Pre-existing systemic inflammation impairs bacterial clearance in the spleen

Area of Science:

• Immunology
• Sepsis Research
• Microbiology

Background:

• Sepsis-induced immunosuppression compromises bacterial clearance and elevates mortality rates.
• Liver and spleen macrophages are critical components of the mononuclear phagocyte system for bacterial elimination.
• Systemic inflammation negatively impacts bacterial clearance in the liver, prompting investigation into spleen function.

Purpose of the Study:

• To investigate the hypothesis that systemic inflammation-induced immunosuppression decreases bacterial clearance by the spleen.
• To evaluate the impact of pre-existing systemic inflammation on splenic bacterial clearance and endotoxin elimination.
• To assess the inflammatory and physiological responses to bacteremia in the context of ongoing inflammation.

Main Methods:

• Anesthetized pigs underwent Escherichia coli infusion in an intensive care setting.
• Groups included Naive (E. coli only), ETX (endotoxin pre-exposure followed by E. coli), and Control (saline).
• Bacterial counts, endotoxin levels, IL-6, TNF, and physiological responses were analyzed.

Main Results:

• No significant differences in arterial, splenic venous, or hepatic venous bacterial counts were observed.
• The splenic venous to arterial bacterial counts ratio was lower in the Naive group compared to the ETX group.
• Peak IL-6 and TNF levels were higher in the Naive group; physiological responses to E. coli were dampened in the ETX group.

Conclusions:

• Pre-existing systemic inflammation impairs splenic bacterial clearance but does not affect endotoxin elimination.
• The inflammatory and physiological response to bacteremia is diminished during ongoing inflammation.
• Results suggest inherent splenic mechanisms are involved, as ex vivo bactericidal capacity remained unaffected.