First description of Mycobacterium tuberculosis and M. canettii concomitant infection: report of two cases

We report the first two cases of tuberculous coinfection with Mycobacterium tuberculosis and M. canettii. Both patients were young Djiboutian females with pulmonary tuberculosis (TB). One had a miliary pattern with concomitant human immunodeficiency virus infection. Both recovered completely with a standard four-drug anti-tuberculosis treatment regimen. Due to the different natural reservoirs and routes of infection of these two strains, our study supports the common belief that multiple strains of infection in TB are related to superinfection rather than concomitant infection.

Genotyping of Pseudomonas aeruginosa reveals high diversity, stability over time and good outcome of eradication

BACKGROUND

Genotyping of Pseudomonas aeruginosa (P.a) is used for surveillance at our CF clinic.

METHODS

P.a from 1999 to 2012 were analysed, using pulsed-field gel electrophoresis (PFGE) and multiple-locus variable number of tandem repeats analysis (MLVA).

RESULTS

Among 232 isolates from 104 patients, we identified 78 unique strains, of which 56 were isolated from individual patients. The B-clone was isolated from 13 patients and the camp transmission clone J-strains from 8 patients at the start of the study. There was no indication of transmission within the clinic. PFGE and MLVA clone identification was in 91% agreement. For patients who provided more than 2 P.a isolates, similar strains were identified over time for 45/49 chronically- and for 6/16 intermittently-colonized patients despite, periods of no detectable P.a after eradication therapy.

CONCLUSIONS

Analyses revealed high genotypic diversity, acceptable outcome of eradication therapy and no indication of cross-infection at the CF centre.

A new highly discriminatory multiplex capillary-based MLVA assay as a tool for the epidemiological survey of Pseudomonas aeruginosa in cystic fibrosis patients

Multiple locus variable number of tandem repeats (VNTR) analysis (MLVA) has been shown to provide a high level of information for epidemiological investigations and the follow-up of Pseudomonas aeruginosa chronic infection. In the present study, an automatized MLVA assay has been developed for the analysis of 16 VNTRs in two multiplex polymerase chain reactions (PCRs), followed by capillary electrophoresis. The result in the form of a code is directly usable for clustering analyses. This MLVA-16(Orsay) scheme was applied to the genotyping of 83 isolates from eight cystic fibrosis patients, demonstrating that the same genotype persisted during eight years of chronic infection in the majority of cases. Comparison with pulsed-field gel electrophoresis (PFGE) analysis showed that both methods were congruent, MLVA providing, in some cases, additional informativity. The evolution of strains during long-term infection was revealed by the presence of VNTR variants.

Molecular epidemiology of human and animal tuberculosis in Ibadan, Southwestern Nigeria

From 2005 to 2007, Mycobacterium tuberculosis complex (MTC) strains were isolated from cattle, goats and pigs samples collected at the Bodija abattoir and from human samples from tuberculosis patients and livestock traders at the Akinyele cattle market in Ibadan, Southwestern Nigeria. Seventy four isolates obtained from humans (24) and livestock (50) were identified as MTC strains. Thirty two isolates were spoligotyped. Nineteen of these 32 isolates were identified as M. tuberculosis whilst 13 were identified as Mycobacterium bovis. M. bovis was isolated from two humans, whereas M. tuberculosis was isolated from a bovine, a pig and a goat. All the M. bovis isolates identified in this study belonged to the Africa 1 clonal complex. Multiple locus VNTR [variable number of tandem repeats] analysis (MLVA) was carried out on the 74 isolates. Three major clusters were defined. Group A consisted of 24 M. tuberculosis isolates (MLVA genotypes 1-18). One strain was isolated from a bovine and one from a pig. Group B consisted of 49 M. bovis strains (MLVA genotypes 19-48), mainly of cattle origin but also included four goat, nine pig and two human isolates. Group C consisted of a single M. tuberculosis isolate (MLVA genotype 49) obtained from a goat. Spoligotyping and MLVA confirmed it as clustering with the East Africa Indian clade found in humans in Sudan and the Republic of Djibouti. The isolation of three M. tuberculosis strains from livestock raises the question of their epidemiological importance as a source of infection for humans.

[Performances of the assay MTBDRplus(®) in the surveillance of rifampicin resistance in Mycobacterium tuberculosis]

The purpose of the survey was the routine assessment of the MTBDRplus(®) kit performance in the determination and characterization of Mycobacterium tuberculosis resistance to rifampicin. The survey was carried out on a collection of 144 strains (126 of which were resistant to rifampicin) isolated on patients from 15 countries. Sensitivity to antituberculosis drugs was determined by a liquid culture system and the reference method was the amplification and sequencing of a target region of the rpoB gene whose mutations are responsible for rifampicin resistance (codons 507 to 533). The assessed kit was based on a reverse hybridization technique using eight overlapping probes covering the target region and four probes representing the most-frequently observed mutations. The assay performance was found excellent, specificity: 100%, sensitivity: 99.2%; 17 mutations affecting 10 codons were reported, two of which were newly identified.

