Protection of Mice against Brucellosis by Intranasal Immunization withBrucella melitensisLipopolysaccharide as a Noncovalent Complex withNeisseria meningitidisGroup B Outer Membrane Protein

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Abstract
Intranasal immunization of mice with purifiedBrucella melitensislipopolysaccharide (LPS) as a noncovalent complex withNeisseria meningitidisgroup B outer membrane protein (GBOMP) elicited a high-titer anti-LPS systemic antibody response and a significant mucosal antibody response. The anti-LPS immunoglobulin G (IgG) antibody was predominantly of the IgG1 subtype, although there was some response of the IgG2a, IgG2b, and IgG3 subtypes. The antibody titer remained high for 16 weeks postimmunization. Immunized mice and sham-immunized control mice were challenged intranasally with 104CFU of virulentB. melitensisstrain 16 M 4 weeks after the second dose of vaccine. The numbers of bacteria in lungs, livers, and spleens at 3 days, 9 days, and 8 weeks postchallenge were determined. Bacteria were found in lungs of all mice on day 3, but there was no disseminated infection of liver or spleen. By day 9, 40% of the mice had infected spleens and livers. At 8 weeks postchallenge, spleens of 25 of 62 immunized mice were infected, compared to 61 of 62 control mice (P< 0.0001). The livers of 12 of 43 immunized mice were infected, compared to 22 of 36 control mice (P= 0.005). In contrast, the lungs of 26 of 46 immunized mice were still infected, compared to 27 of 44 control mice. The numbers of bacterial CFU in lungs of immunized and control animals were identical. These studies show that intranasal immunization withB. melitensisLPS-GBOMP subunit vaccine significantly protects mice against intranasal challenge with virulentB. melitensis.Vaccination reduces bacterial dissemination to spleen and liver but has no effect on the course of lung infection.