Large Peritoneal Macrophages and Transitional Premonocytes Promote Survival during Abdominal Sepsis

Area of Science:

• Immunology
• Infectious Disease
• Cell Biology

Background:

• Monocytes and macrophages are key immune sentinels.
• Peritoneal macrophages consist of self-renewing large peritoneal macrophages (LPMs) and monocyte-derived small peritoneal macrophages (SPMs).
• Monocyte-macrophage dynamics during abdominal sepsis remain poorly understood.

Purpose of the Study:

• To characterize monocyte and macrophage populations in the peritoneum during abdominal sepsis.
• To investigate the role of LPMs and monocytes in sepsis survival.

Main Methods:

• Cecal ligation and puncture (CLP) model of sepsis in mice.
• Flow cytometry to analyze peritoneal immune cells.
• Depletion studies using CD11b-DTR mice.
• Genetic manipulation (CCR2 deficiency) and adoptive transfer of monocytes.
• Pharmacological inhibition of CXCL12-CXCR4 signaling.

Main Results:

• LPMs rapidly disappeared after CLP and were essential for survival; their depletion increased mortality.
• Monocytes infiltrated the peritoneum quickly but SPMs did not increase until later.
• Transitional premonocytes (CD31+, CXCR4hi) were more abundant in mice predicted to survive sepsis.
• Inhibition of CXCL12-CXCR4 signaling worsened sepsis outcomes.

Conclusions:

• LPMs play a critical role in early sepsis survival.
• Monocytes may provide acute protection independent of SPM generation.
• Recruitment of transitional premonocytes to the peritoneum via CXCL12-CXCR4 signaling enhances sepsis survival.