Various gram-negative species sequester host cytokines using outer
membrane proteins or surface modulation by sulfated polysaccharides. An
outer membrane lipoprotein (BilRI) of the periodontal pathogen Aggregatibacter actinomycetemcomitans
binds several cytokines, including interleukin (IL)-8. Because IL-8 is
positively charged at physiological pH, we aimed to determine whether
IL-8 interacts with negatively charged lipopolysaccharide (LPS). Binding
was investigated using electrophoretic mobility shift assays and
microwell-based time-resolved fluorometric immunoassay. LPS from each
tested strain of A. actinomycetemcomitans (N = 13), Pseudomonas aeruginosa (N = 1) and Escherichia coli (N = 1) bound IL-8. The K_d value of the A. actinomycetemcomitans
LPS-IL-8 interaction varied between 1.2–17 μM irrespective of the
serotype and the amount of phosphorus in LPS and was significantly lower
than that of the BilRI-IL-8 interaction. Moreover, IL-8 interacted with
whole A. actinomycetemcomitans cells and outer membrane vesicles. Hence, LPS might be involved in binding of IL-8 to the outer membrane of A. actinomycetemcomitans. This raises an interesting question regarding whether other gram-negative periodontal pathogens use LPS for IL-8 sequestering in vivo.