Mucosal Vaccination Primes NK Cell-Dependent Development of CD8+ T Cells Against Pulmonary Brucella Infection

Abstract

Past studies with the live, double-mutant B. abortus (znBAZ) strain resulted in nearly complete protection of mice against pulmonary challenge with wild-type (wt) Brucella via a dominant CD8+ T cell response. To understand the contribution innate immune cells in priming CD8+ T cell responses, mice were nasally dosed with wt B. abortus, smooth vaccine strain 19 (S19), or znBAZ, and examined for innate immune cell activation. Flow cytometric analysis revealed that znBAZ, but not wt B. abortus nor S19 infection, induces up to a 5-fold increase in the frequency of IFN-γ-producing NK cells in mouse lungs. These NK cells express increased CXCR3 and Ki67, indicating their recruitment and proliferation subsequent to znBAZ infection. Their activation status was augmented noted by the increased NKp46 and granzyme B, but decreased NKG2A expression. Further analysis demonstrated that both lung caspase-1+ inflammatory monocytes and monocyte-derived macrophages secrete chemokines and cytokines responsible for NK cell recruitment and activation. Moreover, neutralizing IL-18, an NK cell-activating cytokine, reduced the znBAZ-induced early NK cell response. NK cell depletion also significantly impaired lung dendritic cell (DC) activation and migration to the lower respiratory lymph nodes (LRLNs). Both lung DC activation and migration to LRLNs were significantly impaired in NK cell-depleted or IFN-γ-/- mice, particularly the CD11b+ and monocytic DC subsets. Furthermore, znBAZ vaccination significantly induced CD8+ T cells, and upon in vivo NK cell depletion, CD8+ T cells were reduced 3-fold compared to isotype-treated mice. In summary, these data show that znBAZ induces lung IFN-γ+ NK cells, which plays a critical role in influencing lung DC activation, migration, and promoting protective CD8+ T cell development.

Live mucosal vaccination stimulates potent protection via varied CD4+ and CD8+ T cell subsets against wild-type Brucella melitensis 16M challenge

“…Complementing vaccine development, an optimized vaccination regimen to improve efficacy needs consideration. In fact, while Brucella primarily infects the host following a mucosal exposure ( 21 – 23 ), research has largely emphasized parenteral infections due to the ability of Brucella to cause systemic infections ( 24 ). Most brucellosis vaccine studies fail to consider mucosal immunization as an integral component for optimal vaccine efficacy or host immunity ( 12 ).…”

“…Conventional livestock vaccines, S19 and RB51 for B. abortus and Rev 1 for B. melitensis , typically induce protective CD4 + Th1 cell responses ( 34 – 36 ), but discount the advantages of mucosal vaccination in stimulating alternative immune cell subsets. In this vein, the thrust toward mucosal vaccination has gained traction with promising results ( 23 , 25 , 29 , 37 ). Like natural infection, which is controlled early on by CD8 + T cells and γ/δ + T cells, consideration of the importance of CD8 + T cell-dependent immunity subsets after mucosal vaccination is being recognized as an alternative arm of protection ( 23 , 37 , 38 ).…”

“…In this vein, the thrust toward mucosal vaccination has gained traction with promising results ( 23 , 25 , 29 , 37 ). Like natural infection, which is controlled early on by CD8 + T cells and γ/δ + T cells, consideration of the importance of CD8 + T cell-dependent immunity subsets after mucosal vaccination is being recognized as an alternative arm of protection ( 23 , 37 , 38 ).…”

Activation of mucosal immunity as a novel therapeutic strategy for combating brucellosis

“…As a means to sustain intracellular survival, Brucella has evolved a number of mechanisms to avoid host recognition and establish infection ( Celli et al, 2019 ; Roop et al, 2021 ). Following bacteremia, macrophages are one of the principal cells targeted by Brucella to sustain infection ( Gomes et al, 2012 ; Celli et al, 2019 ; Bhagyaraj et al, 2021 ). Once brucellae achieve intracellular infection, their elimination proves to be more difficult as these have a number of tools to evade the host immune system.…”

“…Once brucellae achieve intracellular infection, their elimination proves to be more difficult as these have a number of tools to evade the host immune system. As such, brucellae exist in Brucella -containing vacuoles (BCVs; Gomes et al, 2012 ; Celli et al, 2019 ; Roop et al, 2021 ), which traffic in the endocytic pathway incorporating endosomal membrane proteins, e.g., calreticulin and calnexin1, avoiding phagolysosome maturation and killing ( Pizarro-Cerdá et al, 1998 ; Celli et al, 2003 ; Starr et al, 2008 ; Gomes et al, 2012 ; Celli et al, 2019 ; Bhagyaraj et al, 2021 ; Roop et al, 2021 ) in a VirB-dependent fashion ( Celli et al, 2003 ; Starr et al, 2008 ; Gomes et al, 2012 ; Roop et al, 2021 ). To avoid TLR4 and other LPS-sensitive innate detection sensors, Brucella expresses a low endotoxic LPS ( Forestier et al, 2000 ; Martirosyan et al, 2011 ; Conde-Álvarez et al, 2012 ; Byndloss and Tsolis, 2016 ).…”