Drosophila melanogaster S2 cells for expression of heterologous genes: From gene cloning to bioprocess development

In the present review we discuss strategies that have been used for heterologous gene expression in Drosophila melanogaster Schneider 2 (S2) cells using plasmid vectors. Since the growth of S2 cells is not dependent on anchorage to solid substrates, these cells can be easily cultured in suspension in large volumes. The factors that most affect the growth and gene expression of S2 cells, namely cell line, cell passage, inoculum concentration, culture medium, temperature, dissolved oxygen concentration, pH, hydrodynamic forces and toxic metabolites, are discussed by comparison with other insect and mammalian cells. Gene expression, cell metabolism, culture medium formulation and parameters involved in cellular respiration are particularly emphasized. The experience of the authors with the successful expression of a biologically functional protein, the rabies virus glycoprotein (RVGP), by recombinant S2 cells is presented in the topics covered.

Cell Culture Derived AgMNPV Bioinsecticide: Biological Constraints and Bioprocess Issues

We have studied parameters for optimizing the Spodoptera frugiperda (Sf9) cell culture and viral infection for the production of Anticarsia gemmatalis multiple nucleopolyhedrosis virus (AgMNPV) polyhedra inclusion bodies (PIBs) in shaker-Schott or spinner bottles and bioreactors. We have assayed the k(L)a of the systems, initial cell seeding, cell culture volume, dissolved oxygen (DO), multiplicity of infection (MOI), nutrients consumption, and metabolites production. The medium surface oxygen transfer was shown to be higher in shaker bottles than in spinner ones, which was in direct correlation to the higher cell density obtained. Best quantitative performances of PIBs production were obtained with a SF900II medium volume/shaker-bottle volume ratio of 15% and MOI of 0.5 to 1 performed at a cell concentration at infection (CCI) of 1 to 2.5x10(6) cells/ml in a medium containing enough glucose and glutamine. Upon infection, a decrease in the cell multiplication was observed to be dependent on the MOI used, and the muX at the exponential growth phase in infected and non-infected cultures were, respectively, of 0.2832 and 0.3914 (day(-1)). The glucose consumption and lactate production were higher in the infected cultures (muGlucose and muLactate of, respectively, 0.0248 and 0.0089x10(-8) g/cellxday in infected cultures and 0.0151 and 0.0046x10(-8) g/cellxday in non infected ones). The glutamine consumption did not differ in both cultures (muGlutamine of 0.0034 and 0.0037x10(-8) g/cellxday in, respectively, infected and non infected cultures). When a virus MOI of 0.1 to 1 was used for infection, a higher concentration of PIBs/ml was obtained. This was in direct correlation to a higher cell concentration present in these cultures, where a decrease in cell multiplication due to virus infection is minimized. When a MOI of 1 was used, a more effective decrease in cell multiplication was observed and a lower concentration of PIBs/ml was obtained, but with the best performance of PIBs/cell. Correlations between MOI and CCI indicate that a MOI 0.1 to 1.4 and a CCI of 10(6) to 2x10(6) cells/ml led to the best PIBs production performances. The virulence of PIBs produced in cultures infected at low or high MOI showed comparable DL(50). Culture and infection in scaling-up conditions, performed in a bioreactor, were shown to provide the cells with a better environment and be capable of potentially improving the shaker-Schott findings. For an accurate qualitative control of PIB virulence, hemolymph from AgMNPV infected Anticarsia gemmatalis was used as starting material for passages in Sf9 cells. These led to a loss of virulence among the PIBs with an increase in the DL(50). The loss of virulence was accompanied by a loss in budded virus titer, a decreased number of PIBs produced and an altered DNA restriction pattern, suggesting the generation of defective interference particles (DIPs). Transmission electron microscopy (TEM) studies revealed that after cell passages, PIBs lacking virions were progressively synthesized. The study described here point out the biological constraints and bioprocess issues for the preparation of AgMNPV PIBs for biological control.

