ARS | Publication request: Improved Performance of the Interferon Gamma (IFN-gamma) Assay with Alternative Antigens for Stimulation of Whole Blood

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 25, 2009
Publication Date: August 25, 2009
Citation: Schroder, B., Hardegger, R., Marg-Haufe, B., Schiller, I., Moyen, J.L., Waters, W.R., Palmer, M.V., Thacker, T.C., Stamm, C., Nonnecke, B.J., Keck, N., Egnuni, T., Whelan, A., Sigafoose, T., Welsh, M., Cagiola, M., Gordon, S., Meijlis, J., Carter, C., Vordermeier, H.M., Raeber, A.J. 2009. Improved Performance of the Interferon Gamma (IFN-gamma) Assay with Alternative Antigens for Stimulation of Whole Blood [abstract].

Technical Abstract: Bovine tuberculosis caused by infection with Mycobacterium bovis (M. bovis) is a zoonotic disease that affects cattle worldwide and has a significant economic impact on the livestock industry. Although the disease has been effectively eliminated in many countries and regions, it is increasingly reappearing as a result of host reservoirs in wild animal populations. The success of bovine tuberculosis eradication programs in many countries have relied on ante mortem diagnostic tests measuring cell-mediated immune (CMI) responses such as the tuberculin skin test or the interferon gamma test. The BOVIGAM® interferon gamma (IFN-gamma) assay constitutes a laboratory-based tuberculosis test and is widely used complementary to the tuberculin skin test. The assay consists of a first step culturing whole blood with antigens and stimulating leucocytes to produce IFN-gamma which is quantified by ELISA in a second step. Diagnosis is based on a comparative measurement with avian and bovine tuberculins. Numerous field trials showed that the IFN-gamma assay was more sensitive than the intradermal skin test for diagnosis of tuberculosis. However, specificity of the IFN-gamma assay was found to be slightly lower than the skin test suggesting limited use of the IFN-gamma assay as a stand-alone screening tool in cattle herds that are either free or have a low prevalence of tuberculosis. In order to increase the specificity of the IFN-gamma test, defined antigens such as ESAT-6 or CFP-10 in combination with other highly specific antigens from the genome of M. bovis have been evaluated in field trials. Here we show, that a combination of antigens including ESAT-6 and CFP-10 showed a specificity of 99.5 % - 100 % in cattle from TB-free regions whereas sensitivities assessed in herds with skin test reactors in France and Ireland showed comparable sensitivities as with tuberculins. These results suggest that IFN-gamma testing comprising stimulation with well characterized antigen cocktails can be used as a stand alone test system for tuberculosis in cattle.