Oral Vaccination withBrucella melitensisWR201 Protects Mice against Intranasal Challenge with VirulentBrucella melitensis16M

Abstract

Human brucellosis can be acquired from infected animal tissues by ingestion, inhalation, or contamination of conjunctiva or traumatized skin by infected animal products. In addition, Brucella is recognized as a biowarfare threat agent. Although a vaccine to protect humans from natural or deliberate infection could be useful, vaccines presently used in animals are unsuitable for human use. We tested orally administered live, attenuated, purine auxotrophic B. melitensis WR201 bacteria for their ability to elicit cellular and humoral immune responses and to protect mice against intranasal challenge with B. melitensis 16M bacteria. Immunized mice made serum antibody to lipopolysaccharide and non-O-polysaccharide antigens. Splenocytes from immunized animals released interleukin-2 and gamma interferon when grown in cultures with Brucella antigens. Immunization led to protection from disseminated infection and enhanced clearance of the challenge inoculum from the lungs. Optimal protection required administration of live bacteria, was related to immunizing dose, and was enhanced by booster immunization. These results establish the usefulness of oral vaccination against respiratory challenge with virulent Brucella and suggest that WR201 should be further investigated as a vaccine to prevent human brucellosis.Human brucellosis, caused mostly by Brucella abortus, B. melitensis, and B. suis, can be acquired by ingestion, inhalation, or contamination of conjunctiva or traumatized skin by infected animal products (3). Bacteria spread, presumably via lymphatics and blood (8), from the site of entry to the mononuclear phagocyte system. Although generalized symptoms of fever, sweating, and fatigue are nearly universal for patients with acute brucellosis, onset can be insidious and many patients present with or develop localized foci of infection, especially in the bones and joints (24). Control of brucellosis in domestic food animals has markedly reduced the incidence of human brucellosis in the United States, but the disease represents an important cause of morbidity worldwide. A human vaccine would be valuable for individuals who may be occupationally exposed to brucellae and for persons who consume unpasteurized dairy products from areas in which brucellae are endemic. In addition, Brucella species are recognized as biowarfare or bioterror threat agents by the Center for Disease Control, further supporting the need to develop effective medical protective measures against them.We have previously reported that levels of B. melitensis WR201, a purEK deletion mutant of B. melitensis 16M, are attenuated for growth in mononuclear phagocytes (5) and in mice (4) after intraperitoneal (i.p.) inoculation relative to parent strain results. Mice inoculated i.p. with strain WR201 make antibody directed against lipopolysaccharide (LPS) and Brucella protein, and their splenocytes produce gamma interferon (IFN-␥) and interleukin-2 (IL-2) when grown in cultures with Brucella antigens (11). In addition, immunization of mice by i.p. inoculation...

Protective Live Oral Brucellosis Vaccines Stimulate Th1 and Th17 Cell Responses

“…In addition to protecting against systemic disease, oral immunization with ⌬znuA B. melitensis had a significant effect upon brucella replication in the lungs of BALB/c mice. These findings are similar to those by Izadjoo et al (28), who used their ⌬purEK B. melitensis 16M mutant; however, i.p. immunization with the same vaccine confers only modest protection in the lungs (25).…”

“…Moreover, the majority of vaccinated animals showed no live brucellae in their tissues, resulting in a protective efficacy of 83%. Oral immunization has also been proven to be effective against nasal B. melitensis 16M challenge using the ⌬purEK B. melitensis 16M mutant (WR201) strain (28). In addition to protecting against systemic disease, oral immunization with ⌬znuA B. melitensis had a significant effect upon brucella replication in the lungs of BALB/c mice.…”

Selection of Protective Epitopes for Brucella melitensis by DNA Vaccination

“…3). The results showed the pCMVbp26-vaccinated mice elicited a peak IgG titer of 2 16 ; mice vaccinated with pCMVTF showed a lower IgG titer of 2 13.8 , which peaked early at week 6. No detectable titers were observed for the vector immunized mice.…”

Aerosol Infection of BALB/c Mice with Brucella melitensis and Brucella abortus and Protective Efficacy against Aerosol Challenge

“…However, consistent results for B. melitensis required exposure to doses that were 10 to 100 times greater. Although organisms were detected on the fur of animals using cotton swabs, the recovery data suggested that the levels were in the range from 100 to 1,000 organisms per mouse, which is well below the oral dose necessary for infection (12).…”

“…Previous studies have considered intranasal infection of mice and guinea pigs as models for aerosol exposure (1,2,10,12,13,18,29). In this study, we evaluated the kinetics of systemic infection in the mouse model after aerosol exposure of deep lung tissue to both B. abortus and B. melitensis in order to establish a novel exposure route in the mouse model.…”