Salmonella ghosts expressing enterotoxigenic Escherichia coli k88ab, k88ac, k99, and fasa fimbrial antigens induce robust immune responses in a mouse model

Background: Bacterial ghosts can be developed as safe and effective vaccines against bacterial infectious disease such as enterotoxigenic Escherichia coli (ETEC)-induced diarrhea in neonatal piglets.Objective: Immune responses against a Salmonella ghost expressing ETEC K88ab, K88ac, K99, and FasA antigens with various adjuvants and inoculation routes were evaluated in mice.Animals and Methods: A ghost cell expressing K88ab, K88ac, K99, and FasA fimbrial antigens of ETEC on the envelope of oasd Salmonella typhimurium was constructed as a candidate vaccine against ETEC infection. To optimize the immunization strategy, 6-week-old female BALB/c mice were inoculated with the ghost and various adjuvants, and the immune responses against the individual fimbrial antigens were measured. Blood samples from caudal vein to evaluate serum IgG concentrations and fecal samples to evaluate mucosal IgA concentrations were collected up to 14 weeks post-prime immunization.Results: All groups with single, double, and triple inoculations of the ghost showed higher humoral and mucosal immune responses than the control group. In particular, the groups with intramuscular double and triple inoculations showed significantly higher immune responses. In addition, oral inoculation with a combination of the ghost and MONTANIDE IMS 1113 (MI1113) resulted in high and prolonged induction of intestinal IgA levels.Conclusion: These results indicated that both systemic and mucosal immunity against ETEC fimbrial antigens expressed by the ghost are induced by intramuscular booster inoculation with the ghost, and that addition of M1113 to the ghost was found to result in prominent induction of mucosal immunity through oral inoculation.