Clinical characteristics of the smooth tubercle bacilli 'Mycobacterium canettii' infection suggest the existence of an environmental reservoir

Over a 3-year follow-up, 30 out of the 318 unique Mycobacterium tuberculosis complex isolates recovered in the Republic of Djibouti had a smooth-type morphology and were Niacine-negative, the characteristics of 'Mycobacterium canettii' strains. Unlike M. tuberculosis, 'M. canettii' grew on nutrient-poor media at 30°C, and possessed characteristic lipids. They were isolated from respiratory and extra-respiratory sites from patients with typical forms of tuberculosis. Most cases resolved with antibiotic therapy but in two human immunodeficiency virus-positive patients 'M. canettii' infection led to septicaemia and death. No cases of human-to-human transmission were observed. The proportion of tuberculosis cases caused by 'M. canettii' was higher among French patients than among Djiboutian patients. Patients with 'M. canettii' were significantly younger than those with tuberculosis caused by other M. tuberculosis complex strains. Smooth tubercle bacilli could be misidentified as non-tuberculous mycobacteria and appear to be limited to the Horn of Africa. Their characteristics are consistent with the existence of non-human sources of infection.

CRISPR elements in Yersinia pestis acquire new repeats by preferential uptake of bacteriophage DNA, and provide additional tools for evolutionary studies

The remarkable repetitive elements called CRISPRs (clustered regularly interspaced short palindromic repeats) consist of repeats interspaced with non-repetitive elements or 'spacers'. CRISPRs are present in both archaea and bacteria, in association with genes involved in DNA recombination and repair. In the Yersinia pestis genome, three such elements are found at three distinct loci, one of them being highly polymorphic. The authors have sequenced a total of 109 alleles of the three Y. pestis CRISPRs and they describe 29 new spacers, most being specific to one isolate. In nine strains of Yersinia pseudotuberculosis, 132 spacers were found, of which only three are common to Y. pestis isolates. In Y. pestis of the Orientalis biovar investigated in detail here, deletion of motifs is observed but it appears that addition of new motifs to a common ancestral element is the most frequent event. This takes place at the three different loci, although at a higher rate in one of the loci, and the addition of new motifs is polarized. Interestingly, the most recently acquired spacers were found to have a homologue at another locus in the genome, the majority of these inside an inactive prophage. This is believed to be the first time that the origin of the spacers in CRISPR elements has been explained. The CRISPR structure provides a new and robust identification tool.

Identification of variable-number tandem-repeat loci in Leptospira interrogans sensu stricto

Leptospira interrogans sensu stricto is responsible for the most frequent and severe cases of human leptospirosis. The epidemiology and clinical features of leptospirosis are usually associated with the serovars and serogroups of Leptospira. Because of the difficulties associated with serological identification of Leptospira strains, we evaluated a novel PCR-based method for typing L. interrogans serovars. Based upon the genome sequence of L. interrogans serovar Lai type strain 5660, 44 loci were analyzed by PCR for their variability in size due to the presence of variable-number tandem repeats (VNTR). Seven VNTR loci were found to be powerful markers for serovar identification, epidemiology, and phylogenetic studies of L. interrogans. This rapid and easy method should greatly contribute to a better knowledge of the epidemiology of Leptospira.

Tandem repeats analysis for the high resolution phylogenetic analysis of Yersinia pestis

Background

Yersinia pestis, the agent of plague, is a young and highly monomorphic species. Three biovars, each one thought to be associated with the last three Y. pestis pandemics, have been defined based on biochemical assays. More recently, DNA based assays, including DNA sequencing, IS typing, DNA arrays, have significantly improved current knowledge on the origin and phylogenetic evolution of Y. pestis. However, these methods suffer either from a lack of resolution or from the difficulty to compare data. Variable number of tandem repeats (VNTRs) provides valuable polymorphic markers for genotyping and performing phylogenetic analyses in a growing number of pathogens and have given promising results for Y. pestis as well.

Results

In this study we have genotyped 180 Y. pestis isolates by multiple locus VNTR analysis (MLVA) using 25 markers. Sixty-one different genotypes were observed. The three biovars were distributed into three main branches, with some exceptions. In particular, the Medievalis phenotype is clearly heterogeneous, resulting from different mutation events in the napA gene. Antiqua strains from Asia appear to hold a central position compared to Antiqua strains from Africa. A subset of 7 markers is proposed for the quick comparison of a new strain with the collection typed here. This can be easily achieved using a Web-based facility, specifically set-up for running such identifications.

Conclusion

Tandem-repeat typing may prove to be a powerful complement to the existing phylogenetic tools for Y. pestis. Typing can be achieved quickly at a low cost in terms of consumables, technical expertise and equipment. The resulting data can be easily compared between different laboratories. The number and selection of markers will eventually depend upon the type and aim of investigations.

