CD16(+) natural killer cells play a limited role against primary dengue virus infection in tamarins

CD16 is a major molecule expressed on NK cells. To directly assess the role of natural killer (NK) cells in dengue virus (DENV) infection in vivo, CD16 antibody-treated tamarins were inoculated with a DENV-2 strain. This resulted in the transient depletion of CD16(+) NK cells, whereas no significant effects on the overall levels or kinetics of plasma viral loads and antiviral antibodies were observed in the treated monkeys when compared to control monkeys. It remains elusive whether the CD16(-) NK subpopulation could play an important role in the control of primary DENV infection.

T-cell responses to dengue virus in humans

Dengue virus (DENV) is a leading cause of morbidity and mortality in most tropical and subtropical areas of the world. Dengue virus infection induces specific CD4+CD8– and CD8+CD4– T cells in humans. In primary infection, T-cell responses to DENV are serotype cross-reactive, but the highest response is to the serotype that caused the infection. The epitopes recognized by DENV-specific T cells are located in most of the structural and non-structural proteins, but NS3 is the protein that is most dominantly recognized. In patients with dengue hemorrhagic fever (DHF) caused by secondary DENV infection, T cells are highly activated in vivo. These highly activated T cells are DENV-specific and oligoclonal. Multiple kinds of lymphokines are produced by the activated T cells, and it has been hypothesized that these lymphokines are responsible for induction of plasma leakage, one of the most characteristic features of DHF. Thus, T-cells play important roles in the pathogenesis of DHF and in the recovery from DENV infection.

Identification and characterization of the short variable region of the Japanese encephalitis virus 3' NTR

Since the 1980s, the Japanese encephalitis virus (JEV) variants with slightly short variable regions (VR) of the 3' non-translated region (NTR) have been found; however, the implications of these short VR remain unclear. We recently identified two novel types of short VR (5 and 9 nt shorter than that of major group of genotype I JEV strains) of genotype I JEV isolates. To elucidate the impact of these short VR on the replication and virulence of JEV, we generated five recombinant JEV viruses: M41-d5 and M41-d9 have deletions in the VR that correspond to those observed in some recent JEV isolates, M41-d5d9 has both the 5- and 9-nt deletions in the VR, M41-d27 has a large deletion that encompasses both the 5- and 9-nt deletion regions, and M41-a13 has a 13-nt sequence insertion of the genotype III JEV strain Beijing-1 into the parent genotype I JEV strain Mie/41/2002 genome. The recombinant viruses and the parent virus, except for the M41-d27 mutant, showed similar growth properties in mammalian and mosquito cell lines. Mouse challenge experiments indicated that no significant differences among the recombinant viruses M41-d5d9, M41-d27, M41-a13, and the parent virus. Our results suggest that the short VR in JEV 3' NTR do not affect its growth in vitro or its pathogenicity in mice.

High clonality of virus-specific T lymphocytes defined by TCR usage in the brains of mice infected with West Nile virus

It has been reported that brain-infiltrating T lymphocytes play critical roles in the clearance of West Nile virus (WNV) from the brains of mice. We characterized brain-infiltrating T lymphocytes by analyzing the TCR α- and β-chain repertoires, T cell clonality, and CDR3 sequences. CD3(+)CD8(+) T cells were localized in the WNV-infected brains. The expression of CD3, CD8, CD25, CD69, perforin, and granzymes positively correlated with viral RNA levels, and high levels of expression of IFN-γ, TNF-α, and IL-2 were detected in the brains, suggesting that Th1-like cytotoxic CD8(+) T cells are expanded in the brains in response to WNV infection. The brain-infiltrating T lymphocytes dominantly used TCR genes, VA1-1, VA2-1, VB5-2, and VB8-2, and exhibited a highly oligoclonal TCR repertoire. Interestingly, the brain-infiltrating T lymphocytes had different patterns of TCR repertoire usages among WNV-, Japanese encephalitis virus-, and tick-borne encephalitis virus-infected mice. Moreover, CD8(+) T cells isolated from the brains of WNV-infected mice produced IFN-γ and TNF-α after in vitro stimulation with peritoneal cells infected with WNV, but not with Japanese encephalitis virus. The results suggest that the infiltrating CD8(+) T cells were WNV-specific, but not cross-reactive among flaviviruses. T cells from the WNV-infected brains exhibited identical or similar CDR3 sequences in TCRα among tested mice, but somewhat diverse sequences in TCRβ. The results indicate that WNV-specific CD3(+)CD8(+) T cells expanding in the infected brains are highly oligoclonal, and they suggest that TCR α-chains play a dominant and critical role in Ag specificity of WNV-specific T cells.

