Biomedical subjects

N S Xia

Publications and source records attributed to N S Xia.

6 recordsLinked to original sources

PubMed2006

Establishment of multiple sublineages of H5N1 influenza virus in Asia: implications for pandemic control.

Preparedness for a possible influenza pandemic caused by highly pathogenic avian influenza A subtype H5N1 has become a global priority. The spread of the virus to Europe and continued human infection in Southeast Asia have heightened pandemic concern. It remains unknown from where the pandemic strain may emerge; current attention is directed at Vietnam, Thailand, and, more recently, Indonesia and China. Here, we report that genetically and antigenically distinct sublineages of H5N1 virus have become established in poultry in different geographical regions of Southeast Asia, indicating the long-term endemicity of the virus, and the isolation of H5N1 virus from apparently healthy migratory birds in southern China. Our data show that H5N1 influenza virus, has continued to spread from its established source in southern China to other regions through transport of poultry and bird migration. The identification of regionally distinct sublineages contributes to the understanding of the mechanism for the perpetuation and spread of H5N1, providing information that is directly relevant to control of the source of infection in poultry. It points to the necessity of surveillance that is geographically broader than previously supposed and that includes H5N1 viruses of greater genetic and antigenic diversity.

Animals↗

PubMed2001

A bacterially expressed peptide prevents experimental infection of primates by the hepatitis E virus.

A 23 kDa peptide of the major structural protein of the hepatitis E virus (HEV) expressed in E. coli was found to naturally interact with one another to form homodimers and the peptide was recognized strongly in its dimeric form by HEV reactive human sera. To determine if the peptide may confer protection against HEV infection, three monkeys were immunized with the purified peptide and three were given placebo. Both groups of animals were challenged with 10(5) genome equivalent dose of the homologous strain of HEV. All control animals excreted the virus for 10-12 days beginning 5 days after the infection. The viral genome was also present in the peripheral blood monocyte (PBMC) samples from two animals, but it was not detected in the plasma samples from any of the animals. The infection in two control animals was accompanied by HEV seroconversion. Immunization was found to abrogate HEV stool excretion in two animals and reduced the viral excretion to one day in the third. None of the immunized animals showed detectable HEV in plasma or PBMC samples nor did the animals showed evidence of HEV seroconversion. These results suggested that immunization with the bacterially expressed peptide may prevent experimental infection of primates with the homologous strain of HEV.

Animals↗

PubMed2001

Conformational antigenic determinants generated by interactions between a bacterially expressed recombinant peptide of the hepatitis E virus structural protein.

A 23 kDa peptide locating to amino acid residues 394 to 604 of the major Hepatitis E Virus (HEV) structural protein was expressed in E. coli. This peptide was found to interact naturally with one another to form homodimers and it was recognized strongly and commonly in its dimeric form by HEV reactive human sera. The antigenic activity associated with the dimeric form was abrogated when the dimer was dissociated into monomer and the activity was reconstituted after the monomer was re-associated into dimer again. The dimeric form of the peptide elicited a vigorous antibody response in experimental animals and the resulting antisera were found to cross-react against HEV, effecting an efficient immune capture of the virus. These results attributed the antigenic activity associated with the dimeric form of the peptide to conformational antigenic determinants generated as a result of interaction between the peptide molecules. It is suggested that some of these antigenic determinants may be expressed by the HEV capsid and raised the possibility of this bacterially expressed peptide as an HEV vaccine candidate.

Animals↗

PubMed2001

Prokaryotical expression of structural and non-structural proteins of hepatitis G virus.