Characterization of a tandem repeat polymorphism in Legionella pneumophila and its use for genotyping

We have analyzed the variability of minisatellite sequences (also called variable-number tandem repeats [VNTRs]) in the genome of Legionella pneumophila. Based upon the genome sequence of the Philadelphia-1 strain (serogroup 1), 25 minisatellites were selected and their polymorphisms were analyzed by PCR with the DNA of serogroup 1 to 14 reference strains. For 22 markers, a PCR product of the expected size was found with the DNA of the Philadelphia-1 strain. Most of these markers did not amplify the DNA of other Legionella species or other bacteria used as controls. A polymorphism was observed for seven markers among the L. pneumophila strains tested. To check whether these markers could be used to compare strains of L. pneumophila, we analyzed two groups of isolates from clinical and environmental samples which had been independently genotyped by other methods. The results showed that, for the isolates in these two sets of samples, VNTR typing is as informative as pulsed-field gel electrophoresis for comparison of strains. Sequencing of one minisatellite from 14 reference strains was performed. Comparison of the sequences allowed a classification and confirmed the existence of subspecies of L. pneumophila. We also tested the usefulness of one very polymorphic marker as a tool for the rapid screening of colonies grown from water samples. This allowed the rapid identification of the L. pneumophila colonies and gave a first hint as to the presence of several strains in a single sample.

A dominant modifier of transgene methylation is mapped by QTL analysis to mouse chromosome 13

The single-copy hepatitis B virus transgene in the E36 transgenic mouse strain undergoes methylation changes in a parent-of-origin, tissue, and strain-specific fashion. In a C57BL/6 background, the paternally transmitted transgene is methylated in 30% of cells, whereas it is methylated in more than 80% of cells in (BALB/c x C57BL/6) F1 mice. We established previously that several genetic factors were likely to contribute to the transgene methylation profile, some with demethylating and some with de novo methylating activities. Using quantitative trait loci (QTL) mapping, we have now localized one major modifier locus on chromosome 13 (Mod13), which explains a 30% increase in the methylation level of this transgene with no effect on the flanking endogenous sequences. No other QTL could be identified, except for a demethylating activity of low significance located on chromosome 12. Recombinant inbred mice containing a BALB/c allele of Mod13 were then used to show that the presence of Mod13 is sufficient to induce de novo methylation. A segregation between de novo methylation and repression of transgene expression was uncovered, suggesting that this genetic system is also useful for the identification of factors that interpret methylation patterns in the genome.

Negative regulation of autoreactive B cells in transgenic mice expressing a human pathogenic cold agglutinin

Cold agglutinins (CA) are autoantibodies that bind to erythrocyte carbohydrates at low temperatures and induce complement-mediated cell lysis, thus causing hemolytic anemia. Tolerance mechanisms towards CA-expressing B cells and the factors inducing pathogenic CA production are unknown. In order to develop an animal model for CA disease, we have produced transgenic mice expressing the heavy or the light chain of a human CA, previously shown to be pathogenic to the mouse. Expression of the human H chain alone resulted in a B cell maturation block at the pro-B stage, and did not induce allelic exclusion. In double-transgenic mice, co-expression of the human H and L chains restored B cell development but the majority of bone marrow cells expressing the human IgM were eliminated by deletion. In the periphery, B cells were depleted, and a large proportion of the remaining cells co-expressed a human and a murine H chain, secreting "mixed" IgM. A few autoreactive cells, predominating in the peritoneal cavity, escaped tolerance mechanisms and secreted transgenic IgM. The autoreactive B cells are amenable to polyclonal stimulation, making these transgenic mice a suitable model for a human autoimmune disease.

A new family of genes and pseudogenes potentially expressing testis- and brain-specific leucine zipper proteins in man and mouse

We have characterized a new mouse gene highly transcribed in the testis, and a derived intronless gene expressed in the embryo. The latter gene is present in Mus musculus domesticus and in Mus musculus castaneus but is absent in Mus spretus. The sequencing of different clones from a testis cDNA library reveals a complex transcriptional regulation for the intron-containing gene. The use of several promoters, alternative splicing and trans-splicing, and of two different polyadenylation sites account for the diversity. The different cDNAs encode proteins with features of basic helix-loop-helix leucine zipper (bHLH-ZIP) DNA-binding factors with homology to a new brain-specific factor. The presence of multiple CK2 and PKC phosphorylation sites suggests that their activity may be regulated by phosphorylation. In man, a pseudogene, apparently derived from the same transcript as in mouse and showing 90% homology in the coding region, is present within an intron of another gene. Interestingly, although the human pseudogene is highly mutated in human, in the mouse it has only four nucleotide changes compared with the cDNA of origin, and is still capable of encoding a protein.

Association of glucocorticoids and cyclosporin A or rapamycin prevents E-selectin and IL-8 expression during LPS- and TNFalpha-mediated endothelial cell activation

BACKGROUND

Endothelial cell (EC) activation plays an important role in inflammation, hemostasis, and organ rejection of allogeneic and xenogeneic transplantation. These processes leads to rapid and transient up-regulation of proinflammatory molecules, such as the adhesion molecule E-selectin and the chemotactic cytokine IL-8. The purpose of this study was to investigate the specific effects of several major and potentially synergistic immunosuppressive drugs-cyclosporin A (CsA), rapamycin (Rap), and glucocorticoids (GC)-on lipopolysaccharide (LPS)- or tumor necrosis factor (TNF)alpha-induced EC activation

METHODS

The ability of immunosuppressive drugs, used alone or in combination, to prevent in vitro TNFalpha- and LPS-induced expression of E-selectin and interleukin 8 on porcine ECs, as well as their effect on leukocyte-EC interaction, were investigated. In addition, we studied the in vivo effect of these drugs after i.v. administration of recombinant TNFalpha to rats.

