The present study aimed at evaluating serum immunoglobulin G (IgG) avidity to Porphyromonas gingivalis in elderly patients with mild and severe chronic periodontitis. The avidity of antibodies against P. gingivalis present in the sera of 18 patients with mild chronic periodontitis and 18 patients with severe chronic periodontitis was evaluated using an ammonium thiocyanate-dissociated enzyme-linked immunosorbent assay (ELISA). The results showed that the mean absorbance value in serum IgG antibody titers was significantly higher in the severe chronic periodontitis group than in the mild chronic periodontitis group (198 ± 35 ELISA unit [EU] vs. 142 ± 32 EU, p < 0.01). However, there was no significant difference between the two groups in antibody avidity (65 ± 57 EU vs. 54 ± 27 EU). These findings suggest that humoral immune responses to P. gingivalis between mild and severe chronic periodontitis in elderly patients are characterized by the differences in the quantity rather than the quality of the antibodies.

Introduction
 Materials and Methods
  1. Subjects
  2. Serum collection
  3. Growth of Porphyromonas gingivalis
  4. Protein extraction from bacterial cells
  5. Measurement of serum immunoglobulin G antibody titers
  6. Measurement of serum immunoglobulin G avidity levels by dissociation analysis
  7. Statistical analysis
 Results
  1. Serum immunoglobulin G titers and relative avidities
  2. Relationship between titer and avidity
 Discussion
 References

• Yoon-Jeong Choi(Department of Dental Science, School of Dentistry, Chonnam National University)
• Seok-Woo Lee(Departments of Dental Education and Periodontology, School of Dentistry, Chonnam National University, Dental Science Research Institute, School of Dentistry, Chonnam National University) Correspondence to