Dengue virus isolation relying on antibody-dependent enhancement mechanism using FcγR-expressing BHK cells and a monoclonal antibody with infection-enhancing capacity

BACKGROUND

Virus isolation is the most reliable evidence of dengue virus (DENV) infection. However, conventional virus isolation methods generally posses lower sensitivity and are time consuming as compared to other diagnostic methods such as detection of viral genome by RT-PCR, and determination of NS1 antigen and anti-DENV antibody by ELISA.

OBJECTIVES

A virus isolation method relying on the antibody-dependent enhancement mechanism was established and the assay's efficacy in DENV isolation was confirmed.

STUDY DESIGN

FcγR-expressing BHK cells were used for DENV isolation from patient serum samples in the presence of a flavivirus-group reactive monoclonal antibody, mAb4G2, which possesses DENV infection-enhancement activity. DENV genome copy numbers in the culture supernatant fluids of FcγR-expressing BHK cells were assessed and compared to those of parent BHK cells and C6/36 mosquito cells, a cell line commonly used for DENV isolation.

RESULTS

The virus titer levels were higher in the culture supernatant fluid of FcγR-expressing BHK cells in the presence of enhancing antibody in comparison with other cell lines using laboratory-established strains and some clinical samples. DENV was isolated from 7 of 16 serum samples by using FcγR-expressing BHK cells in the presence of mAb4G2, but not by using cell lines commonly employed in conventional isolation assays, the FcγR-negative BHK cells and C6/36 cell lines.

CONCLUSIONS

The results demonstrate that FcγR-expressing BHK cell line in the presence of antibodies, which possess antibody dependent enhancement (ADE) activity, is a useful tool for DENV isolation.

Increased positive selection pressure within the complementarity determining regions of the T-cell receptor β gene in New World monkeys

Because of the long-term co-evolution of TCR and MHC molecules, numerous nucleotide substitutions have accumulated within the domains of TCRβ genes. We previously found that nonsynonymous nucleotide substitutions occurred more frequently in complementarity determining region (CDR)β than in CDRα, even though only a limited number of common marmoset (Callithrix jacchus) and human T-cell receptor β variable (TRBV) sequences were compared. This interesting finding raised the question of whether the increased selective pressure within CDRβ was species-specific. In this study, we identified 21 TRBV region sequences from the common marmoset and performed comparative sequence analyses of the T-cell receptor α variable (TRAV) and TRBV regions from human, chimpanzee, rhesus monkey, cotton-top tamarin, Ma's night monkey, and common marmoset. The ratios of the number of nonsynonymous nucleotide substitutions per site (d(N) ) to the d(S) values (d(N) /d(S) ) were less than 1 within the framework regions (FRs) of TRAV and TRBV region sequences, suggesting that purifying selection is largely dominant within the FRs. In contrast, the d(N) values were statistically significantly greater for CDRβ than for CDRα only in New World monkeys. Also, increased d(N) /d(S) ratios (d(N) /d(S) >1) were observed within CDRβ between humans and New World monkeys and, interestingly, between New World monkeys, which share a relatively recent common ancestor. Moreover, phylogenetic analysis by maximum likelihood analysis provided firm evidence to support that positive selection occurred within CDRβ along New World monkey lineages. These results suggest that increased positive selection pressure within CDRβ is common in New World monkeys rather than being species-specific. This study provides an intriguing insight into the co-evolution of TCR and MHC molecules within primates.

An amino acid substitution (V3I) in the Japanese encephalitis virus NS4A protein increases its virulence in mice, but not its growth rate in vitro

Our previous studies have shown that the Japanese encephalitis virus (JEV) strain Mie/40/2004 is the most virulent of the strains isolated by us in Japan from 2002 to 2004. Comparison of the amino acid sequence of Mie/40/2004 with those of low-virulence strains revealed that an isoleucine residue at position 3 of the Mie/40/2004 NS4A protein may increase viral pathogenicity. A recombinant virus with a single valine-to-isoleucine substitution (V3I) at position 3 in the low-virulence Mie/41/2002 background (rJEV-Mie41-NS4AV3I) exhibited increased virulence in mice compared with the Mie/41/2002 parent strain. The V3I mutation did not affect virus growth in several cell lines. These results demonstrate that the isoleucine at position 3 in the NS4A protein of Mie/40/2004 is responsible for its high virulence in vivo. This is the first report to show that an amino acid substitution in a flavivirus NS4A protein alters viral pathogenicity in mice.

