Evidence and a novel hypothesis for the role of dendritic cells and Porphyromonas gingivalis in adult periodontitis

We have proposed a novel overall hypothesis and approach to understanding t he pathophysiology of adult periodontitis, one of the most common diseases that afflicts the US population. While mortality of the dentition is the mo st familiar outcome of adult periodontitis, its links with other more sever e diseases, including coronary artery disease, respiratory diseases and pre -term labor, cannot be ignored. We have called attention to the many intrig uing parallels between adult periodontitis and contact hypersensitivity (CH S). CHS is among the most common of dermatoses that afflicts mankind and on e of the most intensively studied of in vivo immune responses. Both adult p eriodontitis and CHS target the host integument (gingiva or skin) and appea r to involve the activation and sensitization of similar subsets of antigen capture and presenting cells, the dendritic cells (DCs), as well as simila r T cell subsets. DCs have been termed "nature's adjuvant", being more effi cient at antigen-presentation than macrophages or B cells and the only anti gen-presenting cells that can stimulate naive T cells to proliferate, This immunostimulatory capacity can also have detrimental effects for the host, as typified by graft-vs.-host disease and CHS responses. Both AP and CHS in volve a predominantly destructive T cell response mediated by both regulato ry and effector T cells. In the present paper, we show intriguing evidence that Porphyromonas gingivalis is a unique pathogen in this regard, able to infect, sensitize and activate DCs in vitro and, probably, in situ. Many qu estions about the role of P. gingivalis-sensitized DCs in adult periodontit is, and of the parallels between adult periodontitis and CHS, however, rema in to be answered.