Mucosal Vaccination with a Novel Live Attenuated Brucella melitensis Mutant Protects via IFN-γ-producing Memory CD8+ T Cells in Concert with B Cells

Abstract

Abstract A B. melitensis mutant vaccine expressing mCherry (znBM-mC), when applied mucosally, conferred nearly complete protection against pulmonary challenge with wild-type (wt) BM 16M than did BM Rev-1 vaccine. To identify cellular subsets and mechanisms involved in inducing and maintaining protection post-BMDM vaccination, we hypothesize that both arms of the adaptive immune system are required for optimal protection. Mucosal vaccination with znBM-mC induced both effector memory and resident memory CD8+ T cells in the lungs, which were the primary source of IFN-γ. In the absence of IFN-γ, IL-17 significantly increased, but was insufficient for protection. In the absence of B cells, the total number of lung CD8+ T cells and proinflammatory cytokine production were significantly reduced resulting in diminished systemic protection. Reconstitution with naïve or immune B cells restored some protection in znBM-mC-vaccinated B cell-deficient mice. B cell involvement begins as early as 5 days post-nasal vaccination. Total CD19+ B cells significantly increased in BALB/c head and neck lymph nodes (LNs), lower respiratory LNs, and bronchio-alveolar lavage fluid. mCherry+ BALB/c B cells were elevated in the lungs and spleen correlating to a significant increase in CD8+ T cell expansion in the spleen compared to B cell-deficient mice. In-vitro uptake of znBM-mC by B cells resulted in their activation evidenced by increased CD80, CD86, CD11b, and CD24 expression. Moreover, purified immune CD8+ T cells co-cultured with znBM-mC-infected B cells showed enhanced T cell proliferation. Although B cells become infected with Brucella, these are important for optimal T cell immunity. Work is supported by NIH AI123244 & AI125516.