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Clinical and Vaccine Immunology, December 2006, p. 1343-1348, Vol. 13, No. 12
1071-412X/06/$08.00+0     doi:10.1128/CVI.00291-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Flow Cytometric Detection of Gamma Interferon Can Effectively Discriminate Mycobacterium bovis BCG-Vaccinated Cattle from M. bovis-Infected Cattle

Institute for Animal Health, Compton, Newbury, Berkshire RG207NN, United Kingdom

Received 17 August 2006/ Returned for modification 18 September 2006/ Accepted 19 September 2006

Mycobacterium bovis is the causative agent of bovine tuberculosis, a disease that is increasing in incidence in United Kingdom cattle herds. In addition to increasing economic losses, the rise in bovine tuberculosis poses a human health risk. There is an urgent requirement for effective strategies for disease eradication; this will likely involve vaccination in conjunction with current test and slaughter policies. A policy involving vaccination would require an accurate diagnosis of M. bovis-infected animals and the potential to distinguish these animals from vaccinates. Currently used diagnostic tests, the skin test and gamma interferon (IFN-) blood test, have a sensitivity of up to 95%. A further complication is that M. bovis BCG-vaccinated animals are also scored positive by these tests. We tested the hypothesis that the quantification of IFN--producing lymphocytes by flow cytometric analysis of intracellular IFN- expression would provide a more accurate discrimination of M. bovis-infected animals from BCG vaccinates. Significant numbers of IFN--expressing CD4⁺ T cells were detected following culture of heparinized blood from M. bovis-infected animals, but not from BCG vaccinates, with purified protein derived from M. bovis (PPD-B) or live mycobacteria. Only 1 of 17 BCG-vaccinated animals had a significant number of CD4⁺ T lymphocytes expressing IFN-, compared with 21/22 M. bovis-infected animals. This assay could allow an accurate diagnosis of M. bovis and allow the discrimination of BCG-vaccinated cattle from infected cattle.

Published ahead of print on 27 September 2006.