[The production of high-yielding strain of rubella virus from wild type virus extracted from a patient in the Western Siberia in 2006]

The study was targeted to investigate the propagation of rubella virus in the cell cultures of various origins and with different cultivation methods. The high-yielding strain of rubella virus was produced. The "spinner-culture" cultivation method was applied and the strain's RNA was detected in 10-8 dilution in real time mode. This strain is supposed to be used in preparation of the standard antigen to implement in the development of immune enzyme test system targeted to the rubella virus specific antibodies.

Analysis of the selective advantage conferred by a C-E1 fusion protein synthesized by rubella virus DI RNAs

During serial passaging of rubella virus (RUB) in cell culture, the dominant species of defective-interfering RNA (DI) generated contains an in-frame deletion between the capsid protein (C) gene and E1 glycoprotein gene resulting in production of a C-E1 fusion protein that is necessary for the maintenance of the DI [Tzeng, W.P., Frey, T.K. (2006). C-E1 fusion protein synthesized by rubella virus DI RNAs maintained during serial passage. Virology 356 198-207.]. A BHK cell line stably expressing the RUB structural proteins was established which was used to package DIs into virus particles following transfection with in vitro transcripts from DI infectious cDNA constructs. Packaging of a DI encoding an in-frame C-GFP-E1 reporter fusion protein corresponding to the C-E1 fusion protein expressed in a native DI was only marginally more efficient than packaging of a DI encoding GFP, indicating that the C-E1 fusion protein did not function by enhancing packaging. However, infection with the DI encoding the C-GFP-E1 fusion protein (in the absence of wt RUB helper virus) resulted in formation of clusters of GFP-positive cells and the percentage of GFP-positive cells in the culture following infection remained relatively constant. In contrast, a DI encoding GFP did not form GFP-positive clusters and the percentage of GFP-positive cells declined by roughly half from 2 to 4 days post-infection. Cluster formation and sustaining the percentage of infected (GFP-positive) cells required the C part of the fusion protein, including the downstream but not the upstream of two arginine clusters (both of which are associated with RNA binding and association with mitochondrial p32 protein) and the E1 part through the transmembrane sequence, but not the C-terminal cytoplasmic tail. Among a collection of mutant DI constructs, cluster formation and sustaining infected cell percentage correlated with maintenance during serial passage with wt RUB. We hypothesize that cluster formation and sustaining infected cell percentage increase the likelihood of co-infection by a DI and wt RUB during serial passage thus enhancing maintenance of the DI. Cluster formation and sustaining infected cell percentage were found to be due to a combination of attenuated cytopathogenicity of DIs that express the C-E1 fusion protein and cell-to-cell movement of the DI. In infected cells, the C-GFP-E1 fusion protein was localized to potentially novel vesicular structures that appear to originate from ER-Golgi transport vacuoles. This species of DI expressing a C-E1 fusion protein that exhibits attenuated cytopathogenicity and the ability to increase the number of infected cells through cell-to-cell movement could be the basis for development of an attractive vaccine vector.

Establishment and characterization of a novel genetic hybrid cell line for propagation of four pathogens

Chromosomal DNAs were purified from human epidermoid carcinoma (HEP-2) cells and transfected into human embryonic lung (HEL) cells to establish a genetic hybrid cell line susceptible to infections by toxoplasma, rubella virus, cytomegalovirus, and herpes simplex virus. Karyotype analysis showed that the resultant hybrid cells, designated D3, had a chromosome number of 96, which was stable after passage for 100 generations. Direct microscopy and immunofluorescence showed that the D3 cells could be infected by the four pathogens with overt cytopathic effects. The toxoplasma and three viruses were purified from infected D3 cells by sucrose gradient centrifugation and used as the antigens for detection of specific IgG and/or IgM in serum samples from pregnant women with suspicious infections by the four pathogens, the results of which were consistent with those of commercial kits. These data indicate that a stable genetic hybrid cell line has been generated, which is a valuable tool for the isolation of the four intrauterine pathogens and for the preparation of antigens for serological tests.

Structural maturation of rubella virus in the Golgi complex

Rubella virus (RUB) assembles its replication complexes (RCs) in modified organelles of endo‐lysosomal origin, known as cytopathic vacuoles (CPVs). These peculiar structures are key elements of RUB factories, where rough endoplasmic reticulum, mitochondria, and Golgi are recruited. Bicistronic RUB replicons expressing an antibiotic resistance gene either in the presence or the absence of the RUB capsid (C) gene were used to study the structure of RCs in transfected cells. Confocal microscopy showed that the RUB replicase components P90 and P150 localized to CPVs, as did double‐stranded RNA (dsRNA), a marker for RNA synthesis. Electron microscopy (EM) showed that replicons generated CPVs containing small vesicles and large vacuoles, similar to CPVs from RUB‐infected cells and that the replicase proteins were sufficient for organelle recruitment. Some of these CPVs contained straight membranes. When cross‐sectioned, these rigid membranes appeared to be sheets of closely packed proteins. Immuno‐EM revealed that these sheets, apparently in contact with the cytosol, contained both P150 and P90, as well as dsRNA, and thus could be two‐dimensional arrays of functional viral replicases. Labelling of dsRNA after streptolysin‐O permeabilization showed that replication of viral genome takes place on the cytoplasmic side of CPVs. When present, C accumulated around CPVs. Mitochondrial protein P32 was detected within modified CPVs, the first demonstration of involvement of this protein, which interacts with C, with RCs.