Detection of higher levels of dengue viremia using FcγR-expressing BHK-21 cells than FcγR-negative cells in secondary infection but not in primary infection

It has been reported that levels of viremia reflect the severity of illness in dengue virus infection. We assessed the levels of viremia in patients with primary and secondary infections, using 2 cell lines: FcγR-expressing BHK cells and FcγR-negative cells. In primary infection, virus titers were at similar levels between FcγR-expressing and FcγR-negative cells. In secondary infection, however, virus titers were ∼10 times higher in FcγR-expressing cells on days 1-6 when compared with FcγR-negative cells, indicating discrepancy in viremia titers between FcγR-expressing and FcγR-negative cells. The results suggest that dengue virus-antibody complexes with infectious capacity exist in patients with secondary infection, and these immune complexes can be detected by using FcγR-expressing cells. As it has been reported that principal target cells of dengue virus infection are FcγR-positive, monocyte/macrophage lineage cells, virus titers determined using FcγR-expressing cells may better reflect the actual viremic conditions in vivo.

Common marmoset (Callithrix jacchus) as a primate model of dengue virus infection: development of high levels of viraemia and demonstration of protective immunity

Dengue virus (DENV) causes a wide range of illnesses in humans: dengue fever (DF), dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). Animal models that constantly develop high levels of viraemia are required for the development of protective and preventive measures. Common marmosets (Callithrix jacchus) demonstrated high levels of viraemia after inoculation with clinical isolates of four serotypes of DENV; in particular, over 10(6) genome copies ml(-1) after inoculation with DENV-2. Non-structural protein 1 and DENV-specific IgM and IgG antibodies were consistently detected. The DENV-2 genome was detected in lymphoid organs including the lymph nodes, spleen and thymus, and also in non-lymphoid organs. DENV antigen was detected by immunohistochemistry in the liver and spleen from inoculated marmosets. Four marmosets were reinoculated with DENV-2 at 33 weeks after primary inoculation with DENV-2. The DENV-2 genome was not detected in any of these marmosets, indicating protection from a secondary infection. The results indicate that common marmosets are highly sensitive to DENV infection, and suggest that marmosets could be a reliable primate model for the evaluation of candidate vaccines.

Serotype-specific and cross-reactive neutralizing antibody responses in cynomolgus monkeys after infection with multiple dengue virus serotypes

Neutralizing antibody responses were examined in monkeys after dengue virus infections. In monkeys that had been infected once or twice with DENV-2, neutralizing antibody was cross-reactive with all four serotypes after secondary or tertiary infection with DENV-3. In monkeys that had been inoculated with DENV-1 and DENV-2 in the primary and secondary infections, neutralizing antibody titers did not increase after tertiary infection with DENV-3. These results indicate that antibody responses after secondary and tertiary infections with different serotypes are cross-reactive with all four serotypes, consistent with what has been observed in humans, and suggest that monkeys are useful for determining neutralizing antibody responses.

Importation of dengue virus type 3 to Japan from Tanzania and Cote d'Ivoire

Travelers can introduce viruses from disease-endemic to non–disease-endemic areas. Serologic and virologic tests confirmed dengue virus infections in 3 travelers returning to Japan: 2 from Tanzania and 1 from Côte d’Ivoire. Phylogenetic analysis of the envelope gene showed that 2 genetically related virus isolates belonged to dengue virus type 3 genotype III.

Novel DNA virus isolated from samples showing endothelial cell necrosis in the Japanese eel, Anguilla japonica

Economic loss due to viral endothelial cell necrosis of eel (VECNE) of Anguilla japonica is a serious problem for the cultured Japanese eel market. However, the viral genome responsible for VECNE is unknown. We recently developed a rapid determination system for viral nucleic acid sequences (RDV) to determine viral genome sequences. In this study, viral DNA fragments were obtained using RDV, and approximately 15-kbp circular full genome sequences were determined using a next-generation sequencing system, overlapping PCR, and Southern blot analysis. One open reading frame (ORF) was homologous to the large T-antigen of polyomavirus; other ORFs have no homology with any nucleic or amino acid sequences of polyomavirus. Therefore, as this DNA virus might comprise a novel virus family, we provisionally named it Japanese eel endothelial cells-infecting virus (JEECV). JEECV was detected in both naturally and experimentally infected eels, suggesting that JEECV potentially causes VECNE.