AIM: To study the epitope distribution of hepatitis G virus (HGV) and to seek for the potential recombinant antigens for the development of HGV diagnostic reagents. METHODS: Fourteen clones encompassing HGV gene fragments from core to NS3 and NS5 were constructed using prokaryotic expression vector pRSET and (or) pGEX, and expressed in E.coli. Western blotting and ELISA were used to detect the immunoreactivity of these recombinant proteins. RESULTS: One clone with HGV fragment from core to E1 (G1), one from E2 (G31), three from NS3 (G6, G61, G7), one from NS5B (G821) and one chimeric fragment from NS3 and NS5B (G61-821) could be expressed well and showed obvious immunoreactivity by Western blotting. One clone with HGV framment from NS5B (G82) was also well expressed, but could not show immunoreactivity by Western blotting. No obvious expression was found in the other six clones. All the expressed recombinant proteins were in inclusion body form, except the protein G61 which could be expressed in soluble form. Further purified recombinant proteins G1, G31, G61, G821 and G61-821 were detected in indirected ELISA as coating antigen respectively. Only recombinant G1 could still show immunoreactivity, and the other four recombinant proteins failed to react to the HGV antibody positive sera. Western blotting results indicated that the immunoactivity of these four recombinant proteins were lost during purification. CONCLUSION: Core to E1, E2, NS3 and NS5 fragment of HGV contain antigenic epitopes, which could be produced in prokaryotically expressed recombinant proteins. A high-yield recombinant protein (G1) located in HGV core to E1 could remain its epitope after purification, which showed the potential that G1 could be used as a coating antigen to develop an ELISA kit for HGV specific antibody diagnosis.

Blotting, Western↗

PubMed2000

[Construction and application of an Escherichia coli high effective expression vector with an enhancer].

In this study, we constructed a high effective fusion expression-vector in E. coli. This vector, pTO-T7, was characterized as: (1) an enhancer from tobacco mosaic virus (TMV), omega sequence, was ligated in front of a T7 promoter in the regulatory sequence; (2) the multi-cloning sites include eight restriction enzyme sites. It can facilitate fusion or nonfusion expression; (3) the N terminal of a fusion protein starts with the first 12 amino acids of T7 gene 10, and the C terminal is the hexahistidine tag; (4) kanmycin resistance gene was used as a selective marker. EGFP gene was inserted into pTO-T7 vector as a reporter gene. Expression data showed that fused-EGFP accounted to more than 50% of the total E. coli protein, and more than 90% of which was soluble. The fluorescence characters of fused-EGFP were also studied. The expression yield of target gene from plasmid pTO-T7 compared with that from pT-T7 without omega sequence suggested that omega sequence in pTO-T7 can improve the expression of target gene significantly.

Base Sequence↗

PubMed1994

cDNA cloning of c33-c antigen gene derived from NS3 region of Chinese HCV genome, expression in Escherichia coli and development of HCV EIA second-generation diagnostic kit.

A cDNA fragment of about 860 bp corresponding to the c33-c gene in the non-structural region 3 (NS3) of HCV genome was obtained from one plasma derived from a Chinese HCV carrier who came from Tai' an of Shandong Province, China by the application of reverse transcription (RT) and polymerase chain reaction (PCR) techniques. After the sequence of the cDNA fragment was determined and compared with the equivalent region of the HCV-I (HCV-US) and HCV-II (HCV-BK) genomes, the nucleotide/amino acid sequence homologies were found to be 79.2%/91.3%/ and 91.3%/93.9%, respectively. The prokaryotic expression vector pBV220 was employed for the overproduction of c33-c native recombinant protein in E. coli cells. The expression products were detected by enzyme-linked immunosorbent assay (ELISA) and Western blotting with antisera of chronic hepatitis C patients, and a molecular weight 31 kD of c33-c viral protein was shown to account for 14% of the total cellular soluble proteins. This product was extracted from the bacterial lysate by lysozyme, Triton X-100 and urea treatment, and purified through ion exchange chromatography. The purified c33-c protein combined with a branch peptide MAP-C-19 representing immunodominant epitopes on the nucleocapsid region of HCV genome was used to develop a Chinese HCV EIA 2nd-generation diagnostic kit for the detection of anti-HCV antibodies. Its specificity, sensitivity and reproducibility were all in keeping with the indexes of the national standard for the quality control of the HCV diagnostic kit. The agreement rate between our kit and Abbott company's HCV EIA second-generation diagnostic kit was 99.33%, and the identified rate of positive anti-HCV of our kit was 2% more than that of the Abbott company's kit.

Amino Acid Sequence↗