood into the brain was attenuated following lethal WNV infection of Il22−/− mice. Our results suggest that IL-22 signaling exacerbates lethal WNV encephalitis likely by promoting WNV neuroinvasion.
The Lyme disease agent, Borrelia burgdorferi, is primarily transmitted to vertebrates by Ixodes ticks. The classical and alternative complement pathways are important in Borrelia eradication by the vertebrate host. We recently identified a tick salivary protein, designated P8 that reduced complement-mediated killing of Borrelia. We now discover that P8 interferes with the human lectin complement cascade resulting in impaired neutrophil phagocytosis and chemotaxis, and diminished Borrelia lysis. Therefore, P8 was renamed the lectin complement pathway inhibitor (TSLPI). TSLPI-silenced ticks, or ticks exposed to TSLPI-immune mice, were hampered in Borrelia transmission. Moreover, Borrelia acquisition and persistence in tick midguts was impaired in ticks feeding on TSLPI-immunized B. burgdorferi-infected mice. Together, our findings suggest an essential role for the lectin complement cascade in Borrelia eradication and demonstrate how a vector-borne pathogen co-opts a vector protein to facilitate early mammalian infection and vector colonization.
MBL; lectin; ficolin; tick immunity; Borrelia burgdorferi; complement; vaccine
Polymorphonuclear leukocytes (PMN) are key in innate immunity but their role in viral pathogenesis is incompletely understood. In infection with West Nile virus (WNV), we found that expression of two PMN-attracting chemokines, Cxcl1 and Cxcl2, was rapidly and dramatically elevated in macrophages. PMN are rapidly recruited to the site of WNV infection in mice and support efficient replication of WNV. Mice depleted of PMN after WNV inoculation developed higher viremia and earlier death compared to the control group, suggesting a protective role for PMN. In contrast, when PMN were depleted prior to infection with WNV, and in mice deficient in Cxcr2, a chemokine receptor gene, viremia was reduced and survival was enhanced or delayed. Collectively, these data suggest that PMN have a biphasic response to WNV infection, serving as a reservoir for replication and dissemination in early infection and later contributing to viral clearance.
Neutrophil; PMN; West Nile virus; chemokine; innate immunity
Polymorphonuclear leukocytes (PMNs) are key in innate immunity, but their role in viral pathogenesis is incompletely understood. In infection due to West Nile virus (WNV), we found that expression of 2 PMNattracting chemokines, Cxcl1 and Cxcl2, was rapidly and dramatically elevated in macrophages. PMNs are rapidly recruited to the site of WNV infection in mice and support efficient replication of WNV. Mice depleted of PMNs after WNV inoculation developed higher viremia and experienced earlier death, compared with the control group, which suggest a protective role for PMNs. In contrast, when PMNs were depleted prior to infection with WNV, and in mice deficient in Cxcr2 (a chemokine receptor gene), viremia was reduced and survival was enhanced. Collectively, these data suggest that PMNs have a biphasic response to WNV infection, serving as a reservoir for replication and dissemination in early infection and later contributing to viral clearance.
Dengue virus (DENV) and West Nile virus (WNV), close siblings of the Flaviviridae family, are the causative agents of Dengue hemorraghic shock or West Nile meningoencephalitis respectively. Vaccines against these two flaviviruses are currently unavailable. Interferon- Stimulated Gene 15 (ISG15), encoding an ubiquitin-like protein, is significantly induced by type I interferons or viral infections. Its roles in viral infections, however, vary with viruses, being either anti- or pro-viral. The exact roles of ISG15 in DENV and WNV infections remain unknown. In the current study, we evaluated the relevancies of ISG15 to DENV and WNV infection of a mouse macrophage cell line RAW264.7.
Quantitative PCR showed that mouse Isg15 was dramatically induced in DENV or WNV- infected RAW264.7 cells compared with non-infected cells. Isg15 and two other Jak-Stat related genes, Socs1 and Socs3, were silenced using siRNA mediated RNA interference. The intracellular DENV and WNV loads, as determined by quantitative PCR, were significantly higher in Isg15 silenced cells than control cells. The expression levels of interferon beta 1 (Ifnb1) were increased significantly in Isg15, Socs1 or Socs3 siRNA treated cells. Further investigation indicated that protein modification by ISG15, so called ISGylation, was significantly enhanced in DENV-infected cells compared to that in non-infected cells.
