Differential cytokine responses from primary human Kupffer cells following infection with wild-type or vaccine strain yellow fever virus

Wild-type yellow fever virus (YFV) infections result in a hepatotropic disease which is often fatal, while vaccination with the live-attenuated 17-D strain results in productive infection yet is well-tolerated with few adverse events. Kupffer cells (KCs) are resident liver macrophages that have a significant role in pathogen detection, clearance and immune signaling. Although KCs appear to be an important component of YF disease, their role has been under-studied. This study examined cytokine responses in KCs following infection with either wild-type or vaccine strains of YFV. Results indicate that KCs support replication of both wild-type and vaccine strains, yet wild-type YFV induced a prominent and prolonged pro-inflammatory cytokine response (IL-8, TNF-α and RANTES/CCL5) with little control by a major anti-inflammatory cytokine (IL-10). This response was significantly reduced in vaccine strain infections. These data suggest that a differentially regulated infection in KCs may play a critical role in development of disease.     

Molecular and biological changes associated with HeLa cell attenuation of wild-type yellow fever virus.

Six passages of the mosquito-borne flavivirus yellow fever (YF) wild-type strain Asibi in HeLa cells attenuated the virus for monkeys and newborn mice and resulted in loss of mosquito competence. Attenuation after the passage in HeLa cells was not unique to YF virus strain Asibi as demonstrated by the HeLa passage attenuation of wild-type YF virus strain French viscerotropic virus and YF vaccine virus 17D-204 for newborn mice. In contrast, wild-type strain Dakar 1279 and the French neurotropic vaccine virus remained virulent for newborn mice after six passages in HeLa cells. Thus not all strains of YF virus can be attenuated by passage in HeLa cells. Attenuation of YF virus strains Asibi and French viscerotropic virus was accompanied by alterations in the antigenic and biological properties of the viruses, including changes to envelope protein epitopes. Attenuation for newborn mice was coincidental with the acquisition by the HeLa-passaged viruses of the vaccine-specific envelope protein epitope recognized by monoclonal antibody H5. This suggests that this conformational change may play a role in the attenuation process. Wild-type Dakar 1279, which remained virulent for newborn mice after passage in HeLa cells, retained its wild-type antigenic character. The genome of Asibi HeLa p6 virus differed from wild-type Asibi virus by 29 nucleotides that encoded 10 amino acid substitutions: 5 in the envelope protein, 1 in NS2A, 3 in NS4B, and 1 in NS5. The substitution at NS4B-95 is seen in three different attenuation processes of wild-type YF virus, leading us to speculate that it is involved in the attenuation of virulence of wild-type strain Asibi.     

Antibody responses against wild-type yellow fever virus and the 17D vaccine strain: characterization with human monoclonal antibody fragments and neutralization escape variants

Human monoclonal antibody fragments neutralizing wild-type and vaccine strains of yellow fever (YF) virus (genotypes West Africa I + II, East/Central Africa, 17D-204-WHO) were generated by repertoire cloning from YF patients. Analysis of virus escape variants identified amino acid (aa) 71 in domain II of the envelope glycoprotein (E) as the most critical residue for neutralization, with aa 153-155 in domain I contributing to the epitope. These data confirm the previous mapping of YFV neutralizing epitopes using mouse monoclonal antibodies but suggest that a conformational epitope could be formed by amino acids from domains I and II opposing each other in the dimeric form of the E protein. While the sera of the YF patients showed up to 10-fold reduced neutralizing activity against the 17D escape variants, sera from 17D vaccinees retained their neutralizing titers. Mutations in this major neutralizing epitope of YFV thus do not seem to carry the risk of immune escape in persons immunized with the YFV-17D vaccine.     

