Avidity and titer of immunoglobulin G subclasses to Porphymmonas gingivalis in adult periodontitis patients

The relative avidity and titer of antibodies representing the 4 immunoglobulin G (IgG) subclasses (IgG1-4) reactive with Porphyromonas gingivalis, P. gingivalis-lipopolysaccharide (-LPS), streptokinase (SK) and tetanus toxoid (TT) in the sera of patients having adult periodontitis and of healthy controls were measured. Patient antibody titers to P. gingivalis and P. gingivalis-LPS were found to be significantly elevated for IgG, IgG1 (no P. gingivalis-LPS antibodies) and IgG2. The predominant antibody response to P. gingivalis and P. gingivalis-LPS occurred in the IgG2 subclass. When the relative avidity of the antibodies to P. gingivalis and P. gingivalis-LPS were examined, no significant differences between control and patient sera could be identified. However, anti-P. gingivalis and P. gingivalis-LPS antibodies were found to possess significantly lower relative avidity than either SK or TT antibodies. The IgG1 subclass antibodies to P. gingivalis, SK and TT all appeared to be of high relative avidity. In contrast, anti-P. gingivalis and P. gingivalis-LPS of the IgG2 subclass were of significantly lower relative avidity. Since the predominant humoral response to P. gingivalis occurs in the IgG2 subclass, the low relative avidity of these antibodies predominates in measurements of whole serum activity.