PD-1 expression by macrophages plays a pathologic role in altering microbial clearance and the innate inflammatory...

Area of Science:

• Immunology
• Pathophysiology
• Molecular Biology

Background:

• Sepsis is a life-threatening condition characterized by excessive inflammation and impaired bacterial clearance.
• Macrophage dysfunction is central to sepsis pathogenesis, but the underlying mechanisms are not fully understood.
• The programmed cell death protein 1 (PD-1) and its ligand (PD-L) pathway's role in sepsis remains largely unexplored.

Purpose of the Study:

• To investigate the role of the PD-1:PD-L pathway in sepsis.
• To determine how PD-1 affects macrophage function during sepsis.
• To explore PD-1 as a potential therapeutic target for sepsis.

Main Methods:

• Utilized PD-1 knockout (PD-1(-/-)) mice to study sepsis outcomes.
• Assessed bacterial burden, inflammatory cytokine levels, and survival rates in septic mice.
• Depleted peritoneal macrophages in PD-1(-/-) mice to evaluate their specific contribution.
• Measured PD-1 expression on monocytes from septic mice and human patients with septic shock.

Main Results:

• PD-1(-/-) mice exhibited significantly improved survival from sepsis, with reduced bacterial load and suppressed inflammation.
• Septic macrophages showed increased PD-1 expression, correlating with cellular dysfunction.
• Macrophage depletion in PD-1(-/-) mice reversed the protective effects, increasing inflammation and mortality.
• Elevated PD-1 levels were observed on monocytes from both septic mice and human septic shock patients.

Conclusions:

• The PD-1:PD-L pathway critically regulates the balance between beneficial and detrimental immune responses in sepsis.
• PD-1 expression on macrophages/monocytes is linked to sepsis-induced immune dysfunction.
• Targeting the PD-1 pathway represents a promising therapeutic strategy for sepsis management.