Responses to the Sb epitope contributed to antigenic drift of the influenza A 2009 H1N1 virus.

Immunodominance is recognized as a key factor in the antigenic drift of seasonal influenza viruses. In the immunodominance model, each individual in a population predominantly responds to a single epitope among the five antigenic epitopes of the viral hemagglutinin (HA), driving escape mutations one at a time, and sequential mutations in multiple individuals who respond to different epitopes eventually generate a drifted strain with mutations in epitopes that are targeted by a majority of the population. A focused antibody response to the Sa epitope in people born between 1965 and 1979 was believed to contribute to a mutation at HA residue 163 and the first antigenic drift of the 2009 pandemic influenza A H1N1 virus. A serine-to-threonine mutation at HA residue 185 in the Sb epitope emerged in 2010 even before the 163 mutation. We show here that a large fraction of the population in 2010-2011 had responses to the Sb epitope, as shown by 47% of tested sera having altered titers to the S185T mutant. Responses to the Sb epitope showed an age-specific trend similar to that found for the response to Sa epitope in these subjects. Together, the focused responses to Sa and Sb epitopes may have driven the first antigenic drift of the 2009 pandemic H1N1 virus.

Relative contribution of dengue prM- and E-specific polyclonal antibodies to neutralization and enhancement.

Viral surface proteins, premembrane protein (prM) and envelope (E) protein have been shown to induce a production of antibodies that are involved in both enhancement and neutralization. To explore the feasibility of modifying the relative immune responses to prM and E proteins, four DNA constructs were created and administered into groups of Balb/c mice; pPW01 contains prM and E genes of DENV1, pPW02 contains prM and E genes of DENV2, pPW03 contains DENV1 prM and DENV2 E, and pPW04 contains DENV2 prM and DENV1 E. Exchange of either prM or E from a heterologous serotype does not appear to have an effect on the immunogenicity of the proteins. We have proved that the chimeric pPW03 and pPW04 constructs can produce humoral response in mice. Immunized sera were subjected to neutralization and enhancement assays against DENV2. The results showed that only serotype-specific anti-E antibodies conferred protective function, while the cross-reactive anti-E and anti-prM enhanced infection. In addition, the enhancement of DENV2 infection exhibited a serotype-preference for anti-E antibodies while such response was not observed with anti-prM, reflecting a degree of structural conservation of prM. Taken together, neutralization and enhancement appeared to occur at the same time during the course of infection. Successful prevention of severe symptoms of DENV infection depends on the ability to induce high levels of neutralizing antibodies to subdue the effect of enhancing antibodies.

[Codon optimization of hemagglutinin as a promising tool for improving of the influenza vaccines immunogenicity].

Modification of the codon bias of sequences is a promising tool of the gene expression control. The theoretical basis of the codon optimization is reviewed, data on experiments in changing the viral gene codon bias for purposes of vaccine development are discussed. Research into the field of the influenza vaccine immunogenicity improvement with codon optimization method is reviewed. Prospects of the use of the codon optimization technique for influenza vaccine development are considered.

Effects of the Q223R mutation in the hemagglutinin (HA) of egg-adapted pandemic 2009 (H1N1) influenza A virus on virus growth and binding of HA to human- and avian-type cell receptors.

The 2009 swine-origin influenza A virus (H1N1) and its initial reassortant vaccine strains did not grow well in embryonated eggs. The glutamine to arginine mutation at the amino acid position 223 (Q223R) of the hemagglutinin (HA) gene is the major mutation previously found in egg-adapted 2009 H1N1 strains and shown to enhance viral growth in embryonated eggs. However, the effect of this mutation on the receptor-binding preference had not been directly demonstrated. In this study, the Q223R mutation was shown to change the viral HA binding preference from the human-type receptor, α2,6-linked sialic acid, to the avian-type receptor, α2,3-linked sialic acid; and to enhance the viral growth in embryonated eggs but not in cell culture.

A haplotype of the human CXCR1 gene protective against rapid disease progression in HIV-1+ patients.

