Abstract
Porphyromonas gingivalis (Pg) is one of the main pathogens in chronic periodontitis (CP). Studies on the immunogenicity of its virulence factors may contribute to understanding the host response to infection. The present study aimed to use in silico analysis as a tool to identify epitopes from Lys-gingipain (Kgp) and neuraminidase virulence factors of the Pg ATCC 33277 strain. Protein sequences were obtained from the NCBI Protein Database and they were scanned for amino acid patterns indicative of MHC II binding using the MHC-II Binding Predictions tool from the Immune Epitope Database (IEDB). Peptides from different regions of the proteins were chemically synthesized and tested by the indirect ELISA method to verify IgG immunoreactivity in serum of subjects with CP and without periodontitis (WP). T cell epitope prediction resulted in 16 peptide sequences from Kgp and 18 peptide sequences from neuraminidase. All tested Kgp peptides exhibited IgG immunoreactivity whereas tested neuraminidase peptides presented low IgG immunoreactivity. Thus, the IgG reactivity to Kgp protein could be reaffirmed and the low IgG reactivity to Pg neuraminidase could be suggested. The novel peptide epitopes from Pg were useful to evaluate its immunoreactivity based on the IgG-mediated host response. In silico analysis was useful for preselecting epitopes for immune response studies in CP.
Highlights
Chronic periodontitis is a multifactorial and polymicrobial disease, which may negatively influence systemic diseases (Hajishengallis 2015)
Porphyromonas gingivalis, a keystone pathogen related to periodontal dysbiosis (Hajishengallis 2014), produces various virulence factors that can act as immunogenic molecules
The IgG reactivity of the chronic periodontitis (CP) sera pool was similar to the without peri‐ odontitis (WP) sera pool for all of the peptides and it could not be compared to the immunoreactivity observed when the P. gingivalis extract was used as an antigen (Additional file 1: Figure S1)
Summary
Chronic periodontitis is a multifactorial and polymicrobial disease, which may negatively influence systemic diseases (Hajishengallis 2015). Gingipains (cysteine proteases) are the main proteases of P. gingivalis (Guo et al 2010), one of their main functions being heme acquisition (Smalley and Olczak 2017) These proteases are immunogenic proteins, contributing to the pathogen’s ability to induce chronic periodontitis, since they can elicit a humoral immune response in humans, inducing higher serum levels of specific IgG in individuals with chronic periodontitis (O’Brien-Simpson et al 2000; Inagaki et al 2003; Nguyen et al 2004). The sialidase activity may be involved in the production, maturation and secretion of gingipains and other virulence factors of P. gingivalis, probably due to their sialylation (glycosylation) (Aruni et al 2011; Xu et al 2017) Inhibitors of these two virulence factors studied could be promising for use in the treatment of chronic periodontitis and associated systemic diseases (Cueno et al 2014; Olsen and Potempa 2014; Inaba et al 2016; Xu et al 2017). Selected epitopes were evaluated concerning their immunoreactivity based on the IgG-mediated host response in order to contribute to immunogenicity studies of this keystone pathogen
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