Proinflammatory effect in whole blood by free-soluble bacterial components released from planktonic and biofilm cells
Aggregatibacter actinomycetemcomitans is an oral bacterium associated with aggressive forms of periodontitis. Increasing evidence points to a link between periodontitis and cardiovascular diseases, however, the underlying mechanisms are poorly understood.
This study investigated the pathogenic potential of free-soluble surface material, released from live planktonic and biofilm A. actinomycetemcomitans cells.
Results: By employing an ex vivo insert model (filter pore size 20 nm) we demonstrated that the A. actinomycetemcomitans strain D7S and its derivatives, in both planktonic and in biofilm life form, released free-soluble material independent of outer membrane vesicles.
This material clearly enhanced the production of several proinflammatory cytokines (IL-1beta, TNF-alpha, IL-6, IL-8, MIP-1beta) in human whole blood, as evidenced by using a cytokine antibody array and dissociation-enhanced-lanthanide-fluorescent-immunoassay. In agreement with this, quantitative real-time PCR indicated a concomitant increase in transcription of each of these cytokine genes.
Experiments in which the LPS activity was blocked with polymyxin B showed that the stimulatory effect was only partly LPS-dependent, suggesting the involvement of additional free-soluble factors. Consistent with this, MALDI-TOF-MS and immunoblotting revealed the release of GroEL-like protein in free-soluble form.
Conversely, the immunomodulatory toxins, cytolethal distending toxin and leukotoxin, and peptidoglycan-associated lipoprotein, appeared to be less important, as evidenced by studying strain D7S cdt/ltx double, and pal single mutants.
Conclusion: A.
actinomycetemcomitans, grown planktonic and in biofilm form, releases free-soluble surface material independent of outer membrane vesicles, which induces proinflammatory responses in human whole blood. Our findings therefore suggest that release of bacterial components from live cells could constitute a mechanism for systemic stimulation and be of particular importance in chronic localized infections, such as periodontitis.
Author: Jan Oscarsson, Maribasappa Karched, Bernard Thay, Casey Chen and Sirkka Asikainen
Credits/Source: BMC Microbiology 2008, 8:206
Published on: 2008-11-27
Copyright by the authors listed above - made available via BioMedCentral (Open Access). Please
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