Aggregatibacter actinomycetemcomitans LPS binds human interleukin-8.

Area of Science:

• Microbiology
• Immunology
• Biochemistry

Background:

• Gram-negative bacteria employ outer membrane proteins and surface polysaccharides to sequester host cytokines.
• The periodontal pathogen Aggregatibacter actinomycetemcomitans possesses an outer membrane lipoprotein (BilRI) that binds interleukin-8 (IL-8).

Purpose of the Study:

• To investigate the potential interaction between the positively charged IL-8 and the negatively charged lipopolysaccharide (LPS) of A. actinomycetemcomitans.
• To compare the binding affinity of LPS-IL-8 interaction with the previously identified BilRI-IL-8 interaction.

Main Methods:

• Electrophoretic mobility shift assays (EMSA).
• Microwell-based time-resolved fluorometric immunoassay (TRFIA).
• Binding assays using whole bacterial cells and outer membrane vesicles.

Main Results:

• LPS from A. actinomycetemcomitans, Pseudomonas aeruginosa, and Escherichia coli demonstrated binding to IL-8.
• The dissociation constant (Kd) for the A. actinomycetemcomitans LPS-IL-8 interaction ranged from 1.2-17 μM.
• IL-8 also interacted with whole A. actinomycetemcomitans cells and their outer membrane vesicles.

Conclusions:

• Lipopolysaccharide (LPS) is implicated in the binding of IL-8 to the outer membrane of A. actinomycetemcomitans.
• The LPS-IL-8 binding affinity is significantly stronger than the BilRI-IL-8 interaction.
• This finding suggests that LPS may be a key mechanism for IL-8 sequestration by gram-negative periodontal pathogens in vivo.