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GFPuv-Expressing Recombinant Rickettsia typhi: a Useful Tool for the Study of Pathogenesis and CD8+ T Cell Immunology
Matthias Hauptmann1, Nicole Burkhardt2, Ulrike Munderloh2
1Department of Immunology, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany.
Abstract:
Rickettsia typhi is the causative agent of endemic typhus, a disease with increasing incidence worldwide that can be fatal. Because of its obligate intracellular life style, genetic manipulation of the pathogen is difficult. Nonetheless, in recent years, genetic manipulation tools have been successfully applied to rickettsiae. We describe here for the first time the transformation of R. typhi with the pRAM18dRGA plasmid that originally derives from Rickettsia amblyommatis and encodes the expression of GFPuv (green fluorescent protein with maximal fluorescence when excited by UV light). Transformed R. typhi (R. typhiGFPuv) bacteria are viable, replicate with kinetics similar to those of wild-type R. typhi in cell culture, and stably maintain the plasmid and GFPuv expression under antibiotic treatment in vitro and in vivo during infection of mice. CB17 SCID mice infected with R. typhiGFPuv succumb to the infection with kinetics similar to those for animals infected with wild-type R. typhi and develop comparable pathology and bacterial loads in the organs, demonstrating that the plasmid does not influence pathogenicity. In the spleen and liver of infected CB17 SCID mice, the bacteria are detectable by immunofluorescence microscopy in neutrophils and macrophages by histological staining. Finally, we show for the first time that transformed rickettsiae can be used for the detection of CD8+ T cell responses. GFP-specific restimulation of spleen cells from R. typhiGFPuv-infected BALB/c mice elicits gamma interferon (IFN-γ), tumor necrosis factor alpha (TNF-α), and interleukin 2 (IL-2) secretion by CD8+ T cells. Thus, R. typhiGFPuv bacteria are a novel, potent tool to study infection with the pathogen in vitro and in vivo and the immune response to these bacteria.
Insights
Researchers successfully genetically modified Rickettsia typhi (R. typhi) bacteria to express GFPuv. This transformed R. typhi is a viable tool for studying endemic typhus and immune responses in vitro and in vivo.
Area of Science:
- Microbiology and Infectious Diseases
- Genetic Engineering and Molecular Biology
- Immunology
Background:
- Endemic typhus, caused by Rickettsia typhi, is a potentially fatal disease with increasing global incidence.
- The obligate intracellular lifestyle of R. typhi poses significant challenges for genetic manipulation.
- Recent advancements have enabled genetic manipulation tools for rickettsiae.
Purpose of the Study:
- To describe the first successful transformation of R. typhi with a plasmid encoding GFPuv.
- To evaluate the viability, replication, and stability of transformed R. typhi (R. typhi^GFPuv).
- To assess the pathogenicity and utility of R. typhi^GFPuv in studying host immune responses.
Main Methods:
- Transformation of R. typhi with the pRAM18dRGA plasmid encoding GFPuv.
- Assessment of bacterial viability, replication kinetics in cell culture, and plasmid stability in vitro and in vivo (mice).
- Pathogenicity studies in CB17 SCID mice and immune response analysis (IFN-γ, TNF-α, IL-2) in BALB/c mice.
Main Results:
- Transformed R. typhi^GFPuv bacteria are viable, replicate similarly to wild-type R. typhi, and stably express GFPuv.
- R. typhi^GFPuv infection in mice shows kinetics, pathology, and bacterial loads comparable to wild-type R. typhi, indicating no influence on pathogenicity.
- Detection of R. typhi^GFPuv in neutrophils and macrophages in mouse spleen and liver via immunofluorescence microscopy.
- Restimulation of spleen cells from infected mice elicits IFN-γ, TNF-α, and IL-2 secretion by CD8+ T cells, demonstrating utility in detecting T cell responses.
Conclusions:
- R. typhi^GFPuv represents a novel and effective tool for studying R. typhi infections in vitro and in vivo.
- The transformed bacteria facilitate the investigation of host immune responses, particularly CD8+ T cell activity.
- This genetic tool enhances research capabilities for understanding endemic typhus pathogenesis and host-pathogen interactions.
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