Structural maturation of rubella virus in the Golgi complex

Rubella virus is a small enveloped virus that assembles in association with Golgi membranes. Freeze-substitution electron microscopy of rubella virus-infected cells revealed a previously unrecognized virion polymorphism inside the Golgi stacks: homogeneously dense particles without a defined core coexisting with less dense, mature virions that contained assembled cores. The homogeneous particles appear to be a precursor form during the virion morphogenesis process as the forms with mature morphology were the only ones detected inside secretory vesicles and on the exterior of cells. In mature virions potential remnants of C protein membrane insertion were visualized as dense strips connecting the envelope with the internal core. In infected cells Golgi stacks were frequently seen close to cytopathic vacuoles, structures identified as the sites for viral RNA replication, along with the rough endoplasmic reticulum and mitochondria. These associations could facilitate the transfer of viral genomes from the cytopathic vacuoles to the areas of rubella assembly in Golgi membranes.

Effect of site-directed asparagine to isoleucine substitutions at the N-linked E1 glycosylation sites on rubella virus viability

The role of three N-linked glycosylation sites in rubella virus (RV) E1 protein on virion release was analyzed by transfecting Vero 76 cells with infectious RV RNA (Robo302WT) containing isoleucine substitutions at N76, N177, and N209 (individually and in combinations). RV RNAs were detected and found to retain substitutions in the transfected cells, but RV capsid indicative of infection was undetectable, except for in Robo302WT and Robo302-N177I transfected cells. Only culture supernatants of Robo302WT and Robo302-N177I RNA transfected cells were positive for RV, suggestive of the virion release into the culture medium. Further, detection of intracellular RV E1 and newly released virion-associated E1 was possible only from cells previously incubated with Robo302-N177I and Robo302WT culture supernatants, suggesting that N177I substituted virus retained infectivity. These results suggest that while glycosylation at N177 is not critical, N76I and N209I mutations are lethal to RV viability.

Mutations in the GDD motif of rubella virus putative RNA-dependent RNA polymerase affect virus replication

Rubella virus (RV) nonstructural proteins are translated as a p200 polyprotein that undergoes proteolytic cleavage into p150 and p90. From conserved amino acid sequence motifs in polypeptides, p90 has been proposed to be the RV RNA-dependent RNA polymerase (RdRp). To test whether the conserved GDD motif is involved in RdRp catalytic activity, three different alanine substitutions were introduced into it. Substitution of glycine by alanine (G1966A) resulted in impaired virus infectivity. Alteration of either aspartate residue completely abolished virus replication. A fully infectious variant was isolated from the G1966A mutant. Sequencing analysis showed that the alanine residue substituted in G1966A mutant had reverted to glycine in this variant. Complementation experiments were carried out to rescue the replication-defective RNA carrying G1966A, D1967A, or D1968A mutations. The defective RNA with G1966A mutation in p90 replicated efficiently when the helper genome that supplied a wild-type p90 was provided in trans. However, the replication-defective RNA with D1967A or D1968A was not rescued by supplementation of p90 in trans. Our studies support the idea that the GDD motif is critical for RV replication and p90 function as RV RdRp.

Inhibition of rubella virus growth by Fungizone

Fungizone added to agar overlay medium inhibited plaque formation in both size and number by rubella virus in rabbit kidney 13 cells. In the presence of 1 microg/ml of Fungizone, the diameter of the plaques was reduced to one half of that in the absence of the drug, and at 5 microg/ml, plaque formation was inhibited by 80%. When the drug was added to the culture medium, the growth of infectious virus was also inhibited with reduction in the synthesis of envelope glycoprotein E1 and capsid protein C in infected cells.

RC-IAL cell line: sensitivity of rubella virus grow

OBJECTIVE

The rapid growth of the rubella virus in RC-IAL2 with development of cytopathic effect, in response to rubella virus infection, is described. For purposes of comparison, the rubella virus RA-27/3 strain was titered simultaneously in the RC-IAL, Vero, SIRC and RK13 cell lines.

METHODS

Rubella virus RA-27/3 strain are inoculated in the RC-IAL cell line (rabbit Kidney, Institute Adolfo Lutz). Plates containing 1.5x10(5) cells/ml of RC-IAL line were inoculated with 0.1ml s RA-27/3 strain virus containing 1x 10(4)TCID50/0.1ml. A 25% cytopathic effect was observed after 48 hours and 100% after 96 hours. The results obtained were compared to those observed with the SIRC, Vero and RK13 cell lines. Rubella virus was detected by immunohistochemistry.

RESULTS

With the results, it was possible to conclude that the RC-IAL cell line is a very good substrate for culturing rubella virus. The cells inoculated with rubella virus were examined by phase contrast microscopy and showed the characteristic rounded, bipolar and multipolar cells. The CPE in RC-IAL was observed in the first 48 hours and the curve of the increased infectivity was practically the same as observed in other cell lines.

CONCLUSIONS

These findings are important since this is one the few cell lines described in the literature with a cytopathic effect. So it can be used for antigen preparation and serological testing for the diagnosis of specific rubella antibodies.