Phenotypic and molecular characterization of a non-lethal, hamster-viscerotropic strain of yellow fever virus

Viscerotropic yellow fever virus (YFV) infection occurs primarily in humans and non-human primates. Lack of an appropriate small animal model of viscerotropic YFV infection has been a major deterrent to molecular studies of viscerotropism. A hamster model of viscerotropic YFV infection has recently been described; however, these studies have focused on hamster-viscerotropic strains of YFV (including Asibi hamster P7 virus) that caused outward clinical signs of infection and mortality. In order to map more closely the molecular determinants of viscerotropism in the hamster model, a second sequential series of seven liver-to-liver passages of Asibi virus was undertaken through hamsters to generate Asibi P7b virus. Asibi hamster P7b virus did not cause clinically detectable signs of YFV infection; however, high quantities of circulating virus were isolated from the serum, and microscopic evaluation of the liver and spleen demonstrated histopathological lesions consistent with YFV infection. The genomic sequence of Asibi P7b virus was determined and compared to wild-type Asibi virus and the lethal, hamster-viscerotropic Asibi P7 virus and found to differ by only two amino acids in the envelope protein, E-98 and E-331.     

The enigma of yellow fever in East Africa

Despite a safe and effective vaccine, there are approximately 200 000 cases, including 30 000 deaths, due to yellow fever virus (YFV) each year, of which 90% are in Africa. The natural history of YFV has been well described, especially in West Africa, but in East Africa yellow fever (YF) remains characterised by unpredictable focal periodicity and a precarious potential for large epidemics. Recent outbreaks of YF in Kenya (1992-1993) and Sudan (2003 and 2005) are important because each of these outbreaks have involved the re-emergence of a YFV genotype (East Africa) that remained undetected for nearly 40 years and was previously unconfirmed in a clinically apparent outbreak. In addition, unlike West Africa and South America, YF has yet to emerge in urban areas of East Africa and be vectored by Aedes (Stegomyia) aegypti. This is a significant public health concern in a region where the majority of the population remains unvaccinated. This review describes historical findings, highlights a number of disease indicators, and provides clarification regarding the natural history, recent emergence and future risk of YF in East Africa. Copyright (c) 2008 John Wiley & Sons, Ltd.     

Heterogeneity in envelope protein sequence and N-linked glycosylation among yellow fever virus vaccine strains.

We have compared the deduced envelope (E) protein sequences of two biologically well-characterized yellow fever (YF) virus vaccine strains. The 17DD strain has been produced in Brazil for more than 50 years and used to successfully vaccinate millions of people worldwide. The 17D-213 is a candidate vaccine strain produced in tissue culture which has previously passed the monkey neurovirulence assay for testing human YF vaccines. Nucleotide sequence analysis of polymerase chain reaction-amplified cDNA revealed a number of mutations which were strain- and substrain-specific. A major difference of 17DD and 17D-213 as compared to 17D-204 and Asibi was the existence of a potential N-linked glycosylation site located at amino acid residues 153 and 151 of 17DD and 17D-213, respectively. These acceptor sites are apparently utilized for the addition of high-mannose carbohydrate chains as shown by endoglycosidase analyses of immunoprecipitated E proteins. Glycosylated E protein is also used to assemble YF vaccine virions. This work and eventual complete nucleotide sequence analysis of both vaccine strains should help to define possible changes involved in YF virus attenuation and allow their biological importance to be determined using a recently developed system for generating YF virus from cDNA. In addition, these data provide an estimate on the extent of genetic variability among YF 17D seeds and vaccines.     

