Induction of anti-microbial immune responses in severely immunodeficient hosts by IFNγ-expressing Salmonella enterica serovar Typhimurium correlates with efficient activation of macrophage effectors (VAC8P.1050)

Abstract

Abstract Susceptibility to infection by the intracellular bacterial pathogen, Salmonella enterica serovar Typhimurium (S. typhimurium), is controlled by many genes of innate and adaptive immunity. One of the most critical genes is IFN-γ and mice deficient in IFN-γ synthesis are highly susceptible to Salmonella. Previously, we also demonstrated that mice deficient in MyD88, an adaptor that regulates TLR signaling, are susceptible to Salmonella infection. In the current study, we compared immune responses in mice deficient in IFN-γ or MyD88 with wild-type controls following infection with an attenuated strain of S. typhimurium (designated BRD509) or a recombinant derivative engineered to express murine IFN-γ (GIDIFN). Infection studies with BRD509 or GIDIFN revealed that the latter strain was significantly less virulent in immunodeficient mice than BRD509 and correlated with decreased bacterial loads in systemic organs. Enhanced responsiveness was due to GIDIFN strain’s ability to activate effector macrophages, as shown by increased synthesis of inflammatory cytokines and anti-microbial effector molecules, including NO. Gene expression profiling by qPCR demonstrated stronger induction of key inflammatory modulators by GIDIFN in macrophages of immunodeficient animals. These findings suggest that immunotherapeutic approaches using attenuated bacterial strains expressing immunomodulatory genes is more efficacious and offers a superior safety profile even in severely immunodeficient hosts.