Epstein-Barr Virus DNA Exacerbates Arthritis in a Mouse Model via Toll-like Receptor 9.

Epstein-Barr virus (EBV) DNA is known to be shed upon reactivation of latent EBV. Based on our previous findings linking Toll-like receptor-9 (TLR9) to an EBV DNA-driven surge in IL-17A production, we aimed to examine the therapeutic potential of TLR9 inhibition in EBV DNA-exacerbated arthritis in a collagen-induced arthritis (CIA) mouse model. C57BL/6J mice were administered either collagen, EBV DNA + collagen, EBV DNA + collagen + TLR9 inhibitor, or only the TLR9 inhibitor. After 70 days, paw thicknesses, clinical scores, and gripping strength were recorded. Moreover, affected joints, footpads, and colons were histologically scored. Furthermore, the number of cells co-expressing IL-17A, IFN-γ, and FOXP3 in joint sections was determined by immunofluorescence assays. Significantly decreased paw thicknesses, clinical scores, and histological scores with a significantly increased gripping strength were observed in the group receiving EBV DNA + collagen + TLR9 inhibitor, compared to those receiving EBV DNA + collagen. Similarly, this group showed decreased IL-17A+ IFN-γ+, IL-17A+ FOXP3+, and IL-17A+ IFN-γ+ FOXP3+ foci counts in joints. We show that inhibiting TLR9 limits the exacerbation of arthritis induced by EBV DNA in a CIA mouse model, suggesting that TLR9 could be a potential therapeutic target for rheumatoid arthritis management in EBV-infected individuals.

Tubular expression of Toll-like receptor 9 in lupus and primary membranous nephropathy.

INTRODUCTION: Toll-like- receptors (TLR) control important aspects of innate and adaptive immune responses. Renal cells are among the non-immune cells that express (TLR). Therefore, their activation might be implicated in renal tubulo-interstitial injury. AIM: The study aimed to compare TLR9 expression in patients with primary membranous nephropathy (MN) to patients with lupus membranous nephropathy. METHODS: Kidney sections from 10 Lupus nephritis (LN) patients and ten patients with primary MN were analyzed by immunohistochemistry using anti-human TLR9 antibody. RESULTS: Results showed that TLR9 expression was weak and exclusively tubular in primary MN patients' biopsies. There was a significant difference between LN patients' biopsies and primary MN patients' biopsies. TLR9 expression was more diffused in LN patients' specimen than in those with primary MN. CONCLUSION: This study focuses on molecular level pathogenesis of MN. The data suggest that the receptors TLR9 may play role in tubulointerstitial injury in the pathogenesis of LN but not primary membranous nephropathy.

Surface charge-dependent cytokine production using near-infrared emitting silicon quantum dots.

Toll-like receptor 9 (TLR-9) is a protein that helps our immune system identify specific DNA types. Upon detection, CpG oligodeoxynucleotides signal the immune system to generate cytokines, essential proteins that contribute to the body's defence against infectious diseases. Native phosphodiester type B CpG ODNs induce only Interleukin-6 with no effect on interferon-α. We prepared silicon quantum dots containing different surface charges, such as positive, negative, and neutral, using amine, acrylate-modified Plouronic F-127, and Plouronic F-127. Then, class B CpG ODNs are loaded on the surface of the prepared SiQDs. The uptake of ODNs varies based on the surface charge; positively charged SiQDs demonstrate higher adsorption compared to SiQDs with negative and neutral surface charges. The level of cytokine production in peripheral blood mononuclear cells was found to be associated with the surface charge of SiQDs prior to the binding of the CpG ODNs. Significantly higher levels of IL-6 and IFN-α induction were observed compared to neutral and negatively charged SiQDs loaded with CpG ODNs. This observation strongly supports the notion that the surface charge of SiQDs effectively regulates cytokine induction.

The Effects of Endosomal Toll-like Receptor Inhibitors in an EBV DNA-Exacerbated Inflammatory Bowel Disease Mouse Model.

Epstein-Barr virus (EBV), a Herpesviridae family member, is associated with an increased risk of autoimmune disease development in the host. We previously demonstrated that EBV DNA elevates levels of the pro-inflammatory cytokine IL-17A and that inhibiting Toll-like receptor (TLR) 3, 7, or 9 reduces its levels. Moreover, this DNA exacerbated colitis in a mouse model of inflammatory bowel disease (IBD). In the study at hand, we examined whether inhibition of TLR3, 7, or 9 alleviates this exacerbation. Mice were fed 1.5% dextran sulfate sodium (DSS) water and administered EBV DNA. Then, they were treated with a TLR3, 7, or 9 inhibitor or left untreated. We also assessed the additive impact of combined inhibition of all three receptors. Mice that received DSS, EBV DNA, and each inhibitor alone, or a combination of inhibitors, showed significant improvement. They also had a decrease in the numbers of the pathogenic colonic IL-17A+IFN-γ+ foci. Inhibition of all three endosomal TLR receptors offered no additive benefit over administering a single inhibitor. Therefore, inhibition of endosomal TLRs reduces EBV DNA exacerbation of mouse colitis, offering a potential approach for managing IBD patients infected with EBV.

Hepatocyte mitochondrial DNA mediates macrophage immune response in liver injury induced by trichloroethylene.

