We identified antibody isotypes and subclass proportions in gingival crevicular fluid to understand the potential protective ability of these antibodies towards infection withActinobacillus actinomycetemcomitans.Immunoglobulin G (IgG) 1–4 antibody levels toA. actinomycetemcomitansserotype b were quantified in serum and‐gingival crevicular fluid from 20 periodontitis patients who had at least one subgingival plaque sample with cultivableA. actinomycetemcomitans.The subclass antibody levels in the patients' sera were IgG1 = IgG2)IgG3)IgG4. A portion of the gingival crevicular fluid samples had IgG (15.7%; range: 0–52%) and IgA (2.5%; range: 0–15%) antibody that was significantly elevated compared with serum. Gingival crevicular fluid samples with elevated IgG antibody were analyzed for the subclass distribution and showed elevated IgG3 (58%), IgG4 (35%), IgGl (25%) and IgG2 (25%) antibody in the gingival crevicular fluid. These results demonstrated a characteristic distribution of both serum and gingival crevicular fluid IgG subclass responses toA. actinomycetemcomitans.We also examined the sites with elevated antibody in each subclass for the presence ofA. actinomycetemcomitansin the subgingival microbiota. The results showed that>95% of sites with elevated IgG4 were colonized, whereas (50% of sites with elevated IgG2 demonstrated this microorganism. IgG2 and IgG4 levels were primarily elevated in diseased sites, whereas IgG4 elevations were absent in healthy sites. The frequency and distribution of antibody in the gingival crevicular fluid as related to colonization with this microorganism were consistent with localized host‐parasite interactions at individual tooth sites. The relative subclass distribution of elevated gingival crevicular fluid antibody was shown to be IgG3)Ig‐G4)IgG2 = IgG1. These antibody types suggest that the potential exists for this local antibody toA. actinomycetemcomitansto play an important role in the gingival sulcus in relationship to colonization and clinical p
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