Immune response induced by recombinant plasmid expressing double preS_2 of hepatitis B virus genome in mice

Objective:To evaluate humoral immune response in normal BALB/c mice induced by inoculation with mammalian expression plasmid pcDNA3.1/S_2S-S_2 as a candidate DNA vaccine. It could express the fuse protein as a single S peptide with double preS_2 peptides by the series connection of preS_2, S, and preS_2 domains of hepatitis B virus genome. The preS_2 peptides had strong antigenicity and immune protection against infection of hepatitis B virus.Methods:Recombinant plasmid pcDNA3.1/S_2S-S_2, pcDNA3.1/S_2S, pcDNA3.1/S_1S_2S were constructed, and inoculated muscularly into BALB/c mice 100 μg per mouse, then boosted 2 and 4 weeks later serially. The sera samples were collected at time schedule to detect for anti-preS_2, anti-HBs.Results:5 weeks later after the first inoculation, the positive rate of anti-preS_2 in group of pcDNA3.1/S_2S-S_2 were 87.5% and lasted for 12 weeks. The titers of anti-preS_2 was 1∶2 000. In the other groups for control, the positive rates of anti-preS_2 were lower than 62.5%, and the titer of anti-preS_2 were low as 1∶500-1∶50. Meanwhile the positive rate and titer of anti-HBs in the group of pcDNA3.1/S_2S-S_2 were lower than those in control groups.Conclusion:It suggested that pcDNA3.1/S_2S-S_2, by which the double preS_2 peptides with a single S peptide could be expressed as fuse protein, could induce stronger humoral immune response against preS_2 antigen and poorer response against HBsAg, compared with the control plasmids by which only single preS_2 could be expressed.