Chemokines and their receptors are key factors in the onset and progression of AIDS. Among them, accumulating evidence strongly indicates the involvement of IL-8 and its receptors, CXCR1 and CXCR2, in AIDS-related conditions. Through extensive investigation of genetic variations of the human CXCR1-CXCR2 locus, we identified a haplotype of the CXCR1 gene (CXCR1-Ha) carrying two nonsynonymous single nucleotide polymorphisms, CXCR1_300 (Met to Arg) in the N terminus extracellular domain and CXCR1_142 (Arg to Cys) in the C terminus intracellular domain. Transfection experiments with CXCR1 cDNAs corresponding to the CXCR1-Ha and the alternative CXCR1-HA haplotype showed reduced expression of CD4 and CXCR4 in CXCR1-Ha cells in human osteosarcoma cells as well as in Jurkat and CEM human T lymphocytes. Furthermore, the efficiency of X4-tropic HIV-1(NL4-3) infection was significantly lower in CXCR1-Ha cells than in CXCR1-HA cells. The results were further confirmed by a series of experiments using six HIV-1 clinical isolates from AIDS patients. A genetic association study was performed by using an HIV-1(+) patient cohort consisting of two subpopulations of AIDS with extreme phenotypes of rapid and slow progression of the disease. The frequency of the CXCR1-Ha allele is markedly less frequent in patients with rapid disease onset than those with slow progression (P = 0.0003). These results provide strong evidence of a protective role of the CXCR1-Ha allele on disease progression in AIDS, probably acting through modulation of CD4 and CXCR4 expression.

Genesis of a highly pathogenic and potentially pandemic H5N1 influenza virus in eastern Asia.

A highly pathogenic avian influenza virus, H5N1, caused disease outbreaks in poultry in China and seven other east Asian countries between late 2003 and early 2004; the same virus was fatal to humans in Thailand and Vietnam. Here we demonstrate a series of genetic reassortment events traceable to the precursor of the H5N1 viruses that caused the initial human outbreak in Hong Kong in 1997 (refs 2-4) and subsequent avian outbreaks in 2001 and 2002 (refs 5, 6). These events gave rise to a dominant H5N1 genotype (Z) in chickens and ducks that was responsible for the regional outbreak in 2003-04. Our findings indicate that domestic ducks in southern China had a central role in the generation and maintenance of this virus, and that wild birds may have contributed to the increasingly wide spread of the virus in Asia. Our results suggest that H5N1 viruses with pandemic potential have become endemic in the region and are not easily eradicable. These developments pose a threat to public and veterinary health in the region and potentially the world, and suggest that long-term control measures are required.

Application of HIV-1-green fluorescent protein (GFP) reporter viruses in neutralizing antibody assays.

We made reporter HIV-1 DNA constructs carrying green fluorescent protein (GFP) gene and exchangeable env of subtype E. The recombinant constructs were used to produce infectious reporter viruses, which induced infected cells to emit green fluorescent light and rendered them easily detectable at single cell level. Because the env in this construct can be easily exchanged, viruses with different antigenic epitopes can be made. We used these reporter viruses to set up a neutralizing antibody assay based on fluorescence reduction by flow cytometric measurement. The result of this new assay correlated with the standard infectivity reduction assay using primary isolates. Because this new assay is faster and much less costly than the standard assay using a p24 endpoint and can be performed in peripheral blood mononuclear cells (PBMC), it provides a useful tool for analysis of HIV-1 immune responses.

Quantitation of human immunodeficiency virus type 1 DNA by competitive nested PCR assay.

A quantitative competitive nested PCR assay was developed for quantifying HIV-1 proviral DNA in clinical samples. A competitor DNA was constructed from a conserved region of the HIV-1 gag gene by deleting a sequence of 18 base pairs. We quantitated HIV-1 proviral DNA copy number in clinical samples. Peripheral blood mononuclear cells (PBMCs) from 35 HIV-infected patients with a CD4 count range of 4-728 cell/mm3 were analyzed by this method. The copy numbers of HIV-1 DNA detected ranged between 518 to 67,340 copies per 10(6) CD4+ T-cells. The copy numbers correlated inversely with the CD4 counts.