Streptococcus mutans biofilm adhesion on composite resin surfaces after different finishing and polishing techniques

This study evaluated Streptococcus mutans biofilm adhesion on the surface of three composite resins (nanofilled, Filtek Z350, 3M ESPE, Salt Lake City, UT, USA; nanohybrid, Vit-1-escence, Ultradent Products, South Jordan, UT, USA; and microhybrid, Esthet X, Dentsply, Milford, DE, USA) following different finishing and polishing techniques. Sixty standardized samples (6 × 3 mm) of each composite were produced and randomly divided into three finishing and polishing treatments (n=20): 1) control group: composite resin surface in contact with Mylar matrix strips with no finishing or polishing performed, 2) Sof-Lex aluminum oxide disc technique (3M ESPE, and 3) carbide bur finishing and Astrobrush polishing technique (Ultradent). Half the samples of each group were incubated in human saliva for 1 hour, and all the samples were subjected to S mutans (ATCC 35688) biofilm development. The mean log of CFU/mL present in the S mutans biofilm was calculated, and data were statistically analyzed by three-way analysis of variance and the Tukey test (p<0.05). Human saliva incubation promoted a significant increase of bacterial adherence on all three of the composites' surfaces, regardless of the polishing treatment performed (p<0.05). Of the three, the nanofilled composite (Filtek Z350) had the lowest bacterial adherence with each of the finishing and polishing techniques despite the presence or absence of human saliva (p<0.05). Mylar matrix strips (control group) promoted the lowest bacterial adhesion on the surface of the microhybrid and nanofilled composites in the absence of human saliva.

Tempol ameliorates murine viral encephalomyelitis by preserving the blood-brain barrier, reducing viral load, and lessening inflammation

Multiple sclerosis (MS) is a progressive inflammatory and/or demyelinating disease of the human central nervous system (CNS). Most of the knowledge about the pathogenesis of MS has been derived from murine models, such as experimental autoimmune encephalomyelitis and viral encephalomyelitis. Here, we infected female C57BL/6 mice with a neurotropic strain of the mouse hepatitis virus (MHV-59A) to evaluate whether treatment with the multifunctional antioxidant tempol (4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy) affects the ensuing encephalomyelitis. In untreated animals, neurological symptoms developed quickly: 90% of infected mice died 10 days after virus inoculation and the few survivors presented neurological deficits. Treatment with tempol (24 mg/kg, ip, two doses on the first day and daily doses for 7 days plus 2 mM tempol in the drinking water ad libitum) profoundly altered the disease outcome: neurological symptoms were attenuated, mouse survival increased up to 70%, and half of the survivors behaved as normal mice. Not surprisingly, tempol substantially preserved the integrity of the CNS, including the blood-brain barrier. Furthermore, treatment with tempol decreased CNS viral titers, macrophage and T lymphocyte infiltration, and levels of markers of inflammation, such as expression of inducible nitric oxide synthase, transcription of tumor necrosis factor-alpha and interferon-gamma, and protein nitration. The results indicate that tempol ameliorates murine viral encephalomyelitis by altering the redox status of the infectious environment that contributes to an attenuated CNS inflammatory response. Overall, our study supports the development of therapeutic strategies based on nitroxides to manage neuroinflammatory diseases, including MS.

DiGeorge Syndrome: a not so rare disease

INTRODUCTION

The DiGeorge Syndrome was first described in 1968 as a primary immunodeficiency resulting from the abnormal development of the third and fourth pharyngeal pouches during embryonic life. It is characterized by hypocalcemia due to hypoparathyroidism, heart defects, and thymic hypoplasia or aplasia. Its incidence is 1:3000 live births and, despite its high frequency, little is known about its natural history and progression. ←This is probably due to diagnostic difficulties and the great variety of names used to describe it, such as velocardiofacial, Shprintzen, DiGeorge, and CATCH 22 Syndromes, as well as conotruncal facial anomaly. All represent the same genetic condition, chromosome 22q11.2 deletion, which might have several clinical expressions.

OBJECTIVES

To describe clinical and laboratorial data and phenotypic characteristics of patients with DiGeorge Syndrome.

METHODS

Patients underwent standard clinical and epidemiological protocol and tests to detect heart diseases, facial abnormalities, dimorphisms, neurological or behavioral disorders, recurrent infections and other comorbidities.

RESULTS

Of 14 patients (8m - 18y11m), only one did not have 22q11.2 deletion detected. The main findings were: conotruncal malformation (n = 12), facial abnormalities (n = 11), hypocalcemia (n = 5) and low lymphocyte count (n=2).

