Serodiagnosis of Porphyromonas gingivalis infection by immunoblot analysis with recombinant collagenase.

The Porphyromonas gingivalis collagenase-specific serum immunoglobulin A (IgA), IgM, and IgG responses from 20 patients with early-onset periodontitis (EOP), 20 patients with adult periodontitis, (AP), and 20 age- and sex-matched healthy controls were examined by immunoblot analysis. A recombinant collagenase antigen used for the immunoblot analysis was produced by using the plasmid pGEX-2T, which allows the fusion between the collagenase and glutathione S-transferase. There was no significant difference in collagenase-specific IgG antibody detection between samples from the EOP, AP, and control groups. In contrast, 85% of AP and EOP sera had collagenase-specific IgA antibodies, whereas only 20% of control sera showed collagenase-specific IgA reactivity. Plaque samples from all groups were assessed by PCR with primers complementary to the collagenase-encoding gene prtC. The results indicated that 90% of AP and EOP plaque samples and 10% of control samples were positive for P. gingivalis. All patients with collagenase-specific IgA antibodies were PCR positive. The results of the study indicate a nearly complete concordance (k = 0.856) between the presence of collagenase-specific IgA antibodies and PCR detection of P. gingivalis. By using PCR as the "gold standard," the sensitivity and specificity of the IgA immunoblot test were 94.7 and 90.9%, respectively. Therefore, the recombinant collagenase is a potential candidate for use in the serodiagnosis of periodontitis.