Antibody responses against Porphyromonas gingivalis infection in patients with early-onset periodontitis

Background, aims: The aim of this study was to evaluate antibody responses against Porphyromonas gingivalis (P. gingivalis) infection in early-onset periodontitis (EOP) patients to elucidate further the host-parasite interactions in the pathogenesis of EOP. Method: 16 P. gingivalis-infected EOP and 20 adult periodontitis (AP) patients, and 18 periodontally healthy subjects (HS) participated in this study. Serum immunoglobulin G (IgG) antibody levels and avidities against extracted P. gingivalis whole cells were measured. The components of P. gingivalis outer membrane antigens (OMA) reacting to patients' sera were analysed from the molecular weights by Western blotting. Serum antibody levels against P. gingivalis lipopolysaccharide (LPS) were also measured. The ability of the patients' sera to block interleukin-1 β (IL-1β) production by human mononuclear cells in response to P. gingivalis LPS was examined. Results: Antibody levels were positively correlated with antibody avidities in both EOP and AP patients (r=0.91, r=0.72, p<0.0005, respectively), while not significantly so in HS (r=0.09). There was variability in the antigen recognition of P. gingivalis OMA in EOP and AP patients. Smear and 53-kDa protein were more frequently recognized by sera of EOP and AP patients rather than that of HS (p<0.05). The smear was partly diminished by absorption with P. gingivalis LPS, indicating the smear antigen was partly composed of LPS. There was high correlation between antibody levels against P. gingivalis whole-cell extracts and LPS in EOP and AP patients (r=0.81, p=0.0002, r=0.87, p<0.0001, respectively), while not significant in HS (r=0.22). The sera of EOP and AP patients with high IgG titre to P. gingivalis LPS blocked IL-1β production more effectively than that of the patients with low IgG titre to P. gingivalis LPS. Conclusions: These results indicate that EOP patients' antibody response against P. gingivalis infection does not differ significantly from that of AP patients. The person-to-person heterogeneous antibody production against P. gingivalis LPS could contribute to our understanding of the relationship between the defensive ability of EOP patients and their chronic infection with this pathogen.