Evidence for multiple sylvatic transmission cycles during the 2016–2017 yellow fever virus outbreak,Brazil

ObjectivesSince December 2016, Brazil has experienced an unusually large outbreak of yellow fever (YF). Whether urban transmission may contribute to the extent of the outbreak is unclear. The objective of this study was to characterize YF virus (YFV) genomes and to identify spatial patterns to determine the distribution and origin of YF cases in Minas Gerais, Espírito Santo and Rio de Janeiro, the most affected Brazilian states during the current YFV outbreak.MethodsWe characterized near-complete YFV genomes from 14 human cases and two nonhuman primates (NHP), sampled from February to April 2017, retrieved epidemiologic data of cases and used a geographic information system to investigate the geospatial spread of YFV.ResultsAll YFV strains were closely related. On the basis of signature mutations, we identified two cocirculating YFV clusters. One was restricted to the hinterland of Espírito Santo state, and another formed a coastal cluster encompassing several hundred kilometers. Both clusters comprised strains from humans living in rural areas and NHP. Another NHP lineage clustered in a basal relationship. No signs of adaptation of YFV strains to human hosts were detected.ConclusionsOur data suggest sylvatic transmission during the current outbreak. Additionally, cocirculation of two distinct YFV clades occurring in humans and NHP suggests the existence of multiple sylvatic transmission cycles. Increased detection of YFV might be facilitated by raised awareness for arbovirus-mediated disease after Zika and chikungunya virus outbreaks. Further surveillance is required, as reemergence of YFV from NHPs might continue and facilitate the appearance of urban transmission cycles.     

Antigenic analysis of yellow fever virus glycoproteins: use of monoclonal antibodies in enzyme-linked immunosorbent assays

A sensitive enzyme-linked immunosorbent assay with biotin and streptavidin (B/SA ELISA) was developed for the specific detection of yellow fever (YF) viruses. Monoclonal antibodies (MCA) specific for the envelope (E) glycoprotein or the non-structural glycoprotein (NV3) of YF virus-infected cell lysates were tested by antigen and antibody capture B/SA ELISA against YF viruses and a large number of other flaviviruses. In an antigen capture assay, with suckling mouse brain antigens, MCA directed against the envelope glycoprotein clearly differentiated YF viruses from any other flaviviruses, wild-type YF viruses from YF vaccine viruses and YF17D-204 substrains from other YF vaccine viruses. Specific MCA could identify YF viruses in an antibody capture assay with concentrated YF-infected tissue culture supernatant medium as the solid phase. On the basis of the principles established above, MCA binding profiles of purified YF virus strains were compared. No qualitative differences in immunoreactivity could be detected between closely related strains of YF virus. An antibody capture assay on infected tissue culture monolayers was developed to enable in situ detection of YF viruses using MCA specific for both the envelope glycoprotein and the non-structural NV3 glycoprotein.     

Detection of a new yellow fever virus lineage within the South American genotype I in Brazil

Nucleotide sequences of two regions of the genomes of 11 yellow fever virus (YFV) samples isolated from monkeys or humans with symptomatic yellow fever (YF) in Brazil in 2000, 2004, and 2008 were determined with the objective of establishing the genotypes and studying the genetic variation. Results of the Bayesian phylogenetic analysis showed that sequences generated from strains from 2004 and 2008 formed a new subclade within the clade 1 of the South American genotype I. The new subgroup is here designated as 1E. Sequences of YFV strains recovered in 2000 belong to the subclade 1D, which comprises previously characterized YFV strains from Brazil. Molecular dating analyses suggested that the new subclade 1E started diversifying from 1D about 1975 and that the most recent 2004–2008 isolates arose about 1985. J. Med. Virol. 82:175–185, 2010. © 2009 Wiley‐Liss, Inc.     

Analysis of two imported cases of yellow fever infection from Ivory Coast and The Gambia to Germany and Belgium.

