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A lipid A-associated protein of Porphyromonas gingivalis, derived from the haemagglutinating domain of the RI protease gene family, is a potent stimulator of interleukin 6 synthesis

Cellular Microbiology Research Group and Microbiology University College London, 256 Gray's Inn Road, London WClX 8LD, UK
Department, Eastman Dental Institute, University College London, 256 Gray's Inn Road, London WClX 8LD, UK
Division of Endocrinology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar EN6 3QG, UK
Department of Oral Microbiology, Medical Research Council Molecular Pathogenesis Group, The Royal London School of Medicine and Dentistry, London E l 2AA, UK

⁵Author for correspondence: Brian Henderson. Tel: +44 171 915 1190. Fax: +44 171 915 1190.e-mail: b.henderson@eastman.ucl.ac.uk

ABSTRACT

SUMMARY: There is evidence that the lipid A-associated proteins (LAPs) of enteric bacteriacan induce the synthesis of interleukin 1 (IL-1) and therefore may be important virulence factors. Porphyromonas gingivdis is now recognized as a major pathogen in the chronic inflammatory periodontal diseases and it has previously been reported that a crude LAP fraction from this organism could induce IL-1 and interleukin 6 (IL-6) synthesis. In the present study the chemical and biological properties of the LAPs of this bacterium have been further characterized. Analysis by SDS-PAGE has shown that the LAPs comprise nine proteins of molecular masses 81,68,48,47,28,25,20,17 and 16 kDa. These LAPS, at concentrations as low as 100 ng mV, were shown to stimulate human gingival fibroblasts, human peripheral blood mononuclear cells and whole human blood t o produce the pro-inflammatory cytokine IL-6. The cytokine-inducing activity of the LAPs was reduced after heat-inactivation and trypsinization, suggesting that the activity was not due to contaminating LPS. To establish which proteins in this mixture were the active cytokine inducers, the LAPs were separated by electrophoresis on polyacrylamide gels. The majority of the activity was associated with the 17 kDa LAP. N-terminal sequence analysis demonstrated that this protein was homologous t o an internal region of a conserved adhesin domain contained within a family of P. gingivdis extracellular proteins including the RI protease, Lys-gingipain, porphypain and haemagglutinin A. In addition to a role in adherence, the adhesin domain(s) of these proteins may also have cytokine-inducing properties. Furthermore, it has also been shown that the previously observed degradation of cytokines by P. gingivelis may be attributable to the catalytic domain of the RI protease. Thus, different domains within the same molecule appear t o have opposing actions on pro-inflammatory cytokine levels and the balance between these two activities may influencethe cytokine status of the periodontiurn in patients with the common chronic inflammatory conditions known as the periodontal diseases.

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