Oral Immunization of Mice with Gamma-Irradiated Brucella neotomae Induces Protection against Intraperitoneal and Intranasal Challenge with Virulent B. abortus 2308

Abstract

Brucella spp. are Gram-negative, facultative intracellular coccobacilli that cause one of the most frequently encountered zoonosis worldwide. Humans naturally acquire infection through consumption of contaminated dairy and meat products and through direct exposure to aborted animal tissues and fluids. No vaccine against brucellosis is available for use in humans. In this study, we tested the ability of orally inoculated gamma-irradiated B. neotomae and B. abortus RB51 in a prime-boost immunization approach to induce antigen-specific humoral and cell mediated immunity and protection against challenge with virulent B. abortus 2308. Heterologous prime-boost vaccination with B. abortus RB51 and B. neotomae and homologous prime-boost vaccination of mice with B. neotomae led to the production of serum and mucosal antibodies specific to the smooth LPS. The elicited serum antibodies included the isotypes of IgM, IgG1, IgG2a, IgG2b and IgG3. All oral vaccination regimens induced antigen-specific CD4+ and CD8+ T cells capable of secreting IFN-γ and TNF-α. Upon intra-peritoneal challenge, mice vaccinated with B. neotomae showed the highest level of resistance against virulent B. abortus 2308 colonization in spleen and liver. Experiments with different doses of B. neotomae showed that all tested doses of 109, 1010 and 1011 CFU-equivalent conferred significant protection against the intra-peritoneal challenge. However, a dose of 1011 CFU-equivalent of B. neotomae was required for affording protection against intranasal challenge as shown by the reduced bacterial colonization in spleens and lungs. Taken together, these results demonstrate the feasibility of using gamma-irradiated B. neotomae as an effective and safe oral vaccine to induce protection against respiratory and systemic infections with virulent Brucella.

Nasal vaccination stimulates CD8+ T cells for potent protection against mucosal Brucella melitensis challenge

“…One such study tested oral immunization with γ-irradiated Brucella neotomae , and found that bacterial colonization of spleen and lung tissues was reduced only by 15.8-fold. 11 In another study, oral vaccination with Brucella melitensis WR201 was able to confer lung protection by only 3-fold. 13 RB51 or RB51SOD given nasally failed to show protection against pulmonary disease.…”

“…12 Although oral vaccination was highly effective, one caveat was that it required a large vaccine dose similar to what others have found. 11,13 One alternative to oral vaccination is to exploit the nasal route in conferring protection in the respiratory tract. The advantages over the oral route include readily accessible mucosal tissue, the need of less vaccine, and the lack of exposure of the vaccine to low pH or to the digestive enzymes present in the gastrointestinal tract.…”

Vaccination with a ΔnorD ΔznuA Brucella abortus mutant confers potent protection against virulent challenge

“…It has been presumed that CD4 + T cells are the major source for IFN-γ and TNF-α [42,43], and only a handful of studies has implicated the importance of CD8 + T cells [40,44]. The route of vaccination may be a contributing factor in CD8 T cell elevations [19, 45, 46]. Alternatively, attributes of the mutant strain used for vaccination may influence the T cell bias as evidenced here by the enhanced vaccine potency, and the contributions of both CD4 + and CD8 + T cells in znBAZ-vaccinated mice compared to those induced T cell responses by RB51-vaccinated mice.…”

Comparison of Immunologic Responses Following Intranasal and Oral Administration of a USDA-Approved, Live-Attenuated Streptococcus equi Vaccine

“…Use of the oral poliovirus vaccine established 99% eradication as it induced both systemic and mucosal immunity especially in the intestines where the virus multiplies and contributes to transmission (Behrend et al 2014). An attenuated, gamma-irradiated Brucella neotomae administered orally to mice stimulated serum IgG and IgM, mucosal IgG, IgM, and IgA, and antigen-specific T lymphocytes capable of secreting interferon (IFN)-γ and tumor necrosis factor (TNF)-α (Dabral et al 2014). This Brucella vaccine was protective against intraperitoneal and intranasal challenge compared to control mice (Dabral et al 2014).…”

“…An attenuated, gamma-irradiated Brucella neotomae administered orally to mice stimulated serum IgG and IgM, mucosal IgG, IgM, and IgA, and antigen-specific T lymphocytes capable of secreting interferon (IFN)-γ and tumor necrosis factor (TNF)-α (Dabral et al 2014). This Brucella vaccine was protective against intraperitoneal and intranasal challenge compared to control mice (Dabral et al 2014). Piglets that were immunized with oral ovalbumin (OVA) and adjuvant produced significantly more anti-OVA IgG, IgA, and IgM compared to OVA alone and control (Pasternak et al 2014).…”