Antibody synthesis specific for nonoral antigens in inflamed gingiva

In vitro experimentation indicates that periodontitis-associated bacteria contain potent polyclonal B-cell activators (PBA). We reasoned that if PBA were operative in vivo, plasma cells specific for nonoral antigens should be present in the inflamed gingival tissues, which are characterized by a plasma cell infiltrate. To test this, rabbits with experimental periodontitis were immunized in the hind legs with the histochemically detectable antigen horseradish peroxidase (HRP) or glucose oxidase (GO). At various times after secondary immunization, inflamed gingival tissue was removed, sectioned, and treated histochemically to reveal plasma cells that specifically bound HRP or GO. Remarkably, by 9 days after secondary immunization, hundreds of HRP- or GO-binding plasma cells were found in the inflamed gingival tissue of immunized rabbits. The presence of these plasma cells, observed 7 to 10 days after booster immunization, was further substantiated by the presence of large amounts of locally produced HRP- or GO-specific antibody in gingival crevicular fluid. By 1 month after secondary immunization, the number of antigen-binding plasma cells had decreased dramatically, but a small number of antigen-specific plasma cells were detected for as long as 9 months after secondary immunization. The large number of HRP- or GO-specific plasma cells observed 9 days after immunization led us to see whether recently stimulated cells were more susceptible to PBA. Peripheral blood lymphocytes (PBL) were obtained at different times after booster immunization and cultured in the presence or absence of a PBA from Fusobacterium nucleatum. At 7 days after immunization, PBL spontaneously differentiated into antibody-forming cells in culture, and this process was enhanced by PBA. In contrast, PBL taken months after immunization produced little antibody in culture, and enhancement by PBA was difficult to detect. Compared with resting B cells, the recently stimulated B cells clearly differentiated more readily into antibody-forming cells. In conclusion, antibody synthesis specific for nonoral antigens did occur in inflamed gingival tissue, and a number of mechanisms, including PBA, probably contributed to this phenomenon.