Re-evaluation of the genome sequence of guinea pig cytomegalovirus

Congenital infection by human cytomegalovirus (HCMV) is a major cause of birth defects and developmental abnormalities. Since guinea pig cytomegalovirus (GPCMV) crosses the placenta and causes infection in utero, GPCMV models are useful for studies of the mechanisms of transplacental transmission. During our characterization of a genomic locus required for GPCMV dissemination in animals, we found that the nucleotide sequence in and around the nearby immediate-early genes in our lineage of GPCMV strain 22122 [designated GPCMV (ATCC-P5)] showed clear differences from that reported previously for the same strain [designated GPCMV (UMN)] passaged extensively in vitro. Since in vitro passaging of HCMV is known to result in genetic alterations, especially in the UL128-UL131A locus, and loss of growth ability in particular cell types, in this study we determined the complete genome sequence of GPCMV (ATCC-P5), which grows efficiently in animals. A total of 359 differences were identified between the genome sequences of GPCMV (UMN) and GPCMV (ATCC-P5), and these resulted in structural differences in 29 protein-encoding regions. In addition, some genes predicted from our analysis but not from GPCMV (UMN) are well conserved among cytomegaloviruses. An additional 18 passages of GPCMV (ATCC-P5) in vitro generated no further marked alterations in these genes or in the locus corresponding to the HCMV UL128-UL131A. Our analyses indicate that the published sequence of GPCMV (UMN) contains a substantial number of sequencing errors and, possibly, some mutations resulting from a long history of passaging in vitro. Our re-evaluation of the genetic content of GPCMV will provide a solid foundation for future studies.

Dengue fever as an acute febrile disease after overseas travel: a report of two cases

Dengue fever (DF) is a relatively common infection in travelers, with about 100 cases being reported annually in Japan, and this number is increasing. We herein describe two patients who developed a fever after returning to Japan from Southeast Asia and who were serologically diagnosed with DF. Patient 1 was a 19-year-old man who spent 6 days in Thailand and developed diarrhea and a fever after returning to Japan. Virological studies showed dengue virus (DV) serotype 3 by reverse transcriptase PCR (RT-PCR), and anti-DV IgM and IgG antibodies were both positive by enzyme-linked immunosorbent assay (ELISA). Patient 2 was a 43-year-old man who spent time in various Asian countries and developed a fever and arthralgia after returning to Japan. Virological studies showed DV serotype 2 by RT-PCR, and anti-DV IgM and IgG antibodies were both positive by ELISA. DF and other febrile diseases, including Chikungunya fever, should be strongly suspected in patients who develop fever after returning to Japan from other Asian countries, irrespective of whether patients remember being bitten by mosquitoes.

Long-term observation of herpes simplex virus type 1 (HSV-1) infection in a child with Wiskott-Aldrich syndrome and a possible reactivation mechanism for thymidine kinase-negative HSV-1 in humans

Herpes simplex virus type 1 (HSV-1) infections in a child with congenital immunodeficiency syndrome were observed over a 10-year period. The child suffered from recurrent and severe HSV-1 mucocutaneous infections. He frequently suffered from acyclovir (ACV)-resistant (ACV(r)) HSV-1 infection in the later phase of his life, especially after the episode of ACV(r) HSV-1 infection. Virological analyses on the HSV-1 isolates recovered from this patient revealed that all the ACV(r) HSV-1 isolates were thymidine kinase (TK)-negative (TK(-)) due to a single cytosine (C) deletion within the 4-C residues (positions 1061 to 1064) in the TK gene, indicating that the recurrent TK(-)/ACV(r) HSV-1 infections throughout the patient's life were due to the identical ACV(r) HSV-1 strain. Furthermore, it was found that the ACV-sensitive (ACV(s)) isolate recovered from the skin lesions that appeared between the episodes of ACV(r) infection at the ages of 8 and 9 contained ACV(r) HSV-1 with the same mutation in the TK gene. These results indicate that, although TK activity is required for reactivation of TK(+)/ACV(s) HSV-1 from latency and TK(-)/ACV(r) HSV-1 is unable to reactivate from latency, the TK(-)/ACV(r) HSV-1 strain isolated herein reactivated in this patient, possibly by using the TK activity induced by the latently co-infected TK(+)/ACV(s) HSV-1.

