Table 1.

Microbiota-driven immune signaling pathways and their effects on the hematopoietic system

Microbiome-driven signaling pathwayEffects on hematopoietic systemReference
NOD1 signaling Promotes steady-state hematopoiesis indirectly through the induction of cytokines by mesenchymal stromal cells 42  
RAC1-NOD1-RIPK2-NF-κB axis initiates inflammatory signaling in the HE, resulting in HSPC specification 25  
NOD1 signaling in hematopoietic compartment regulates proinflammatory macrophage polarization and neutrophil infiltration in adipose tissue 22  
TLR-MYD88 signaling Bacterial recognition during infection promotes the G-CSF secretion from endothelial cells and monocytes, leading to the acceleration of granulopoiesis 23  
TLR4 signaling promotes B-cell maturation 43  
Toll-like receptor activation in human monocytes induces rapid differentiation DC-SIGN+CD16+ macrophages and CD1b+DC-SIGN dendritic cells 44  
TLR7 stimulation at epithelial surfaces drives emergency myelopoiesis 29  
TLR2 activation results in HSC expansion in both the BM and spleen, increased HSC cycling, and a reduction in BM megakaryocyte-erythroid progenitors 31  
RIG-I MAVS signaling Controls the emergence of hematopoietic precursors in zebrafish embryos through downstream IFN signaling 33  
Activation of RIG-1 by repetitive element RNA, expressed during the endothelial-to-hematopoietic transition modulates the inflammatory signaling ie, crucial for HSPC formation during development 34  
cGAS-STING signaling cia-cGAS is a suppressor of cGAS. deficiency of cia-cGAS promotes STING activation leading to increased HSC cycling and cGAS-mediated HSC exhaustion 45  
Excessive R-loop accumulation because of DDX41 insufficiency, results in cGAS-STING-NF-κB pathway activation to promote HSPC expansion 35  
Activation of STING pathway by bacterial c-di-GMP activates in a cGAS-independent manner, induces HSPC proliferation, and mobilization as well as myeloid-biased differentiation, but reduces HSC self-renewal and mobilization 46  
Microbiome-driven signaling pathwayEffects on hematopoietic systemReference
NOD1 signaling Promotes steady-state hematopoiesis indirectly through the induction of cytokines by mesenchymal stromal cells 42  
RAC1-NOD1-RIPK2-NF-κB axis initiates inflammatory signaling in the HE, resulting in HSPC specification 25  
NOD1 signaling in hematopoietic compartment regulates proinflammatory macrophage polarization and neutrophil infiltration in adipose tissue 22  
TLR-MYD88 signaling Bacterial recognition during infection promotes the G-CSF secretion from endothelial cells and monocytes, leading to the acceleration of granulopoiesis 23  
TLR4 signaling promotes B-cell maturation 43  
Toll-like receptor activation in human monocytes induces rapid differentiation DC-SIGN+CD16+ macrophages and CD1b+DC-SIGN dendritic cells 44  
TLR7 stimulation at epithelial surfaces drives emergency myelopoiesis 29  
TLR2 activation results in HSC expansion in both the BM and spleen, increased HSC cycling, and a reduction in BM megakaryocyte-erythroid progenitors 31  
RIG-I MAVS signaling Controls the emergence of hematopoietic precursors in zebrafish embryos through downstream IFN signaling 33  
Activation of RIG-1 by repetitive element RNA, expressed during the endothelial-to-hematopoietic transition modulates the inflammatory signaling ie, crucial for HSPC formation during development 34  
cGAS-STING signaling cia-cGAS is a suppressor of cGAS. deficiency of cia-cGAS promotes STING activation leading to increased HSC cycling and cGAS-mediated HSC exhaustion 45  
Excessive R-loop accumulation because of DDX41 insufficiency, results in cGAS-STING-NF-κB pathway activation to promote HSPC expansion 35  
Activation of STING pathway by bacterial c-di-GMP activates in a cGAS-independent manner, induces HSPC proliferation, and mobilization as well as myeloid-biased differentiation, but reduces HSC self-renewal and mobilization 46  

cGAS, cyclic GMP-AMP synthase; GMP, guanosine monophosphate; HE, hemogenic endothelium.

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