These findings suggest that ISG15 plays an anti-DENV/WNV function via protein ISGylation.
ISG15; Dengue Virus; West Nile Virus; ISGylation
Borrelia burgdorferi, the causative agent of Lyme disease, is transmitted to humans by bite of Ixodes scapularis ticks. The mechanisms by which the bacterium is transmitted from vector to host are poorly understood. In this study, we show that the F(ab)2 fragments of BBE31, a B.burgdorferi outer-surface lipoprotein, interfere with the migration of the spirochete from tick gut into the hemolymph during tick feeding. The decreased hemolymph infection results in lower salivary glands infection, and consequently attenuates mouse infection by tick-transmitted B. burgdorferi. Using a yeast surface display approach, a tick gut protein named TRE31 was identified to interact with BBE31. Silencing tre31 also decreased the B. burgdorferi burden in the tick hemolymph. Delineating the specific spirochete and arthropod ligands required for B. burgdorferi movement in the tick may lead to new strategies to interrupt the life cycle of the Lyme disease agent.
Lyme disease, the most common tick-borne illness in North America, is caused by Borrelia burgdorferi. Currently, spirochete and tick molecules that facilitate Borrelia migration within the vector, a key step for mammalian infection by tick-transmitted spirochetes, have not yet been identified. In this study, we show that F(ab)2 fragments of BBE31, a B.burgdorferi outer-surface lipoprotein, interfere with the spirochete migration from the tick gut into the hemolymph. Our results indicated that decreased hemolymph infection by blocking BBE31 resulted in lower salivary glands infection, which eventually attenuated murine infection by tick-transmitted B.burgdorferi. We also found that a tick gut protein TRE31 enables Borrelia movement by interacting with BBE31. This finding provides novel insights into the transmission of spirochete within the vector and provides potential vaccine targets to block the microbial life cycle within the vector.
West Nile virus (WNV) is the most common arthropod-borne flavivirus in the United States; however, the vector ligand(s) that participate in infection are not known. We now show that an Aedes aegypti C-type lectin, mosGCTL-1, is induced by WNV, interacts with WNV in a calcium-dependent manner, and facilitates infection in vivo and in vitro. A mosquito homologue of human CD45 in A. aegypti, designated mosPTP-1, recruits mosGCTL-1 to enable viral attachment to cells, and to enhance viral entry. In vivo experiments show that mosGCTL-1 and mosPTP-1 function as part of the same pathway and are critical for WNV infection of mosquitoes. A similar phenomenon was also observed in Culex quinquefasciatus, a natural vector of WNV, further demonstrating that these genes participate in WNV infection. During the mosquito blood-feeding process, WNV infection was blocked in vivo with mosGCTL-1 antibodies. A molecular understanding of flaviviral-arthropod interactions may lead to strategies to control viral dissemination in nature.
West Nile virus; C-type lectin; protein tyrosine phosphatases; mosquito; arthropod-based vaccine
Ticks are distributed worldwide and affect human and animal health by transmitting diverse infectious agents. Effective vaccines against most tick-borne pathogens are not currently available. In this study, we characterized a tick histamine release factor (tHRF) from Ixodes scapularis and addressed the vaccine potential of this antigen in the context of tick engorgement and B. burgdorferi transmission. Results from western blotting and quantitative Reverse Transcription-PCR showed that tHRF is secreted in tick saliva, and upregulated in Borrelia burgdorferi-infected ticks. Further, the expression of tHRF was coincident with the rapid feeding phase of the tick, suggesting a role for tHRF in tick engorgement and concomitantly, for efficient B. burgdorferi transmission. Silencing tHRF by RNA interference (RNAi) significantly impaired tick feeding and decreased B. burgdorferi burden in mice. Interfering with tHRF by actively immunizing mice with recombinant tHRF, or passively transferring tHRF antiserum, also markedly reduced the efficiency of tick feeding and B. burgdorferi burden in mice. Recombinant tHRF was able to bind to host basophils and stimulate histamine release. Therefore, we speculate that tHRF might function in vivo to modulate vascular permeability and increase blood flow to the tick bite-site, facilitating tick engorgement. These findings suggest that blocking tHRF might offer a viable strategy to complement ongoing efforts to develop vaccines to block tick feeding and transmission of tick-borne pathogens.
