Genetic recombination is a well-known phenomenon for enteroviruses. To investigate the genetic characterization and the potential recombination of enterovirus 71 (EV71) circulating in China, we determined the 16 complete genome sequences of EV71 isolated from Hand Foot Mouth Disease (HFMD) patients during the large scale outbreak and non-outbreak years since 1998 in China. The full length genome sequences of 16 Chinese EV71 in present study were aligned with 186 genome sequences of EV71 available from GenBank, including 104 China mainland and 82 international sequences, covering the time period of 1970–2011. The oldest strains of each subgenotype of EV71 and prototype strains of HEV-A were included to do the phylogenetic and Simplot analysis. Phylogenetic analysis indicated that all Chinese strains were clustered into C4 subgenotype of EV71, except for HuB/CHN/2009 clustered into A and Xiamen/CHN/2009 clustered into B5 subgenotype. Most of C4 EV71 were clustered into 2 predominant evolutionary branches: C4b and C4a evolutionary brunches. Our comprehensive recombination analysis showed the evidence of genome recombination of subgenotype C4 (including C4a and C4b) sequences between structural genes from genotype C EV71 and non-structural genes from the prototype strains of CAV16, 14 and 4, but the evidence of intratypic recombination between C4 strains and B subgenotype was not enough strong. This intertypic recombination C4 viruses were first seen in 1998 and became the predominant endemic viruses circulating in China mainland for at least 14 years. A shift between C4a and C4b evolutionary brunches of C4 recombination viruses were observed, and C4a viruses have been associated with large scale nationwide HFMD outbreak with higher morbidity and mortality since 2007.
Mesothelial cell injury plays an important role in peritoneal fibrosis. Present clinical therapies aimed at alleviating peritoneal fibrosis have been largely inadequate. Mesenchymal stem cells (MSCs) are efficient for repairing injuries and reducing fibrosis. This study was designed to investigate the effects of MSCs on injured mesothelial cells and peritoneal fibrosis.
Rat bone marrow-derived MSCs (5 ×106) were injected into Sprague-Dawley (SD) rats via tail vein 24 h after peritoneal scraping. Distinct reductions in adhesion formation; infiltration of neutrophils, macrophage cells; number of fibroblasts; and level of transforming growth factor (TGF)-β1 were found in MSCs-treated rats. The proliferation and repair of peritoneal mesothelial cells in MSCs-treated rats were stimulated. Mechanically injured mesothelial cells co-cultured with MSCs in transwells showed distinct increases in migration and proliferation. In vivo imaging showed that MSCs injected intravenously mainly accumulated in the lungs which persisted for at least seven days. No apparent MSCs were observed in the injured peritoneum even when MSCs were injected intraperitoneally. The injection of serum-starved MSCs-conditioned medium (CM) intravenously reduced adhesions similar to MSCs. Antibody based protein array of MSCs-CM showed that the releasing of TNFα-stimulating gene (TSG)-6 increased most dramatically. Promotion of mesothelial cell repair and reduction of peritoneal adhesion were produced by the administration of recombinant mouse (rm) TSG-6, and were weakened by TSG-6-RNA interfering.
Collectively, these results indicate that MSCs may attenuate peritoneal injury by repairing mesothelial cells, reducing inflammation and fibrosis. Rather than the engraftment, the secretion of TSG-6 by MSCs makes a major contribution to the therapeutic benefits of MSCs.
In China, rubella vaccination was introduced into the national immunization program in 2008, and a rubella epidemic occurred in the same year. In order to know whether changes in the genotypic distribution of rubella viruses have occurred in the postvaccination era, we investigate in detail the epidemiological profile of rubella in China and estimate the evolutionary rate, molecular clock phylogeny, and demographic history of the predominant rubella virus genotypes circulating in China using Bayesian Markov chain Monte Carlo phylodynamic analyses. 1E was found to be the predominant rubella virus genotype since its initial isolation in China in 2001, and no genotypic shift has occurred since then. The results suggest that the global 1E genotype may have diverged in 1995 and that it has evolved at a mutation rate of 1.65 × 10−3 per site per year. The Chinese 1E rubella virus isolates were grouped into either cluster 1 or cluster 2, which likely originated in 1997 and 2006, respectively. Cluster 1 viruses were found in all provinces examined in this study and had a mutation rate of 1.90 × 10−3 per site per year. The effective number of infections remained constant until 2007, and along with the introduction of rubella vaccine into the national immunization program, although the circulation of cluster 1 viruses has not been interrupted, some viral lineages have disappeared, and the epidemic started a decline that led to a decrease in the effective population size. Cluster 2 viruses were found only in Hainan Province, likely because of importation.
