title: Identification, characterisation and expression analysis of natural killer receptor genes in Chlamydia pecorum infected koalas (Phascolarctos cinereus).
abstract: BACKGROUND
  Koalas (Phascolarctos cinereus), an iconic Australian marsupial, are being heavily impacted by the spread of Chlamydia pecorum, an obligate intracellular bacterial pathogen. Koalas vary in their response to this pathogen, with some showing no symptoms, while others suffer severe symptoms leading to infertility, blindness or death. Little is known about the pathology of this disease and the immune response against it in this host. Studies have demonstrated that natural killer (NK) cells, key components of the innate immune system, are involved in the immune response to chlamydial infections in humans. These cells can directly lyse cells infected by intracellular pathogens and their ability to recognise these infected cells is mediated through NK receptors on their surface. These are encoded in two regions of the genome, the leukocyte receptor complex (LRC) and the natural killer complex (NKC). These two families evolve rapidly and different repertoires of genes, which have evolved by gene duplication, are seen in different species.
  
  
  METHODS
  In this study we aimed to characterise genes belonging to the NK receptor clusters in the koala by searching available koala transcriptomes using a combination of search methods. We developed a qPCR assay to quantify relative expression of four genes, two encoded within the NK receptor cluster (CLEC1B, CLEC4E) and two known to play a role in NK response to Chalmydia in humans (NCR3, PRF1).
  
  
  RESULTS
  We found that the NK receptor repertoire of the koala closely resembles that of the Tasmanian devil, with minimal genes in the NKC, but with lineage specific expansions in the LRC. Additional genes important for NK cell activity, NCR3 and PRF1, were also identified and characterised. In a preliminary study to investigate whether these genes are involved in the koala immune response to infection by its chlamydial pathogen, C. pecorum, we investigated the expression of four genes in koalas with active chlamydia infection, those with past infection and those without infection using qPCR. This analysis revealed that one of these four, CLEC4E, may be upregulated in response to chlamydia infection.
  
  
  CONCLUSIONS
  We have characterised genes of the NKC and LRC in koalas and have discovered evidence that one of these genes may be upregulated in koalas with chlamydia, suggesting that these receptors may play a role in the immune response of koalas to chlamydia infection.
authors.affiliation: Faculty of Veterinary Science, University of Sydney, Camperdown, NSW, Australia. katrina.morris@roslin.ed.ac.uk.
authors.forename: Katrina M
authors.initials: KM
authors.lastname: Morris
authors.affiliation: Institute of Health and Biomedical Innovation, Queensland University of Technology, Kelvin Grove, Brisbane, QLD, Australia. marina.mathew@hdr.qut.edu.au.
authors.forename: Marina
authors.initials: M
authors.lastname: Mathew
authors.affiliation: Institute of Health and Biomedical Innovation, Queensland University of Technology, Kelvin Grove, Brisbane, QLD, Australia. cwaugh@usc.edu.au.|Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, Sippy Downs, QLD, Australia. cwaugh@usc.edu.au.
authors.forename: Courtney
authors.initials: C
authors.lastname: Waugh
authors.affiliation: Faculty of Veterinary Science, University of Sydney, Camperdown, NSW, Australia. beata.ujvari@deakin.edu.au.|Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Waurn Ponds, Geelong, VIC, Australia. beata.ujvari@deakin.edu.au.
authors.forename: Beata
authors.initials: B
authors.lastname: Ujvari
authors.affiliation: Institute of Health and Biomedical Innovation, Queensland University of Technology, Kelvin Grove, Brisbane, QLD, Australia. ptimms@usc.edu.au.|Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, Sippy Downs, QLD, Australia. ptimms@usc.edu.au.
authors.forename: Peter
authors.initials: P
authors.lastname: Timms
authors.affiliation: Institute of Health and Biomedical Innovation, Queensland University of Technology, Kelvin Grove, Brisbane, QLD, Australia. apolking@usc.edu.au.|Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, Sippy Downs, QLD, Australia. apolking@usc.edu.au.
authors.forename: Adam
authors.initials: A
authors.lastname: Polkinghorne
authors.affiliation: Faculty of Veterinary Science, University of Sydney, Camperdown, NSW, Australia. Kathy.belov@sydney.edu.au.
authors.forename: Katherine
authors.initials: K
authors.lastname: Belov
mesh_terms: D000818:Animals; D001315:Australia; D002689:Chlamydia / Q000302:isolation & purification* / Q000472:pathogenicity; D002690:Chlamydia Infections / Q000235:genetics* / Q000382:microbiology; D016678:Genome; D006801:Humans; D048368:Phascolarctidae / Q000235:genetics / Q000382:microbiology*; D055607:Receptors, Natural Killer Cell / Q000096:biosynthesis / Q000235:genetics*
chemical_list: D055607:Receptors, Natural Killer Cell