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Clinical and Vaccine Immunology, January 2006, p. 37-44, Vol. 13, No. 1
1071-412X/06/$08.00+0     doi:10.1128/CVI.13.1.37-44.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Diagnostic Implications of Antigen-Induced Gamma Interferon Production by Blood Leukocytes from Mycobacterium bovis-Infected Reindeer (Rangifer tarandus)

National Animal Disease Center, ARS, USDA, 2300 Dayton Avenue, P.O. Box 70,¹ Iowa State University, Veterinary Microbiology and Preventive Medicine, Ames, Iowa,³ CSL Animal Health, Parkville, Victoria, Australia²

Received 11 August 2005/ Accepted 24 October 2005

The only approved method of tuberculosis (TB) surveillance of reindeer within the United States is tuberculin skin testing; however, skin testing has an apparent lack of specificity, since numerous reindeer are classified as reactors, yet Mycobacterium bovis is not isolated from tissues upon necropsy. The objective of this study was to evaluate the ability of an in vitro assay (the Cervigam assay) to detect gamma interferon (IFN-) produced by blood leukocytes in response to mycobacterial antigens from M. bovis-infected reindeer. Thirteen male reindeer 9 months of age were inoculated with 10⁵ CFU M. bovis in their tonsillar crypts. Stimulation of whole-blood cultures with a mitogen resulted in significant production of IFN- compared to that by nonstimulated samples. Responses by infected reindeer to M. bovis purified protein derivative (PPD) were as much as 3.5-fold higher than those by noninfected reindeer (n = 4). Despite differences in responses to PPD by the two groups, reindeer within the noninfected group had responses of >0.1 change in optical density (OD) (a level generally considered positive) to PPD. Mean responses by infected reindeer to a rESAT-6-CFP-10 fusion protein (Mycobacterium tuberculosis complex specific) were as much as 20-fold higher than respective responses by noninfected reindeer at all time points. Additionally, responses by 3/4 noninfected reindeer were <0.1 OD (considered negative) at each time point. To further evaluate the specificity of the assay, samples were collected from reindeer in a TB-free herd. All reindeer had responses to mitogen; however, only 1 of 38 had a response to PPD, and none of the reindeer responded to rESAT-6-CFP-10. Together, these findings indicate that IFN--based tests may prove useful for TB surveillance of reindeer.

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