Differential cytokine induction by two types of Porphyromonas gingivalis

The presence of Porphyromonas gingivalis with type II fimA is strongly associated with adult periodontitis. However, the importance of specific fimA types in the immune response is unknown. Two types of P. gingivalis (type I and type II) and Actinomyces naeslundii were assessed for their degree of cytokine induction in the macrophage‐like human cell line U937. Real‐time reverse transcriptase polymerase chain reaction was used to determine mRNA expression of 12 cytokines. Significant levels of interleukin (IL)‐8 induction and a similar cytokine expression pattern were observed at 6 h postinfection for all three bacterial strains. However, type II P. gingivalis infection showed statistically higher levels of IL‐1β, IL‐8, IL‐12 and tumor necrosis factor‐α mRNA induction than those of control at 24 h postinfection, whereas type I P. gingivalis and A. naeslundii showed no significant induction of these cytokines. These data suggest that compared with A. naeslundii and type I P. gingivalis, type II P. gingivalis prolongs the cytokine response. Although other factors may also be involved, the sustained cytokine response induced by type II P. gingivalis may play an important role in enhanced periodontal tissue inflammation and destruction.