RESULTS

At high concentrations, which correspond to the acceptable experimental levels in primate xenograft recipients, CsA, Rap, and GC individually inhibited E-selectin protein induction in a dose-dependent manner in cultured porcine ECs treated with LPS with an additive effect when the drugs were associated. The pattern of drug-mediated inhibition was related to the stimulus used to activate ECs (i.e., LPS vs. TNFalpha). Reduced expression of E-selectin on ECs activated in the presence of the tested immunosuppressive drugs correlated with a weaker adhesion of human U937 cells to ECs. Messenger RNA analysis demonstrated that the presence of CsA, Rap, and GC during EC activation inhibited E-selectin and interleukin 8 at the gene expression level. LPS-mediated induction of IbetaBalpha expression was not observed in ECs treated with CsA, whereas GC reduced its transcripts by approximately 50%. It is interesting that in vivo studies confirmed that CsA and GC inhibited EC activation at therapeutic doses (1 mg/kg and 10 mg/kg for GC and CsA, respectively) and showed that the combination of CsA and GC efficiently prevents TNFalpha-mediated induction of E-selectin on cardiac ECs.

CONCLUSION

Our data show that, besides their specific immunosuppressive effects on T cells, CsA, Rap, and GC can efficiently contribute to the attenuation of EC activation in vivo and the resulting inhibition is enhanced by the association of CsA with GC.

Mutated cytochrome b as a determinant of a new monoclonal antibody (H8.98) on renal carcinoma cell lines recognized by a Vgamma3Vdelta1(+) T-cell clone

We generated a monoclonal antibody (MAb), H8.98, that recognizes an antigen shared by 50% of examined renal carcinoma cell (RCC) lines and is susceptible to lysis by a Vgamma3Vdelta1(+) T-cell clone derived from RCC tumor-infiltrating lymphocytes. H8.98 inhibited Vgamma3Vdelta1(+ )T-cell clone-mediated lysis of RCC lines. It did not stain normal kidney lines, melanomas, fibroblasts, Burkitt's lymphoma or Epstein-Barr virus-transformed B-cell lines but it did stain 2 of 4 tested breast cancer lines. Through screening of a renal carcinoma cDNA library using H8.98, we isolated a cDNA clone which, upon sequencing, was found to be cytochrome b with 2 point mutations.

Intracellular expression in pig cells of anti-alpha1,3galactosyltransferase single-chain FV antibodies reduces Gal alpha1,3Gal expression and inhibits cytotoxicity mediated by anti-Gal xenoantibodies

BACKGROUND

The carbohydrate structure Gal alpha1,3Gal expressed on pig cells is the major antigen recognized by xenoreactive natural antibodies in the higher primates. In xenotransplantation, natural antibodies binding to that structure initiate hyperacute rejection, and the anti-Gal alpha1,3Gal antibodies that are elicited probably take part in later phases of vascularized graft rejection. This epitope also appears to be involved in innate cellular responses. Inactivation of alpha1,3 galactosyltransferase in transgenic pigs would certainly lead to the success of xenotransplantation, but gene knockout in pigs is not feasible yet.

METHODS

As a novel strategy to inhibit alpha1,3 galactosylation, we generated recombinant single-chain Fv (ScFv) antibodies directed against pig alpha1,3-galactosyltransferase and evaluated the effect of their intracellular expression on enzyme activity and Gal alpha1,3Gal expression.

RESULTS

After in vitro transfection in pig cells, the scFv antibody anti-pig alpha1,3-galactosyltransferase reduced the amount or function of enzyme by up to 70% as evidenced by immunofluorescence and measurement of cell-associated activity. Consequently, Gal alpha1,3Gal on cell membranes was reduced to the same extent. This led to a profound (more than 90%) reduction in the cytotoxicity involving anti-Gal antibodies and complement.

CONCLUSION

Although not sufficient to knock out the overall human anti-pig natural xenoreactivity, intracellular expression of the scFv antibody anti-alpha1,3-galactosyltransferase in pig cells significantly decreases the amount of Gal alpha1,3Gal and could be important to protect cells from elicited antibodies as well as from innate effectors.

Recent human-specific spreading of a subtelomeric domain

The recent spreading of a subtelomeric region at nine different human chromosome ends was characterized by a combination of segregation analyses, physical mapping, junction cloning, and FISH investigations. The events occurred very recently in human genome evolution as demonstrated by sequence analysis of different alleles and the single location of the ancestral site at chromosome 17qter in chimpanzee and orangutan. The domain successfully colonized most 1p, 5q, and 6q chromosome ends and is also present at a significant frequency of 6p, 7p, 8p, 11p, 15q, and 19p ends. On 6qter, the transposed domain is immediately distal to the highly conserved, single-copy gene PDCD2.