CONCLUSION

The authors pointed out the necessity of DGS suspicion in all patient presenting with heart defects, facial abnormalities (associated or not with hypocalcemia), and immunological disorders because although frequency of DGS is high, few patients with a confirmed diagnosis are followed up.

Expression of membrane proteins in Drosophila Melanogaster S2 cells: Production and analysis of a EGFP-fused G protein-coupled receptor as a model

In the process of selecting an appropriate host for the heterologous expression of functional eukaryotic membrane proteins, Drosophila S2 cells, although not yet fully explored, appear as a valuable alternative to mammalian cell lines or other virus-infected insect cell systems. This nonlytic, plasmid-based system actually combines several major physiological and bioprocess advantages that make it a highly potential and scalable cellular tool for the production of membrane proteins in a variety of applications, including functional characterization, pharmacological profiling, molecular simulations, structural analyses, or generation of vaccines. We present here a series of protocols and hints that would serve the successful expression of membrane proteins in S2 cells, using an enhanced green fluorescent protein (EGFP)/G protein-coupled receptor (EGFP-GPCR) as a model.

Conservation of hepatitis C virus nonstructural protein 3 amino acid sequence in viral isolates during liver transplantation

As a consequence of selective pressure exerted by the immune response during hepatitis C virus (HCV) infection, a high rate of nucleotide mutations in the viral genome is observed which leads to the emergence of viral escape mutants. The aim of this study was to evaluate the evolution of the amino acid (aa) sequence of the HCV nonstructural protein 3 (NS3) in viral isolates after liver transplantation. Six patients with HCV-induced liver disease undergoing liver transplantation (LT) were followed up for sequence analysis. Hepatitis C recurrence was observed in all patients after LT. The rate of synonymous (dS) nucleotide substitutions was much higher than that of nonsynonymous (dN) ones in the NS3 encoding region. The high values of the dS/dN ratios suggest no sustained adaptive evolution selection pressure and, therefore, absence of specific NS3 viral populations. Clinical genotype assignments were supported by phylogenetic analysis. Serial samples from each patient showed lower mean nucleotide genetic distance when compared with samples of the same HCV genotype and subtype. The NS3 samples studied had an N-terminal aa sequence with several differences as compared with reference ones, mainly in genotype 1b-infected patients. After LT, as compared with the sequences before, a few reverted aa substitutions and several established aa substitutions were observed at the N-terminal of NS3. Sites described to be involved in important functions of NS3, notably those of the catalytic triad and zinc binding, remained unaltered in terms of aa sequence. Rare or frequent aa substitutions occurred indiscriminately in different positions. Several cytotoxic T lymphocyte epitopes described for HCV were present in our 1b samples. Nevertheless, the deduced secondary structure of the NS3 protease showed a few alterations in samples from genotype 3a patients, but none were seen in 1b cases. Our data, obtained from patients under important selective pressure during LT, show that the NS3 protease remains well conserved, mainly in HCV 3a patients. It reinforces its potential use as an antigenic candidate for further studies aiming at the development of a protective immune response.

Characterization of growth and metabolism of Drosophila melanogaster cells transfected with the rabies-virus glycoprotein gene

In the present study, the growth and key metabolic features of a gene-transfected Drosophila melanogaster (fruitfly) S2 (Schneider 2) cell population (S2AcRVGP cells), cultured in Sf900-II medium, have been evaluated to provide substantial support for the development of a bioprocess to produce RVGP (rabies-virus glycoprotein). Experimental cultures were grown both in a 100 ml Schott flask incubated in a shaker at 28 degrees C and 100 rev./min and in a 3 litre stirred-tank bioreactor at 28 degrees C, with increasing agitation. In small-scale culture, S2AcRVGP cells reached a maximum cell concentration of 1.13 x 10(7) cell/ml, presented a mu(max) (maximum specific growth rate) of 0.037 h(-1) and the growth was limited by oxygen deprivation. An early and remarkably long stationary phase was observed under hypoxia. Cell cultures grown in the bioreactor without oxygen limitation exhibited a maximum cell concentration of 2.2 x 10(7) cells/ml and mu(max) values as high as 0.048 h(-1). The main substrate consumed in order to reach such a high growth rate was the amino acid proline, which seems to play an important role as a source of metabolic energy in the culture of S2AcRVGP cells. Under conditions of hypoxia, the cells were able to survive for 15 h without apparent damage, recovering their previous metabolic activity.

