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Clinical and Vaccine Immunology, February 2008, p. 208-214, Vol. 15, No. 2
1071-412X/08/$08.00+0 doi:10.1128/CVI.00374-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

University of California, Department of Medical Microbiology and Immunology, One Shields Avenue, Davis, California 95616,1 Texas A&M University College Of Veterinary Medicine, Department of Veterinary Pathobiology, College Station, Texas 77843-44672
Received 18 September 2007/ Returned for modification 1 October 2007/ Accepted 21 November 2007
The Brucella species type IV secretion system, encoded by the virB1-12 locus, is required for intracellular replication and persistent infection in vivo. The requirement of VirB proteins for infection suggests that they are expressed in vivo and may therefore represent serological markers of infection. To test this idea, we purified recombinant VirB1, VirB5, VirB11, and VirB12 and tested for their recognition by antibodies in sera from experimentally infected mice and goats by using an indirect enzyme-linked immunosorbent assay. Antibody responses to VirB12 but not to VirB1, VirB5, or VirB11 were detected in 20/20 mice experimentally inoculated with Brucella abortus and 12/12 goats experimentally infected with Brucella melitensis. The potential use of VirB12 as a serological tool for the diagnosis of brucellosis was evaluated in the natural bovine host. Serum samples from 145 cattle of known serology (29% negative and 71% positive) were analyzed for the production of antibody responses to VirB12. One hundred two cattle samples (70.3%) were positive for antibodies to VirB12, while 43 samples were negative (29.7%). A positive serological response to VirB12 correlated with positive serology to whole B. abortus antigen in 99% of samples tested. These results show that VirB12 is expressed during infection of both experimental and natural hosts of Brucella species, and they suggest that VirB12 may be a useful serodiagnostic marker for brucellosis.
Published ahead of print on 12 December 2007.
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