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Characterization of T Cell Responses to the RgpA-Kgp Proteinase-Adhesin Complexes of Porphyromonas gingivalis in BALB/c Mice¹

Cooperative Research Centre for Oral Health Science, School of Dental Science, The University of Melbourne, Victoria, Australia

Porphyromonas gingivalis is a Gram-negative bacterium strongly associated with chronic periodontitis, an inflammatory oral disease. A major virulence factor common to all characterized strains of P. gingivalis is the RgpA-Kgp proteinase-adhesin complexes (RgpA-Kgp complexes). In this study, we investigated T cell proliferative and cytokine responses to the RgpA-Kgp complexes and identified T cell epitopes in BALB/c mice utilizing Pepscan methodology. T cell proliferative responses were found to be predominantly directed toward the proteinase catalytic domains. Eleven T cell epitopes were identified using RgpA-Kgp-primed lymph node T cells (IL-4 dominant) and 21 using an RgpA-Kgp-specific T cell line (IFN- dominant), with 5 T cell epitopes, including the immunodominant epitope peptide 22, common to both T cell populations. Peptide 22 (⁴³⁹ANYTAHGSETAWADP⁴⁵³) from the Kgp proteinase catalytic domain induced a Th2 cytokine response in mice, and peptide 22-primed T cells had a Th2 cytokine profile when stimulated with the RgpA-Kgp complexes. Truncation and alanine scanning of peptide 22 identified the minimum epitope (⁴⁴²TAHGSETAWA⁴⁵¹), and residues His⁴⁴⁴, Glu⁴⁴⁷, and Trp⁴⁵⁰ as critical for T cell proliferation. With a view to vaccine development, peptide 22 was incorporated into a synthetic peptide polymer. Peptide 22 polymer induced strong T cell proliferation and crossreactivity to native RgpA-Kgp complexes. In conclusion, we have identified a major T cell epitope of P. gingivalis and established that antigenicity of the T cell epitope is retained when delivered as a peptide polymer. The strategies employed here may have potential in the development of a synthetic peptide vaccine for P. gingivalis.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported by National Health and Medical Research Council (Australia) Grant 454475.

² Address correspondence and reprint requests to Dr. Eric C. Reynolds, Centre for Oral Health Science, School of Dental Science, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Victoria 3010, Australia. E-mail address: e.reynolds{at}unimelb.edu.au

³ Abbreviations used in this paper: S.I., stimulatory index; rhIL-2, recombinant human IL-2.