Nomenclature and guideline to express the amount of a membrane protein synthesized in animal cells in view of bioprocess optimization and production monitoring

Studies of a bioprocess optimization and monitoring for protein synthesis in animal cells face a challenge on how to express in quantitative terms the system performance. It is possible to have a panel of calculated variables that fits more or less appropriately the intended goal. Each mathematical expression approach translates different quantitative aspects. We can basically separate them into two categories: those used for the evaluation of cell physiology in terms of product synthesis, which can be for bioprocess improvement or optimization, and those used for production unit sizing and for bioprocess operation. With these perspectives and based on our own data of kinetic S2 cells growth and metabolism, as well as on their synthesis of the transmembrane recombinant rabies virus glycoprotein, here indicated as P, we show and discuss the main characteristics of calculated variables and their recommended use. Mainly applied to a bioprocess improvement/optimization and that mainly used for operation definition and to design the production unit, we expect these definitions/recommendations would improve the quality of data produced in this field and lead to more standardized procedures. In turn, it would allow a better and easier comprehension of scientific and technological communications for specialized readers.

Purification and Characterization of an Anti-Apoptotic Protein Isolated from Lonomia obliqua Hemolymph

Previously it was reported that supplementation of insect cell culture with Lonomia obliqua hemolymph could extend culture longevity (Maranga et al. Biotechnol. Prog. 2003, 19, 58-63). In this work the anti-apoptotic properties of this hemolymph in Spodoptera frugiperda (Sf-9) cell culture were investigated. The presence or absence of apoptotic cells was characterized by light microscopy, flow cytometry, and agarose gel electrophoresis. Hemolymph was fractionated by several ion exchange and gel filtration chromatographic steps for identification of the compounds responsible for this effect. Fractions exhibiting a potent anti-apoptotic effect were isolated and tested in cell culture. A protein of about 51 kDa was identified, isolated, and tested for apoptosis inhibition. Addition of this purified protein to Sf-9 cultures was able to prevent apoptosis induced by nutrient depletion as well as by potent apoptosis chemical inducers such as Actinomycin D. This work confirms that the enhanced culture longevity obtained by supplementation with L. obliqua hemolymph is due to the presence of potent anti-apoptotic factors.

Expression of the hepatitis B virus surface antigen in Drosophila S2 cells

Drosophila melanogaster S2 cells were transfected with a plasmid vector (pAcHBsAgHy) containing the S gene, coding for the hepatitis B virus surface antigen (HBsAg), under control of the constitutive drosophila actin promoter (pAc), and the hygromycin B (Hy) selection gene. The vector was introduced into Schneider 2 (S2) Drosophila cells by DNA transfection and a cell population (S2AcHBsAgHy) was selected by its resistance to hygromycin B. The pAcHBsAgHy vector integrated in transfected S2 cell genome and approximately 1,000 copies per cell were found in a higher HBsAg producer cell subpopulation. The HBsAg production varied in different subpopulations, but did not when a given subpopulation was cultivated in different culture flasks. Higher HBsAg expression was found in S2AcHBsAgHy cells cultivated in Insect Xpress medium (13.5 mug/1E7 cells) and SFX medium (7 mug/1E7 cells) in comparison to SF900II medium (0.6 mug/1E7 cells). An increase of HBsAg was observed in culture maintained under hygromycin selection pressure. Data presented in the paper show that S2AcHBsAgHy cells produce efficiently the HBsAg which is mainly found in the cell supernatant, suggesting that HBsAg is secreted from the cells. The data also show that our approach using the Drosophila expression system is suitable for the preparation of other viral protein preparation.

Health-related quality of life and right ventricular function in the midterm follow-up assessment after tetralogy of fallot repair

BACKGROUND

Few data are available on quality of life after surgical repair of tetralogy of Fallot (ToF), and on its relationship to right ventricle function.

