Large-scale purification of rubella virus and preparation of an experimental split rubella virus vaccine

Purification of rubella virus E1-E2 protein complexes by immunoaffinity chromatography

A murine monoclonal antibody directed against the E1 membrane glycoprotein of rubella virus was immobilized on an N-hydroxysuccinimide-activated chromatographic support. The antibody was used to purify rubella virus E1-E2 protein complexes from Tween-80/diethyl ether extracts of cell culture supernatants containing virus particles. The adsorption behaviour of immunosorbents with ligand densities of 2.9, 5.4 and 11.1 mg monoclonal antibody per millilitre of gel was investigated using batchwise conditions. Then the immunoaffinity purification process was optimized with regard to adsorption efficiency by adjusting the flow rate, the bed height and the amount of sample loaded onto the column. The optimized immunoaffinity purification process which is reproducible and relatively simple (one-step) had a yield of 73%, a concentration factor of 5-8 and a purification factor of about 2600. No mouse IgG due to ligand leakage could be detected in the immunopurified product using an enzyme immunoassay. High-performance size exclusion chromatography, sodium dodecyl sulphate polyacrylamide gel electrophoresis, immunoblotting and electron microscopy showed that the immunopurified product contained rosette-like structures formed by complexes of E1 and E2 proteins. The product retained its hemagglutinating activity and proved to be suitable for application in a fluorescent enzyme immunoassay for determination of anti-rubella IgG in human serum.

Characterisation of rubella virus hemagglutinin rosettes

Purified rubella virus treated with Triton X-100 was subjected to centrifugation in a sucrose density gradient containing nonionic detergent beta-D-octylglucoside. The result of this treatment was the formation of hemagglutinating rosettes containing viral glycoproteins VP2 (50,000 mol. wt.) and VP3 (63,000 mol. wt.). The rosettes have a 26 S sedimentation coefficient and a density of 1.2 g/cm3 in sucrose. Electron microscopy revealed 15 nm rosettes with a hollow center. The molecular weight of the rosettes was extrapolated at 850,000.

Efficacy and immune response to rubella subunits vaccines

Antibody and cell-mediated immunity (CMI) was measured in rabbits immunized with wild or attenuated virus and in rabbits vaccinated with a rubella subunit vaccine containing the viral envelope or nucleocapsid. The data presented show that a subunit vaccine containing the envelope proteins could induce a good antibody and CMI response. The results also suggest that such a vaccine was highly effective since 60 per cent of the rabbits immunized with the envelope proteins were protected when challenged with wild virus. This protection rate was identical as the protection achieved with a live attenuated vaccine.

Morphology, biochemical analysis and neuraminidase activity of rubella virus

A simple and reproducible method for the production of purified rubella virus is described. Purified virus was subjected to morphological and chemical analysis. The virus particles were rather pleomorphic (60 nm diameter), sometimes with one or more peripheral protrusions. The viral surface, revealed by negative staining, was composed of spikes 6 nm long, featuring enlarged ends. In SDS-urea-polyacrylamide gel electrophoresis, 4 major and 4 minor polypeptide bands were revealed. Total lipids and phospholipids were analysed on the same preparation. The viral particles were composed of RNA: 0.030 mg, and lipids: 0.245 mg, of which 0.169 mg were phospholipids for each mg of viral protein. Biologically, the purified virus preparation showed high infectivity, a high hemagglutination titre and a weak neuraminidase activity under defined conditions.

Structural proteins and subunits of rubella virus

Polyacrylamide gel electrophoresis of purified rubella virus revealed two distinct structural proteins VP1 and VP3, which had molecular weights of 62,500 and 35,000, respectively. In addition, a broad variable peak, designated VP2, with a molecular weight of about 47,500, was seen. Sucrose gradient analysis of virus disrupted by neutral detergents separated a labile 150S ribonucleoprotein, containing 40S ribonucleic acid and VP3, from the envelope fraction containing VP1 and VP2. VP1 and particularly VP2 were labeled with glucosamine and are thus glycoproteins. Labeling the polypeptides with different amino acids indicated that VP3, the "core" protein, is relatively rich in arginine but not in lysine. The size of the two main polypeptides, VP1 and VP3, corresponds to those of group A arboviruses.