Relative avidities of
antibodies to Porphyromonas (Bacteroides) gingivalis in the sera of 15 patients having
adult periodontitis and 15 healthy subjects were evaluated using an
ammonium thiocyanate-dissociated ELISA. Graded concentrations of
ammonium thiocyanate were added to a single dilution of serum in order to dissociate low avidity antibody binding to P. gingivalis. The concentration of
thiocyanate resulting in 50% reduction in binding (absorbance) was termed the ID50 for that serum. When
IgG-class
antibodies were examined, the ID50 of anti-P. gingivalis
antibodies in the sera of patients was significantly elevated (0.96M vs 0.71M; p less than 0.01, Student's t-test). In contrast, when
IgM-class
antibodies were examined no significant differences in ID50 between patients and controls were found for P. gingivalis (0.54M vs 0.53M). While the ID50 values of patient
antibodies were found to be elevated relative to those of healthy controls, comparison with
antibodies from rabbits immunized with P. gingivalis and with ID50 values from other human studies suggests that adult humans, in general, produce very low-avidity
antibodies to P. gingivalis. It is suggested that the presence of low-avidity
antibodies contributes to the pathology associated with
periodontal disease.