METHODS

Patients with at least 1 year of follow-up evaluation after surgery were studied. Right ventricle function was evaluated by the Doppler-derived myocardial performance index (MPI), and health-related quality of life (HRQL) was assessed by the Child Health Questionnaire, Parent Form-50. Findings were compared with those for an age- and sex-matched group of healthy children.

RESULTS

The study enrolled 35 successfully repaired ToF patients with 4.9 years (range, 3-7 years) of follow-up evaluation after surgery and 36 healthy children. The MPI demonstrated right ventricle dysfunction in patients compared with controls (0.34; range, 0.26-0.49 vs 0.2; range, 0.13-0.27; p < 0.01), although HRQL for the psychosocial domain was similar between patients and healthy children (summary score, 47.9; range, 45-52 vs 47.5; range, 44.5-50; p = 0.17). A trend for poorer physical area results was observed in patients (summary score, 44; range, 31-52 vs 48.5; range, 45.7-51.7; p = 0.06). Neither physical nor psychosocial summary scores for HRQL had any correlation with right ventricle MPI.

CONCLUSIONS

Right ventricle dysfunction is present in postoperative ToF patients. The psychosocial domain of HRQL is preserved after surgery. A trend for worse results was observed in the physical domain. The right ventricle function is not related to quality of life after surgical repair of ToF.

Analytical approach for the extraction of recombinant membrane viral glycoprotein from stably transfected Drosophila melanogaster cells

Parameters for storage, lysis and concentration of Drosophila melanogaster Schneider 2 (S2AcRVGP) cells expressing the recombinant rabies virus glycoprotein (RVGP) were studied with regard to RVGP quantification by ELISA, for productivity evaluation and future purification. Lysis buffers were formulated with Tris, NaCl, glycerol, EDTA, KCl, Na(2)PO(4), MgCl(2), PMSF and NP-40 or CHAPS. S2AcRVGP cells (10(7) cells at the exponential growth phase) were frozen at -20 degrees C as a dry pellet, suspended in buffer (B) formulations or after treatment with lysis buffer (LB) formulations. They were then thawed as cell pellets or with B formulations or PBS at 4 degrees C or at room temperature and then lysed with LB formulations. For RVGP quantification by ELISA, a protocol was chosen of cell preparation including cell freezing as dry pellet, cell thawing at 4 degrees C with B4 (Tris, NaCl, MgCl(2), PMSF) and cell lysis with the LB4 (B4 + NP-40) since it fulfilled requirements of high RVGP detection, and was easily performed with mixtures freezing quickly, and a cost-saving LB formulation could be used. Using these established conditions, we examined the optimal cell concentration for RVGP quantification by ELISA. Results showed that an increase in the RVGP detection (from 62.5 to 1083 ng/10(7) cells) paralleled a decrease in the cell number (3 x 10(7) - 10(5) cells) used. The NP-40 concentration present in the LB4 was further investigated as a function of the cell number used for sample preparation. Previous results were confirmed indicating that higher NP-40 concentrations led to a decreased detection of RVGP. Altogether our data clearly pointed out the crucial effects of cell freeze, thaw, lysis and concentration on immune detection of recombinant membrane glycoproteins and can be useful as a guideline for sample preparation for this purpose.

Culture of transgenic Drosophila melanogaster Schneider 2 cells in serum-free media based on TC100 basal medium

Requirements of eliminating animal proteins from cell culture have intensified in recent years, with the pressure of regulatory agencies related to biopharmaceuticals production. In this work, the substitution of fetal bovine serum by yeastolate and a soy hydrolysate (Hy Soy) for the culture of Drosophila melanogaster Schneider 2 cells transfected for the production of rabies virus G glycoprotein was evaluated. TC100 supplemented with glucose, glutamine, lipid emulsion and Pluronic F68 was employed as basal medium. Results show that yeastolate was more efficient on cell growth stimulation than Hy Soy. Cells adapted in medium formulation supplemented with 3 g/L yeastolate, 1% lipid emulsion, 10 g/L glucose, 3.5 g/L glutamine and 0.1% Pluronic F68 attained a maximum concentration of 10.7 x 10(6) cells/mL, with the expression of 9.4 ng/mL G glycoprotein.

