Characterization of genotype II Rubella virus strains

Area of Science:

• Virology
• Molecular Biology
• Immunology

Background:

• Two Rubella virus genotypes, RGI and RGII, are known, differing by 8-9% at the nucleotide level in the E1 glycoprotein gene.
• Genotype II (RGII) is a recently reported genotype, with limited characterization available.
• Understanding genetic and antigenic variations between Rubella virus genotypes is crucial for vaccine development and epidemiology.

Purpose of the Study:

• To characterize two RGII Rubella virus strains: the BRDII vaccine strain and the BR1 wild-type strain.
• To compare the genomic sequences of RGII strains with previously reported RGI sequences.
• To identify potential attenuating mutations in the BRDII vaccine strain by comparing its sequence to the BR1 wild-type strain.

Main Methods:

• Characterization of RGII viruses (BRDII and BR1) using monoclonal antibodies and polyclonal anti-rubella virus sera.
• Western blot analysis of purified virions to assess antigenic relatedness between RGII and RGI strains.
• Genomic sequencing of RGII strains and comparison with RGI sequences at nucleotide and amino acid levels.

Main Results:

• RGII and RGI strains showed similar reactions with most antibodies, indicating close antigenic relationship, with one exception for an anti-E2 MAb.
• Genomes of RGI and RGII strains were 9762 nucleotides long with identical UTR and ORF lengths.
• Overall nucleotide difference between RGI and RGII was ~8%, with ~4% amino acid difference; replicase proteins showed conserved N-terminal regions and variable C-terminal regions, including a hypervariable site.
• BRDII and BR1 sequences differed by 252 residues (2.59%), with no vaccine-specific differences identified in BRDII compared to RGI strains.

Conclusions:

• Rubella virus genotypes RGI and RGII are antigenically closely related despite genetic divergence.
• Specific regions within replicase proteins, particularly the C-terminal P150, exhibit significant variation.
• The genetic differences observed between the BRDII vaccine and BR1 wild-type strains do not indicate a common pathway for live attenuated rubella vaccine generation.