Ticks are distributed worldwide and affect human and animal health by transmitting diverse infectious agents. Safe and effective vaccines against most tick-borne pathogens are not currently available. Typical vaccines target microbes directly, using extracts of the organism, or recombinant antigens as the immunogen; the transmission of tick-borne pathogens can also theoretically be prevented by interfering with the ability of ticks to feed on a mammalian host. In this study, we have characterized a putative histamine release factor (tHRF) from I. scapularis ticks, the predominant vector of B. burgdorferi, the agent of Lyme disease in North America. Our results suggested that tHRF is presented in tick saliva and critical for tick feeding; blocking tHRF markedly reduced the efficiency of tick feeding, and reduced the B. burgdorferi burden in mice. This finding provides novel insights into the molecular mechanisms of tick feeding and provides a potential vaccine target to block tick feeding and pathogen transmission.
Traditionally, vaccines directly target a pathogen or microbial toxin. Lyme disease, caused by Borrelia burgdorferi, is a tick-borne illness for which a human vaccine is not currently available. B. burgdorferi binds a tick salivary protein, Salp15, during transmission from the vector, and this interaction facilitates infection of mice. We now show that Salp15-antiserum significantly protected mice from B. burgdorferi infection. Salp15-antiserum also markedly enhanced the protective capacity of antibodies against B. burgdorferi antigens, such as OspA or OspC. Mice actively immunized with Salp15 were also significantly protected from tick-borne Borrelia. In vitro assays showed that Salp15-antiserum increased the clearance of Salp15-coated B. burgdorferi by phagocytes, suggesting a mechanism of action. Vaccination with a vector molecule that a microbe requires for infection of the mammalian host suggests a new strategy for the prevention of Lyme disease, and this paradigm may be applicable to numerous arthropod-borne pathogens of medical importance.
Lyme disease; Ixodes ticks; vaccine; Salp15; antibody
West Nile virus (WNV) is the most-common cause of mosquito-borne encephalitis in the United States. Invasion of the brain by WNV is influenced by viral and host factors, and the molecular mechanism underlying disruption of the blood-brain barrier is likely multifactorial. Here we show that matrix metalloproteinase 9 (MMP9) is involved in WNV entry into the brain by enhancing blood-brain barrier permeability. Murine MMP9 expression was induced in the circulation shortly after WNV infection, and the protein levels remained high even when viremia subsided. In the murine brain, MMP9 expression and its enzymatic activity were upregulated and MMP9 was shown to partly localize to the blood vessels. Interestingly, we also found that cerebrospinal fluid from patients suffering from WNV contained increased MMP9 levels. The peripheral viremia and expression of host cytokines were not altered in MMP9−/− mice; however, these animals were protected from lethal WNV challenge. The resistance of MMP9−/− mice to WNV infection correlated with an intact blood-brain barrier since immunoglobulin G, Evans blue leakage into brain, and type IV collagen degradation were markedly reduced in the MMP9−/− mice compared with their levels in controls. Consistent with this, the brain viral loads, selected inflammatory cytokines, and leukocyte infiltrates were significantly reduced in the MMP9−/− mice compared to their levels in wild-type mice. These data suggest that MMP9 plays a role in mediating WNV entry into the central nervous system and that strategies to interrupt this process may influence the course of West Nile encephalitis.
Determining how West Nile virus crosses the blood-brain barrier is critical to understanding the pathogenesis of encephalitis. Here, we show that ICAM-1−/− mice are more resistant than control animals to lethal West Nile encephalitis. ICAM-1−/− mice have a lower viral load, reduced leukocyte infiltration, and diminished neuronal damage in the brain compared to control animals. This is associated with decreased blood-brain barrier leakage after viral infection. These data suggest that ICAM-1 plays an important role in West Nile virus neuroinvasion and that targeting ICAM-1 signaling may help control viral encephalitis.