Viral antigen production in cell cultures on microcarriers Bovine parainfluenza 3 virus and MDBK cells

Viral antigens can be obtained from infected mammalian cells cultivated on microcarriers. We have worked out parameters for the production of bovine parainfluenza 3 (PI-3) virus by Mandin-Darby Bovine Kidney (MDBK) cells cultivated on Cytodex 1 microcarriers (MCs) in spinners flasks and bioreactor using fetal bovine serum (FBS) supplemented Eagle minimal essential medium (Eagle-MEM). Medium renewal during the cell culture was shown to be crucial for optimal MCs loading (>90% MCs with confluent cell monolayers) and cell growth (2.5 x 10(6)cells/mL and a micro(x) (h(-1)) 0.05). Since cell cultures performed with lower amount of MCs (1g/L), showed good performances in terms of cell loading, we designed batch experiments with a lower concentration of MCs in view of optimizing the cell growth and virus production. Studies of cell growth with lower concentrations of MCs (0.85 g/L) showed that an increase in the initial cell seeding (from 7 to 40 cells/MC) led to a different kinetic of initial cell growth but to comparable final cell concentrations ((8-10)x10(5)cells/mL at 120 h) and cell loading (210-270 cells/MC). Upon infection with PI-3 virus, cultures showed a decrease in cell growth and MC loading directly related to the multiplicity of infection (moi) used for virus infection. Infected cultures showed also a higher consumption of glucose and production of lactate. The PI-3 virus and PI-3 antigen production among the cultures was not significantly different and attained values ranging from, respectively, 7-9 log(10) TCID(50)/mL and 1.5-2.2 OD. The kinetics of PI-3 virus production showed a sharp increase during the first 24h and those of PI-3 antigen increased after 24h. The differential kinetics of PI-3 virus and PI-3 antigen can be explained by the virus sensitivity to temperature. In view of establishing a protocol of virus production and based on the previous experiments, MDBK cell cultures performed under medium perfusion in a bioreactor of 1.2L were infected and the PI-3 virus production in 12L attained 12 log(10) TCID(50). Other than establishing a protocol for PI-3 production in MDBK cell cultures on Cytodex 1, the experiments are proposed as a basis for approaching the development of a virus production protocol in mammalian cells cultivated on microcarriers in bioreactors.

Improving heterologous protein expression in transfected Drosophila S2 cells as assessed by EGFP expression

Drosophila melanogaster S2 cells were co-transfected with plasmid vectors containing the enhanced green fluorescent protein gene (EGFP), under the control of metallothionein promoter (pMt), and the hygromycin selection gene, in view of establishing parameters for optimized gene expression. A protocol of transfection was worked out, leading after hygromycin selection, to approximately 90% of S2MtEGFP fluorescent cells at day 5 after copper sulfate (CuSO(4)) induction. As analyzed by confocal microscopy, S2MtEGFP cell cultures were shown to be quite heterogeneous regarding the intensity and cell localization of fluorescence among the EGFP expressing cells. Spectrofluorimetry kinetic studies of CuSO(4) induced S2MtEGFP cells showed the EGFP expression at 510 nm as soon as 5 h after induction, the fluorescence increasing progressively from this time to attain values of 4.6 x 10(5) counts/s after 72 h of induction. Induction with 700 muM of CuSO(4) performed at the exponential phase of the S2MtEGFP culture (10(6) cells/mL) led to a better performance in terms of cell growth, percent of fluorescent cells and culture intensity of fluorescence. Sodium butyrate (NaBu) treatment of CuSO(4) induced S2MtEGFP cell cultures, although leading to a loss of cell culture viability, increased the percent of EGFP expressing cells and sharply enhanced the cell culture fluorescence intensity. The present study established parameters for improving heterologous protein expression in stably transfected Drosophila S2 cells, as assessed by the EGFP expression.