Evaluation of a quantitative real-time PCR assay for the detection of JC polyomavirus DNA in cerebrospinal fluid without nucleic acid extraction

The JC polyomavirus (JCV) is the causative agent of progressive multifocal leukoencephalopathy (PML), a fatal demyelinating disease. The current diagnostic standard for PML is real-time PCR testing of extracted DNA for assessing the presence of JCV DNA in cerebrospinal fluid (CSF). This study was aimed at evaluating the feasibility of a real-time PCR assay without nucleic acid extraction for the rapid quantification of JCV DNA in CSF. CSF samples were heat-treated or treated with DNAzol Direct, a commercially available reagent for direct PCR, and the performances of the real-time PCR assays using templates obtained by either treatment were compared with that using DNA extracts. JCV DNA was detected in the heat- or DNAzol Direct-treated samples containing only a few copies of the viral genome per reaction, and a linear relationship was noted between the copy number detected and the amount of input virus ascertained by the DNA extraction method. The sensitivities of the assays using the heat and DNAzol Direct treatments were 85.7 and 90.5%, respectively, with the results of the DNA extraction method being used as reference. These data demonstrate that the real-time PCR assay introduced in this study can serve as a rapid and cost-effective method of testing for JCV without DNA extraction and thereby facilitate the assessment of PML.

Human Rickettsia heilongjiangensis infection, Japan

A case of Rickettsia heilongjiangensis infection in Japan was identified in a 35-year-old man who had rash, fever, and eschars. Serum contained R. heilongjiangensis antibodies, and eschars contained R. heilongjiangensis DNA. R. heilongjiangensis was also isolated from ticks in the suspected geographic area of infection.

The effect of global warming on infectious diseases

Global warming has various effects on human health. The main indirect effects are on infectious diseases. Although the effects on infectious diseases will be detected worldwide, the degree and types of the effect are different, depending on the location of the respective countries and socioeconomical situations.

Among infectious diseases, water- and foodborne infectious diseases and vector-borne infectious diseases are two main categories that are forecasted to be most affected. The effect on vector-borne infectious diseases such as malaria and dengue fever is mainly because of the expansion of the infested areas of vector mosquitoes and increase in the number and feeding activity of infected mosquitoes. There will be increase in the number of cases with water- and foodborne diarrhoeal diseases.

Even with the strongest mitigation procedures, global warming cannot be avoided for decades. Therefore, implementation of adaptation measures to the effect of global warming is the most practical action we can take. It is generally accepted that the impacts of global warming on infectious diseases have not been apparent at this point yet in East Asia. However, these impacts will appear in one form or another if global warming continues to progress in future. Further research on the impacts of global warming on infectious diseases and on future prospects should be conducted.

Recent progress in the treatment of Crimean–Congo hemorrhagic fever and future perspectives

Crimean–Congo hemorrhagic fever (CCHF) caused by the CCHF virus, a member of the family Bunyaviridae, genus Nairovirus, is a tick-borne acute viral hemorrhagic fever with a high case–fatality rate. Ribavirin has been used as a treatment for patients with CCHF. Although the efficacy of ribavirin in the treatment of CCHF has not yet been proven conclusively, its use in the early stage of the disease is recommended. A number of clinical and virological insights into CCHF have been revealed. Virus-associated hemophagocytic syndrome has been found to contribute to the exacerbation of CCHF in some patients, and the administration of methylprednisolone at high doses was observationally undertaken in patients with CCHF and virus-associated hemophagocytic syndrome, with promising results. It is expected that effective therapeutics and preventive measures will be developed in the future.

Restoration of replication-defective dengue type 1 virus bearing mutations in the N-terminal cytoplasmic portion of NS4A by additional mutations in NS4B

Flavivirus NS4A has an N-terminal hydrophilic cytoplasmic portion; however, the role of this portion remains poorly understood. In this study, we show that a recombinant dengue type 1 virus (DENV-1) in which a subportion (amino acids 27-34) of the N-terminal portion of NS4A is replaced by the corresponding region from Japanese encephalitis virus (JEV) is defective in replication. Using the defective mutant clone NS4A(27-34(JEV)), we recovered suppressor mutant viruses that carry various non-synonymous mutations. Site-directed mutational analysis indicated that a single non-synonymous mutation in NS4B that is found in the suppressor viruses is sufficient to restore NS4A(27-34(JEV)). Recombinant DENV-1 with single mutations in NS4B had increased growth properties as compared to the wild-type virus and NS4A(27-34(JEV)) virus bearing the same NS4B mutation. Collectively, our results suggest that the NS4B mutation enhanced the growth of DENV-1, irrespective of the sequence of the 27-34 subportion NS4A.