Control of expression and methylation of a hepatitis B virus transgene by strain-specific modifiers

In transgenic animals, genotype-specific modifiers exert a control over transgene methylation and expression that may or may not be position dependent. These factors belong to different classes, some of them possibly related to modifiers of position-effect variegation in Drosophila. The study of hepatitis B virus (HBV) gene expression in transgenic mice has revealed the existence of many factors influencing transcription, including hormones and tissue-specific transcription factors. We now report the effect of genotype-specific modifiers on HBV surface antigen (HBsAg) expression and transgene methylation. Compared with the C57BL/6 background, the DBA/2 and 129sv backgrounds cause enhancement of HBsAg expression, with little or not effect on transgene methylation or transcription. In contrast, a single cross with a BALB/c mouse is responsible for de novo methylation and silencing of the transgene in all offspring. Several modifiers appear to segregate in the progeny of a transgenic E36 male mouse crossed with (C57BL/6 x BALB/c) F1 females, with the emergence of a high-expressor group. Our observations suggest that different modifiers act cooperatively, at both the transcriptional and post-transcriptional levels, as part of a complex system regulating transgene expression. This transgenic model provides a system to genetically map new mouse strain-specific modifiers, some of them involved in epigenetic modification and transcription control.

Porcine alpha1,3-galactosyltransferase: tissue-specific and regulated expression of splicing isoforms

Expression of the Gal alpha1,3 Gal epitope on membrane glycolipids and glycoproteins is known to vary widely from one tissue to another. In the course of studying the mechanisms underlying this variability, we have isolated from pig cDNA four sequences corresponding to four isoforms of alpha1,3-galactosyltransferase (alpha1,3GT), the Golgi enzyme that links galactose in alpha1,3 on the galactose residue of N-acetyllactosamine. The isoforms differ from each other in the alternative presence of two nucleotide stretches of 36 and 63 base pairs in a segment encoding the stem region of the protein. Stable expression experiments show that all four isoenzymes can confer alpha-galactosyltransferase activity to HeLa cells, and that they are all located within the Golgi compartment, indicating that variations in length in the stem region do not affect enzyme activity or cellular localization. Analysis of RNA from different pig organs and cells shows quantitative differences between tissues in levels of alpha1,3GT, as well as qualitative differences, the four isoforms being unequally represented in different tissues.

Simultaneous expression by porcine aorta endothelial cells of glycosphingolipids bearing the major epitope for human xenoreactive antibodies (Gal alpha 1-3Gal), blood group H determinant and N-glycolylneuraminic acid

Glycosphingolipids were isolated from primary cultures of porcine endothelial cells labelled with 14C-galactose or 14C-glucosamine. They were characterized by their mobility on thin layer chromatogram, their sensitivity to exoglycosidases, and their labelling with antibodies. In addition to the major glycosphingolipids, globotetra- and globotriaosylceramide, minor ones were identified as penta- and heptaglycosylceramide of the neolactoseries terminated by either Gal alpha 1-3Gal- (xenoreactive epitope) or Fuc alpha 1-2Gal- (H determinant). Two gangliosides were found, GM3 and GD3, and N-glycolylneuraminic acid was their major sialic acid. Therefore, porcine endothelial cells differ from human endothelial cells by expression of glycosphingolipids that are absent in man: two Gal alpha 1-3Gal-terminated glycolipids recognized by human natural antibodies, and two N-glycolylneuraminic acid-terminated gangliosides which are potent immunogens.

Transgenesis in rats: technical aspects and models

The production of transgenic rats by DNA-microinjection into fertilized ova has now become an established procedure, although fewer than 20 lines have been described during the last 5 years. Overall, transgenic rats remain more difficult to produce than transgenic mice, but satisfactory yields have been obtained by several laboratories. A review of the methods used to generate transgenic rats shows considerable variation between different laboratories, particularly in choice of strain, superovulation protocols and the use of embryo culture before reimplantation. In some instances, the production of transgenic rats has provided data that are new and relevant, compared to data obtained in mice bearing the same transgene. Models have been developed for human diseases such as hypertension and autoimmunity, and applications have been found in the study of carcinogenesis and in pharmacological research. Transgenic rat technology also opens up interesting perspectives for transplantation research, in which microsurgery is an essential procedure. Intensive research is in progress in several laboratories to produce rat embryonic stem (ES) cell lines, but existing lines have not participated in germ line formation a prerequisite for their use in gene knock out experiments.

Inhibition of hepatitis B virus surface antigen gene expression in carcinogen-induced liver tumors from transgenic mice

We previously showed that hepatitis B surface antigen (HBsAg)-producing transgenic mice were more sensitive to hepatocarcinogens than their normal littermates were. We have now investigated the regulation of hepatitis B virus (HBV) gene expression in carcinogen-induced liver tumors of HBV-carrier transgenic mice and in three cell lines derived from tumor samples. Transcription of the S gene was repressed in 17 tumors even though they had normal levels of liver-specific mRNAs such as albumin and transferrin. Three hepatoma cell lines, derived from independent tumor samples, were analyzed for their capacity to express the S gene after transfection of cloned DNA. Although they no longer expressed the endogenous S gene, they were still able to express it from transfected viral DNA both transiently and stably. The loss of HBsAg expression in tumors and in the cell lines was accompanied by de novo methylation of the S region, which is a way to permanently repress gene expression. Our data confirm in an animal model previous observations of S-gene expression in human hepatocarcinoma and suggest a role for its downregulation in tumor progression.

