title: Porphyromonas gingivalissuppresses adaptive immunity in periodontitis, atherosclerosis, and Alzheimer's disease.
abstract: Porphyromonas gingivalis, a keystone pathogen in chronic periodontitis, has been found to associate with remote body organ inflammatory pathologies, including atherosclerosis and Alzheimer's disease (AD). AlthoughP. gingivalishas a plethora of virulence factors, much of its pathogenicity is surprisingly related to the overall immunosuppression of the host. This review focuses onP. gingivalisaiding suppression of the host's adaptive immune system involving manipulation of cellular immunological responses, specifically T cells and B cells in periodontitis and related conditions. In periodontitis, this bacterium inhibits the synthesis of IL-2 and increases humoral responses. This reduces the inflammatory responses related to T- and B-cell activation, and subsequent IFN-γ secretion by a subset of T cells. The T cells further suppress upregulation of programmed cell death-1 (PD-1)-receptor on CD+cells and its ligand PD-L1 on CD11b+-subset of T cells. IL-2 downregulates genes regulated by immune response and induces a cytokine pattern in which the Th17 lineage is favored, thereby modulating the Th17/T-regulatory cell (Treg) imbalance. The suppression of IFN-γ-stimulated release of interferon-inducible protein-10 (IP-10) chemokine ligands [ITAC (CXCL11) and Mig (CXCL9)] byP. gingivaliscapsular serotypes triggers distinct T cell responses and contributes to local immune evasion by release of its outer membrane vesicles. In atherosclerosis,P. gingivalisreduces Tregs, transforms growth factor beta-1 (TGFβ-1), and causes imbalance in the Th17 lineage of the Treg population. In AD,P. gingivalismay affect the blood-brain barrier permeability and inhibit local IFN-γ response by preventing entry of immune cells into the brain. The scarcity of adaptive immune cells in AD neuropathology impliesP. gingivalisinfection of the brain likely causing impaired clearance of insoluble amyloid and inducing immunosuppression. By the effective manipulation of the armory of adaptive immune suppression through a plethora of virulence factors,P. gingivalismay act as a keystone organism in periodontitis and in related systemic diseases and other remote body inflammatory pathologies.
authors.affiliation: Department of Oral Biology, Faculty of Dentistry, University of Oslo, Oslo, Norway; ingar.olsen@odont.uio.no.
authors.forename: Ingar
authors.initials: I
authors.lastname: Olsen
authors.affiliation: Department of Immunology and Infectious Diseases, Forsyth Institute, Cambridge, MA, USA.|Department of Developmental Biology, Harvard School of Dental Medicine, Harvard Medical School, Boston, MA, USA.
authors.forename: Martin A
authors.initials: MA
authors.lastname: Taubman
authors.affiliation: Dementia & Neurodegeneration Research Group, School of Dentistry, College of Clinical and Biomedical Sciences, University of Central Lancashire, Preston, UK.
authors.forename: Sim K
authors.initials: SK
authors.lastname: Singhrao
keywords: Alzheimer’s disease; P. gingivalis; adaptive immunity; atherosclerosis; periodontitis; suppression