Oligomerization of Hepatitis C Virus Core Protein is Crucial for Interaction with the Cytoplasmic Domain of E1 Envelope Protein

Hepatitis C virus (HCV) contains two membrane-associated envelope glycoproteins, E1 and E2, which assemble as a heterodimer in the endoplasmic reticulum (ER). In this study, predictive algorithms and genetic analyses of deletion mutants and glycosylation site variants of the E1 glycoprotein were used to suggest that the glycoprotein can adopt two topologies in the ER membrane: the conventional type I membrane topology and a polytopic topology in which the protein spans the ER membrane twice with an intervening cytoplasmic loop (amino acid residues 288 to 360). We also demonstrate that the E1 glycoprotein is able to associate with the HCV core protein, but only upon oligomerization of the core protein in the presence of tRNA to form capsid-like structures. Yeast two-hybrid and immunoprecipitation analyses reveal that oligomerization of the core protein is promoted by amino acid residues 72 to 91 in the core. Furthermore, the association between the E1 glycoprotein and the assembled core can be recapitulated using a fusion protein containing the putative cytoplasmic loop of the E1 glycoprotein. This fusion protein is also able to compete with the intact E1 glycoprotein for binding to the core. Mutagenesis of the cytoplasmic loop of E1 was used to define a region of four amino acids (residues 312 to 315) that is important for interaction with the assembled HCV core. Taken together, our studies suggest that interaction between the self-oligomerized HCV core and the E1 glycoprotein is mediated through the cytoplasmic loop present in a polytopic form of the E1 glycoprotein

Importation of Dengue Virus Type 3 to Japan from Tanzania and Côte 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

Dengue Virus Infection-Enhancing Activity in Serum Samples with Neutralizing Activity as Determined by Using FcγR-Expressing Cells

Dengue has become a major international public health concern in recent decades. There are four dengue virus serotypes. Recovery from infection with one serotype confers life-long protection to the homologous serotype but only partial protection to subsequent infection with other serotypes. Secondary infection with a serotype different from that in primary infection increases the risk of development of severe complications. Antibodies may play two competing roles during infection: virus neutralization that leads to protection and recovery, or infection-enhancement that may cause severe complications. Progress in vaccine development has been hampered by limited understanding on protective immunity against dengue virus infection. We report the neutralization activity and infection-enhancement activity in individuals with dengue in Malaysia. We show that infection-enhancement activity is present when neutralizing activity is absent or low, and cross-reactive neutralizing activity may be hampered by infection-enhancing activity. Conventional assays for titration of neutralizing antibody do not consider infection-enhancement activity. We used an alternative assay that determines the sum of neutralizing and infection-enhancement activity in sera from dengue patients. In addition to providing insights into antibody responses during infection, the alternative assay provides a new platform for the study of immune responses to vaccine

Correction to: A loop-mediated isothermal amplification assay for the detection and quantification of JC polyomavirus in cerebrospinal fluid: a diagnostic and clinical management tool and technique for progressive multifocal leukoencephalopathy

In the original publication of article [1], ‘20 × 101 copies’, which is in the sentence ‘As seen in Fig. 4, the sensitivity of the specimens containing equal to or more than 20 × 10 1 copies in 2 μL of extracted DNA (equivalent to ≥3.0 × 103 copies/mL CSF) was 100% (29/29)’ changes to ‘2.0 × 101 copies’ in results section. The publisher apologizes to the readers and authors for the inconvenience

Dengue virus enhancement activities in serum samples obtained from patients with secondary dengue infection and from selected non acute dengue patients.

a<p>Infecting serotype indicates the DENV serotype detected in the serum sample as determined by RT-PCR.</p>b<p>Fold enhancement values are enhancement ratio calculated by the fornula: mean plaque count at 1∶10 serum dilution/plaque count without addition of serum using FcγR-expressing BHK cell lines.</p>c<p>Underline indicates positive infection-enhancing activity. Positive infection-enhancing activity is defined as fold-enhancement value greater than cut-off value plus 2 times SD in the mean plaque count in the presence of human serum samples as compared to the cut-off value. Cut-off value was determined in the absence of serum.</p>d<p>Serum samples obtained from selected non acute dengue patients.</p

Infection-enhancement activity in serum samples with neutralizing activity to DENV-2.

<p>Six serum samples with high neutralizing activity to DENV-2 at 1∶10 serum dilutions were tested for presence of infection-enhancement activity to DENV-2 at serum dilutions of 1∶10 to 1∶10⁶. (A) serum sample #40, (B) #42, (C) #44 (D) #49, (E) #54 and, (F) #58. Infection-enhancement activity to each DENV serotype was determined by using FcγR-expressing BHK cells and BHK cells by the formula: (mean plaque count at each serum dilution)/(mean plaque count in the absence of human serum samples), and expressed as fold enhancement to DENV-2. Closed bars indicate FcγR-expressing BHK cells and open bars indicate FcγR-negative BHK cells.</p

Level of neutralizing activity in serum samples obtained from patients with secondary acute dengue infection and from selected non acute dengue patients against each of the 4 DENV serotypes.

a<p>Infecting serotype indicates the DENV serotype detected in the serum sample as determined by RT-PCR.</p>b<p>Neutralizing titers (PRNT₅₀) to each of the 4 DENV serotypes for five DENV-1 patients and for two DENV-3 patients were less than 10 (PRNT₅₀<10) by using FcγR-negative BHK cells and FcγR-expressing BHK cells and the results were not included in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0001536#pntd-0001536-t003" target="_blank">Table 3</a>. Neutralizing antibody titer to 4 DENV serotypes were determined by a conventional PRNT method using FcγR-negative BHK cells and FcγR-expressing BHK cells as indicated in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0001536#s2" target="_blank">Materials and Methods</a>.</p>c<p>Neutralizing antibody titers were determined for samples from selected non acute dengue patients.</p

Characteristics of the study populations.

a<p>History of previous flavivirus infection of each patient was not determined.</p>b<p>DENV infection was confirmed as described in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0001536#s2" target="_blank">Materials and Methods</a>. Primary DENV infection was defined as serum samples that were negative for neutralizing to all of the four DENV serotypes at serum dilution of 1∶10.</p>c<p>DENV infection was confirmed as described in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0001536#s2" target="_blank">Materials and Methods</a>. Secondary DENV infection was defined as serum samples that were positive for neutralizing to any of the four DENV serotypes at serum dilution of 1∶10.</p>d<p>A total of 55 serum samples from 55 non acute dengue patients were used. Serum samples were derived from the following categories: DENV genome and NS1 antigen negative (n = 34), and chikungunya virus (CHIKV) genome positive (n = 21).</p