Aggregatibacter actinomycetemcomitansLPS binds human interleukin-8

Abstract

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.

Commensal and pathogenic biofilms differently modulate peri‐implant oral mucosa in an organotypic model

“…After challenge with the A. actinomycetemcomitans biofilm, the levels of CXCL1, CXCL8, and CCL2 were lower than in the control (Figure ). Previously, it was found that A. actinomycetemcomitans can sense and bind cytokines; among them was CXCL8 (T. Ahlstrand et al, ; T. Ahlstrand et al, ; T. Ahlstrand, Kovesjoki, Maula, Oscarsson, & Ihalin, ). Lower metabolic activity of biofilms induced by cytokine binding could lead to higher resistance (A. Paino et al, ) and could reduce the production of virulence factors providing an explanation why the peri‐implant mucosa was not impaired after challenge with the A. actinomycetemcomitans biofilm.…”

Outer membrane vesicle-mediated serum protection inAggregatibacter actinomycetemcomitans

“…LPS was isolated from A. actinomycetemcomitans cells harvested from 12 blood agar plates, using a combination of procedures [48,49], as described [35]. LPS preparations were resuspended in 100 µl H 2 O and the yield (typically 1.5-2.8 × 10 6 endotoxin units [EU]) was estimated using the ToxinSensor™ chromogenic Limulus Amebocyte Lysate (LAL) endotoxin kit (BioNordika, Sweden).…”

“…Lipopolysaccharide (LPS) is one of the most abundant components of OMVs, including those released by A. actinomycetemcomitans, and is displayed on the outer surface of the vesicles [23][24][25]. It was recently shown that LPS is involved in the binding of IL-8 by A. actinomycetemcomitans OMVs [35], and it cannot be excluded that the LPS in OMVs also may interact with complement. The serotype-specific polysaccharide (S-PA) determinant of A. actinomycetemcomitans resides in the LPS O antigen, which is immunodominant [36][37][38][39].…”

Tools of Aggregatibacter actinomycetemcomitans to Evade the Host Response

“…It has also been demonstrated that A. actinomycetemcomitans OMVs can carry small molecules, including lipopolysaccharide (LPS), which can interact with complement [93]. LPS may also play a role in the observed binding of A. actinomycetemcomitans OMVs to IL-8 [94]. Evidence that A. actinomycetemcomitans OMVs carry NOD1- and NOD2-active peptidoglycan, which can be internalized into non-phagocytic human cells including gingival fibroblasts [19], reveals a role of the vesicles as a trigger of innate immunity.…”