Immune responses in mice vaccinated with a DNA vaccine expressing serine protease-like protein from the new-born larval stage of Trichinella spiralis.

Trichinella spiralis is a parasitic helminth that can infect almost all mammals, including humans. Trichinella spiralis infection elicits a typical type 2 immune responses, while suppresses type 1 immune responses, which is in favour of their parasitism. DNA vaccines have been shown to be capable of eliciting balanced CD4(+) and CD8(+) T cell responses as well as humoral immune responses in small-animal models, which will be advantage to induce protective immune response against helminth infection. In this study, serine protease (Ts-NBLsp) was encoded by a cDNA fragment of new-born T. spiralis larvae, and was inserted after CMV promoter to construct a DNA vaccine [pcDNA3.1(+)-Ts-NBLsp]. Ts-NBLsp expression was demonstrated by immunofluorescence. Sera samples were obtained from vaccinated mice, and they showed strong anti-Ts-NBLsp-specific IgG response. Mice immunized with the pcDNA3.1(+)-Ts-NBLsp DNA vaccine showed a 77.93% reduction in muscle larvae (ML) following challenge with T. spiralis ML. Our results demonstrate that the vaccination with pcDNA3.1(+)-Ts-NBLsp plasmid promoted the balance of type 1 and 2 immune responses and produced a significant protection against T. spiralis infection in mice.