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Research article2001Peer reviewed

The plasmid pcDNA3 differentially induces production of interferon-alpha and interleukin-6 in cultures of porcine leukocytes

Magnusson, M; Johansson, E; Berg, M; Eloranta, ML; Fuxler, L; Fossum, C


An adjuvant effect of invertebrate DNA has been attributed to its relative high frequency of unmethylated CpG dinucleotides. Here we describe the interferon-alpha (IFN-alpha) and interleukin-6 (IL-6) inducing properties of a commonly used eukaryotic expression vector, pcDNA3, in porcine leukocytes. The magnitude of the cytokine response was compared to that induced by the synthetic ds RNA analogue poly(I):poly(C), inactivated preparations of Aujeszky's disease virus (ADV) and the Gram-negative bacteria Actinobacillus pleuropneumoniae. The plasmid, as well as poly(I):poly(C), required lipofectin to induce IFN-alpha production whereas both preparations induced IL-6 irrespective of preincubation with lipofectin. However, the nucleic acid-induced levels of IL-6 were low compared to those induced by A. pleuropneumoniae. The IFN-alpha response elicited by pcDNA3 in the presence of lipofectin was as high as, or higher than that induced by ADV. Interestingly, also A. pleuropneumoniae induced a substantial production of IFN-alpha when preincubated with lipofectin. Plasmid expression was not necessary for induction of IFN-alpha. Furthermore, the IFN-alpha. inducing capacity of pcDNA3 was not reduced when the two predicted immunostimulatory sequences 5'AACGTT3' were deleted. Nor did the ability of the plasmid to induce IFN-alpha production decrease when the ampicillin resistance (ampR) gene was replaced with the kanamycin resistance (kanR) gene. However, methylation of all cytidines in CpG dinucleotides of pcDNA3 abolished the IFN-alpha inducing capacity. These in vitro results indicate an immunomodulatory role of bacterial DNA also in the pig. Unmethylated CpG dinucleotides are crucial for induction of IFN-alpha by the plasmid, but other CpG motifs than those within the 5'AACGTT3' sequences of the ampR gene contribute to this induction in porcine cells. (C) 2001 Elsevier Science B.V. All rights reserved.


immunostimulatory DNA; plasmid; IFN-alpha; IL-6; unmethylated CpG dinucleotides; porcine

Published in

Veterinary Immunology and Immunopathology
2001, Volume: 78, number: 1, pages: 45-56 Publisher: ELSEVIER SCIENCE BV

      SLU Authors

    • Fossum, Caroline

      • Department of Veterinary Microbiology, Swedish University of Agricultural Sciences

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