Londesborough, Philip; (1991) Biological and biochemical characterisation of rubella virus strains. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In this thesis the biological and biochemical properties of 6 strains of rubella virus (vaccine strains RA27/3 and HPV77, laboratory strain Judith, and three wild type isolates) were compared. The growth characteristics of all virus strains were similar although they could be distinguished by neutralisation kinetics, foci morphology in RK13 cells and rate limiting ELISA. In neutralization kinetics the homologous reaction is, in general, faster than the heterologous reaction. The morphology of the foci of infection varies from strain to strain, some strains produce many small foci (0.1mm in diameter), resulting in extensive CPE whilst others produce large discrete foci (>0.5mm in diameter) with localised CPE (identified by histochemical staining). Rate limiting ELISA shows that the reaction of post vaccination sera with different rubella strains is more varied than that of acute sera or sera from a remote natural infection. These results suggest a degree of antigenic diversity in rubella virus strains. All virus strains show similar structural proteins by western blotting. However different antigenic peptides were identified by limited protease digestion of the virus followed by western blotting. This result suggests a difference in amino acid sequence between strains. The biological and chemical properties of the immunodominant rubella El protein (cloned from laboratory strain Judith and expressed in E. coli) were also studied. Its antigenicity was assessed using sera from individuals with natural or vaccine induced rubella immunity. The results obtained showed that the reaction of specific sera to the recombinant antigen distinguished between strains of virus and RA27/3. The reaction of RA27/3 was significantly slower at 20% of the reaction rate of other strains of virus. Overall the results presented in this thesis demonstrate a difference in antigenic specificity between strains of virus, particularly between RA27/3 and other strains, possibly explaining the high rate of reinfection after vaccination compared with naturally immune individuals.

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