Serum immunoglobulin G (IgG) and IgG subclass responses to the RgpA-Kgp proteinase-adhesin complex of Porphyromonas gingivalis in adult periodontitis

Serum immunoglobulin G (IgG), IgM, and IgG subclass responses to the RgpA-K gp proteinase-adhesin complex of Porphyromonas gingivalis were examined by enzyme-linked immunosorbent assay using adult periodontitis patients and ag e- and sex-matched controls. Twenty-five sera from subjects with adult peri odontitis (diseased group) and 25 sera from healthy subjects (control group ) were used for the study, Sera and subgingival plaque samples from 10 site s were collected from each patient at the time of clinical examination. The level of P. gingivalis in the plaque samples was determined using a DNA pr obe. Highly significant positive associations between the percentage of sit es positive for P. gingivalis and measures of disease severity (mean pocket depth, mean attachment loss, and percentage of sites that bled on probing) were found. The diseased group had significantly higher specific IgG respo nses to the RgpA-Kgp complex than did the control group, and the responses were significantly associated with mean probing depths and percentage of si tes positive for P. gingivalis. Analysis of the IgG subclass responses to t he RgpA-Kgp complex revealed that the subclass distribution for both the di seased and control groups was IgG4 > IgG2 > IgG3 = IgG3. The IgG2 response to the complex was positively correlated with mean probing depth, whereas t he IgG3 response was negatively correlated with this measure of disease sev erity. Immunoblot analysis of the RgpA-Kgp complex showed that sera from he althy subjects and those with low levels of disease, with high IgG I and lo w IgG2 responses, reacted with the RgpA27, Kgp39, and RgpA44 adhesins; howe ver, sera from diseased subjects with low IgG4 and high IgG2 responses reac ted only with the RgpA44 and/or Kgp44 adhesins. Epitope mapping of the RgpA 27 adhesin localized a major epitope recognized by IgG4 antibodies in sera from subjects with high IgG4 and low IgG2 responses to the RgpA-Kgp complex which was not recognized by sera from diseased subjects with low IgG4 and high IgG2 responses.