Mutational analysis of the rubella virus nonstructural polyprotein and its cleavage products in virus replication and RNA synthesis

Rubella virus nonstructural proteins, translated from input genomic RNA as a p200 polyprotein and subsequently processed into p150 and p90 by an intrinsic papain-like thiol protease, are responsible for virus replication. To examine the effect of p200 processing on virus replication and to study the roles of nonstructural proteins in viral RNA synthesis, we introduced into a rubella virus infectious cDNA clone a panel of mutations that had variable defective effects on p200 processing. The virus yield and viral RNA synthesis of these mutants were examined. Mutations that completely abolished (C1152S and G1301S) or largely abolished (G1301A) cleavage of p200 resulted in noninfectious virus. Mutations that partially impaired cleavage of p200 (R1299A and G1300A) decreased virus replication. An RNase protection assay revealed that all of the mutants synthesized negative-strand RNA as efficiently as the wild type does but produced lower levels of positive-strand RNA. Our results demonstrated that processing of rubella virus nonstructural protein is crucial for virus replication and that uncleaved p200 could function in negative-strand RNA synthesis, whereas the cleavage products p150 and p90 are required for efficient positive-strand RNA synthesis.

The construction of defective interfering rubella virus particles

Two defective viral vectors containing nucleic acid sequences from rubella virus strains RJ and RS linked to the reporter gene luciferase have been constructed. The vector RNAs are shown to replicate and interfere with wildtype virus in co-infected cells. The interference is associated with a polymorphic nucleotide at nt34 in the 5' stem-loop. The use of these constructs as expression vectors is discussed.

A single-amino-acid substitution of a tyrosine residue in the rubella virus E1 cytoplasmic domain blocks virus release

Rubella virus particles, consisting of a nucleocapsid surrounded by a lipid envelope in which two virus-encoded glycoproteins E1 and E2 are embedded, assemble on intracellular membranes and are secreted from cells, possibly via the cellular secretory pathway. We have recently demonstrated that the cytoplasmic domain of E1 (residues 469 to 481, KCLYYLRGAIAPR) is required for virus release. Alteration of cysteine 470 to alanine did not affect virus release, whereas mutation of leucine 471 to alanine reduced virus production by 90%. In the present study, substitutions of remaining amino acids in the E1 cytoplasmic domain were made in order to investigate the role of each amino acid in regulating rubella virus release. Generated mutants were analyzed in the context of infectious full-length cDNA clone and virus-like particles using combined genetic, biochemical, and electron microscopic approaches. Substitution of a single residue of tyrosine 472 to alanine or tyrosine 473 to serine resulted in a block in virus release without affecting protein transport and virus budding into the lumen of the Golgi complexes. Infectious RNA transcripts bearing these mutations were incapable of forming plaques. Mutants with substitutions at the amino-terminal region (leucine 474, arginine 475, and glycine 476) in the E1 cytoplasmic domain had reduced virus release and small-plaque phenotype, while mutants with substitutions at the carboxy-terminal region (alanine 477, isoleucine 478, alanine 479, proline 480, and arginine 481) had only marginal defects in virus release. Plaque-forming revertants could be isolated from mutants Y472A and Y473S. Sequencing analysis revealed that the substituted serine residue in mutant Y473S reverted to the original tyrosine residue, whereas the substituted alanine residue in mutant Y472A was retained. These results indicate that the E1 cytoplasmic domain modulates virus release in a sequence-dependent manner and that the tyrosine residues are critical for this function. We postulate that residues YYLRG constitute a domain in the E1 tail that may interact with other proteins and this interaction is involved in regulating virus release.

Mapping of genetic determinants of rubella virus associated with growth in joint tissue

Rubella virus (RV) strains vary in their abilities to replicate and persist in cell cultures derived from human joint tissue (synovial cells [SC]), and this arthrotropism appears to be linked to their association with joint symptoms in vivo. In order to map the genetic determinants of arthrotropism, an infectious clone of the Cendehill vaccine strain of RV was constructed, as well as two chimeric clones containing cDNAs from both Cendehill and Therien (wild-type) strains. Replacement of the entire structural gene region of Therien in the infectious clone pROBO302 with the corresponding region of Cendehill did not affect growth in SC. A further observation that Cendehill bound equally well to SC and the permissive Vero cell line indicated that restriction was not at the level of receptor binding, a function of the envelope proteins. Mutations that affected growth in joint cells were mapped to two locations in the nonstructural gene region. The first of these (nucleotides 2803 and 6416) resulted in a 10-fold decrease in yield of progeny virus from SC. This region contained five mutations, at nucleotides 2829, 3060, 3164, and 3528 (near the carboxy terminus of P150 where the protease domain is located) and at nucleotide 4350 in p90. Further substitution of the sequence representing nucleotides 1 to 2803 to give a complete Cendehill infectious clone restricted growth in SC by a further 100-fold to less than 10 PFU/ml. This region contains three mutations, at nucleotides 34, 37, and 55, within the 5' stem-loop structure. In conclusion, the Cendehill-specific mutations believed to be determinants of joint cell growth are located in two regions, the 5' nontranslated region and in a sequence that encodes the carboxy-terminal region of p150 extending into the helicase domain of p90.

Synthesis and biological evaluation of 2-methoxy- and 2-methylthio-6-[2'-alkylamino)ethyl]-4(3H)-pyrimidinones with anti-rubella virus activity

The synthesis of a new family of antiviral compounds, 2-methoxy-, and 2-methylthio-6-[(2'-alkylamino)ethyl]-4(3H)-pyrimidinones, has been accomplished. The activity of these agents against positive strand (rubella virus and sindbis virus) and negative strand (vesicular stomatitis virus) RNA viruses is reported. Some of these compounds are efficient and selective inhibitors of rubella virus.

