Pathogen Traffic by Dendritic Cells in Periodontitis: Links to Coronary Heart Disease

Abstract

Chronic low-grade infections, such as chronic periodontitis (CP), are suspected of increasing Coronary Artery Disease (CAD) risk; however, the linking mechanisms are just emerging. Porphyromonas gingivalis (Pg), commonly implicated in CP, along with multiple other pathogens, have been associated with the pathogenesis of coronary artery disease (CAD). However, it is unclear how these pathogens travel to and invade the arteries and their precise role in the disease process. P. gingivalis is known for invading epithelial, fibroblast, endothelial and myeloid dendritic cells (mDCs). Recent in-vitro evidence has demonstrated that P. gingivalis targets DC-SIGN+ (Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin) mDCs via its DC-invasin minor (mfa-1) fimbriae and uncouples dendritic cell maturation from the cytokine response, leading to intracellular bacterial persistence. Unlike epithelial and endothelial cells, mDCs are highly migratory. Thus P. gingivalis could potentially traffic to atherosclerotic plaques via mDCs. Moreover, DC-SIGN+ mDCs increase dramatically in unstable atherosclerotic plaques, as observed in gingival tissue lesions from patients with CP. Thus we hypothesize that Pg infected mDCs in CP lesions redistribute to the peripheral blood. These along with blood mDCs that pick up Pg directly in the blood, contribute to the infiltrating pool of mDCs observed in patients with CAD. The objectives of this study were to determine the frequency of blood and tissue mDCs in CP and CAD patients relative to healthy individuals. In addition, we began to establish the role of blood mDCs in dissemination of periodontal pathogens to atherosclerotic plaques. Accordingly, we examined the infection status of mDCs in gingival tissues and coronary artery atherosclerotic (ATH) plaque biopsies, as well as peripheral blood mDCs of a cohort of CP patients, with or without existing acute coronary syndrome (ACS). We initially focused on confirming that CP patients (n=26) were colonized by P. gingivalis, by analysis of the oral biofilm (i.e. subgingival dental plaque) by qRT-PCR of 16s rDNA; followed by genomic blast sequence analysis (qRT-PCR/GBS) of the 197 bp PCR-amplified product. The results indicate a 44% subgingival colonization rate with P. gingivalis in CP patients. Gingival biopsies from the Pg-infected CP patients were then analyzed by immunofluorescence-laser confocal microscopy (IF-LCM), focusing on colocalization of the DC-invasin of P. gingivalis, mfa-1 (AEZ? Mfa1), and on its target receptor on mDCs, DC-SIGN. The results reveal mfa-1 + DC-SIGN+ mDCs in CP lesions. These Pg "infected" DC-SIGN+ mDCs were also observed in post-mortem coronary artery ATH plaques. The presumed conduit for transfer of Pg to ATH plaques, migratory CD19- DC-SIGN+ CD1c+ mDCs were then isolated from peripheral blood of CP and ACS/CP patients and analyzed by IF-LCM. The results confirm the presence of mfa-1+ P. gingivalis infected blood mDCs in the blood of CP and ACS/CP patients. The estimated CFUs (eCFUs) of Pg in blood mDCs equaled 1.32 (+ 1.21) X 105. Other pathogens identified in blood mDCs included Pseudomonas spp., Moraxella catarrhalis, Klebsiella pneumonia, among other species. Overall, the findings support blood mDCs as a conduit for transport of infectious agents from gingival tissues to coronary arteries and possibly other distant sites in the human body.