BACKGROUND: Yellow fever remains one of the great burdens for public health in the endemic regions in Africa and South America. The under reporting of yellow fever cases in the respective regions and lack of international interest leads to an underestimation of the constant danger in these areas. Non-vaccinated travelers take a high risk without the effective protection of YFV 17D vaccination. OBJECTIVES: Two YF cases were imported to Europe in the last 4 years. We characterized two yellow fever virus (YFV) isolates from severely infected patients coming back from Africa, Ivory Coast and The Gambia, by genome sequencing and phylogenetic analysis. STUDY DESIGN: The virus infections in different organs were analyzed with pathological, immunohistological, electronmicroscopical and quantitative real-time PCR methods. RESULTS AND CONCLUSION: High virus loads in spleen and liver (2.4 x 10 (6) to 3 x 10 (7)GE/mL) demonstrated by real time PCR show massive virus replication leading to extraordinary progression of the disease in these patients. Immunohistological and electronmicroscopical analysis confirms virus particles in liver tissue. In all other organs no virus could be detected. A fast, specific and sensitive virus PCR detection is recommended for diagnostic of acute infections. The further sequence alignments show that the new isolates belong to the type II West African strain with great homology to over 40-year old YF isolates from Senegal and Ghana. The divergence observed was on average 3.3%, ranging from 0.0% to 5.0% in the coding region of Gambia 2001 strain and 2.9 %, ranging from 0.0% to 4.3% in the coding region of the Ivory C 1999 strain. Most mutations (5.0%/4.3%, respectively) occurred in the envelope protein.     

Intrathecal antibody production in two cases of yellow fever vaccine associated neurotropic disease in Argentina

During the period 2007-2008 several epizootics of Yellow fever with dead of monkeys occurred in southeastern Brasil, Paraguay, and northeastern Argentina. In 2008 after a Yellow fever outbreak an exhaustive prevention campaign took place in Argentina using 17D live attenuated Yellow fever vaccine. This vaccine is considered one of the safest live virus vaccines, although serious adverse reactions may occur after vaccination, and vaccine-associated neurotropic disease are reported rarely. The aim of this study was to confirm two serious adverse events associated to Yellow fever vaccine in Argentina, and to describe the analysis performed to assess the origin of specific IgM against Yellow fever virus (YFV) in cerebrospinal fluid (CSF). Both cases coincided with the Yellow fever vaccine-associated neurotropic disease case definition, being clinical diagnosis longitudinal myelitis (case 1) and meningoencephalitis (case 2). Specific YFV antibodies were detected in CSF and serum samples in both cases by IgM antibody-capture ELISA. No other cause of neurological disease was identified. In order to obtain a conclusive diagnosis of central nervous system (CNS) infection the IgM antibody index (AI(IgM) ) was calculated. High AI(IgM) values were found in both cases indicating intrathecal production of antibodies and, therefore, CNS post-vaccinal YFV infection could be definitively associated to YFV vaccination.     

Recombinant vaccinia virus producing the prM and E proteins of yellow fever virus protects mice from lethal yellow fever encephalitis.

Four recombinant vaccinia viruses were constructed for expression of different portions of the 17D yellow fever virus (YFV-17D) open reading frame. A recombinant, vP869, expressing prM and E induced high titers of neutralizing and hemagglutination inhibiting antibodies in mice and was protective against intracranial challenge with the French neurotropic strain of YFV. Levels of protection were equivalent to those achieved by immunization with the YFV-17D vaccine virus. Recombinant vaccinia viruses expressing E and NS1, C prM, E, NS1, or only NS1 failed to protect mice against challenge with YFV despite eliciting antibodies to NS1. The vP869-infected HeLa cells produced a particulate extracellular hemagglutinin (HA) similar to that produced by YFV-infected cells, supporting previous studies with Japanese encephalitis virus (Mason et al., 1991), suggesting that the ability of recombinant vaccinia virus to produce extracellular HA particles is important for effective flavivirus immunity.     

Crimean Congo hemorrhagic fever virus infects human monocyte-derived dendritic cells

For some patients infection with Crimean Congo hemorrhagic fever virus (CCHFV) causes a severe disease characterized by fever, vascular leakage and coagulopathy. Knowledge of CCHF pathogenesis is limited and today there is no information about the specific target cells of CCHFV. In this study we analyzed the permissiveness of human peripheral blood mononuclear cells (PBMCs) including monocyte-derived dendritic cells (moDCs) to CCHFV infection. Interestingly, we found that moDCs are the most permissive to CCHFV infection and this infection induced cytokine release from moDCs. Furthermore, supernatants from infected moDCs were found to activate human endothelial cells.     