Rabies virus glycoprotein expression in Drosophila S2 cells. I. Functional recombinant protein in stable co-transfected cell line

Recombinant rabies virus glycoprotein (rRVGP) was expressed in Drosophila melanogaster Schneider 2 (S2) cells. The cDNA encoding the entire RVGP gene was cloned in an expression plasmid under the control of the constitutive actin promoter (Ac), which was co-transfected into S2 cells together with a hygromycin selection plasmid. Selected S2 cell populations (S2AcRVGP) had a decreased ability to grow and consume substrates, when compared to the non-transfected cells (S2). They were shown, by PCR, to express the RVGP gene and mRNA and, by immunoblotting, to synthesize the rRVGP in its expected molecular mass of 65 kDa. ELISA kinetic studies showed the rRVGP expression in cell lysates and supernatants attaining concentrations of 300 microg/L. By flow cytometry analysis, about 30% of the cells in the co-transfected populations were shown to express the rRVGP. Cell populations selected by limiting dilution expressed higher rRVGP yields. Mice immunized with rRVGP were shown to synthesize antibodies against rabies virus and be protected against experimental infection with rabies virus. The data presented here show that S2 cells can be suitable hosts for the rRVGP expression, allowing its synthesis in a high degree of physical and biological integrity.

Association between nitric oxide synthesis and vaccination-acquired resistance to murine hepatitis virus by spf mice

Murine hepatitis virus strain 3 (MHV-3) produces a strain-dependent pattern of disease, with A/J and BALB/c mice being considered models of resistance and susceptibility, respectively. A role for nitric oxide in controlling infection remains debatable; thus, we monitored nitric oxide levels in blood and liver of immunized and nonimmunized spf mice during infection by electron paramagnetic resonance. In parallel, liver histology, virus titers, and plasma alanine aminotransferase (ALT) activity were monitored. Nitric oxide synthesis was barely detectable in BALB/c mice, which showed a progressive increase in virus titers and ALT activity. These animals died with a shorter survival time than A/J mice. The latter displayed a less severe infection and presented detectable levels of nitric oxide as nitrosyl complexes in blood and liver at 72 hpi. Immunized mice from both strains became resistant to MHV-3 and showed comparable levels of nitrosyl complexes in blood and liver at an early time (24 hpi). Thereafter, nitric oxide levels decreased but remained detectable in blood up to 96 hpi. Immunized mice were capable of clearing the virus and clearance was inhibited by administration of a nitric oxide synthase inhibitor. Overall, the results support a role for nitric oxide in controlling MHV-3 infection.

Mouse hepatitis virus 3 binding to macrophages correlates with resistance to experimental infection

Mouse hepatitis virus 3 (MHV3) infection of A/J and BALB/c mice has been used as a model of resistance/susceptibility. A/J mice recover from a mild disease after 4–6 days of infection and the BALB/c mice develop an acute hepatitis and die after 3–4 days of infection. In view of studying the MHV3 binding to cells or cell extracts, we performed an enzyme‐linked immunosorbent assay‐like virus‐binding assay, preparing microplates with L929 cells, A/J or BALB/c mouse macrophages and also with proteins extracted from these cells. Higher MHV3 bindings were observed to proteins of BALB/c macrophages than to the A/J ones. The interferon‐γ (IFN‐γ) activation led to a reduction of MHV3 binding only to proteins of resistant A/J mouse macrophages. Our experiments contribute to the hypothesis that IFN‐γ activation of macrophages plays an important role against MHV3 infection by downregulating the expression of viral receptors.

Overexpression of a synthetic gene encoding human alpha interferon in Escherichia coli

Interferons (IFNs) represent an important defense mechanism in vertebrates. In this work, we describe gene synthesis and assembly using the polymerase chain reaction as a method for single-step synthesis of DNA sequences. The oligonucleotides designed were based on Escherichia coli codon usage and two genes of IFN were synthesized: one containing a DNA sequence already known and the other, a mutated form in which two cysteine amino acid residues were replaced by serines in an attempt to improve the stability of the protein. DNA sequences were cloned into pAE, an E. coli vector that allows heterologous protein expression with or without a histidine tag. Recombinant human interferons (rhIFNs) were identified by Western blotting and ELISA using anti-human interferon polyclonal antibodies. Purification of the recombinant His-tagged proteins was achieved in a single step by Ni(2+)-charged column chromatography while proteins without His-tag were purified by extensively washing the inclusion bodies, the final yields being approximately 210 and 75mg/L, respectively. The rhIFNs expressed within this system were biologically active ( approximately 1,1x10(8)IU/mg) based on antiviral assay. The combined methodologies described here proved to be cost-effective and could be extended to other genes/proteins of interest.