Higher activation of TLR9 in plasmacytoid dendritic cells by microbial DNA compared with self-DNA based on CpG-specific recognition of phosphodiester DNA.
TLR9 detects DNA in endolysosomal compartments of human B cells and PDC. Recently, the concept of the CpG motif specificity of TLR9-mediated detection, specifically of natural phosphodiester DNA, has been challenged. Unlike in human B cells, CpG specificity of natural phosphodiester DNA recognition in human PDC has not been analyzed in the literature. Here, we found that the induction of IFN-alpha and TNF-alpha in human PDC by phosphodiester ODNs containing one or two CG dinucleotides was reduced to a lower level when the CG dinucleotides were methylated and was abolished if the CGs were switched to GCs. Consistent with a high frequency of unmethylated CG dinucleotides, bacterial DNA induced high levels of IFN-alpha in PDC; IFN-alpha was reduced but not abolished upon methylation of bacterial DNA. Mammalian DNA containing low numbers of CG dinucleotides, which are frequently methylated, induced IFN-alpha in PDC consistently but on a much lower level than bacterial DNA. For activation of PDC, phosphodiester ODNs and genomic DNA strictly required complexation with cationic molecules such as the keratinocyte-derived antimicrobial peptide LL37 or a scrambled derivative. In conclusion, we demonstrate that self-DNA complexed to cationic molecules activate PDC and thus, indeed, may function as DAMPs; nevertheless, the preference of PDC for CpG containing DNA provides the basis for the discrimination of microbial from self-DNA even if DNA is presented in the condensed form of a complex.
Coch
Christoph
C
Institute of Clinical Chemistry and Pharmacology, University Hospital of Bonn, D-53127 Bonn, Germany.
Busch
Nicolas
N
Wimmenauer
Vera
V
Hartmann
Evelyn
E
Janke
Markus
M
Abdel-Mottaleb
Mona Mohamed Ahmed
MM
Lamprecht
Alf
A
Ludwig
Janos
J
Barchet
Winfried
W
Schlee
Martin
M
Hartmann
Gunther
G
D023181:Antimicrobial Cationic Peptides / Q000276:immunology*; D054804:Cathelicidins; D002460:Cell Line; D002478:Cells, Cultured; D018899:CpG Islands / Q000235:genetics / Q000276:immunology; D004247:DNA / Q000235:genetics / Q000276:immunology; D019175:DNA Methylation; D004269:DNA, Bacterial / Q000235:genetics / Q000276:immunology* / Q000302:isolation & purification; D003713:Dendritic Cells / Q000276:immunology*; D015226:Dinucleoside Phosphates / Q000276:immunology*; D006801:Humans; D007668:Kidney / Q000166:cytology; D007963:Leukocytes, Mononuclear / Q000276:immunology; D008213:Lymphocyte Activation / Q000276:immunology; D054735:Phosphorothioate Oligonucleotides / Q000276:immunology*; D051217:Toll-Like Receptor 9 / Q000276:immunology*
D023181:Antimicrobial Cationic Peptides; D054804:Cathelicidins; D004247:DNA; D004269:DNA, Bacterial; D015226:Dinucleoside Phosphates; D054735:Phosphorothioate Oligonucleotides; D051217:Toll-Like Receptor 9; C015772:CpG dinucleotide