Target cell populations of human immunodeficiency virus type 1 in peripheral blood lymphocytes with different chemokine receptors at various stages of disease progression.

We studied the distribution of human immunodeficiency virus type 1 (HIV-1) DNA in CCR5-positive and -negative peripheral blood lymphocyte populations in HIV-1-infected individuals. While HIV-1 DNA in the CCR5-positive population showed no correlation with CD4 count, the increase of total HIV-1 DNA with lower CD4 count was mainly contributed by the increase of HIV-1 DNA in the CCR5-negative population. This might indicate the change in coreceptor usage from CCR5 to CXCR4 in later stages of disease progression. However, some of the samples with a high viral DNA load in the CCR5-negative population did not have any characteristic of the V3 loop sequence that is compatible with CXCR4 usage or the syncytium-inducing (SI) phenotype. We also did not find any known characteristic change predictive of the SI phenotype in V1 and V2 sequences. Our findings showed that there might be a shift in target cell populations during disease progression, and this shift was not necessarily associated with the genetic changes characteristic of CXCR4 usage.

Differential susceptibility of quiescent CD4+ lymphocytes to syncytial-inducing and non-syncytial-inducing isolates of HIV-1.

It is generally believed that quiescent CD4+ T cells are not susceptible to HIV-1 infection. However, infection of unstimulated peripheral mononuclear cells by syncytial-inducing (SI) viruses has been shown to be much more efficient than with non-syncytial-inducing (NSI) viruses. This suggested that SI, CXCR4-tropic viruses may be able to infect quiescent CD4+ T cells. We studied the infection of highly purified quiescent CD4+ T cells by SI and NSI viruses. In this article we show that although NSI viruses failed to significantly infect quiescent cells, SI viruses consistently infected these cells and produced viruses upon cellular activation by interleukin-2, 2 to 7 days after initial infection. To examine whether the difference was the result of viral or host factors, we purified CCR5+ quiescent CD4+ T cells and showed that these cells can be infected by dual tropic (R5X4) but not by R5 virus. This indicated that CCR5+ quiescent T cells were also susceptible to HIV-1 infection, and the failure of NSI, CCR5-tropic viruses to infect quiescent cells may be due to some intrinsic properties of these viruses.

TT virus infection in Thailand: prevalence in blood donors and patients with aplastic anemia.

Aplastic anemia has been reported to occur after viral hepatitis of unknown etiology. Recently, TT virus (TTV), a novel DNA virus, was identified in a Japanese patient with posttransfusion non-A-E hepatitis. The prevalence of TTV infection was investigated among blood donors and patients with aplastic anemia in Thailand. Of 99 blood samples from blood donors, 37 tested positive for TTV DNA via semi-nested polymerase chain reaction (PCR) using TTV-specific primers. Seventeen percent of samples from blood donors younger than 20 were positive for TTV DNA, whereas 48% from donors older than 20 were positive. The high prevalence of TTV infection in Thailand is comparable to that reported in China (28%), Mongolia (43%), and Egypt (29%). Forty-two percent of newly diagnosed aplastic anemia patients tested also had TTV DNA in blood. The detection rate of TTV DNA in aplastic anemia patients does not differ significantly from rates in normal blood donors. Our present data thus argue against the role of this novel hepatitis-associated virus in the pathogenesis of aplastic anemia in Thailand. However, larger epidemiological studies may be needed to further evaluate their association.

Differential stability of the mRNA secondary structures in the frameshift site of various HIV type 1 viruses.

For many retroviruses, one or more ribosomal frameshift events are required for translation of the Gag-Pol precursor protein, which is subsequently processed into the structural and enzymatic proteins found in mature virions. A specific nucleotide motif, the slippery sequence, as well as a downstream mRNA secondary structure are generally believed to have roles in the frameshift event. In HIV-1, a particular stem-loop mRNA secondary structure has been proposed for subtype B. On the basis of this model, HIV-1 subtypes A, E, and F were found in this study to share a similar stem-loop structure predicted to have a lower thermodynamic stability as compared with HIV-1 subtypes B, C, and D. The potential impact of this differential thermodynamic stability on HIV-1 replication remains to be determined.