The incidence of measles in China from 1991 to 2008 was reviewed, and the nucleotide sequences from 1507 measles viruses (MeV) isolated during 1993 to 2008 were phylogenetically analyzed. The results showed that measles epidemics peaked approximately every 3 to 5 years with the range of measles cases detected between 56,850 and 140,048 per year. The Chinese MeV strains represented three genotypes; 1501 H1, 1 H2 and 5 A. Genotype H1 was the predominant genotype throughout China continuously circulating for at least 16 years. Genotype H1 sequences could be divided into two distinct clusters, H1a and H1b. A 4.2% average nucleotide divergence was found between the H1a and H1b clusters, and the nucleotide sequence and predicted amino acid homologies of H1a viruses were 92.3%–100% and 84.7%–100%, H1b were 97.1%–100% and 95.3%–100%, respectively. Viruses from both clusters were distributed throughout China with no apparent geographic restriction and multiple co-circulating lineages were present in many provinces. Cluster H1a and H1b viruses were co-circulating during 1993 to 2005, while no H1b viruses were detected after 2005 and the transmission of that cluster has presumably been interrupted. Analysis of the nucleotide and predicted amino acid changes in the N proteins of H1a and H1b viruses showed no evidence of selective pressure. This study investigated the genotype and cluster distribution of MeV in China over a 16-year period to establish a genetic baseline before MeV elimination in Western Pacific Region (WPR). Continuous and extensive MeV surveillance and the ability to quickly identify imported cases of measles will become more critical as measles elimination goals are achieved in China in the near future. This is the first report that a single endemic genotype of measles virus has been found to be continuously circulating in one country for at least 16 years.
Emerging epidemics of hand-foot-and-mouth disease (HFMD) associated with enterovirus 71 (EV71) has become a serious concern in mainland China. It caused 126 and 353 fatalities in 2008 and 2009, respectively. The epidemiologic and pathogenic data of the outbreak collected from national laboratory network and notifiable disease surveillance system. To understand the virological evolution of this emerging outbreak, 326 VP1 gene sequences of EV71 detected in China from 1987 to 2009 were collected for genetic analyses. Evidence from both traditional and molecular epidemiology confirmed that the recent HFMD outbreak was an emerging one caused by EV71 of subgenotype C4. This emerging HFMD outbreak is associated with EV71 of subgenotype C4, circulating persistently in mainland China since 1998, but not attributed to the importation of new genotype. Originating from 1992, subgenotype C4 has been the predominant genotype since 1998 in mainland China, with an evolutionary rate of 4.6∼4.8×10−3 nucleotide substitutions/site/year. The phylogenetic analysis revealed that the majority of the virus during this epidemic was the most recent descendant of subgenotype C4 (clade C4a). It suggests that the evolution might be one of the potential reasons for this native virus to cause the emerging outbreak in China. However, strong negative selective pressure on VP1 protein of EV71 suggested that immune escape might not be the evolving strategy of EV71, predicting a light future for vaccine development. Nonetheless, long-term antigenic and genetic surveillance is still necessary for further understanding.
The primary immunogenic component of the currently approved anthrax vaccine is the protective antigen (PA) unit of the binary toxin system. PA-specific antibodies neutralize anthrax toxins and protect against infection. Recent research has determined that in humans, only antibodies specific for particular determinants are capable of effecting toxin neutralization, and that the neutralizing epitopes recognized by these antibodies are distributed throughout the PA monomer. The mechanisms by which the majority of these epitopes effect neutralization remain unknown. In this report we investigate the process by which a human monoclonal antibody specific for the amino-terminal domain of PA neutralizes lethal toxin in an in vitro assay of cytotoxicity, and find that it neutralizes LT by blocking the requisite cleavage of the amino-terminal 20 kD portion of the molecule (PA20) from the remainder of the PA monomer. We also demonstrate that the epitope recognized by this human monoclonal does not encompass the 166RKKR169 furin recognition sequence in domain 1 of PA.