Induction of anti-hepatitis B surface antigen (HBsAg) antibodies in HBsAg producing transgenic mice: a possible way of circumventing "nonresponse" to HBsAg

As a model for studying possible mechanisms of nonresponse toward hepatitis B surface antigen (HBsAg) in hepatitis B virus (HBV) carriers, we used transgenic (Tg) mice which constitutively express this antigen in the liver from before birth. The mice secrete large amounts of HBsAg particles into the sera without producing antibodies. Tg and control mice were immunized with either recombinant HBsAg particles of a different subtype, or with recombinant hybrid HBsAg particles carrying a human immunodeficiency virus (HIV) envelope determinant. The presence of determinants to which the mice are tolerant on the injected particles does not hamper the response to the foreign epitope. Moreover, a weak but significant anti-HBs response is clearly detectable in Tg mice immunized with these particles. Antibodies to epitopes carried by the transgenic antigen are made even after injection of homologous antigen, and a concomitant decrease in circulating HBsAg is observed. This immune response does not induce any liver damage. It was demonstrated that in these Tg mice, B cell self-tolerance toward HBsAg can be overcome by immunization. This phenomenon raises the possibility of designing more effective methods of immunotherapy for HBV carriers.

Chronic alcohol intoxication decreases the serum level of hepatitis B surface antigen in transgenic mice

Hepatitis B virus (HBV) infections with an unusual serological profile, viz. positivity of HBV-DNA in the absence of hepatitis B surface antigen (HBsAg), have been described in alcoholics. This atypical pattern could be due to a low circulating level of viral particles rendering HBsAg undetectable with commercial kits, whereas HBV-DNA remains positive using the highly sensitive hybridization technique. We hypothesize that the well-known alcohol-induced impairment of protein secretion could also concern HBsAg particles and leads to a decrease in serum levels of the HBs antigen. To verify this hypothesis, we used HBsAg-positive transgenic mice as an animal model. Twelve HBsAg+ mice were separated into two groups; one group (n = 6) was submitted to increasing alcoholisation over an 18-week period, while the other (n = 6) was water fed. Seven HBsAg- littermates acted as controls: three received the alcohol regimen and the remaining four water. Chronic excessive alcoholisation lead to a significant decrease in serum HBsAg concentrations, while there was no obvious change in liver S mRNA. Ultrastructural studies showed a significant decrease in the number of microtubules in the livers of alcohol-fed mice. Finally, immunohistochemical studies performed at the end of the experiment showed a greater accumulation of HBsAg in the livers of HBsAg+ alcohol-fed (mainly located in the centrilobular area) than in the HBsAg+ water-fed mice. Our results (i) validate our initial hypothesis that chronic alcohol abuse leads to a decrease in serum HBsAg concentrations. This could explain, in part at least, the serological dissociations which were observed. (ii) Confirm the utility of screening serum HBV-DNA in alcoholics.(ABSTRACT TRUNCATED AT 250 WORDS)

Transgenic mice containing hepatitis B virus sequences are more susceptible to carcinogen-induced hepatocarcinogenesis

Transgenic mice containing one copy of hepatitis B virus (HBV) genome without the core gene and expressing hepatitis B surface antigen (HBsAg) were crossed with C3H/He mice. The F1 hybrids (approximately 50% HBV positive and approximately 50% HBV negative) were treated with a single dose of diethylnitrosamine (NDEA) or p-dimethylaminoazobenzene (DAB) given at 7 days of age, or were untreated. Mice were kept under observation without further treatments until 30 weeks old and then killed. Stereological analysis of liver nodules and estimations of their size distribution demonstrated a significative enhancing effect of HBV transgene in both NDEA- and DAB-induced hepatocarcinogenesis in male mice. Hepatocellular adenomas and carcinomas were also more frequent in NDEA-treated HBV-positive than HBV-negative male mice. Female mice showed a lower tumorigenic response than males without significant differences between groups of HBV-positive and HBV-negative mice. It is proposed that the presence of the transgene enhanced carcinogen-induced hepatocarcinogenesis.

Transcription of the S gene in transgenic mice is associated with hypomethylation at specific sites and with DNase I sensitivity

The methylation status of hepatitis B virus (HBV) DNA was investigated in different organs from two strains of transgenic mice (E36 and E11) expressing the hepatitis B surface antigen (HBsAg) gene specifically in the liver. Specific sites in the S gene were shown to be methylated in all the organs of adult mice except in the liver. These sites were methylated in 14-day-old fetal liver and were progressively demethylated during development and after birth. In one strain in which HBsAg expression is lost upon transmission by females, extensive de novo methylation of the transgene was detected in the livers and bodies of 14-day-old fetuses from transgenic females. The extent of methylation was such that activation of the gene was no longer possible. DNase I-hypersensitive sites were detected in the enhancer region of HBV in the liver of HBsAg-positive mice but not in HBsAg-negative progeny of E36 females. These data indicated that in two independent transgenic lines, HBV sequences are reproducibly activated in the developing liver along with cellular liver-specific genes and that transcription is associated with demethylation at specific sites in the S gene and with DNase hypersensitivity.

