Distribution of immunoglobulin isotypes including IgA subclasses in adult, juvenile, and rapidly progressive periodontitis.

The plasma cell population in gingival biopsies from 3 groups of patients with adult, juvenile, and rapidly progressive periodontitis was characterized with respect to the distribution of individual immunoglobulin isotypes, including IgA subclasses, by paired immunofluorescence staining. The median ratios of IgG:IgA plasma cells in gingival connective tissue from the 3 groups were 2.7 (range 2.0-6.5), 3.0 (1.4-6.2), and 2.0 (1.2-4.0), respectively. Cells staining for intracellular IgM were found in low numbers in all biopsies (range 0.3-6.3% of all plasma cells). No statistically significant differences were observed between the 3 patient groups. In all 3 groups, the IgA plasma cell population was predominantly of the IgA1 isotype. One function of IgA seems to be to dampen inflammatory side-effects of other immune effector systems. The demonstrated predominance of IgA1 plasma cells indicates that the majority of IgA produced locally in gingivae of patients with periodontal diseases is susceptible to the IgA1-specific proteases excreted by important members of the disease-associated subgingival microflora. This may be an important factor in the apparently uncontrolled inflammation and tissue degradation taking place in the marginal periodontium during active periodontal disease.