TLR7 and TLR3 Sense Brucella abortus RNA to Induce Proinflammatory Cytokine Production but They Are Dispensable for Host Control of Infection

Abstract

Brucella abortus is a Gram-negative, facultative intracellular bacterium that causes brucellosis, a worldwide zoonotic disease leading to undulant fever in humans and abortion in cattle. The immune response against this bacterium relies on the recognition of microbial pathogen-associated molecular patterns, such as lipoproteins, lipopolysaccharides, and DNA; however, the immunostimulatory potential of B. abortus RNA remains to be elucidated. Here, we show that dendritic cells (DCs) produce significant amounts of IL-12, IL-6, and IP-10/CXCL10, when stimulated with purified B. abortus RNA. IL-12 secretion by DCs stimulated with RNA depends on TLR7 while IL-6 depends on TLR7 and partially on TLR3. Further, only TLR7 plays a role in IL-12 production induced by B. abortus infection. Moreover, cytokine production in DCs infected with B. abortus or stimulated with bacterial RNA was reduced upon pretreatment with MAPK/NF-κB inhibitors. By confocal microscopy, we demonstrated that TLR7 is colocalized with B. abortus in LAMP-1 + Brucella-containing vacuoles. Additionally, type I IFN expression and IP-10/CXCL10 secretion in DCs stimulated with bacterial RNA were dependent on TLR3 and TLR7. Our results suggest that TLR3 and TLR7 are not required to control Brucella infection in vivo, but they play an important role on sensing B. abortus RNA in vitro.

Modulation of Microtubule Dynamics Affects Brucella abortus Intracellular Survival, Pathogen-Containing Vacuole Maturation, and Pro-inflammatory Cytokine Production in Infected Macrophages

“…Staying inside vesicular compartments throughout most of their intracellular life is one of the strategies developed by stealthy pathogens to hide from cytoplasmic innate immune receptors. However, endosomal receptors such as TLR3, TLR7-8 and TLR9, also take part in Brucella recognition ( Gomes et al, 2016 ; Campos et al, 2017 ; Milillo et al, 2017 ) and likely encounter BCVs during bacterial intracellular trafficking. Since vesicular traffic is largely performed by MTs, we investigated whether treatment of infected macrophages with nocodazole, paclitaxel or rTcpB could also affect innate immune responses against Brucella infection.…”

B. abortus RNA is the component involved in the down-modulation of MHC-I expression on human monocytes via TLR8 and the EGFR pathway

“…abortus RNA to induce the production of pro-inflammatory cytokines and type I IFN expression in murine DCs. However, these receptors were not required to control Brucella infection in vivo [ 39 ]. To explain the latter, they hypothesized that TLR13, a PRR involved in sensing a specific sequence from bacterial 23S rRNA [ 40 , 41 ], could play a role in B .…”

Relation between Cytokines and Brucella Arthritis, Spondylitis, and Sacroiliitis

“…In a recent study, the role of toll-like receptors (TLR) was demonstrated to affect the production of IL-6 and IL-12 simulated by Brucella RNA in vitro. The authors added that brucella ribonucleic acid had significant immunostimulatory function, and the cytokines released by dendritic cells in the response to this stimulation were TLR-dependent [23]. In another study carried out on 173 patients with Saadati et al…”