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.