Somatostatin (SS) DNA vaccine has been used to improve the growth and lactation of animals, however, the immune response is still unsatisfactory, especially in large animals. The present study aimed to investigate whether tissue plasminogen activator (tPA) could be applied as signal peptide for enhancing the effect of somatostatin DNA vaccine. A novel recombinant plasmid pEGS/2SS-tPA encoding two copies of somatostatin genes fused to tPA signal sequence was succesfully constructed and identified in MCF-7 cells. Subsequently, thirty female mice randomly were divided into three groups, treating with 50 μg pEGS/2SS-tPA (group T1), 50 μg pEGS/2SS (group T2), and 50 μg pEGFP-N1 (Control group) at weeks 0, 2, 4 and 6. Mating with male mice was performed at 2 weeks post final immunization. Results showed that mice both in T1 and T2 groups elicited significantly stronger anti-SS antibody level than that in control (p < 0.05), and mice in T1 group induced significantly higher serum GH and PRL concentration in comparison with T2 and control groups (p < 0.05). Expectantly, mice in T1 group also showed significantly higher average weight gain and offspring weaning weight than that in T2 and control groups, respectively (p < 0.05). Overall, these results suggested that novel somatostatin plasmid fused to tPA signal peptide obtained stronger immunogenicity, and better potentials of promoting growth and lactation, indicating that tPA is an effective signal peptide for enhancing the immune efficacy and performance of somatostatin DNA vaccine.
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