Effects of IL-12 coexpression level on antigen expression and immune responses induced by HBsAg DNA vaccination / 中华微生物学和免疫学杂志

ABSTRACT

Objective To investigate the effects of IL-12 coexpression level on antigen expression and immune responses induced by HBsAg DNA vaccination. Methods DNA vaccine plasmid pHBV carrying codon-optimized preS2-S gene of reference sequence CHN-HBV07-C in China was constructed. Three DNA vaccine plasmids pHBV-12i, pHBV-12l and pHBV-12h were also constructed by subcloning three different IL-12 expression cassettes with various expression strengths to plasmid pHBV, respectively. Expression levels of IL-12 and HBsAg in vaccine plasmid-tranfected 293T cells were measured by quantitative ELISA. DNA vaccines were administered intramuscularly to BALB/c mice and HBsAg-specific cellular immune responses were determined by IFN-γ ELISPOT. HBsAg-specific antibodies were tested by Chemiluminescence Quantitative Immunoassay. Results The HBsAg expression level in 293T cells was 70 ng/ml when transfected by plasmid pHBV without IL-12 expression cassette, and the HBsAg level was 18 ng/ml when transfected by plasmid pHBV-12l carrying low-level IL-12 expression cassette, whereas the HBsAg level was only 6 ng/ml when transfected by plasmid pHBV-12h carrying high-level IL-12 expression cassette.Results of DNA vaccination revealed that HBsAg-specific humoral and cellular immune responses were significantly decreased in mice administering vaccine pHBV-12h carrying high-level IL-12 expression cassette. Although HBsAg-specific antibody responses in mice inoculated with pHBV-12l were also decreased when compared with those in pHBV-vaccinated mice without IL-12 expression, the HBsAg-specific cellular immune responses were significantly increased. Conclusion High-level coexpression of IL-12 may suppress the expression of HBsAg, Whereas modest coexpression of IL-12 significantly enhanced the HBsAg-specific T cell responses induced by DNA vaccination. Therefore, it is so important to balance the expression between adjuvant and antigen to enhance the immune response.