Branched actin networks mediate macrophage-dependent host-microbiota homeostasis

Area of Science:

• Immunology
• Cell Biology
• Microbiology

Background:

• Branched actin networks, crucial for immune function, are formed by the Arp2/3 complex.
• Loss-of-function mutations in ARPC5, a subunit of the Arp2/3 complex, lead to inflammation and immunodeficiency.
• The underlying mechanisms for these phenotypes are not well understood.

Purpose of the Study:

• To investigate the role of ARPC5 in the hematopoietic system and its impact on immune function.
• To elucidate the basis for inflammation and immunodeficiency observed in ARPC5-deficient individuals.

Main Methods:

• Utilized a mouse model with ARPC5 deficiency in the hematopoietic system.
• Analyzed intestinal inflammation, microbial invasion, and immune cell function (macrophages and neutrophils).
• Assessed phagocytosis and intracellular bacterial killing capabilities of ARPC5-deficient macrophages.

Main Results:

• ARPC5 deficiency, but not ARPC5L, in mouse hematopoietic cells caused early-onset intestinal inflammation post-weaning.
• Microbiota breaching the ileal mucosa initiated the inflammation, leading to systemic effects.
• ARPC5-deficient macrophages and neutrophils infiltrated the ileum but were impaired in restricting microbial invasion.
• Macrophages lacking ARPC5 exhibited defective phagocytosis and intracellular bacterial killing.

Conclusions:

• ARPC5 is essential for mononuclear phagocyte function and maintaining host-microbiota homeostasis.
• ARPC5-containing Arp2/3 complexes, not ARPC5L-containing ones, are critical for these processes.
• The study identifies a key role for ARPC5 in preventing inflammatory and immunodeficiency conditions.