Immune response induced by ppGpp-defective Salmonella enterica serovar Gallinarum in chickens

Abstract

To protect chickens from typhoid caused by Salmonella enterica serovar Gallinarum (S. Gallinarum), the attenuated 9R strain has been used in the field as a vaccine. However, safety concerns have been raised because the mutations in 9R are undefined while its efficacy is still a question under debate. A global regulator, ppGpp, synthesized by RelA and SpoT, has been shown to induce various virulence genes in S. Gallinarum (Jeong et al., 2008). In this study, two mutant strains defective in ppGpp-synthesis were constructed in wild-type S. Gallinarum (ΔppGpp) and 9R strain (9R-ΔppGpp) backgrounds and tested as live vaccines in chickens. After oral inoculation, the LD(50) values of ΔppGpp and 9R-ΔppGpp were approximately 5×10(10) colony forming unit (CFU) similarly as 9R strain, which was ∼10(5)-fold higher than that of the wildtype S. Gallinarum strain. Immunological analyses revealed immunization with either of the two attenuated ppGpp-defective strains induced significant antibody responses, the production of antibody-secreting B cells in blood, proliferation of CD4+ and CD8+ T cells in the spleen, and splenic expression of proinflammatory cytokines, such as IFN-γ and TGF-β4, at levels comparable to the 9R strain. Chickens immunized with the mutants (1×10(8) CFU) were 80% protected against oral challenge with 1×10(9) wild-type virulent bacteria (4,000-fold LD(50) dose), similar to the level of protection achieved by 9R immunization. Based on these data, live attenuated ΔppGpp-defective strains may serve as novel vaccines to control fowl typhoid in chickens.

Evaluation of Salmonella Gallinarum ghost formulated with Montanide™ ISA 70 VG adjuvant as a vaccine against fowl typhoid

“…A number of studies have demonstrated that the expression of acquired resistance to fowl typhoid depends upon the combined humoral and cell-mediated immune response of the infected host (Rana and Kulshreshtha, 2006;Park et al, 2010;Matsuda et al, 2011). In the present study, we observed a significant induction of systemic IgG responses in the immunised groups, especially in chickens immunised with a combination of ghost cells with Montanide TM ISA 70 VG (Fig.…”

“…4). Without a doubt, the Th1-cell immunity developed by the vaccinated chickens fits with the protection conferred against fowl typhoid (Chappell et al, 2009;Park et al, 2010). Table 2 and Fig.…”

Characterization of a Novel Inactivated Salmonella enterica Serovar Enteritidis Vaccine Candidate Generated Using a Modified cI857/λ PR/GeneEExpression System

“…As the ghosts harbor surface antigens identical to those of live bacteria, they induce a strong CMI response (12). A previous report regarding vaccination of chickens with Salmonella described the involvement of the CD4 ϩ and CD8 ϩ T cell response in protection (36). In the present study, we evaluated CMI by determining the S. Enteritidis antigen-specific lymphocyte proliferative response and the CD3 ϩ…”

“…5I, 5II, and 5III). CD4 ϩ major histocompatibility complex type II (MHC II)-restricted T cells are important for protection against intracellular pathogens, as they are involved in the production of macrophage-activating factors (27,36), assist B cells to produce more antibodies, and aid in generating Salmonella-specific CD8 ϩ T cells (32). The CD8 ϩ T cells differentiate into cytotoxic T lymphocytes, which play a protective role by liberating intracellular Salmonella from infected macrophages (8).…”

Role of RelA and SpoT in Burkholderia pseudomallei Virulence and Immunity

“…In S. Typhimurium, the ppGpp mutant elicited serum and mucosal antibody responses, measured by IgA and IgG titers, as well as cellular immune responses, measured by a delayed-type hypersensitivity (DTH) response (33). Similarly, in S. enterica, vaccination induced a B-cell response in blood measured by IgM, IgA, and IgG levels and induced CD4 ϩ and CD8 ϩ T-cell proliferation and gamma interferon (IFN-␥) and transforming growth factor (TGF)-␤4 production in spleens (37). This may render ppGpp-deficient Salmonella strains promising candidates as live-attenuated vaccines against typhoid in chicken.…”