Reinfection-induced increase of rubella persistently infected cells in a macrophage-like cell line

The establishment and relevant characteristics of a long-term rubella persistent infected immortalised murine macrophage culture with a high proportion of persistent infected cells over uninfected is described. The high proportion of persistent infected macrophages was obtained through reinfection with the original virus. Prior to reinfection, 35-50% of the cells expressed viral antigen, 0.05-1.5% produced infective virus and extra-cellular virus was continuously produced with infective titers cyclically fluctuating between 10(2) and 10(7) TCID50/ml. After reinfection, the macrophages which expressed viral antigen and produced infective virus had increased to 75-90% and 30-45% respectively and extracellular virus was continuously produced with stable titer between 10(2)-10(3) TCID50/ml. Furthermore, in the reinfected culture no significant variation was observed in the percentage of cells expressing antigen, producing virus and in the titer of extracellular virus for longer than a year of passages.

Use of reverse-transcription polymerase chain reaction for detection of rubella virus RNA in cell cultures inoculated with clinical samples

A recently developed reverse transcription-nested polymerase chain reaction (RT-nPCR) method for rubella virus (RV) RNA detection was assessed in a series of African green monkey kidney (AGMK) cell cultures inoculated with clinical samples from patients with suspected RV infection. Results were compared with those of conventional virus isolation/identification. The assay included an internal control of amplification consisting of a synthetic RNA molecule mimicking the RV E1 target sequence. A semiquantitation of RV RNA was achieved by comparing the relative band intensity of internal control and RV E1 fragment. RT-nPCR was positive in 15/16 (94%) RV isolation-positive cultures and in 12/60 (20%) RV isolation-negative cultures. All 27 cell cultures positive by RT-nPCR had been inoculated with clinical samples taken from patients with ascertained RV infection or given RV vaccination and consisted of cells harvested 1-10 days after primary inoculation of clinical samples. No RV RNA was found in any of the cell cultures inoculated with 14 clinical samples from 6 patients in whom RV infection was excluded. When considering the time-course of RV infection, it was found that RV RNA could be detected as early as 4 days p.i. in 10/21 (48%), and by 7-10 days p.i. in 27/28 (96%) cell cultures, whereas by the same time RV was isolated in only 7/16 (44%) cell cultures. Semiquantitation showed that: i) viral RNA amount progressively increased with time; ii) cell cultures containing very low levels of viral RNA one week p.i. either required a few blind passages for virus recovery or remained negative for RV isolation. Finally, PCR inhibitors were found in 10/164 (6%) cell cultures examined. In conclusion, RT-nPCR proved to be very sensitive and very specific and greatly reduced RV detection time in inoculated cell cultures.

The in vitro growth and serial passage of RA 27/3 rubella vaccine virus in cord blood mononuclear leukocytes from normal babies

Because of our inability to isolate rubella virus from peripheral blood lymphocytes from patients with chronic symptoms after rubella immunization we performed a series of experiments with cord blood mononuclear cells (CBL) to determine whether and to what extent these cells supported the growth of rubella virus in vitro. CBL were stimulated with phytohemagglutinin for 48-72 h, washed, and inoculated with 1000 tissue culture 50% infection dose of rubella virus and placed in RPMI 1640 medium with 10% fetal bovine serum and IL-2. Approximately every 9 d the volume was halved, and new CBL were added. Aliquots at 2- to 9-d intervals were obtained and quantitatively cultured in African green monkey tissue culture. Rubella virus growth was determined by echovirus 11 challenge. Controls consisted of rubella virus in RPMI 1640 medium. Rubella virus persisted in CBL culture longer than in control medium in seven of 11 experiments, and in three instances there was evidence of productive infection.

Improved potency assay of rubella vaccine: parameters for plaque formation

Parameters for plaque formation by rubella vaccine strains licensed in Japan were studied. Formation of clear and large plaques on RK13 cells depends on several essential parameters. Plaques differed in morphology among five vaccine strains and the distinctiveness of the plaques was affected by pH of the agar overlay medium during incubation at 35 degrees C. Plaques became progressively larger in size as the concentration of sodium bicarbonate in the agar overlay medium increased from 0.04% to 0.15%, but the contrast of plaques to the background cells decreased markedly. The most distinct plaques of all vaccine strains were formed in the agar overlay medium containing 0.07% of sodium bicarbonate, i.e., pH 6.83, incubated in a humidified atmosphere containing 5% CO2. The number of plaques formed by vaccine strains decreased at 37 degrees C. Vaccine strains other than MEQ11 and TCRB19 formed larger and more contrasted plaques with sharp outline at 35 degrees C than at 32 degrees C. MEQ11 and TCRB19 strains yielded higher infective virus titres at 32 degrees C, but they formed distinct plaques at 35 degrees C and 32 degrees C. For the plaque test, the inoculum volume was another critical factor for obtaining an approximate titre that reflected the absolute titre of the sample. A volume of 0.1 ml was feasible for a well with a diameter of 35 mm.

Comparison of four enzyme immunoassays for detection of immunoglobulin M antibodies against rubella virus

We evaluated four tests for the detection of rubella virus-specific immunoglobulin M antibodies. Primarily, consecutive serum samples were tested by two different assays. Selected panels of sera from patients with proven or likely recent rubella and false-positive and true-negative results in the two primary assays were further tested with two recently developed, fully automated techniques. The four tests were comparable in overall accuracy, but their dynamic ranges may differ considerably. Ways to optimize the predictive values are discussed. We conclude that automated assays may be used without causing significant changes in diagnostic accuracy or distortions in notifications of the incidence of rubella compared with the use of established tools.

