Lipopolysaccharide enhances CD11b/CD18 function but inhibits neutrophil aggregation

Area of Science:

• Immunology
• Cell Biology
• Microbiology

Background:

• Human neutrophils play a critical role in innate immunity.
• Lipopolysaccharide (LPS), a component of Gram-negative bacteria, activates immune cells.
• Neutrophil adhesion and aggregation are crucial for inflammatory responses.

Purpose of the Study:

• To investigate the effect of LPS/lipopolysaccharide-binding protein (LBP) complexes on neutrophil adhesive molecule expression and aggregation.
• To elucidate the role of CD14 and L-selectin in LPS-induced changes in neutrophil function.

Main Methods:

• Neutrophil priming with LPS/LBP complexes.
• Analysis of surface protein expression (CD11b/CD18 and L-selectin) using flow cytometry.
• Assessment of neutrophil aggregation in response to formyl peptides.
• Blocking experiments using CD14-specific monoclonal antibodies and L-selectin blocking agents.

Main Results:

• LPS/LBP priming enhanced CD11b/CD18 surface expression and latex bead binding but did not induce aggregation.
• Increased LPS/LBP concentration led to decreased neutrophil aggregation, correlating with L-selectin shedding.
• Blocking L-selectin inhibited aggregation, and blocking CD14 prevented L-selectin shedding and preserved aggregation.

Conclusions:

• LPS/LBP-induced inhibition of neutrophil aggregation is mediated by CD14-dependent L-selectin shedding.
• CD14 plays a central role in regulating neutrophil adhesive properties during bacterial endotoxin exposure.
• These findings highlight a novel mechanism by which bacterial endotoxins modulate neutrophil function.