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  1. Jidong Zhang1,
  2. Jianguo Liu2,
  3. Wei Cui1,
  4. Fan Liu1,
  5. Xiaohong Yang1,
  6. Guoqiang Gu1,
  7. Jingchao Lu1,
  8. Yuzhou Wu1,
  9. Jianguo Liu2
  1. 1Second Affiliated Hospital of Hebei Medical University, Shijiazhuang 050000, Hebei Province, China
  2. 2Division of Infectious Diseases, Allergy, and Immunology, Department of Internal Medicine, Saint Louis University School of Medicine, St. Louis, MO 63104, USA


    Objectives Accumulation of T cells and macrophages in atherosclerotic plaques and the formation of antibodies directed against plaque proteins suggests that adaptive immunity contributes to the development of atherosclerosis. Apolipoprotein E (apoE) exerts potent anti-inflammatory effects that may contribute to protection against atherosclerosis independent of its role in lipid metabolism. Here, we investigated the expression of pro-inflammatory cytokine interleukin-12 (IL-12) in macrophages of apoE/ mice and then further explored the molecular mechanisms.

    Methods In this study, peritoneal macrophages and bone marrow- derived macrophages elicited from wild-type (WT) or apoE knockout (apoE/) mice were stimulated with low-dose lipopolysaccharide (LPS), interferon-r (IFN-r) or LPS plus IFN-r for 24 h, followed by collection of culture supernatants for measurement of IL-12 p40 and p70 protein secretion by ELISA. Meanwhile, cells treated with these stimuli for 4 h were used for RNA isolation and IL-12 p35 and p40 mRNA detection by quantitative real-time PCR. Then, we transiently co-transfected a human IL-12 p35 promoter luciferase construct with different amounts of apoE expression vector or PTYB2 vector into THP-1 cells (a human macrophage cell line) by electroporation, followed by measurement of luciferase activity in cell lysates.

    Results The expression of IL-12 were upregulated to a significantly greater extent in apoE-deficient mice than in WT mice at both the mRNA and protein levels following administration of LPS or LPS plus IFN-r. ApoE suppressed IL-12 p35 promoter in a dose-dependent manner, indicating that apoE-mediated p35 gene suppression is regulated at the level of transcription. Moreover, cells co-transfected with the p35 promoter and the apoE-expressing vector showed decreased promoter activities in response to IFN-r and LPS treatments compared with cells co-transfected with the empty vector, PTYB2, further demonstrating that apoE suppressed IL-12 p35 gene transcription under both basal and inducible conditions.

    Conclusions Our study reveals that apoE suppresses IL-12 production at the level of transcription in macrophages, this effect may represent a novel anti-inflammatory activity of apoE.

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