Impaired Control ofBrucella melitensisInfection inRag1-Deficient Mice

Abstract

After intranasal inoculation, Brucella melitensis chronically infects the mononuclear phagocyte system in BALB/c mice, but it causes no apparent illness. Adaptive immunity, which can be transferred by either T cells or antibody from immune to naive animals, confers resistance to challenge infection. The role of innate, non-B-, non-T-cell-mediated immunity in control of murine brucellosis, however, is unknown. In the present study, we documented that BALB/c and C57BL/6 mice had a similar course of infection after intranasal administration of 16M, validating the usefulness of the model in the latter mouse strain. We then compared the course of infection in Rag1 knockout mice (C57BL/6 background) (referred to here as RAG-1 mice) which have no B or T cells as a consequence of deletion of Rag1 (recombination-activating gene 1), with infection in normal C57BL/6 animals after intranasal administration of B. melitensis 16M. C57BL/6 mice cleared brucellae from their lungs by 8 to 12 weeks and controlled infection in the liver and spleen at a low level. In contrast, RAG-1 mice failed to reduce the number of bacteria in any of these organs. From 1 to 4 weeks after inoculation, the number of splenic bacteria increased from 2 to 4.5 logs and remained at that level. In contrast to the consistently high numbers of brucellae observed in the spleens, the number of bacteria rose in the livers sampled for up to 20 weeks. Immunohistologic examination at 8 weeks after infection disclosed foci of persistent pneumonia and large amounts of Brucella antigen in macrophages in lung, liver, and spleen in RAG-1, but not C57BL/6, mice. These studies indicate that T-and B-cell-independent immunity can control Brucella infection at a high level in the murine spleen, but not in the liver. Immunity mediated by T and/or B cells is required for clearance of bacteria from spleen and lung and for control of bacterial replication in the liver.Brucellosis, a zoonosis that affects several species of domestic animals, manifests itself in humans as a systemic, febrile illness. Most human disease is caused by Brucella melitensis, but B. abortus and B. suis are also highly pathogenic. The disease is recognized in more than 100 countries, with an estimated one million new cases per year. Most cases occur as a result of occupational exposure to animals or ingestion of nonpasteurized dairy products (6). Laboratory workers exposed to the agent are also at high risk of infection. Brucellosis can be acquired through ingestion and through breaks in the skin; aerosol transmission also occurs (6). There are no suitably attenuated, well-characterized human vaccines available.To simulate infection by a mucosal or aerosol route of infection, we have recently established a murine model of brucellosis in which BALB/c mice are inoculated intranasally with B. melitensis 16M (14, 17). In this model, the organism infects the lung and disseminates to the blood, liver, and spleen. Both antibody and cellular immune effectors mediate control of dissemination and replication of ...

BrucellaLumazine Synthase Elicits a Mixed Th1-Th2 Immune Response and Reduces Infection in Mice Challenged withBrucella abortus544 Independently of the Adjuvant Formulation Used

“…Independently of the formulation employed, mice immunized with BLS and adjuvants were protected against a virulent Brucella challenge. Protection was observed at the spleen and also at the liver, an important site for the control of Brucella infection by T-and B-cell-mediated defenses (14,20). From a practical point of view, an important conclusion can be drawn from our results.…”

A DNA Vaccine Coding for theBrucellaOuter Membrane Protein 31 Confers Protection againstB. melitensisandB. ovisInfection by Eliciting a Specific Cytotoxic Response

“…Mice immunized with the Omp31 DNA vaccine were significantly protected against B. ovis and B. melitensis infection. Protection was observed in the spleen and also in the liver, an important site for the control of Brucella infection (17,32). Levels of protection afforded in the spleen and the liver after B. ovis challenge were comparable to the ones achieved by the H38 control vaccine.…”

Humoral Immunity and CD4+ Th1 Cells Are Both Necessary for a Fully Protective Immune Response upon Secondary Infection with Brucella melitensis

“…This result is not expected or predictable on the basis of previous studies. IFN-g-and IFN regulatory factor 1-deficient mice, but not RAG-, IL-12-, or MyD88-deficient mice, succumb to primary infection by Brucella (46,55,57,60,77,78), suggesting that IFN-g can be induced at low level by MyD88/IL-12-independent pathways. Our results confirm the importance of using IL-12-inducing adjuvant in Brucella vaccination.…”