Characterization of rubella virus replication complexes using antibodies to double-stranded RNA

A feature of the rubella virus (RV) replication cycle is the formation of cytoplasmic vesicle-containing structures known as replication complexes. Following detergent treatment of RV-infected cells, pre-embedding immunogold labeling electron microscopy using antiserum to double-stranded (ds) RNA was employed to characterize the replication complexes. Concentrations of gold particles were found associated with amorphous material located within the RV replication complex. Unlabeled long fine strands, 3-5 nm in width, were also frequently seen associated with this gold-labeled material. On some occasions gold-labeled vesicles within the replication complexes were also detected. The gold-labeled amorphous material was first detected in RV replication complexes at 12 hr postinfection, soon after the reported latent period of 8 hr. Concentrations of gold particles were not detected in mock-infected cells. The findings in this study indicate that the amorphous material is released from detergent-disrupted vesicles within the replication complex and that the vesicles contain the dsRNA. When cells were infected with the related Semliki Forest virus (SFV) and examined using the same antibody, similar gold-labeled material associated with unlabeled fine strands was also observed in SFV replication complexes. For both RV and SFV, the vesicles which line the inner membrane of the replication complexes contain the dsRNA which represent the viral replicative forms and replicative intermediates.

Identification and characterization of host factor interactions with cis-acting elements of rubella virus RNA

We have analyzed the function of cis-acting elements of rubella virus RNA and the components which interact with these elements in viral RNA replication. We demonstrated that the 5'- and 3'-terminal sequences from RV RNA promote translation and negative-strand RNA synthesis of chimeric chloroamphenicol acetyltransferase (CAT) RNAs. These sequences have a potential to form stem-loop (SL) structures and bind cellular proteins specifically in RNA gel-shift and UV cross-linking assays. The 5' end binding proteins were identified to be Ro/SSA-associated antigens by virtue of being recognized in an RNA complex by an autoimmune patient serum with Ro antigen type specificity. Purification and sequence analysis of the 3' end binding protein revealed that it is a homologue of human calreticulin. The role of host protein in RV replication is discussed.

Structural gene products and morphogenesis of a hybrid between rubella virus and a hamster latent retrovirus

We studied the structural gene products and morphogenesis of the hybrid between rubella virus (RV) and a latent retrovirus (R-type virus or R virus) of a baby hamster kidney cell line, BHK21/WI-2. In electron microscopic analysis, the rubella virion measures 80 nm in diameter and has a round nucleoid form with an electron-lucid centre, while R-type virus is 110 nm in diameter and has a round nucleoid with radial spokes. The type 2 hybrid (H2) virion is pleomorphic, ranging from 85 to 110 nm in diameter, and has a nucleoid structure similar to R virus, with short spokes. Indirect immunofluorescence staining of H2-infected cells with polyclonal and monoclonal antibodies (mAb) against the RV structural proteins demonstrated expression of the homologous RV gene products. SDS-PAGE of 35S-methionine-labelled proteins in RV- and H2-infected cells revealed that they both produce four major immunoprecipitable proteins, three of which (E2a, E2b and C) are products of the two genetic homologous loci (e2 and c). In nonhomologous regions, RV-infected cells exhibited E1 protein, while H2-infected cells produced the Env protein of R virus. Western immunoblotting analysis of RV and H2 viral proteins with mAb confirmed that H2 virions carry rubella viral E2 and C proteins and that E1 protein is carried by RV but not H2 virion. These results explained the absence of serological cross-neutralization of haemagglutination and plaque-forming ability of RV and H2 viruses.

Characterization of rubella virus strain differences associated with attenuation

A comparison of the phenotypic properties of three rubella vaccines (HPV77/DE5, RA27/3 and Cendehill) and four wild-type (wt+) isolates (M33, Therien, Thomas and IB2) has been carried out. Differences in growth characteristics, plaque morphology and temperature sensitivity were identified. In addition differential reactivity of the strains to polyclonal and a monoclonal anti-E1 antibody were found in immunoperoxidase-staining reactions. The ability of the wt+ and vaccine strains to infect lymphoreticular cells and chondrocytes, also varied in that the RA27/3 and Cendehill strains were highly restricted in both these cell types while the wt+ strains and HPV77/DE5 vaccine grew to higher titer. This biological variation was associated with differences in E1 and E2 glycoproteins detected on immunoblots.

Role of membrane phospholipids and glycolipids in the Vero cell surface receptor for rubella virus

Membrane receptors for rubella virus (RV) in Vero cells were studied by means of two different approaches: (i) by enzyme treatment of the whole cell membrane and (ii) by testing the ability of isolated plasma membrane molecules to compete with cells for virus binding. The replication of RV was studied with both indirect immunofluorescence assay and molecular hybridization techniques. Phospholipases A2 and C digestion of cells greatly reduced the infectivity by the virus, pointing towards the involvement of lipid structures as receptor sites for RV. Furthermore, susceptibility of Vero cells to virus infection was also reduced after beta-N-acetyl-D-glucosaminidase, alpha-glucosidase and beta-galactosidase treatment, suggesting that carbohydrate residues may participate in a complex cellular receptor structure for RV. When the major membrane lipids were examined separately for their ability to inhibit viral infectivity, several phospholipids (phosphatidylserine, phosphatidylinositol, phosphatidylethanolamine, phosphatidylcholine, sphingomyelin) and glycolipids (gangliosides, lactosylceramide, cerebroside sulphate) showed a strong neutralizing activity, confirming the role of membrane lipid moiety in the cell surface receptor for RV.

