Cutting edge: LPS-induced emergency myelopoiesis depends on TLR4-expressing nonhematopoietic cells

Area of Science:

• Immunology
• Hematopoiesis
• Infectious Disease

Background:

• Systemic bacterial infections are medical emergencies characterized by neutrophil release and increased myeloid cell production.
• The precise mechanisms linking infection sensing to emergency myelopoiesis remain unclear.

Purpose of the Study:

• To investigate the role of Toll-like receptor 4 (TLR4) in sensing bacterial infection and initiating emergency myelopoiesis.
• To elucidate the cellular compartments responsible for pathogen sensing and the signaling pathways involved.

Main Methods:

• In vivo mouse models were utilized to study the effects of lipopolysaccharide (LPS) on myelopoiesis.
• Selective deletion or expression of TLR4 in hematopoietic and nonhematopoietic cells was employed.
• Analysis of G-CSF mediated responses and IL-1RI signaling was performed.

Main Results:

• Selective TLR4 expression in the hematopoietic compartment did not induce LPS-driven emergency myelopoiesis.
• TLR4-expressing nonhematopoietic cells are essential for LPS-induced, G-CSF-mediated myelopoietic responses.
• LPS-induced emergency myelopoiesis proceeds independently of intact IL-1RI signaling and inflammasome activation.

Conclusions:

• Nonhematopoietic cells play a critical, nonredundant role in sensing pathogens during systemic bacterial infections.
• Pathogen sensing by nonhematopoietic cells leads to cytokine release, driving demand-adapted myeloid cell production.
• This highlights a novel mechanism for translating infection detection into an effective immune response.