Aggregatibacter actinomycetemcomitans LPS binds human interleukin-8

Abstract

<p>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 <i>Aggregatibacter actinomycetemcomitans</i> 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 <i>A. actinomycetemcomitans</i> (<i>N</i> = 13), <i>Pseudomonas aeruginosa</i> (<i>N</i> = 1) and <i>Escherichia coli</i> (<i>N</i> = 1) bound IL-8. The K_d value of the <i>A. actinomycetemcomitans</i> 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 <i>A. actinomycetemcomitans</i> cells and outer membrane vesicles. Hence, LPS might be involved in binding of IL-8 to the outer membrane of <i>A. actinomycetemcomitans</i>. This raises an interesting question regarding whether other gram-negative periodontal pathogens use LPS for IL-8 sequestering <i>in vivo</i>.</p>