Human influenza virus infection and apoptosis induction in human vascular endothelial cells

Acute encephalopathy accompanying influenza virus infection results in brain and systemic organ failure mainly through vasogenic edema with high levels of inflammatory cytokines, such as blood tumor necrosis factor (TNF)-alpha and interleukin (IL)-6, as well as the cytochrome c apoptosis marker. A highly virulent strain of avian influenza virus causes fatal infection in chickens by infecting vascular endothelial cells in systemic organs, inducing apoptosis therein. To verify the possibility of apoptosis induction by human influenza virus in infected human vascular endothelial cells, purified influenza virus-infected human umbilical vein endothelial cells (HUVECs) were examined using a tissue culture method. When pre-treated with TNF-alpha, influenza virus (Philippine strain, H3N2) promoted TNF-alpha induced apoptosis of HUVECs. Viral replication was confirmed in HUVECs infected with the Philippine strain in the absence of TNF-alpha by measurement of the amount of infective virus in the culture supernatant using the tissue culture infectious dose (TCID) method, immunohistochemistry and real-time PCR. The number of influenza virus genomes in the infected HUVECs at 24 hr post-infection increased about fivefold compared to that just after virus adsorption. Many TUNEL-positive influenza virus-infected HUVECs were observed using the TUNEL method. Furthermore, cleaved caspase 3 was also detected in influenza virus-infected cells by immunofluorescence staining. These results demonstrated that human influenza virus can infect and replicate in human vascular endothelial cells and induce apoptosis therein.     

Production and characterization of vaccines based on flaviviruses defective in replication

To develop new vaccine candidates for flavivirus infections, we have engineered two flaviviruses, yellow fever virus (YFV) and West Nile virus (WNV), that are deficient in replication. These defective pseudoinfectious viruses (PIVs) lack a functional copy of the capsid (C) gene in their genomes and are incapable of causing spreading infection upon infection of cells both in vivo and in vitro. However, they produce extracellular E protein in form of secreted subviral particles (SVPs) that are known to be an effective immunogen. PIVs can be efficiently propagated in trans-complementing cell lines making high levels of C or all three viral structural proteins. PIVs derived from YFV and WNV, demonstrated very high safety and immunization produced high levels of neutralizing antibodies and protective immune response. Such defective flaviviruses can be produced in large scale under low biocontainment conditions and should be useful for diagnostic or vaccine applications.     

Homogeneity of Yellow Fever Virus Strains Isolated During an Epidemic and a Post-epidemic Period in West Africa

Three strains of yellow fever virus (YFV) were isolated in 1982 in The Ivory Coast, one from a human case and two from Aedes luteocephalus, during and subsequent to an epidemic. The complete genomic sequence of the human strain was determined and compared to that of the 1927 Asibi strain of YFV. The divergence observed was on average of 8.3%, ranging from 5.5 to 11.7% in the coding region. The transitions to transversions ratio was 5.9. Most mutations (84.3%) occurred on the third position of the codons, with synonymous mutations representing 92.5%. However, when partial sequences representing 60% of each genome were compared, homology between the three Ivory Coast strains was greater than 99%. These results demonstrate the homogeneity of the virus strains circulating in different hosts and vectors in a limited geographical region and validate the concept of topotype in viral quasi-species. This revised version was published online in July 2006 with corrections to the Cover Date.     

