Path of differentiation defines human macrophage identity

Area of Science:

• Immunology
• Developmental Biology
• Stem Cell Biology

Background:

• Macrophages are crucial for immunity, wound healing, and homeostasis.
• Their functional diversity is linked to developmental origins, but human ontogeny's impact is unclear.
• Human fetal liver (HFL) hematopoietic stem cells (HSCs) are key to understanding early macrophage development.

Purpose of the Study:

• To investigate the divergent pathways of macrophage specification from human fetal liver HSCs.
• To characterize the distinct identities and properties of macrophages derived from these pathways.
• To explore the therapeutic potential of targeting these pathways in inflammatory conditions.

Main Methods:

• Utilized human fetal liver HSCs to trace macrophage differentiation pathways.
• Employed aryl hydrocarbon receptor (AHR) antagonism to modulate macrophage populations.
• Assessed macrophage properties, including self-renewal and inflammatory responses.
• Validated findings in preclinical models of atopic dermatitis (AD).

Main Results:

• Identified two distinct macrophage specification pathways from HFL HSCs: a monocyte-dependent pathway and a fetal-specific expedited differentiation pathway.
• The fetal pathway generates tissue-resident-like macrophages (TRMs) exhibiting HSC-like self-renewal, regulated by AHR.
• AHR antagonism promoted TRM expansion and reduced inflammation in atopic dermatitis models.
• Directly linked differentiation pathways to specific macrophage functional properties.

Conclusions:

• Human fetal macrophage development involves distinct ontogenetic pathways with differing functional outcomes.
• AHR-regulated TRMs represent a promising target for managing inflammatory diseases.
• Targeting macrophage differentiation offers a novel therapeutic strategy for diseases involving macrophage dysfunction.