( Department of Microbiology, Second Military Medical University, Shanghai 200433, China;
¹Institute of Basic Medicine, General Hospital of PLA, Beijing 100853, China;
²Department of Etiological Biology, Second Military Medical University, Shanghai 200433， China )

Abstract The promoter of phoP activated gene C (PpagC) of Salmonella typhimurium was cloned and used as transcriptionally regulating element for a plasmid that expresses hepatitis C virus core antigen. The resultant plasmid was transformed into attenuated Salmonella typhimurium SL7207 and its expression activity in vitro was determined. Mg²⁺ inhibited the recombinant bacteria to express HCV core antigen in a dose-dependent manner. This recombinant strain, and another bacterial strain that constitutively expresses HCV core antigen were orally inoculated BALB/c mice respectively. The stability of the plasmid in the bacteria and the immune responses was analyzed. The results showed that the in vivo activated PpagC promoter could stabilize the plasmid in the bacteria and enhance the humoral and cellular immune responses greatly, showing a novel way to produce effective, cheap oral vaccine against hepatitis C.