INCREASED TITER AND AVIDITY OF IGG ANTIBODIES TO PORPHYROMONAS-GINGIVALIS WHOLE CELLS AND A CELL-SURFACE PROTEIN IN SUBJECTS WITH ADULT PERIODONTITIS

The titre and avidity of IgG antibodies to Porphyromonas gingivalis wh ole cells and a 47 kDa cell surface protein were determined in serum s amples taken from 20 subjects with adult periodontitis and 20 controls , matched for age, gender, ethnic origin and oral hygiene status. Anti body titres were measured by ELISA and antibody avidity was determined by a chaotrope-dissociation ELISA. Avidity was defined as the molarit y of chaotrope required to reduce absorbance by 50% (ID50). The mean I gG antibody log titre to whole cells (8.29 vs. 6.92; p <0.01) and to t he 47 kDa antigen (7.61 vs. 6.77; p <0.05) were higher in cases than i n controls. Mean IgG antibody avidity to whole cells (4.59 vs. 2.47; p <0.001) and to the surface protein (2.54 vs. 1.67; p <0.001) were als o higher in cases than in controls. In cases, IgG antibody titre was h ighly correlated with avidity for both whole cells (r=0.878; p=<0.001) and the 47 kDa protein (r=0.683; p <0.001). There was a weaker positi ve correlation between the titre and the avidity of antibody to whole cells (r=0.591; p <0.01) in the control population but antibody titre and avidity for the 47 kDa sonicate antigen were not correlated in the controls (r=0.104). We conclude that many patients with adult periodo ntitis have effective humoral immunity to P. gingivalis. However, in u p to half the patients with adult periodontitis, antibody titres and a vidities were low and similar to control values, indicating either sus ceptibility due to poor host response or that disease is not associate d with this particular pathogen.