Porphyromonas gingivalis-specific serum IgG and IgA antibodies originate from immunoglobulin-secreting cells in inflamed gingiva

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Abstract
Patients with adult periodontitis (AP) exhibit elevated serum antibody levels to Porphyromonas (Bacteroides) gingivalis; however, it is not known whether these antibodies originate from plasma cells in the local disease site or From peripheral lymphoid tissues. We studied the isotype and subclass levels and origin of antibodies to P. gingivalis fimbriae, since elevated serum anti‐fimbriae responses were seen when compared with sera of healthy controls. IgG unti‐fimbriae litres were dominant and the subclass response was IgG3 ≫ IgG1 > IgG2 ≫ IgG4; however, some IgA anti‐fimbriae antibodies were also seen. The IgA subclass fimbriae‐specific response was mainly IgA1; however, significant IgA2 anti‐fimbrae antibodies were seen. We also assessed numbers of anti‐fimbriae antibody producing cells from peripheral blood mononuclear cells (PMBC) and from either healthy or inflamed gingiva of AP subjects. Gingival mononuclear cells (GMC) of AP patients exhibited high numbers of immunoglobulin‐producing (spot‐forming) cells (SFC) including fimbriae‐specific antibody secreting cells in a pattern of IgG > IgA > > > IgM. However, low numbers of SFC were seen in GMC from healthy gingiva; further, no anti‐timbriac SFC responses were noted in healthy GMC. Although no fimbriae‐specific immunoglobulin‐producing cells were seen in PBMC. low numbers of antigen‐specific SFC were found in pokeweed mitogen‐triggercd PBMC from AP subjects. Treatment of AP patients for plaque and surgical removal of inflamed gingiva resulted in significant reductions in serum anti‐fimbriac responses. These studies show that AP patients exhibit brisk serum IgG and IgA subclass anti‐fimbriac antibodies, whose origin appear to be the plasma cells present in the localized inflamed tissues.