title: Potent innate immune response to pathogenic leptospira in human whole blood.
abstract: BACKGROUND
  Leptospirosis is caused by pathogenic spirochetes of the genus Leptospira. The bacteria enter the human body via abraded skin or mucous membranes and may disseminate throughout. In general the clinical picture is mild but some patients develop rapidly progressive, severe disease with a high case fatality rate. Not much is known about the innate immune response to leptospires during haematogenous dissemination. Previous work showed that a human THP-1 cell line recognized heat-killed leptospires and leptospiral LPS through TLR2 instead of TLR4. The LPS of virulent leptospires displayed a lower potency to trigger TNF production by THP-1 cells compared to LPS of non-virulent leptospires.
  
  
  RESULTS
  We investigated the host response and killing of virulent and non-virulent Leptospira of different serovars by human THP-1 cells, human PBMC's and human whole blood. Virulence of each leptospiral strain was tested in a well accepted standard guinea pig model. Virulent leptospires displayed complement resistance in human serum and whole blood while in-vitro attenuated non-virulent leptospires were rapidly killed in a complement dependent manner. In vitro stimulation of THP-1 and PBMC's with heat-killed and living leptospires showed differential serovar and cell type dependence of cytokine induction. However, at low, physiological, leptospiral dose, living virulent complement resistant strains were consistently more potent in whole blood stimulations than the corresponding non-virulent complement sensitive strains. At higher dose living virulent and non-virulent leptospires were equipotent in whole blood. Inhibition of different TLRs indicated that both TLR2 and TLR4 as well as TLR5 play a role in the whole blood cytokine response to living leptospires.
  
  
  CONCLUSIONS
  Thus, in a minimally altered system as human whole blood, highly virulent Leptospira are potent inducers of the cytokine response.
authors.affiliation: Royal Tropical Institute (KIT), KIT Biomedical Research, Amsterdam, The Netherlands. m.goris@kit.nl
authors.forename: Marga G A
authors.initials: MG
authors.lastname: Goris
authors.forename: Jiri F P
authors.initials: JF
authors.lastname: Wagenaar
authors.forename: Rudy A
authors.initials: RA
authors.lastname: Hartskeerl
authors.forename: Eric C M
authors.initials: EC
authors.lastname: van Gorp
authors.forename: Simone
authors.initials: S
authors.lastname: Schuller
authors.forename: Avril M
authors.initials: AM
authors.lastname: Monahan
authors.forename: Jarlath E
authors.initials: JE
authors.lastname: Nally
authors.forename: Tom
authors.initials: T
authors.lastname: van der Poll
authors.forename: Cornelis
authors.initials: C
authors.lastname: van 't Veer
mesh_terms: D000818:Animals; D002460:Cell Line; D004797:Enzyme-Linked Immunosorbent Assay; D006168:Guinea Pigs; D006801:Humans; D007113:Immunity, Innate / Q000276:immunology*; D015850:Interleukin-6 / Q000378:metabolism; D007919:Leptospira / Q000276:immunology* / Q000472:pathogenicity*; D007963:Leukocytes, Mononuclear / Q000276:immunology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D014774:Virulence
chemical_list: D015850:Interleukin-6; D014409:Tumor Necrosis Factor-alpha