Anti-phosphorylcholine-opsonized low-density lipoprotein promotes rapid production of proinflammatory cytokines by dendritic cells and natural killer cells

Kikuchi T, El Shikh MM, El Sayed RM, Purkall DB, Elaasser MM, Sarraf A, Barbour SE, Schenkein HA, Tew JG. Anti‐phosphorylcholine opsonized low‐density lipoprotein promotes rapid production of proinflammatory cytokines by dendritic cells and natural killer cells. J Periodont Res 2010; 45: 720–730. © 2010 John Wiley & Sons A/S Background and Objective: Epidemiological and animal studies suggest that periodontal infections increase atherosclerosis risk. Periodontitis patients have elevated levels of anti‐phosphorylcholine (anti‐PC) reactive not only with numerous periodontal organisms but also with minimally modified low‐density lipoprotein (mmLDL). Dendritic cells (DCs) reside in arterial walls and accumulate in atherosclerotic lesions. The ability of anti‐PC to bind mmLDL prompted the hypothesis that opsonized mmLDL would stimulate DCs and enhance the production of proinflammatory cytokines that promote atherogenic plaque development. Material and Methods: Monocyte‐derived DCs (mDCs) were generated using granulocyte–macrophage colony‐stimulating factor (GM‐CSF) and interleukin (IL)‐4, then stimulated with mmLDL or with anti‐PC‐opsonized mmLDL. The anti‐PC effect was determined using flow cytometry, cofocal microscopy and cytokine assays. The production of CD83, IL‐12p35 mRNA, IL‐12p40 mRNA, IL‐12p70 and IL‐10 by DCs was monitored. Results: Dendritic cells stimulated with mmLDL expressed little CD83 and produced little IL‐12p70. However, anti‐PC‐opsonized mmLDL enhanced DC maturation, as indicated by upregulated CD83 and rapid (≤ 48 h) production of IL‐12p70 if a source of interferon‐γ (IFN‐γ) was available. In leukocyte cultures, natural killer (NK) cells rapidly produced IFN‐γ (≤ 48 h) when interacting with IL‐12‐producing DCs activated by anti‐PC‐opsonized mmLDL. Moreover, IFN‐γ promoted DC IL‐12 responses that were further augmented when mmLDL was opsonized with anti‐PC. Conclusion: Minimally modified LDL‐stimulated DCs and NK cells were mutually stimulatory, with DC IL‐12p70 needed by NK cells and with NK cell IFN‐γ needed by DCs. Moreover, production of these proinflammatory cytokines was markedly enhanced when LDL was opsonized by anti‐PC. In short, the data suggest that the elevated anti‐PC levels in periodontitis patients could promote a mechanism that facilitates atherosclerosis.