Improvement in potency assay of measles-mumps-rubella trivalent vaccine: interference between components and measures for its elimination

In the potency assay of trivalent measles-mumps-rubella (MMR) vaccine by the immunocytochemical focus assay reported previously (Fukuda et al., 1987), development of rubella foci in RK13 cells was inhibited in the presence of a large excess of mumps component, resulting in an underestimation of the titre of the rubella component. When RK13 cells are infected with the mixture of mumps and rubella viruses, mumps virus interfered with the growth of rubella virus. Interference was mediated most likely by interferon induced by mumps virus. The interference was eliminated by a partial neutralization of mumps component by the addition of anti-mumps serum to the inoculum to RK13 cells. Improved method of potency assay of MMR vaccine incorporating the above measures and other modifications are described.

Growth of rubella virus in a glass bead propagator

A glass sphere propagator with an air lift pump to circulate the medium, has been successfully used to produce large volumes of rubella virus. The system was productive, flexible and easy to operate.

Rubella virus: mechanism of attenuation in the vaccine strain (HPV77)

The vaccine type (HPV77 strain) of rubella virus replicates slower and manifests a delayed appearance of cytopathic effect in Vero-76 cells as compared to wild-type virus (M33). The change in cytopathic effect coincides with the delayed appearance of both genomic and subgenomic RNA as well as viral structural proteins in the cell. The delay in the appearance of the viral proteins in the cells was also evident when the cells infected with the vaccine-type virus were treated with the lysosomotropic agent such as chloroquine. Binding studies using [35S]methionine-labeled virus showed that the vaccine-type virus bound to the cells poorly and the binding was not completely competed out with the cold virus.

Time course of virus-specific macromolecular synthesis during rubella virus infection in Vero cells

Virus specific macromolecular synthesis was studied in Vero cells infected with plaque-purified rubella virus under one-step multiplication conditions. Under these conditions, the rate of virus production was found to increase rapidly until 24 hr postinfection after which time the rate of virus production rose more slowly, reaching a peak level at 48 hr postinfection. This peak rate of virus production was maintained through 72 hr postinfection. A majority of the cells remained alive through 96 hr postinfection, although a 20 to 30% decrease in the number of living cells occurred between 24 and 48 hr postinfection, the time period at which cytopathic effect was first observed. The virus structural proteins were first detected intracellularly at 16 hr postinfection. The rate of synthesis of these proteins was already maximal at 16 hr postinfection and remained constant through 48 hr postinfection. By immunofluorescence, cells expressing virus proteins were first observed at 12 hr postinfection. At 24 hr postinfection, 35 to 50% of the cells in the infected culture were exhibiting immunofluorescence, at 36 hr postinfection, 65 to 90% of the cells were exhibiting immunofluorescence, and at 48 hr postinfection, all of the cells were exhibiting immunofluorescence. The virus genomic and subgenomic RNA species were first detectable by 12 hr postinfection. The rate of synthesis of both of these species peaked at 26 hr postinfection. Rubella virus infection was found to have no effect on total cell RNA synthesis. However, a modest inhibition of total cell protein synthesis which reached 40% by 48 hr postinfection was observed. When Northern analysis of RNA extracted from infected cells was performed, a negative-polarity, virus-specific RNA probe hybridized only to the virus genomic and subgenomic RNA species. A positive-polarity, virus-specific RNA probe hybridized predominantly to a negative-polarity RNA of genome length indicating that both the genomic and subgenomic RNAs are synthesized from a genome-length negative-polarity template. Defective interfering (DI) RNAs were not detected in infected cells through 96 hr postinfection or in cells onto which virus released through 96 hr postinfection was passaged. Thus, the generation of DI particles by rubella virus appears to play no role in the slow, noncytopathic replication of this virus or in the ability of rubella virus-infected cells to survive for extended periods of time.

Stability of rubella virus after long-term persistence in human cell line

Primary infection of HEp-2 cells with rubella virus resulted in non-cytophatic long-term persistent infection. During four years of persistence the virus was produced in sufficient quantities (up to 6 logs PFU/ml) and did not differ from the parental variant in its pathogenicity for BHK-21 or RK-13 cells, or hemagglutinating activity, but formed smaller plaques. Persistent virus preserved the original antigenicity as judged from reciprocal hemagglutination-inhibition or plaque reduction-neutralization tests with polyclonal antisera. Both original and persistent rubella viruses were thermoresistant (T 56 degrees C) and slightly temperature-sensitive. Clonal analysis revealed presence of ts-mutants among both original and persistent virus clones with different degrees of plating efficiency at 40 degrees/34 degrees C. RNA fingerprinting showed only minor changes in persistent rubella virus.

The development and standardization of an antigen detection ELISA for rubella virus grown in rabbit cells

A double antibody sandwich ELISA for the detection of rubella virus antigen was developed and standardized. Commercially available antisera were chosen in order to make the assay readily available. Antigen detection gave an excellent correlation to titers obtained by examination of cytopathogenic effect (CPE, r = 0.986). Replication of rubella virus grown in rabbit cells was identified with CPE and positive ELISA appearing within a difference of +/- one day. ELISA provided an objective detection of rubella virus which is often difficult by the reading of CPE. The method was found to be both sensitive and reproducible and facilitated work in rubella virus control involving a large number of virus titrations.

