Original Investigation

Medical Microbiology and Immunology

, Volume 202, Issue 1, pp 49-61

First online:

IFNγ expression by an attenuated strain of Salmonella enterica serovar Typhimurium improves vaccine efficacy in susceptible TLR4-defective C3H/HeJ mice

  • Samia M. Al-OjaliAffiliated withDepartment of Medical Microbiology and Immunology, Faculty of Medicine and Health Sciences, United Arab Emirates UniversitySchool of Biomedical Science, University of Ulster
  • , C. B. Tara MooreAffiliated withSchool of Biomedical Science, University of Ulster
  • , Maria J. Fernandez-CabezudoAffiliated withDepartment of Biochemistry, Faculty of Medicine and Health Sciences, United Arab Emirates University
  • , Basel K. al-RamadiAffiliated withDepartment of Medical Microbiology and Immunology, Faculty of Medicine and Health Sciences, United Arab Emirates University Email author 

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C3H/HeJ mice carry a mutated allele of TLR4 gene (TLR4 d ) and thus are hyporesponsive to the lethal effects of lipopolysaccharide (LPS). Characteristically, however, the mice are also hypersusceptible to infections, particularly by Gram-negative bacteria such as Salmonella enterica serovar Typhimurium (S. typhimurium) and are known to be difficult to vaccinate against virulent exposure. This is observed despite the expression of wild-type allele of Nramp1 gene, another important determinant of Salmonella susceptibility. In contrast, C3H/HeN mice (TLR4 n Nramp1 n ) express a functional TLR4 protein and are resistant to infection, even by virulent strains of S. typhimurium. In the present study, we describe the immune system-enhancing properties of an attenuated strain of S. typhimurium engineered to express murine IFN-γ. This strain (designated GIDIFN) was able to modulate immune responses following systemic inoculation by upregulating the production of inflammatory mediators (IL-6 and IL-12) and anti-bacterial effector molecules (nitric oxide; NO). Consequently, this led to a more effective control of bacterial proliferation in systemic target organs in both C3H/HeJ and C3H/HeN mice. Although evidence for the enhancement in immune responses could be observed as early as few hours post-inoculation, sustained improvements required 2–3 days to manifest. Vaccination of C3H/HeJ mice with GIDIFN strain, even at low doses, conferred a significantly higher degree of protection against challenge with virulent Salmonella in susceptible C3H/HeJ mice. Our data demonstrate that IFNγ-expressing Salmonella are immunogenic and confer excellent protection against virulent challenge in susceptible C3H/HeJ mice; in addition they may be used as an effective mucosal delivery vectors against virulent infection and for boosting immune responses in immunodeficient hosts.


TLR4 Innate immunity Salmonella typhimurium IFN-γ C3H/HeJ