The Roles of Toll-Like Receptor 9, MyD88, and DNA-Dependent Protein Kinase Catalytic Subunit in the Effects of Two Distinct CpG DNAs on Dendritic Cell Subsets

Abstract

Oligodeoxynucleotides containing unmethylated CpG motifs (CpG DNAs) can function as powerful immune adjuvants by activating APC. Compared with conventional phosphorothioate-backbone CpG DNAs, another type of CpG DNAs, called an A or D type (A/D-type), possesses higher ability to induce IFN-α production. Conventional CpG DNAs can exert their activity through Toll-like receptor 9 (TLR9) signaling, which depends on a cytoplasmic adapter, MyD88. However, it remains unknown how A/D-type CpG DNAs exhibit their immunostimulatory function. In this study we have investigated murine dendritic cell (DC) responses to these two distinct CpG DNAs. Not only splenic, but also in vitro bone marrow-derived, DCs could produce larger amounts of IFN-α in response to A/D-type CpG DNAs compared with conventional CpG DNAs. This IFN-α production was mainly due to the B220+ DC subset. On the other hand, the B220− DC subset responded similarly to both CpG DNAs in terms of costimulatory molecule up-regulation and IL-12 induction. IFN-α, but not IL-12, induction was dependent on type I IFN. However, all activities of both CpG DNAs were abolished in TLR9- and MyD88-, but were retained in DNA-PKcs-deficient DCs. This study demonstrates that the TLR9-MyD88 signaling pathway is essential for all DC responses to both types of CpG DNAs.

IFN-α production by human mononuclear cells infected with varicella-zoster virus through TLR9-dependent and -independent pathways

“…42 However, recent reports have shown that DNA-PK is not essential for CpG DNA responses. 43,44 Our results were consistent with the latter reports, and DNA-PK seems to be dispensable for VZV-induced IFN-a production. In contrast to DNA-PK, PKR was involved in VZV-induced IFN-a production in PBMCs.…”

TLR signaling

“…While pDCs deficient of IRF3 normally respond to these TLRs, type I IFN and inflammatory cytokine induction is totally abolished in MyD88-and IRAK4-deficient pDCs. [64][65][66][67] Unlike other types of DCs, pDCs constitutively express high levels of IRF7. 68,69 Furthermore, treatment of pDCs with TLR9 ligands causes nuclear translocation of IRF7, and pDCs derived from IRF7-deficient mice are incapable of producing type I IFN in response to TLR7/8 and TLR9 ligands.…”

Suppression of Skin Lesions by Transdermal Application of CpG-Oligodeoxynucleotides in NC/Nga Mice, a Model of Human Atopic Dermatitis

“…Signaling through TLR9 leads to the secretion of proinflammatory cytokines such as IL-1, IL-6, TNF-␣, and IL-12 (15)(16)(17). IL-12 acts on T cells and NK cells inducing the production of cytokines, primarily IFN-␥.…”

“…Both bacterial dinucleotides flanked by certain bases (CpG-motif) and synthetic oligodeoxynucleotides (ODN) containing a CpG-motif (CpG-ODN) activate cells such as B cells, macrophages, and dendritic cells through TLR9 (15)(16)(17). Signaling through TLR9 leads to the secretion of proinflammatory cytokines such as IL-1, IL-6, TNF-␣, and IL-12 (15)(16)(17).…”