Inability of Japanese rubella vaccines to induce antibody response in rabbits is due to growth restriction at 39 degrees C

We have compared the kinetic growth patterns of To-336, MEQ11, KRT, and SK2 rubella vaccine strains licensed in Japan at 37 degrees and 39 degrees C with those of progenitor wild strains of rubella virus. The growth of vaccine strains was depressed at 39 degrees C to a level about 3 log10 lower than that at 37 degrees C. The difference in virus titer attained by wild strains at 37 degrees and 39 degrees C was less than tenfold. The growth potential at 39 degrees C paralleled the immunogenic marker of rubella virus, i.e. the capability of virus to induce antibody response upon subcutaneous injection in rabbits for all wild and vaccine strains examined, including one strain at an intermediate level of attenuation. Several clones were isolated from the progeny produced by a vaccine strain during the growth at 39 degrees C. Among them were partial revertants in immunogenic marker as well as in the growth potential at 39 degrees C. It was concluded that the immunogenic marker of rubella virus in rabbits represented its capability to replicate at the body temperature of the animal.

Persistent rubella virus infection of human synovial cells cultured in vitro

Primary and passaged human synovial cell cultures inoculated with wild-type and vaccine strains of rubella virus were incubated at 32 C and 37 C. At 32 C, the temperature close to that in human peripheral joints, infection persisted with extracellular virus titers of approximately 10(4) fluorescent focus-forming units/ml. Extracellular titers at 37 C first stabilized at one-tenth the level of the titers at 32 C and then declined after 20 days to undetectable levels. Cellular expression of viral antigen rose at 32 C and fell at 37 C. Infection was noncytocidal at all stages. Virus yields reflected the temperature in the subsequent incubation rather than during virus adsorption. Interferon was found only in cultures held at 37 C and was mainly alpha with a minor beta fraction, a result suggesting retention of functional characteristics of the type A macrophage-like synovial cell. We conclude that persistent infection of synovial tissue in vivo is a feasible explanation for the presence of rubella virus in peripheral joints of patients with chronic arthritis.

Changes in glycosylation of rubella virus envelope proteins during maturation

Tunicamycin treatment of radioactively labelled infected Vero cells followed by electrophoresis in polyacrylamide gels showed that the mol. wt. of the putative polypeptide backbones of GP59(E1) and GP43(E2), the intracellular counterparts to the envelope proteins E1 and E2 of rubella virus, were 53000 and 34000, respectively. Two possible intermediates in the glycosylation of GP43(E2) were also identified. [3H]Mannose-labelled E1, E2, GP59(E1) and GP43(E2) were digested with Pronase and the glycopeptides separated by gel filtration. GP59(E1) contained glycopeptides in two size classes, designated R1.5 and R2.1; E1 contained these and an additional size class, R2.7. GP43(E2) contained glycopeptides in three size classes, R1.5, R2.1 and R2.7; E2 contained these and size class R3.3. The glycopeptides derived from GP59(E1) and GP43(E2) were all sensitive to endoglycosidase H treatment whereas the glycopeptides of E1 and E2 contained both sensitive and resistant components.

[Virological studies on the feto-maternal tissues infected with rubella virus]

In studies on the congenital rubella syndrome, trans-placental rubella virus (RV) infection was investigated in vitro with human chorionic, decidual and fetal tissues obtained by artificial abortion from RV-infected pregnant women showing high hemagglutination-inhibiting and complement-fixing RV antibodies (1:512 and 1:16). RV was isolated from both chorionic (CR) and the fetal cells (FR) derived from RV-infected pregnant woman and the neutralization test disclosed that their antigenicity and biological properties were similar to that of the standard RV strain, M-33. These CR and FR cells showed a constant release of RV ranging from 2 to 4 log10 FFU (focus forming unit)/0.1ml into the culture media. Moreover, positive staining by immunofluorescent technique (IF) over 70 days seems to indicate RV persistent infection in these cells. However, decidual cells derived from RV-infected pregnant woman gave negative results in the RV release and IF staining. The above evidence strongly indicates that the chorionic cells are easily infected and converted to the RV-carrier. One possible mode of trans-placental RV infection is via an initial infection of the chorionic cells followed by the establishment of persistent RV infection.

Further studies on the restriction of rubella virus replication in rat glial cells in culture

We have shown previously that normal rat glial cells in tissue culture are nonpermissive for rubella virus (RV) replication for up to 2 weeks postinfection and that during that time, only five of the seven intracellular polypeptides associated with a normal productive infection could be observed following autoradiography. In this note we report three changes observed to occur simultaneously upon continuous subculture of these infected glia. Cell morphology and growth characteristics were significantly altered, infectious virus particles could be detected in tissue culture media, and analysis of intracellular viral polypeptides revealed the synthesis of ll seven polypeptides associated with a productive RV infection. These data indicate that under the appropriate conditions normal rubella virions may be reexpressed in a manner characteristic of many persistent viral infections. In addition, immunofluorescence techniques have been employed which show that during a nonproductive infection RV antigens are expressed in some glia which bear a striking morphological resemblance to oligodendrocytes.

Antibody response to rubella virus proteins in different physical forms

The immunogenicity of different antigens, containing rubella virus hemagglutinating (HA) membrane protein, was studied using live virus, beta-propiolactone-inactivated virus, detergent and lipid-free octamers and virosomes. Whole virus particles, live or inactivated, induced hemagglutination inhibition (HAI) antibodies in rabbits after one subcutaneous injection of 0.16 micrograms of HA protein. Hemagglutinin rosettes or virosomes failed to induce antibodies even at a dose of 120 micrograms. Apparently, the extraction of viral membrane hemagglutinin, for the preparation of a rubella subunit vaccine, led to destruction of the antigenicity responsible for the induction of hemagglutination inhibiting antibodies. These results are discussed in the light of earlier studies on the preparation of a rubella subunit vaccine.