anthrax; Bacillus anthracis; antibody epitope; paratope; human monoclonal antibody; protective antigen; furin; toxin neutralization
Molecular characterization of wild-type measles viruses in China during 1995-2004 demonstrated that genotype H1 was endemic and widely distributed throughout the country. H1-associated cases and outbreaks caused a resurgence of measles beginning in 2005. A total of 210,094 measles cases and 101 deaths were reported by National Notifiable Diseases Reporting System (NNDRS) and Chinese Measles Laboratory Network (LabNet) from 2006 to 2007, and the incidences of measles were 6.8/100,000 population and 7.2/100,000 population in 2006 and 2007, respectively. Five hundred and sixty-five wild-type measles viruses were isolated from 24 of 31 provinces in mainland China during 2006 and 2007, and all of the wild type virus isolates belonged to cluster 1 of genotype H1. These results indicated that H1-cluster 1 viruses were the predominant viruses circulating in China from 2006 to 2007. This study contributes to previous efforts to generate critical baseline data about circulating wild-type measles viruses in China that will allow molecular epidemiologic studies to help measure the progress made toward China's goal of measles elimination by 2012.
Protective antigen (PA) is the cell surface recognition unit of the binary anthrax toxin system and the primary immunogenic component in both the current and proposed “next-generation” anthrax vaccines. Several studies utilizing animal models have indicated that PA-specific antibodies, acquired by either active or passive immunization, are sufficient to protect against infection with Bacillus anthracis. To investigate the human antibody response to anthrax immunization, we have established a large panel of human PA-specific monoclonal antibodies derived from multiple individuals vaccinated with the currently approved anthrax vaccine BioThrax. We have determined that although these antibodies bind PA in standard binding assays such as enzyme-linked immunosorbent assay, Western blotting, capture assays, and dot blots, less than 25% are capable of neutralizing lethal toxin (LT) in vitro. Nonneutralizing antibodies also fail to neutralize toxin when present in combination with other nonneutralizing paratopes. Although neutralizing antibodies recognize determinants throughout the PA monomer, they are significantly less common among those paratopes that bind to the immunodominant amino-terminal portion of the molecule. These findings demonstrate that PA binding alone is not sufficient to neutralize LT and suggest that for an antibody to effectively block PA-mediated toxicity, it must bind to PA such that one of the requisite toxin functions is disrupted. A vaccine design strategy that directed a higher percentage of the antibody response toward neutralizing epitopes may result in a more efficacious vaccine for the prevention of anthrax infection.
Protective antigen (PA) is the cell surface recognition moiety of the Bacillus anthracis A-B toxin system, and the active immunogenic component in the currently licensed human anthrax vaccine (BioThrax™, or AVA). The serum antibody response to the PA protein is polyclonal and complex both in terms of the antibody combining sites utilized to bind PA and the PA-associated epitopes recognized. We have cloned, sequenced, and expressed a large panel of PA-specific human monoclonal antibodies from 7 AVA-immunized donors. Dot blots, Western blots, and radio-labeled antigen capture assays employing both proteolytic fragments of PA and engineered PA sub-domain fusion proteins were used to determine the region (domain) of the PA monomer to which each of the cloned human antibodies bound. The domain specificity of the isolated monoclonals was highly biased towards the amino-terminal 20kd fragment of PA (PA20), with the majority (62%) of independently arising antibody clones reacting with determinants located on this PA fragment. A similar bias in domain specificity was also demonstrated in the serum response of AVA-vaccinated donors. Since PA20 is cleaved from the remainder of the monomer rapidly following cell surface binding and has no known role in the intoxication process, the immunodominance of PA20-associated epitopes may directly affect the efficacy of PA-based anthrax vaccines.
The active component of the licensed human anthrax vaccine (BioThrax™, or AVA) is a Bacillus anthracis toxin known as protective antigen (PA). Second generation anthrax vaccines currently under development are also based on a recombinant form of PA. Since the current and future anthrax vaccines are based on this toxin, it is important that the immunobiology of this protein in vaccinated humans be understood in detail. We have isolated and analyzed the PA-specific antibody repertoire from an AVA-vaccinated individual. When examined at the clonal level, we find an antibody response that is complex in terms of the combinatorial elements and immunoglobulin variable genes employed. All PA-specific antibodies had undergone somatic hypermutation and class switch recombination, both signs of affinity maturation. Although the antigenic epitopes recognized by the response were distributed throughout the PA monomer, the majority of antibodies arising in this individual following vaccination recognize determinants located on the amino-terminal (PA20) sub-domain of the molecule. This latter finding may have implications for the rational design of future PA-based anthrax vaccines.