Replication and gene expression of hepatitis B virus in a transgenic mouse that contains the complete viral genome

We have sought to address the problem of the host and tissue specificity of the hepatitis B virus (HBV) by using transgenic mice obtained after injection of head-to-tail dimers of the HBV genome. Viral DNA replication and protein synthesis were obtained in one of nine transgenic mice containing integrated HBV DNA. The RNAs encoding the HBV surface antigen and the core antigen were synthesized in the liver, the kidney, and the heart. In these organs, DNA replicative intermediates similar to those found during normal infection were associated with corelike structures. Large amounts of core polypeptides and capsids were detected in the nuclei in the absence of any pathological effect. These results show that the different steps of HBV multiplication can take place in nonliver nonhuman cells once the problem of entry into the host cell is overcome. In the absence of a small laboratory animal infectable by HBV, such transgenic mice should be helpful for the study of many aspects of viral multiplication.

Maternal inhibition of hepatitis B surface antigen gene expression in transgenic mice correlates with de novo methylation

Differential modifications of the genome during gametogenesis result in a functional difference between the paternal and maternal genomes at the moment of fertilization. A possible cause of this imprinting is the methylation of DNA. The insertion of foreign DNA into transgenic mice allows the tagging of regions that are differentially methylated during gametogenesis. We describe here a transgenic mouse strain in which the expression of the hepatitis B surface antigen gene is irreversibly repressed following its passage through the female germ line. This inhibition is accompanied by the methylation of all the HpaII and HhaI sites within the foreign gene, which we have shown to be integrated into a site on chromosome 13. The irreversibility reported here contrasts with what is found with other transgenic mice sequences which are reversibly methylated after passage through the male or female germ line, though in both cases methylation appears to be important in the imprinting process.

Hepatitis B surface antigen gene expression is regulated by sex steroids and glucocorticoids in transgenic mice

We have investigated the basis for liver-specific and sex-linked expression of hepatitis B surface antigen (HBsAg) gene in transgenic mice by monitoring the level of liver HBsAg mRNA and serum HBsAg at different stages of development and in response to sex-hormone regulation. Transcription of the HBsAg gene starts at day 15 of development, together with that of the albumin gene, and reaches a comparable level at birth. HBsAg mRNA level and HBsAg production are parallel in males and females during prenatal development and until the first month of life, but HBsAg gene expression increases 5-10 times in males at puberty. After castration, the level of expression decreases dramatically in both males and females and is subsequently increased by injection of testosterone or estradiol. Glucocorticoids also regulated positively expression of the HBsAg gene. Our results suggest that sex hormones play a role in hepatitis B virus gene expression during natural infection and could explain the difference in incidence of chronic carriers between men and women.

Formation of the pool of covalently closed circular viral DNA in hepadnavirus-infected cells

Covalently closed circular (CCC) double-stranded DNA believed to be the transcriptional template for duck hepatitis B virus (DHBV) is amplified in aging primary cultures of hepatocytes from congenitally infected ducklings. Analysis of 5-bromodeoxyuridine-labeled heavy/light CCC DNA shows that the relaxed circular DNA synthesized in the cytoplasm by reverse transcription is the predominant precursor to the amplified pool of nuclear viral CCC DNA. In vitro infection of uninfected hepatocyte cultures with DHBV demonstrates that a similar 50-fold amplification of CCC DNA occurs during an early stage in the infection before virus production. This amplification allows the establishment of a pool of transcriptional templates in the cell without the need for semiconservative replication or multiple rounds of infection. This process may account for the ability of hepadnavirus-infected cells persistently to produce virus particles in the absence of stable integration of viral DNA.

Specific expression of hepatitis B surface antigen (HBsAg) in transgenic mice

Two transgenic mice were obtained that contain in their chromosomes the complete hepatitis B virus (HBV) genome except for the core gene. These mice secrete particles of HBV surface antigen (HBsAg) in the serum. In one mouse, HBV DNA sequences that had integrated at two different sites were shown to segregate independently in the first filial generation (F1) and only one of the sequences allowed expression of the surface antigen. Among these animals the males produced five to ten times more HBsAg than the females. A 2.1-kilobase messenger RNA species comigrating with the major surface gene messenger RNA is expressed specifically in the liver in the two original mice. The results suggest that the HBV sequences introduced into the mice are able to confer a tissue-specific expression to the S gene. In addition, the HBV transgenic mice represent a new model for the chronic carrier state of hepatitis B virus infection.