Characteristics of a persistent rubella infection in a human cell line

A persistent infection of the human MCF-7 cell line (MCF-7RV) was established with the DBS strain of rubella virus at a low multiplicity of infections. Fluorescent antibody staining revealed that 100% of the cells were positive for rubella antigens. The infected cells were refractory to superinfection with vesicular stomatitis virus (VSV) but were susceptible to herpes simplex virus type 2 (HSV-2). No interferon could be detected in infected cell culture fluid, and continuous passage in the presence of antibody did not lead to a decrease in the percentage of infected cells. Virus production in the persistently infected cells represented a 5- to 10-fold increase over primary infection. Plaque assays at 30 and 39 degree C of the virus produced at 37 degree C revealed the presence of temperature-sensitive (ts) mutants. If MCF-7RV cells were maintained at 30 degree C, significant increases in virus production were observed, leading to cytopathic effect and destruction of the monolayer. If maintained at 39 degree C, MCF-7RV cells produced less virus and demonstrated normal morphology. These data suggest that the naturally selected population of ts mutants being produced by these cells represents the mechanism by which persistence is maintained.

Purification of infectious rubella virus by gel filtration on sepharose 2B compared to gradient centrifugation in sucrose, sodium metrizoate and metrizamide

Rubella virus was purified by chromatography on Sepharose 2B after concentration by ultrafiltration on hollow fibers and hydroextraction with PEG 20,000. Yields of 40% infectivity and 70% hemagglutinating activity were routinely obtained. Chromatographic purification was compared to ultracentrifugation in sucrose, metrizamide and sodium metrizoate. Yields were lower in sucrose and metrizamide, while sodium metrizoate reduced the infectivity of the virus below detectable levels. These results demonstrate the advantage of Sepharose 2B for the purification of infectious rubella virus.

Fatty acid composition of rubella virus and BHK21/13S infected cells

The rubella virus is composed of RNA (2.4 per cent dry weight of the virus), proteins (74.8 per cent), carbohydrates (4:2.5 per cent of which are present as aminosugars, 1.5 per cent as neutral sugars) and lipids (18.8 per cent). The analysis of fatty acids in rubella virus was done at the same time as the analysis of control cells and infected cells. In the virus, the main fatty acids are: palmitic (26 per cent), stearic (15 per cent), oleic (15 per cent). Rubella virus differs from other togaviruses by the presence of fatty acids with odd-numbers of atoms of C (C15, C17, C19) which represent 23 per cent of total acids and of an hydroxyacid. In the cells, the acids oleic, palmitic, stearic and linoleic represent 90 per cent of total fatty acids. The infection of the BHK21/13S cells by rubella virus leads essentially to an increase (35 per cent) of the amount of linoleic acid with a decrease of palmitic and oleic acids.

Replication and expression of rubella virus in human lymphocyte populations

Human mononuclear cells (lymphocytes and monocytes) from peripheral blood were examined for their ability to support the replication of rubella virus (RV) after infection in vitro. Replication was shown to occur in mixed lymphocytes and to be enhanced by stimulation with phytohaemagglutinin or pokeweek mitogen. A comparison of RV polypeptide synthesis in lymphocytes and RK13 cells showed no major differences in the polypeptides induced by infection. However, cellular translation was inhibited in the lymphocytes facilitating identification of virus polypeptides and eliminating the need for hypertonic labelling conditions used with RK13 cells. RV replication was also shown to occur in sub-populations of T-cells but not in B-cells. However, RV could be rescued from the B and monocyte population by co-cultivation with RK13 cells.

Replication of rubella virus in human mononuclear blood cells

Rubella virus was capable of replicating in both unstimulated and phytohemagglutinin-stimulated cultures of human mononuclear blood cells. Monocyte-derived macrophages were the main cell type responsible for viral replication. The susceptibility of macrophages increased during cultivation. Phytohemagglutinin-stimulated lymphocytes were able to support replication to a limited degree. No viral replication was detected in unstimulated lymphocytes. Both stimulation and viral replication in phytohemagglutinin-treated lymphocyte cultures were enhanced by the addition of murine macrophages. Human leukocyte interferon depressed the production of virus in these combined cultures. The finding that rubella virus is able to replicate in human lymphocytes as well as in macrophages may contribute to understanding the mechanisms of the suppressive effect of the virus on in vitro lymphocyte phytohemagglutinin responsiveness and in vivo immune functions.

Mechanism of persistence of rubella virus in LLC-MK2 cells

LLC-MK2 cells chronically infected with two strains of rubella virus, HPV-77 and Thomas, have been examined over several months to find out the mechanism of persistence. Evidence is given for the presence of defective particles in these cultures by finding virion RNA which sedimented at 12S instead of the 40S typical of the fully infectious virus. A 'provirus' DNA copy of the rubella virus genome was not detected by methods which included filter hybridization and in situ hybridization, or by treatment of the chronically infected cells with mitomycin C, antinomycin D or 5-bromodeoxyuridine. In addition, the chronically infected cells contained RNA-dependent RNA polymerase activity, but no RNA-dependent DNA polymerase activity.