Praziquantel (PZQ), which is used to treat all forms of schistosomiasis, has been shown to induce strong T cell activities and decrease T regulatory cell levels. In our study, we investigated whether PZQ may be used as an adjuvant for a hepatitis B surface antigen (HBsAg) DNA vaccine (pcD-S2) in eliciting strong humoral and cellular responses. Our data demonstrate that PZQ as an adjuvant increased T cell proliferation and an HBsAg-specific antibody response that was characterized by a higher ratio of IgG2a/IgG1. Moreover, a higher level of IFN-gamma in CD4(+) and CD8(+) T cells were elicited. In addition, a significantly antigen-specific cytotoxic T lymphocyte response was also observed. The expression of TGF-beta can be induced by HBsAg, while PZQ as an adjuvant can inhibit the expression of TGF-beta and TGF-beta/Smad2,3 signaling. The frequency of CD4(+)CD25(+)Foxp3(+) Treg cells was reduced. Importantly, the regulatory function of CD4(+)CD25(+) Treg cells was correspondingly impaired. Together, these results suggest that PZQ can enhance humoral and cellular responses to HBsAg DNA vaccination through inhibition TGF-beta/Smad2,3 signaling.
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