Toll-like receptors (TLRs) recognize pathogen-derived molecules and play a critical role during the host innate and adaptive immune response. Brucella spp. are intracellular gram-negative bacteria including several virulent species, which cause a chronic zoonotic infection in a wide range of mammalian hosts known as brucellosis. A new Brucella species, Brucella microti, was recently isolated from wild rodents and found to be highly pathogenic in mice. Using this species-specific model, it was previously found that CD8+ T cells are required to control this infection. In order to find out the role of TLR-mediated responses in the control of this pathogen, the course of infection of B. microti was analyzed over 3 weeks in wild-type (WT) and TLR knock out (KO) mice including TLR2−/−, TLR4−/−, TLR9−/−, TLR2×4−/− and TLR2×4×9−/−. WT and single TLR2, TLR4 and TLR9 KO mice similarly control infection in liver and spleen. In contrast, bacterial clearance was delayed in TLR2×4−/− and TLR2×4×9−/− mice at 7 and 14 days post-infection. This defect correlated with impaired maturation and pro-inflammatory cytokine production in B. microti-infected dendritic cells from TLR2×4−/− and TLR2×4×9−/− mice. Finally, it was found that Tc cells from TLR2×4−/− and TLR2×4×9−/− mice showed reduced ability to inhibit growth of B. microti in macrophages, suggesting the involvement of TLR2 and 4 in the generation of specific Tc cells. Our findings indicate that TLR2 and TLR4 are required to control B. microti infection in mice and that this effect could be related to its participation in the maturation of dendritic cells and the generation of specific CD8+ Tc cells.

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Cell-intrinsic response patterns control risks arising from genome-damaged cells, preventing malignant transformation. p53-dependent DNA damage responses halt the cell cycle and induce either repair, senescence or cell death. Cyclic-GMP-AMP synthase (cGAS) has emerged as a new principle detecting genome damage and activating complex response programs. This DNA sensor is activated by micronuclei, chromosome bridges and prolonged mitotic arrest. STING-responses downstream of cGAS can drive cells into senescence or cell death through the induction of antiproliferative type I interferons (IFN) and proapoptotic tumor necrosis factor. Herein, we investigated how DNA damage-dependent and DNA-damage independent chronic activation of cGAS/STING signaling impacts on hematopoiesis. Hematopoietic loss of ribonucleotide excision repair (RER) resulted in chromosomal instability and activation of the cGAS/STING/IFN axis. Mice with hematopoietic RER-deficiency displayed compromised hematopoietic stem cell (HSC) function resulting in cytopenia and ultimately developed leukemia. Additional loss of p53 largely rescued mature blood cell production at the cost of accelerated leukemogenesis, while concurrent loss of cGAS, STING or type I IFN signalling had no detectable effect on HSC function, cytopenia and leukemia development in RER-deficient hematopoiesis. Also in models of acute genome damage, cGAS was irrelevant for the initial cell loss as well as the subsequent recovery of hematopoiesis. In contrast, a constitutive STING gain-of-function mutation impaired HSC functions independently of DNA damage. Collectively, we present in vivo evidence that the cGAS/STING pathway does not influence the capacity of the hematopoietic system to cope with DNA damage. Nevertheless, chronic activation of STING dramatically reduced the fitness of HSCs.