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Protective Immunity Elicited by a Divalent DNA Vaccine Encoding Both the L7/L12 and Omp16 Genes of Brucella abortus in BALB/c Mice

Deyan Luo,^1, Bing Ni,^2, Peng Li,¹ Wei Shi,¹ Songle Zhang,¹ Yue Han,¹ Liwei Mao,² Yangdong He,² Yuzhang Wu,^2* and Xiliang Wang^1*

State Key Laboratory of Pathogen and Biosecurity, Institute of Microbiology and Epidemiology, Academy of Military Medical Science, Beijing 100071, China,¹ Institute of Immunology PLA, Third Military Medical University, Chongqing 400038, China²

Received 14 October 2005/ Returned for modification 28 November 2005/ Accepted 1 February 2006

This study was designed to evaluate the immunogenicity and the protective efficacy of a divalent fusion DNA vaccine encoding both the Brucella abortus L7/L12 protein (ribosomal protein) and Omp16 protein (outer membrane lipoprotein), designated pcDNA3.1-L7/L12-Omp16. Intramuscular injection of this divalent DNA vaccine into BALB/c mice elicited markedly both humoral and cellular immune responses. The specific antibodies exhibited a dominance of immunoglobulin G2a (IgG2a) over IgG1. In addition, the dual-gene DNA vaccine elicited a strong T-cell proliferative response and induced a large amount of gamma interferon-producing T cells upon restimulation in vitro with recombinant fusion protein L7/L12-Omp16, suggesting the induction of a typical T-helper-1-dominated immune response in vivo. This divalent DNA vaccine could also induce a significant level of protection against challenge with the virulent strain B. abortus 544 in BALB/c mice. Furthermore, the protection level induced by the divalent DNA vaccine was significantly higher than that induced by the univalent DNA vaccines pcDNA3.1-L7/L12 or pcDNA3.1-Omp16. Taken together, the results of this study verify for the first time that the Omp16 gene can be a candidate target for a DNA vaccine against brucellosis. Additionally, a divalent genetic vaccine based on the L7/L12 and Omp16 genes can elicit a stronger cellular immune response and better immunoprotection than the relevant univalent vaccines can.

Editor: J. T. Barbieri

D.L. and B.N. contributed equally to the paper.

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