The hepatitis B virus

DNA recombinant technology has radically changed hepatitis B virus (HBV) virology. The genetic organization, transcription and replication of the virus are basically understood, structures of integrated HBV sequences in hepatocellular carcinoma have been characterized, and new vaccines produced by recombinant DNA technique are being developed.

[Expression of hepatitis B virus (HBV) genome in the oocytes of two species of amphibians]

Xenopus laevis and Pleurodeles waltlii oocyte nuclei are injected with a recombinant plasmid pCP 10, carrying two hepatitis B virus (HBV) genomes in a tandem arrangement. Transcription occurs in oocytes of both species and production of viral RNAs is demonstrated; better quantitative results are obtained with P. waltlii oocytes. Two viral proteins are detected: Hepatitis B surface antigen (Ag HBs) and Hepatitis B core antigen (Ag HBc). These proteins can be shown only in oocyte homogenates, and not in the incubation media. Another viral marker (Ag HBe) was not detected.

Molecular comparison of virulence plasmids in Shigella and enteroinvasive Escherichia coli

Virulent isolates of Shigella dysenteriae and Shigella boydii harboured a 140 Mdal plasmid which was either absent or deleted in spontaneously avirulent strains. Together with previous data concerning S. sonnei, S. flexneri and enteroinvasive Escherichia coli, the present results established the general role of extrachromosomal elements in the virulence of such enteroinvasive species. Among different species, these virulence plasmids showed unrelated endonuclease cleavage patterns, whereas hybridization experiments showed that homologous sequences were present throughout the molecules. These plasmids may therefore have derived from a common ancestor molecule which overcame evolutionary alterations in restriction sites. Furthermore, intraspecies and intraserotype comparison of these plasmids by endonuclease cleavage demonstrated highly conserved sequences. The consequences of these data for evolution, epidemiology and diagnosis of Shigella and enteroinvasive E. coli are discussed.

Transcription of the hepatitis B surface antigen gene in mouse cells transformed with cloned viral DNA

Mouse L cells transformed with recombinant plasmids carrying hepatitis B virus (HBV) DNA fragments were used to study the transcription of the viral surface antigen gene (gene S). An HBV-specific, polyadenylated, 2.3-kilobase RNA was mapped on the HBV genome. This RNA hybridized with approximately 75% of the genome and excluded the region of the HBV core antigen gene (gene C). The 2.3-kilobase RNA species was present only in cell lines that produced hepatitis B surface antigen. An HBV-specific 2.3-kilobase RNA was also detected in human hepatoma cell line PLC/PRF/5 which produced hepatitis B surface antigen. A study of gene S expression in the transformed mouse L cells allowed us to localize the regions of initiation and termination of gene S transcription. Our results strongly suggest that the 2.3-kilobase RNA molecule is the mRNA of the major polypeptide of the envelope, which carries the viral surface antigen determinants.

Excretion of hepatitis B surface antigen particles from mouse cells transformed with cloned viral DNA

A plasmid containing two cloned hepatitis B virus genomes in a tandem head-to-tail arrangement has been introduced into mouse fibroblasts by using cotransformation with the cloned herpes simplex virus thymidine kinase gene. Several copies of the plasmid were integrated into high molecular weight cellular DNA. The original tandem structure of the hepatitis B virus DNA was conserved. Hepatitis B surface antigen was synthesized by all the 15 clones examined. The other viral antigens were not detected. The surface antigen was excreted into the cell culture medium as particles having the same characteristics as those found in human serum. It is estimated that 2-4 X 10(4) particles were produced per mouse cell per 24 hr in two clones. This value corresponds to approximately 2-4 X 10(6) surface antigen polypeptides per cell per 24 hr.

Presence of integrated hepatitis B virus DNA sequences in cellular DNA of human hepatocellular carcinoma

Hepatitis B virus (HBV) may be one of the agents involved in the aetiology of human primary liver cancer. This hypothesis is supported by (1) the similarity between the geographical distribution of chronic carriers of the viral surface antigen (HBsAg) and that of hepatocellular carcinoma (HCC); (2) the increase in the prevalence of HBV markers in serum of patients with primary liver cancer when compared with the general population; (3) the observation that HBV infection precedes the development of the tumour. Moreover, these epidemiological indications of an association between HBV infecton and hepatocellular carcinoma are supported by the detection of HBV markers such as HBsAg or viral DNA sequences, although in a non-integrated form in tumour tissue. To study the relationship between HBV and primary liver cancer further, we looked for the presence of free or integrated viral DNA in tumour tissue of human hepatocellular carcinomas and in a HBsAg-producing human hepatoma cell line. Using the blot-transfer hybridization technique and cloned HBV DNA as a probe, we have now demonstrated that the viral DNA is integrated in the cellular genome both in tumour tissue and in a hepatoma cell line.

Cloning in Escherichia coli and physical structure of hepatitis B virion DNA

A restriction map of hepatitis B virion DNA was established after cloning of the whole viral genome in Escherichia coli. By use of EcoRI, Xho I, Bgl II, Xba I, BamHI, HincII, and Hae III endonucleases, a total of 28 restriction sites were mapped. The single-stranded region was localized on the restriction map and 5' end of the short strand was mapped at a fixed position.