Comparative Analysis Of Immune Responses In Mice Immunized With Salmonella Enterica Serovar Typhimurium Mutants Deficient Global Regulators

Approximately 90% of microbial pathogens infects the host via mucosal routes. Mucosal surfaces provide a first line of defense against pathogens that perturb the host. Researches have showed that infections caused by mucosal pathogens can be effectively controlled by mucosal vaccines which induce both protective systemic and mucosal immune responses. It is becoming increasingly clear that administration of vaccines through mucosal route is one of the effective strategies of prevention and control of such diseases. Salmonella is a common mucosal pathogen which infects humans and animals mainly through contaminated food or water. Enteric fever caused by invasive Salmonella infection is an important health problem worldwide. In order to control it, vaccine research has lasted for decades. In all Salmonella serovar, Salmonella enterica serovar Typhimurium (S. Typhimurium) vaccines have been frequently studied. And researches indicated that attenuated vaccines derived from S. Typhimurium UK-1 are the most potential among more than 200 different S. Typhimurium strains.The common strategy used to render bacteria avirulent is the regulated delayed attenuation or direct deletion of certain genes essential for bacteria survival, such as global regulators. S. Typhimurium UK-1 with certain global regulator deletions have been shown to be avirulent and able to induce a protective immune response in mice. But there are currently no data on the difference in mucosal and systemic immune responses between these global regulator mutants. In this study we therefore constructed seven mutants of S. Typhimurium UK-1 by deleting different global regulators including envZ, crp,fis,fur, hilA,mlc and phoP and compared their mucosal and systemic immunogenicity in Balb/c mice by detecting IgG antibody levels in serum and sIgA antibodies in saliva, vaginal washes and fecal supernatant against S. Typhimurium UK-1 LPS and OMP. We found that the antibody response levels induced by different mutants were diverse in blood and mucosal sites.In blood, anti-OMPS IgG antibody levels from mice immunized by △fur, △envZ and Amlc were significantly higher than the other groups; Mice immunized with the △crp, △fur, AenvZ and AphoP mutant developed higher anti-LPS IgG responses among all immuninzed groups. In oral cavity, mice inoculated with AenvZ, △fur and AphoP mutant developed higher OMP-specific sIgA antibody responses and mice inoculated with Acrp, Afur, △phoP developed higher LPS-specific slgA antibody responses than the other groups, In vagina, higher anti-OMP sIgA antibodies were from mice immunized with Acrp and △fur mutants, and higher anti-LPS sIgA antibodies were from mice immunized with Acrp, Afur and AphoP strains. In rectum, mice orally inoculated with Acrp, △envZ and Amlc induced higher sIgA antibody responses against OMPs, mice inoculated with Acrp, △envZ, △phoP and Amlc induced higher anti-LPS sIgA antibody responses. Despite the different level of immunogenicity of these mutants in different effector sites, all immunized mice survived oral challenge with 105 LD50 of the virulent Salmonella Typhimurium UK-1 without showing any signs of illness for at least 30 days after challenge.In conclusion, our findings might pave the way for selecting certain attenuated Salmonella as optimal mucosal vaccine.