Plasmacytoid dendritic cell TLR7/9 response modulation through EGA and α-CD138 antibody.
Plasmacytoid dendritic cells (pDC) have the unique ability to produce an inordinate amount of type 1 interferon (IFN) and other cytokines in response to stimulation with pathogenic and self-nucleic acids mainly through the toll-like receptors, TLR7 and TLR9. In vitro cultures of pDCs exhibit a bifurcated response to distinct TLR7 and TLR9 agonists: a response dominated by type 1 IFN production or pro-inflammatory cytokine production and maturation. The bifurcation of response is hypothesized to occur in distinct signaling endosomes within pDCs. We report that EGA alters the TLR7 and TLR9 response in pDCs by targeting the transition from the early to late endosome. EGA enhances imidazoquinoline-induced pro-inflammatory cytokine while diminishing type 1 IFN production. EGA abrogated the IFN and pro-inflammatory cytokine response of pDCs to both influenza and ODN stimulation. Intriguingly, EGA enhanced the IFN and cytokine response of a "pDC-like" cell line, Gen2.2, to TLR9 stimulation. Mechanistically, EGA pre-incubation caused the retention of ODNs and imidazoquinolines within endosomes characterized by an early/recycling phenotype. These results suggest the presence of unique signaling localizations for TLR7 and TLR9 agonists within pDCs which were not reproducible within a "pDC-like" cell line, Gen2.2. EGA also shows therapeutic potential in SLE patients in diminishing type 1 IFN responsiveness to TLR7 stimulation which is known to be play a role in SLE pathogenesis. It has been suggested that heparan sulfate proteoglycans (HSPG) play a role in the uptake of pathogenic nucleic acid-antimicrobial peptide complexes. We have found that pDCs in the blood of pediatric SLE patients express syndecan-1 (CD138). We also found that α-CD138 antibody treatment resulted in decreased IFNα expression by pDCs stimulated with CpG ODNs and genomic DNAs without affecting the TLR7 response in pDCs. This study demonstrates that pDC response to nucleic acids and their analogues can be controlled by both EGA and α-CD 138. While the mechanisms of action of both EGA and α-CD138 need to be further studied, our findings will help us understand molecular mechanisms for pDC expression of type 1 IFN in response to TLR7/9 ligands.