Secondary Lymphoid Organ Homing Phenotype of Human Myeloid Dendritic Cells Disrupted by an Intracellular Oral Pathogen

Abstract

Several intracellular pathogens, including a key etiological agent of chronic periodontitis, Porphyromonas gingivalis, infect blood myeloid dendritic cells (mDCs). This infection results in pathogen dissemination to distant inflammatory sites (i.e., pathogen trafficking). The alteration in chemokine-chemokine receptor expression that contributes to this pathogen trafficking function, particularly toward sites of neovascularization in humans, is unclear. To investigate this, we utilized human monocyte-derived DCs (MoDCs) and primary endothelial cells in vitro, combined with ex vivo-isolated blood mDCs and serum from chronic periodontitis subjects and healthy controls. Our results, using conditional fimbria mutants of P. gingivalis, show that P. gingivalis infection of MoDCs induces an angiogenic migratory profile. This profile is enhanced by expression of DC-SIGN on MoDCs and minor mfa-1 fimbriae on P. gingivalis and is evidenced by robust upregulation of CXCR4, but not secondary lymphoid organ (SLO)-homing CCR7. This disruption of SLO-homing capacity in response to respective chemokines closely matches surface expression of CXCR4 and CCR7 and is consistent with directed MoDC migration through an endothelial monolayer. Ex vivo-isolated mDCs from the blood of chronic periodontitis subjects, but not healthy controls, expressed a similar migratory profile; moreover, sera from chronic periodontitis subjects expressed elevated levels of CXCL12. Overall, we conclude that P. gingivalis actively "commandeers" DCs by reprogramming the chemokine receptor profile, thus disrupting SLO homing, while driving migration toward inflammatory vascular sites.