Spontaneous formation of nucleic acid-based nanoparticles is responsible for high interferon-alpha induction by CpG-A in plasmacytoid dendritic cells.
Plasmacytoid dendritic cells (PDC) represent a highly specialized immune cell subset that produces large quantities of the anti-viral cytokines type I interferons (IFN-alpha and IFN-beta) upon viral infection. PDC employ a member of the family of toll-like receptors, TLR9, to detect CpG motifs (unmethylated CG dinucleotides in certain base context) present in viral DNA. A certain group of CpG motif-containing oligodeoxynucleotides (CpG ODN), CpG-A, was the first synthetic stimulus available that induced large amounts of interferon-alpha (IFN-alpha) in PDC. However, the mechanism responsible for this activity remained elusive. CpG-A is characterized by a central palindrome and poly(G) at the 5' and 3' end. Here we demonstrate that CpG-A self-assembles to higher order tertiary structures via G-tetrad formation of their poly(G) motifs. Spontaneous G-tetrad formation of CpG-A required the palindrome sequence allowing structure formation in a physiological environment. Once formed, G-tetrad-linked structures were stable even under denaturing conditions. Atomic force microscopy revealed that the tertiary structures formed by CpG-A represent nucleic acid-based nanoparticles in the size range of viruses. Similarly sized preformed polystyrene nanoparticles loaded with a CpG ODN that is otherwise weak at inducing IFN-alpha (CpG-B) gained the potency of CpG-A to induce IFN-alpha. Higher ODN uptake in PDC was not responsible for the higher IFN-alpha-inducing activity of CpG-A or of CpG-B-coated nanoparticles as compared with CpG-B. Based on these results we propose a model in which the spatial configuration of CpG motifs as particle is responsible for the virus-like potency of CpG-A to induce IFN-alpha in PDC.
Kerkmann
Miren
M
Department of Internal Medicine, Division of Clinical Pharmacology, Ludwig-Maximilians-University of Munich, 80336 Muenchen, Germany.
Costa
Lilian T
LT
Richter
Christine
C
Rothenfusser
Simon
S
Battiany
Julia
J
Hornung
Veit
V
Johnson
Judith
J
Englert
Steffen
S
Ketterer
Thomas
T
Heckl
Wolfgang
W
Thalhammer
Stefan
S
Endres
Stefan
S
Hartmann
Gunther
G
D000293:Adolescent; D000328:Adult; D000368:Aged; D002021:Buffers; D002478:Cells, Cultured; D018899:CpG Islands; D016207:Cytokines / Q000378:metabolism; D004247:DNA / Q000737:chemistry; D003713:Dendritic Cells / Q000166:cytology*; D004591:Electrophoresis, Polyacrylamide Gel; D005434:Flow Cytometry; D006801:Humans; D016898:Interferon-alpha / Q000378:metabolism; D018625:Microscopy, Atomic Force; D008875:Middle Aged; D008957:Models, Genetic; D049329:Nanostructures / Q000648:ultrastructure*; D009690:Nucleic Acid Conformation; D009696:Nucleic Acids / Q000737:chemistry*; D009841:Oligonucleotides / Q000737:chemistry; D010950:Plasma Cells / Q000378:metabolism*; D011137:Polystyrenes / Q000737:chemistry; D013696:Temperature
D002021:Buffers; D016207:Cytokines; D016898:Interferon-alpha; D009696:Nucleic Acids; D009841:Oligonucleotides; D011137:Polystyrenes; D004247:DNA