Immune response induced by recombinant plasmid expressing double preS_(2) of hepatitis B virus genome in mice

To evaluate humoral immune response in normal BALB/c mice induced by inoculation with mammalian expression plasmid pcDNA3.1/S_(2)S-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. Recombinant plasmid pcDNA3.1/S_(2)S-S_(2), pcDNA3.1/S_(2)S, pcDNA3.1/S_(1)S_(2)S were constructed, and inoculated muscularly into BALB/c mice 100 mu-g 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. 5 weeks later after the first inoculation, the positive rate of anti-preS_(2) in group of pcDNA3.1/S_(2)S-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_(2)S-S_(2) were lower than those in control groups. It suggested that pcDNA3.1/S_(2)S-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.