A Salmonella typhimurium ghost vaccine induces cytokine expression in vitro and immune responses in vivo and protects rats against homologous and heterologous challenges

PLoS One. 2017 Sep 29;12(9):e0185488. doi: 10.1371/journal.pone.0185488. eCollection 2017.

Abstract

Salmonella enteritidis and Salmonella typhimurium are important food-borne bacterial pathogens, which are responsible for diarrhea and gastroenteritis in humans and animals. In this study, S. typhimurium bacterial ghost (STG) was generated based on minimum inhibitory concentration (MIC) of sodium hydroxide (NaOH). Experimental studies performed using in vitro and in vivo experimental model systems to characterize effects of STG as a vaccine candidate. When compared with murine macrophages (RAW 264.7) exposed to PBS buffer (98.1%), the macrophages exposed to formalin-killed inactivated cells (FKC), live wild-type bacterial cells and NaOH-induced STG at 1 × 108 CFU/mL showed 85.6%, 66.5% and 84.6% cell viability, respectively. It suggests that STG significantly reduces the cytotoxic effect of wild-type bacterial cells. Furthermore, STG is an excellent inducer for mRNAs of pro-inflammatory cytokine (TNF-α, IL-1β) and factor (iNOS), anti-inflammatory cytokine (IL-10) and dual activities (IL-6) in the stimulated macrophage cells. In vivo, STG vaccine induced humoral and cellular immune responses and protection against homologous and heterologous challenges in rats. Furthermore, the immunogenicity and protective efficacy of STG vaccine were compared with those of FKC and non-vaccinated PBS control groups. The vaccinated rats from STG group exhibited higher levels of serum IgG antibody responses, serum bactericidal antibodies, and CD4+ and CD8+ T-cell populations than those of the FKC and PBS control groups. Most importantly, after challenge with homologous and heterologous strains, the bacterial loads in the STG group were markedly lower than the FKC and PBS control groups. In conclusion, these findings suggest that the STG vaccine induces protective immunity against homologous and heterologous challenges.

MeSH terms

  • Animals
  • Antibodies, Bacterial / biosynthesis
  • Antibodies, Bacterial / blood
  • Bacterial Vaccines / administration & dosage*
  • Bacterial Vaccines / immunology
  • CD4-Positive T-Lymphocytes / immunology
  • CD8-Positive T-Lymphocytes / immunology
  • Cell Line
  • Cytokines / genetics
  • Cytokines / metabolism*
  • Inflammation Mediators / metabolism
  • Mice
  • RNA, Messenger / genetics
  • Rats
  • Salmonella Infections, Animal / immunology
  • Salmonella Infections, Animal / prevention & control*
  • Salmonella typhimurium / immunology*

Substances

  • Antibodies, Bacterial
  • Bacterial Vaccines
  • Cytokines
  • Inflammation Mediators
  • RNA, Messenger

Grants and funding

This work was supported by the Human Resource Training Program for Regional Innovation and Creativity through the Ministry of Education and National Research Foundation of Korea (2015035949). As shown in the title of this government project, a final goal of the project is basically fostering graduate students to fit for industries and to have a job experience for a month with a partner company. Of course, graduate students should have performed R&D research to get salaries from the project. After graduation, some qualified graduate students can have a job in the company involved in the project. In this respect, the government requires principal investigators to include a commercial company in this project as a partner. The government and company support 90% and 10% of the fund, respectively. “The commercial funder provided support in the form of salaries for authors [HBN, SO, SJ, HJP], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.