Bacillus anthracis; protective antigen; PA; antibody repertoire; repertoire analysis; anthrax; vaccine; human immune response; human monoclonal antibody
This report describes the genetic characterization of 297 wild-type measles viruses that were isolated in 24 provinces of China between 1995 and 2003. Phylogenetic analysis of the N gene sequences showed that all of the isolates belonged to genotype H1 except 3 isolates, which were genotype A. The nucleotide sequence and predicted amino acid homologies of the 294-genotype H1 strains were 94.7%–100% and 93.3%–100%, respectively. The genotype H1 isolates were divided into 2 clusters, which differed by approximately 2.9% at the nucleotide level. Viruses from both clusters were distributed throughout China with no apparent geographic restriction and multiple co-circulating lineages were present in many provinces. Even though other measles genotypes have been detected in countries that border China, this report shows that genotype H1 is widely distributed throughout the country and that China has a single, endemic genotype. This important baseline data will help to monitor the progress of measles control in China.
It has been suggested that codon insertion and/or deletion may represent a mechanism that, along with hypermutation, contributes to the affinity maturation of antibodies. We used repertoire cloning to examine human antibodies directed against 3 carbohydrate antigens and 1 protein antigen for the presence of such modifications. We find that both the insertion and deletion of codons occur frequently in antigen-specific responses following vaccination. Codon insertions and deletions were observed most often in the complementarity determining regions, and less frequently in the framework regions, of VH, Vκ, and Vλ gene segments, and involved motifs known to be preferred targets of somatic hypermutation. Clonal lineage analysis shows that these events occur through out the course of the somatic maturation of individual antibody clones. We also determined that these alterations of paratope structure have varying effects on the relative affinity of the binding site for its cognate antigen.
This article was reviewed by Mark Shlomchik, Deborah Dunn-Walters (nominated by Dr. Andrew Macpherson), and Rachel M. Gerstein.
Open peer review
Reviewed by Mark Shlomchik, Deborah Dunn-Walters (nominated by Dr. Andrew Macpherson), and Rachel M. Gerstein. For the full reviews, please go to the Reviewers' comments section.
Combinatorial cloning and expression library analysis were used to determine the expressed human antibody repertoire specific for the capsular polysaccharide (PS) of Streptococcus pneumoniae serotype 6B. Sequence analysis of 55 6B-specific antibody Fab fragments isolated from six vaccinated donors reveal that different individuals used a variety of heavy and light chain germ line variable (V) region genes to form pneumococcal capsular PS (PPS) 6B-specific paratopes. Within each donor, however, the response was more restricted, with five of the six donors using at most one or two gene pairs to form combining sites. Analysis also indicated that although the response in each donor was oligoclonal in terms of variable gene usage, the combination of extensive somatic hypermutation, deletion of germ line-encoded residues, insertion of non-germ line-encoded residues, and intraclonal isotype switching generated a surprising degree of paratope diversity within the individuals analyzed. In contrast to previously studied PS-specific responses, we find that the PPS 6B repertoire makes use of a diverse collection of heavy-chain and light-chain V region gene products to form specific paratopes, with no apparent tendency for conservation of immunoglobulin gene usage between individuals.
Combinatorial cloning and expression library analysis were used to isolate human antibody Fab fragments specific for the capsular polysaccharide of Streptococcus pneumoniae serotype 23F. Thirty 23F-specific Fabs were isolated from seven vaccinated donors, and the sequences of the heavy (H)- and light (L)-chain variable regions were determined. All individuals utilized either the Vκ A23 L chain, the Vκ L6 L chain, or both chains in forming the 23F-specific combining site. Vκ A23 L chains paired primarily with VH3-23 H chains. Vκ L6 L chains were more promiscuous in heavy-chain usage between individuals. Both H and L chains were mutated, primarily in the complementarity-determining regions, compared to their closest germ line counterpart, suggesting a recall response that has undergone affinity maturation. H-chain isotypes were reflective of those found in the serum. Shared somatic modifications demonstrated that immunoglobulin G2 (IgG2) and IgA antibodies arose from the same somatically matured B cell. Our results indicate that the response to the serotype 23F pneumococcal capsular polysaccharide is oligoclonal within the individual, with one or two paratope families accounting for the majority of expressed antibody. We also determined that, in spite of the combinatorial diversity available to the immune system, the 23F-specific response is highly restricted at the population level, with the same two L-chain-determined paratope families recurring in all individuals. Lastly, analysis of the isolated Fabs indicate all have undergone extensive somatic mutation, as well as class switch, maturational events that presumably require the participation of T cells.