Serum antibodies against the hemoglobin-binding domain (HA2) of Porphyromonas gingivalis

Background: The hemoglobin-binding domain (HA2) of the Porphyromonasgingivalis gingipains and hemagglutinins strongly binds hemoglobin and hemin and is thought to play a key role in acquisition of this essential metabolite by the microorganism. Methods: In this report, we partially characterized human anti-HA2 humoral antibodies and their relationship to periodontal disease in an analysis of titer and function. Results: Overall, serum anti-HA2 antibodies were relatively low and dominated by the immunoglobulin M (IgM) isotype. Pre-therapy titers had a direct association with periodontal health. Levels of P. gingivalis in the plaque were directly related to pre-therapy anti-HA2 IgG levels, and were an important covariant in a significant direct relationship between pre- and post-therapy anti-HA2 titers. Post-therapy anti-HA2 IgG antibody titers were directly related to the capacity of serum IgG fractions to neutralize hemoglobin binding by Lys-gingipain (Kgp). Further, lower levels of neutralizing activity post-therapy were directly related to severe periodontitis within the patient cohort. Conclusions: These data suggest that anti-HA2 IgG antibodies correspond directly with periodontal health, possibly through their ability to neutralize P. gingivalis hemoglobin capture. The data also suggest that inadvertent or therapeutic inoculation of P. gingivalis in the plaque may contribute to generation of neutralizing anti-HA2 IgG and improvement of periodontal prognosis.