title: Highly sensitive in vivo imaging of Trypanosoma brucei expressing "red-shifted" luciferase.
abstract: BACKGROUND
  Human African trypanosomiasis is caused by infection with parasites of the Trypanosoma brucei species complex, and threatens over 70 million people in sub-Saharan Africa. Development of new drugs is hampered by the limitations of current rodent models, particularly for stage II infections, which occur once parasites have accessed the CNS. Bioluminescence imaging of pathogens expressing firefly luciferase (emission maximum 562 nm) has been adopted in a number of in vivo models of disease to monitor dissemination, drug-treatment and the role of immune responses. However, lack of sensitivity in detecting deep tissue bioluminescence at wavelengths below 600 nm has restricted the wide-spread use of in vivo imaging to investigate infections with T. brucei and other trypanosomatids.
  
  
  RESULTS
  Here, we report a system that allows the detection of fewer than 100 bioluminescent T. brucei parasites in a murine model. As a reporter, we used a codon-optimised red-shifted Photinus pyralis luciferase (PpyRE9H) with a peak emission of 617 nm. Maximal expression was obtained following targeted integration of the gene, flanked by an upstream 5'-variant surface glycoprotein untranslated region (UTR) and a downstream 3'-tubulin UTR, into a T. brucei ribosomal DNA locus. Expression was stable in the absence of selective drug for at least 3 months and was not associated with detectable phenotypic changes. Parasite dissemination and drug efficacy could be monitored in real time, and brain infections were readily detectable. The level of sensitivity in vivo was significantly greater than achievable with a yellow firefly luciferase reporter.
  
  
  CONCLUSIONS
  The optimised bioluminescent reporter line described here will significantly enhance the application of in vivo imaging to study stage II African trypanosomiasis in murine models. The greatly increased sensitivity provides a new framework for investigating host-parasite relationships, particularly in the context of CNS infections. It should be ideally suited to drug evaluation programmes.
authors.affiliation: Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom.
authors.forename: Alex P
authors.initials: AP
authors.lastname: McLatchie
authors.forename: Hollie
authors.initials: H
authors.lastname: Burrell-Saward
authors.forename: Elmarie
authors.initials: E
authors.lastname: Myburgh
authors.forename: Michael D
authors.initials: MD
authors.lastname: Lewis
authors.forename: Theresa H
authors.initials: TH
authors.lastname: Ward
authors.forename: Jeremy C
authors.initials: JC
authors.lastname: Mottram
authors.forename: Simon L
authors.initials: SL
authors.lastname: Croft
authors.forename: John M
authors.initials: JM
authors.lastname: Kelly
authors.forename: Martin C
authors.initials: MC
authors.lastname: Taylor
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D015870:Gene Expression; D054884:Host-Pathogen Interactions; D049409:Luciferases, Firefly / Q000032:analysis* / Q000235:genetics; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D061848:Optical Imaging / Q000379:methods*; D010274:Parasitology / Q000379:methods*; D013194:Staining and Labeling / Q000379:methods*; D014346:Trypanosoma brucei brucei / Q000235:genetics / Q000302:isolation & purification*; D014353:Trypanosomiasis, African / Q000469:parasitology*
chemical_list: C485197:luciferase, Photinus; D049409:Luciferases, Firefly