Mucosal immunization with a flagellin-adjuvanted Hgp44 vaccine enhances protective immune responses in a murinePorphyromonas gingivalisinfection model

Abstract

Chronic periodontitis is caused by interactions between the oral polymicrobial community and host factors. Periodontal diseases are associated with dysbiotic shift in oral microbiota. Vaccination against periodontopathic bacteria could be a fundamental therapeutic to modulate polymicrobial biofilms. Because oral cavity is the site of periodontopathic bacterial colonization, mucosal vaccines should provide better protection than vaccines administered systemically. We previously reported that bacterial flagellin is an excellent mucosal adjuvant. In this study, we investigated whether mucosal immunization with a flagellin-adjuvanted polypeptide vaccine induces protective immune responses using a Porphyromonas gingivalis infection model. We used the Hgp44 domain polypeptide of Arg-gingipain A (RgpA) as a mucosal antigen. Intranasal (IN) immunization induced a significantly higher Hgp44-specific IgG titer in the serum of mice than sublingual (SL) administration. The co-administration of flagellin potentiated serum IgG responses for both the IN and SL vaccinations. On the other hand, the anti-Hgp44-specific IgA titer in the saliva was comparable between IN and SL vaccinations, suggesting SL administration as more compliant vaccination route for periodontal vaccines. The co-administration of flagellin significantly potentiated the secretory IgA response in saliva also. Furthermore, mice administered a mixture of Hgp44 and flagellin via the IN and SL routes exhibited significant reductions in alveolar bone loss induced by live P. gingivalis infections. An intranasally administered Hgp44-flagellin fusion protein induced a comparable level of Hgp44-specific antibody responses to the mixture of Hgp44 and flagellin. Overall, a flagellin-adjuvanted Hgp44 antigen would serve an important component for a multivalent mucosal vaccine against polymicrobial periodontitis.

A built-in adjuvant-engineered mucosal vaccine against dysbiotic periodontal diseases

“…We performed a hemagglutination-inhibition assay (HIA) as previously described. 9 As shown in Fig. 6a, anti-HB and anti-BtA + HB sera inhibited P. gingivalis-mediated hemagglutination, while no inhibition was observed in the anti-BtA, pre-immune serum, or no serum treatments.…”

“…Alveolar bone loss was assessed by the bone volume density (BV/TV; bone volume/ tissue volume) value and the distance from the cemento-enamel junction to the alveolar bone crest (CEJ-ABC), as previously described. 9 The mixed bacterial infection in the non-vaccinated mice (PBS) caused significant alveolar bone loss that manifested as a decreased bone volume fraction (**P < 0.01) and increased CEJ-ABC (***P < 0.001) (Fig. c).…”

“…The divalent vaccine induced protective immune responses in a F. nucleatum and P. gingivalis infection model Next, to investigate whether the immune responses induced by the divalent mucosal vaccine would confer protection against periodontitis in vivo, we carried out a bacterial challenge experiment as previously described. 9 Briefly, the vaccinated mice were orally infected with a mixture of live F. nucleatum and P. gingivalis three times ( Fig. 7a).…”

“…An effective vaccine should prevent the shifting of the subgingival microbiome toward pathologic dysbiosis by specifically suppressing key etiologic microorganisms in the dental plaque. [9][10][11] Therefore, the polyvalent vaccine strategy targeting keystone periodontitis pathogens 8,12 would be ideal for the prevention and treatment of periodontal diseases. A metagenomic analysis of the subgingival microbiome in periodontitis patients demonstrated that Porphyromonas gingivalis, one of the so-called 'red-complex bacteria', 13 is significantly abundant in the diseased than resolved states.…”

“…15,16 F. nucleatum scavenges oxygen and reactive oxygen radicals in the subgingival plaque, which fosters favorable growth conditions for major strictly anaerobic periodontopathogens such as P. gingivalis. 17 In the present study, we employ, as vaccine antigens, the Hgp44 domain polypeptide of Arg-gingipain A (RgpA) 9 of P. gingivalis and an immunogenic outer membrane protein FomA of F. nucleatum. [18][19][20] (Table 2) F. nucleatum is divided into subspecies (nucleatum, polymorphum, vincentii, animalis, and fusiforme) based on the polyacrylamide gel electrophoretic pattern of the whole-cell proteins and DNA homology.…”