title: IP-10 Is a Sensitive Biomarker of Antigen Recognition in Whole-Blood Stimulation Assays Used for the Diagnosis of Mycobacterium bovis Infection in African Buffaloes (Syncerus caffer).
abstract: African buffaloes (Syncerus caffer) are maintenance hosts of Mycobacterium bovis, the causative agent of bovine tuberculosis. They act as reservoirs of this infection for a wide range of wildlife and domestic species, and the detection of infected animals is important to control the geographic spread and transmission of the disease. Interferon gamma (IFN-γ) release assays (IGRAs) utilizing pathogen-derived peptide antigens are highly specific tests of M. bovis infection; however, the diagnostic sensitivities of these assays are suboptimal. We evaluated the diagnostic utility of measuring antigen-dependent interferon gamma-induced protein 10 (IP-10) release as an alternative to measuring IFN-γ levels. M. bovis-exposed buffaloes were tested using the Bovigam PC-EC and Bovigam PC-HP assays and a modified QuantiFERON TB-Gold (mQFT) assay. IP-10 was measured in the harvested plasma and was produced in significantly greater abundance in response to M. bovis antigens in Bovigam-positive than in Bovigam-negative animals. For each assay, using the Bovigam results as a reference, receiver operating characteristic curve analysis was done to determine diagnostically relevant cutoff values for IP-10. Thereafter, mQFT test results derived from measurement of IP-10 and IFN-γ were compared and a larger number of Bovigam-positive animals were detected using IP-10 as a diagnostic marker. Moreover, using IP-10, agreement between the mQFT assay and the Bovigam assays was increased, while the excellent agreement between the Bovigam assays was retained. We conclude that IP-10 is a sensitive marker of antigen recognition and that measurement of this cytokine in antigen-stimulated whole blood might increase the sensitivity of conventional IGRAs in African buffaloes.
authors.affiliation: DST/NRF Centre of Excellence for Biomedical Tuberculosis Research/SAMRC Centre for Tuberculosis Research/Division of Molecular Biology and Human Genetics, Faculty of Medicine and Health Sciences, Stellenbosch University, Stellenbosch, South Africa.
authors.forename: Wynand J
authors.initials: WJ
authors.lastname: Goosen
authors.affiliation: Ezemvelo KZN Wildlife, St. Lucia, South Africa.
authors.forename: David
authors.initials: D
authors.lastname: Cooper
authors.affiliation: DST/NRF Centre of Excellence for Biomedical Tuberculosis Research/SAMRC Centre for Tuberculosis Research/Division of Molecular Biology and Human Genetics, Faculty of Medicine and Health Sciences, Stellenbosch University, Stellenbosch, South Africa.
authors.forename: Michele A
authors.initials: MA
authors.lastname: Miller
authors.affiliation: DST/NRF Centre of Excellence for Biomedical Tuberculosis Research/SAMRC Centre for Tuberculosis Research/Division of Molecular Biology and Human Genetics, Faculty of Medicine and Health Sciences, Stellenbosch University, Stellenbosch, South Africa.
authors.forename: Paul D
authors.initials: PD
authors.lastname: van Helden
authors.affiliation: DST/NRF Centre of Excellence for Biomedical Tuberculosis Research/SAMRC Centre for Tuberculosis Research/Division of Molecular Biology and Human Genetics, Faculty of Medicine and Health Sciences, Stellenbosch University, Stellenbosch, South Africa sparsons@sun.ac.za.
authors.forename: Sven D C
authors.identifier: http://orcid.org/0000-0002-9033-9686
authors.initials: SD
authors.lastname: Parsons
mesh_terms: D000818:Animals; D000942:Antigens, Bacterial / Q000276:immunology*; D015415:Biomarkers / Q000097:blood*; D002020:Buffaloes; D002417:Cattle; D054357:Chemokine CXCL10 / Q000097:blood*; D004197:Disease Reservoirs; D059425:Interferon-gamma Release Tests; D009163:Mycobacterium bovis / Q000276:immunology*; D012680:Sensitivity and Specificity; D014376:Tuberculosis / Q000175:diagnosis / Q000662:veterinary*
chemical_list: D000942:Antigens, Bacterial; D015415:Biomarkers; D054357:Chemokine CXCL10