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

Abstract

Brucellosis remains a significant zoonotic threat worldwide. Humans and animals acquire infection via their oropharynx and upper respiratory tract following oral or aerosol exposure. After mucosal infection, brucellosis develops into a systemic disease. Mucosal vaccination could offer a viable alternative to conventional injection practices to deter disease. Using a nasal vaccination approach, the ΔznuA B. melitensis was found to confer potent protection against pulmonary Brucella challenge, and reduce colonization of spleens and lungs by more than 2500-fold, with more than 50% of vaccinated mice showing no detectable brucellae. Furthermore, tenfold more brucellae-specific, IFN-γ-producing CD8+ T cells than CD4+ T cells were induced in the spleen and respiratory lymph nodes. Evaluation of pulmonary and splenic CD8+ T cells from mice vaccinated with ΔznuA B. melitensis revealed that these expressed an activated effector memory (CD44hiCD62LloCCR7lo) T cells producing elevated levels of IFN-γ, TNF-α, perforin, and granzyme B. To assess the relative importance of these increased numbers of CD8+ T cells, CD8−/− mice were challenged with virulent B. melitensis, and they showed markedly increased bacterial loads in organs in contrast to similarly challenged CD4−/− mice. Only ΔznuA B. melitensis- and Rev-1-vaccinated CD4−/− and wild-type mice, not CD8−/− mice, were completely protected against Brucella challenge. Determination of cytokines responsible for conferring protection showed the relative importance of IFN-γ, but not IL-17. Unlike wild-type mice, IL-17 was greatly induced in IFN-γ−/− mice, but IL-17 could not substitute for IFN-γ’s protection, although an increase in brucellae dissemination was observed upon in vivo IL-17 neutralization. These results show that nasal ΔznuA B. melitensis vaccination represents an attractive means to stimulate systemic and mucosal immune protection via CD8+ T cell engagement.

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.…”

“…Intracellular IFN-γ and TNF-α expression levels by immune lymphocytes were measured by flow cytometry similar to that previously described [19]. Groups of mice i.p.…”

Targeting resident memory T cell immunity culminates in pulmonary and systemic protection against Brucella infection

“…Lung and splenic mononuclear cells were cultured in vitro (2×10 6 cells / well) in 48-well plates in 1 ml CM, and stimulated with 10 9 CFUs/ml HKRB51 for 84 hours. Supernatants were evaluated for IFN-γ, TNF-α, IL-4, IL-10, and IL-17a by capture ELISA using mAb pairs as previously described [22,23]. Production of cytokines by unstimulated cells was subtracted from all measurements.…”

“…The importance of the T cell subsets varies by the route of immunization and the vaccine components [11][12][13][14][15][16][17][18]. Recent reports showed that mucosal exposure to this pathogen stimulates IFN-γ-producing CD8 + T cells for protection against brucellosis, not by their cytotoxic function [19][20][21][22][23].…”

Research progress on the role of immune cells in Brucella infection

“…Therefore, the occurrence of brucellosis may be related to the imbalance in Treg/Th17 cells. Clapp et al [15] have observed from nasal mucosa infection that when Brucella invades organisms through the nasal mucosa, CD8 + T cells play an important role in immune protection. Based on these research reports, we summarize the pathogenesis of inherent immune cells, as well as the role of Th1 cell/Th2 cell in CD4 + T cell subsets, Treg and Th17 cells, and CD8 + T cells in brucellosis.…”