Evaluation of circulating IgG antibodies against Porphyromonas gingivalis or its gingipains as serological markers of periodontitis and carriage of the bacterium

Abstract

Background: Increasing evidence indicates that periodontitis contributes to systemic low-grade inflammation. Porphyromonas gingivalis is strongly associated with periodontitis, and antibodies against the bacterium may be used as a serological proxy to account for periodontal status, when studying diseases associated with periodontitis. The aim of the present study is to identify an easily accessible and reliable serological biomarker for determination of periodontal status and oral carriage of the bacterium.

Methods: Saliva and serum samples were collected from periodontally healthy controls (n = 27), and patients with periodontitis stage II (n = 12) or stages III or IV (n = 44). Serum levels of immunoglobulin G (IgG) antibodies against intact and fragmented P. gingivalis, recombinant gingipains (RgpA and RgpB), and the bacteria Escherichia coli and Capnocytophaga ochracea as controls were quantified with a multiplex bead-based assay. P. gingivalis was identified in saliva using quantitative polymerase chain reaction (qPCR).

Results: Serum IgG antibodies against P. gingivalis whole bacteria were good indicators of periodontitis (area under the curve [AUC]: 0.75, 95% confidence interval [CI]: 0.64-0.85). The same was observed for levels of antibodies against P. gingivalis fragments (AUC: 0.78, 95% CI: 0.68-0.88). Likewise, levels of antibodies against P. gingivalis whole bacteria or P. gingivalis fragments were good indicators of oral carriage of P. gingivalis (AUC: 0.92, 95% CI: 0.86-0.98 and AUC: 0.96, 95% CI: 0.92-1, respectively). Conversely, antibodies against recombinant RgpA and RgpB were not good indicators of periodontitis or oral carriage of the bacterium. None of the antibody levels differed significantly between stage II and stage III or IV periodontitis.

Conclusion: Serum IgG antibody levels against heat-inactivated whole P. gingivalis proved to be the preferable biomarker for periodontitis and oral carriage of the bacterium.

Keywords: Porphyromonas gingivalis; biomarker; immunoglobulin; periodontitis.

FIGURE 1

Serum antibody levels against bacteria and recombinant Porphyromonas gingivalis gingipains. Antibodies against whole and fragmented bacteria and recombinant gingipains from P. gingivalis were measured in sera from 27 periodontally healthy controls (HCs), 12 patients with periodontitis stage II, and 46 patients with periodontitis stages III or IV (stages III + IV) by means of Luminex technology. Log 10 of median fluorescence intensity (MFI) values is shown. The antigens coupled to the beads were as follows: (A) P. gingivalis whole bacteria, (B) P. gingivalis fragments, (C) recombinant P. gingivalis gingipain A (RgpA), (D) recombinant P. gingivalis gingipain B (RgpB), (E) Escherichia coli whole bacteria, and (F) Capnocytophaga ochracea whole bacteria. Black squares and open circles represent individuals positive and negative, respectively, for presence of P. gingivalis (P.g.) in saliva samples, as determined by quantitative polymerase chain reaction (qPCR). Horizontal bars represent mean values. p values were adjusted for age, sex, and current smoking status.