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Infection and Immunity, September 2008, p. 3932-3939, Vol. 76, No. 9
0019-9567/08/$08.00+0 doi:10.1128/IAI.00150-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Screening of Highly Expressed Mycobacterial Genes Identifies Rv3615c as a Useful Differential Diagnostic Antigen for the Mycobacterium tuberculosis Complex 
,
Ben Sidders,1,
Chris Pirson,2,
Philip J. Hogarth,2
R. Glyn Hewinson,2
Neil G. Stoker,1
H. Martin Vordermeier,2* and
Katie Ewer2*
The Department of Pathology & Infectious Disease, The Royal Veterinary College, Royal College Street, London NW1 0TU, United Kingdom,1 TB Research Group, Veterinary Laboratories Agency—Weybridge, New Haw, Addlestone, Surrey KT15 3NB, United Kingdom2
Received 5 February 2008/ Returned for modification 23 March 2008/ Accepted 22 May 2008
Tuberculous infections caused by mycobacteria, especially tuberculosis of humans and cattle, are important both clinically and economically. Human populations can be vaccinated with Mycobacterium bovis bacille Calmette-Guérin (BCG), and control measures for cattle involving vaccination are now being actively considered. However, diagnostic tests based on tuberculin cannot distinguish between genuine infection and vaccination with BCG. Therefore, identification of differential diagnostic antigens capable of making this distinction is required, and until now sequence-based approaches have been predominant. Here we explored the link between antigenicity and mRNA expression level, as well as the possibility that we may be able to detect differential antigens by analyzing quantified global transcriptional profiles. We generated a list of 14 candidate antigens that are highly expressed in Mycobacterium tuberculosis and M. bovis under a variety of growth conditions. These candidates were screened in M. bovis-infected and naïve cattle for the ability to stimulate a gamma interferon (IFN-
) response. We identified one antigen, Rv3615c, which stimulated IFN- responses in a significant proportion of M. bovis-infected cattle (11 of 30 cattle [37%] [P < 0.01]) but not in naïve or BCG-vaccinated animals. Importantly, the same antigen stimulated IFN- responses in a significant proportion of infected cattle that did not respond to the well-characterized mycobacterial antigens ESAT-6 and CFP-10. Therefore, use of the Rv3615c epitope in combination with previously described differential tests based on ESAT-6 and CFP-10 has the potential to significantly increase diagnostic sensitivity without reducing specificity in BCG-vaccinated populations.
* Corresponding author. Mailing address for H. Martin Vordermeier: TB Research Group, Veterinary Laboratories Agency—Weybridge, New Haw, Addlestone, Surrey KT15 3NB, United Kingdom. Phone: 44 (0)1932 357 884. Fax: 44 (0)1932 357 260. E-mail: m.vordermeier{at}vla.defra.gsi.gov.uk. Present address for Katie Ewer: Jenner Institute, University of Oxford, Old Road Campus Research Bldg., Off Roosevelt Drive, Headington, Oxford OX3 7DQ, United Kingdom. Phone: 44 (0)1865 617 622. E-mail: Katie.Ewer{at}ndm.ox.ac.uk
Published ahead of print on 2 June 2008.
Supplemental material for this article may be found at http://iai.asm.org/.
B.S. and C.P. contributed equally to this work.
Infection and Immunity, September 2008, p. 3932-3939, Vol. 76, No. 9
0019-9567/08/$08.00+0 doi:10.1128/IAI.00150-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
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