登革病毒对人血管内皮细胞分泌ET-1及PGI2的影响

目的　研究登革病毒感染对人血管内皮细胞分泌重要的血管活性物质ＥＴ１ 及ＰＧＩ２ 的影响,以了解登革出血热及登革休克综合征（ＤＨＦＤＳＳ）的发病机制。方法　用登革病毒Ⅱ型,感染人脐静脉内皮细胞（ＨＵＶＥＣ） ,于感染后４ 、２４ 、４８ 、７２ 及９６ 小时,分别收集病毒感染上清液,用放射免疫检测法测定ＥＴ１ 及ＰＧＩ２ 的含量。结果　登革病毒感染可使ＨＵＶＥＣ分泌ＥＴ１ 及ＰＧＩ２ 的能力受到明显抑制。在病毒感染早期（４ 小时）,ＨＵＶＥＣ分泌ＥＴ１ 及ＰＧＩ２ 的能力即受到明显抑制。登革病毒对ＨＵＶＥＣ分泌ＥＴ１ 抑制作用强烈而持久,至感染后９６ 小时,ＨＵＶＥＣ分泌ＥＴ１ 的能力与未受感染的阴性对照组比较,差异仍有显著性。然而,登革病毒对ＨＵＶＥＣ 分泌ＰＧＩ２ 的抑制作用,可随时间的推移而减弱,至感染后９６ 小时,ＨＵＶＥＣ分泌ＰＧＩ２ 的能力已达正常水平。结论　登革病毒感染可影响血管内皮细胞分泌血管活性物质ＥＴ１ 及ＰＧＩ２ 的功能,导致血管通透性增加和凝血、止血功能障碍。因此,登革病毒所致的血管内皮细胞功能障碍,可能是ＤＨＦＤＳＳ重要的发病机制     

北京市4例输入性黄热病病例病毒全基因组特征分析

目的 通过对2016年北京市4例输入性黄热病病毒全基因组深度测序分析,以期对病毒进行溯源、分析疫苗有效性以及防控策略提供分子依据.方法 将荧光PCR检测为阳性的血液、尿液样本利用Ion Torrent PGM平台进行全基因组深度测序,通过MEGA 6.0软件中邻接法进行遗传进化分析,并采用Lasergene Protean软件进行E蛋白氨基酸变异分析及抗原性分析.结果 从首例病人的血液样本和其他3个病例的尿液样本中分别获得了黄热病病毒的全基因组序列.遗传进化树分析结果表明,4例黄热病病毒基因组与安哥拉71株(AY968064)高度同源,相似度分别达99.21％、98.11％、98.02％、98.39％.4例黄热病病毒E蛋白的氨基酸序列与安哥拉71株的序列分析相似度分别达99.6％、99.39％、99.01％、99.59％.4例黄热病病毒E蛋白抗原性与17D疫苗株(X03700)的E蛋白抗原性比较分析无明差异.结论 4例黄热病病毒都是安哥拉流行株类似株,目前使用的17D疫苗具有有效性.     

Human cytotoxic T lymphocyte responses to live attenuated 17D yellow fever vaccine: identification of HLA-B35-restricted CTL epitopes on nonstructural proteins NS1, NS2b, NS3, and the structural protein E

Yellow fever virus (YFV) is a re-emerging problem despite the existence of an effective live-attenuated vaccine. The induction of YFV-neutralizing antibodies undoubtedly contributes to vaccine efficacy, but T lymphocyte responses to YFV likely play a role in long-term efficacy. We studied the T lymphocyte responses to YFV in four vaccinees. Proliferation and cytolytic responses to YFV were demonstrated in all subjects. We isolated 13 YFV-specific CD8(+) CTL lines that recognized epitopes on the E, NS1, NS2b, and NS3 proteins; eight CTL lines were HLA-B35-restricted. YFV-specific T cell responses were detectable by IFN gamma ELISPOT assays 14 days postvaccination, with T cell frequencies sustained for up to 19 months. To our knowledge, this is the first report of human T lymphocyte responses following YFV vaccination. These results indicate that the live 17D YFV vaccine induced CD8(+) T cell responses directed against at least four different HLA-B35-restricted YFV epitopes.