Characterization of sera from subjects infected with HIV-1 subtypes B and E in Thailand by antibody binding and neutralization.

The range and specificity of the humoral immune response to HIV-1 subtypes B and E was investigated in Thai samples. Sera from HIV-1-positive subjects, consisting of subtypes B (n = 24) and E (n = 138), were characterized in relation to the neutralization of primary isolates and T-cell line-adapted (TCLA) strains and binding to monomeric gp120, the CD4/gp120 binding site (BS), and V3 peptides. A subtype-specific pattern of antibody binding was observed with the exception of the CD4/gp 120MN BS. Neutralization of TCLA strains (n = 4) was strongly type-specific (p = .002); however, neutralization of primary isolates (n = 8) was weak and group specific. Thus, the subtype specificity of B and E sera in the neutralization of TCLA strains, but not primary isolates, supports the dominance of the V3 region in TCLA virus neutralization but does not support the distinction of subtypes B and E as discrete neutralization serotypes in Thailand.

PIP: The range and specificity of the humoral immune response to HIV-1 subtypes B and E were investigated in sera and plasma collected from 168 infected patients from Thailand in 1990-94. Specifically, samples were examined for the presence of binding antibody to env regions within monomeric gp120, the CD4/gp120 binding site, and the V3 domain as well as neutralizing antibodies to T-cell line-adapted (TCLA) and primary HIV-1 isolates from subtypes B and E. A subtype-specific pattern of antibody binding was observed with the exception of the CD4/gp120MN binding site. Although neutralization of TCLA strains was highly type-specific, neutralization of primary isolates was weak and group-specific. This finding supports the dominance of the V3 region in TCLA virus neutralization but fails to confirm the distinction of subtypes B and E as discrete neutralization serotypes in Thailand.

Detection and typing of human papilloma virus DNAs in normal cervix, intraepithelial neoplasia and cervical cancer in Bangkok.

We detected and typed HPV-DNA by polymerase chain reaction (PCR) in cervico-vaginal lavages of 102 women with normal cervical cytology, 57 patients with cervical intraepithelial neoplasia (CIN), and 23 cervical cancer patients. HPV-DNA detection and typing by in situ hybridization were also performed in cervical biopsies from CIN lesions and cancers. Five percent of women with normal cervical cytology, 46% of CIN, and 61% of cervical cancer were positive for HPV-DNA. Of CIN cases with positive HPV-DNA, 69, 15, 8, 4 and 4% were HPV-16, -33, -18, -11 and -16/33 respectively. Of cervical cancer cases with positive HPV-DNA, 86% were HPV-16, 7% were HPV-16/33, 7% were HPV-18/31. HPV typing was performed in biopsies from 37 CIN and 18 cervical cancers by in situ hybridization. By this method, 38% of CIN were HPV-DNA positive, of which 71% were HPV-16 and 7% were each of HPV-11, -18, -31 and -33. Thirty-nine percent of cervical cancers were positive, of which 71% and 29% were HPV-16 and HPV-16/18 respectively.

HIV-1 Langerhans' cell tropism associated with heterosexual transmission of HIV.

Heterosexual transmission by vaginal intercourse accounts for most transmission of human immunodeficiency virus-type 1 (HIV-1) in Africa and Asia but is less important in the HIV-1 epidemics of the United States and Western Europe. Epithelial Langerhans' cells (LCs) represent a possible source of initial cell contact for vaginal infection. Fifteen primary isolates of HIV-1 from U.S. homosexuals and 18 HIV-1 isolates from Thailand heterosexuals were evaluated for growth in LCs of U.S. origin. All the viruses from the Thai heterosexuals, which were subtype E, grew more efficiently in the LCs than any of the viruses from the U.S. homosexuals, which are subtype B. These results suggest that LC tropism is associated with the efficiency of heterosexual transmission of HIV.