We have previously shown that excessive activation of macrophage proinflammatory activity plays a key role in TCE-induced immune liver injury, but the mechanism of polarization is unclear. Recent studies have shown that TLR9 activation plays an important regulatory role in macrophage polarization. In the present study, we demonstrated that elevated levels of oxidative stress in hepatocytes mediate the release of mtDNA into the bloodstream, leading to the activation of TLR9 in macrophages to regulate macrophage polarization. In vivo experiments revealed that pretreatment with SS-31, a mitochondria-targeting antioxidant peptide, reduced the level of oxidative stress in hepatocytes, leading to a decrease in mtDNA release. Importantly, SS-31 pretreatment inhibited TLR9 activation in macrophages, suggesting that hepatocyte mtDNA may activate TLR9 in macrophages. Further studies revealed that pharmacological inhibition of TLR9 by ODN2088 partially blocked macrophage activation, suggesting that the level of macrophage activation is dependent on TLR9 activation. In vitro experiments involving the extraction of mtDNA from TCE-sensitized mice treated with RAW264.7 cells further confirmed that hepatocyte mtDNA can activate TLR9 in mouse peritoneal macrophages, leading to macrophage polarization. In summary, our study comprehensively confirmed that TLR9 activation in macrophages is dependent on mtDNA released by elevated levels of oxidative stress in hepatocytes and that TLR9 activation in macrophages plays a key role in regulating macrophage polarization. These findings reveal the mechanism of macrophage activation in TCE-induced immune liver injury and provide new perspectives and therapeutic targets for the treatment of OMDT-induced immune liver injury.

Protein Expression of TLR2, TLR4, and TLR9 on Monocytes in TB, HIV, and TB/HIV.

Toll-like receptors (TLRs) have a critical role in recognizing pathogenic patterns and initiating immune responses against TB and HIV. Previously, studies described the gene expression of TLRs in patients with TB and HIV. Here, we demonstrated TLRs protein expressions and their association with clinical status and plasma markers in TB, HIV, and TB/HIV coinfection. The phenotyping of TLR2, TLR4, and TLR9 on CD14+ monocytes and their subsets were determined by multicolor flow cytometry. Host plasma biomarkers and microbial indices were measured using Luminex Multiplex assay and standard of care tools, respectively. TLR2 expression significantly enhanced in TB, slightly increased in HIV but slightly reduced in TB/HIV coinfection compared to apparently health controls (HC). On the other hand, TLR4 expression was significantly increased in TB, HIV, and TB/HIV compared to HC. Expression of TLR4 was equally enhanced on classical and intermediate monocytes while higher TLR2 expression on intermediate than classical monocytes. TLR4 had a positive correlation pattern with plasma biomarkers while TLR2 had an inverse correlation pattern. TLR4 is associated with disease severity while TLR2 is with the immune-competent status of patients. Our findings demonstrated that the pattern of TLR expression is disease as well as monocyte subset specific and distinct factors drive these differences.

Zhilong Huoxue Tongyu Capsule regulates the macrophage polarization and inflammatory response via the let-7i/TLR9/MyD88 signaling pathway.

ETHNOPHARMACOLOGICAL RELEVANCE: Zhilong Huoxue Tongyu Capsule (ZL) is clinically prescribed for acute ischemic stroke (AIS). However, only a few studies have addressed the mechanisms of ZL in treating AIS. AIM OF THE STUDY: To explore the underlying mechanism of macrophage polarization and inflammation mediated by ZL, and to provide a reference for AIS treatment. MATERIALS AND METHODS: Sixteen SD rats were fed with different dose of ZL (0, 0.4, 0.8, and 1.6 g/kg/d) for 4 days to prepare ZL serum. After 500 ng/mL lipopolysaccharide (LPS) stimulation, RAW264.7 cells were administrated with ZL serum. Then, experiments including ELISA, flow cytometry, real-time quantitative PCR and Western blot were performed to verify the effects of ZL on macrophage polarization and inflammation. Next, let-7i inhibitor was transfected in RAW264.7 cells when treated with LPS and ZL serum to verify the regulation of ZL on the let-7i/TLR9/MyD88 signaling pathway. Moreover, the interaction between let-7i and TLR9 was confirmed by the dual-luciferase assay. RESULTS: ZL serum significantly decreased the expression of interleukin (IL)-6 and tumor necrosis factor-α (TNF-α), and increased the expression of IL-10 and transforming growth factor ß1 (TGF-ß1) of LPS stimulated-macrophages. Furthermore, ZL serum polarized macrophages toward M2, decreased the expressions of TLR9, MyD88, and iNOS, as well as increased the expressions of let-7i, CHIL3, and Arginase-1. It is worth mentioning that the effect of ZL serum is dose-dependent. However, let-7i inhibitor restored all the above effects in LPS stimulated-macrophages. In addition, TLR9 was the target of let-7i. CONCLUSIONS: ZL targeted let-7i to inhibit TLR9 expression, thereby inhibiting the activation of the TLR9/MyD88 pathway, promoting the M2 polarization, and inhibiting the development of inflammation in AIS.

TLR9 mediates IgA production in the porcine small intestine during PEDV infection.

IgA plays a vital role in defending against the infectious pathogens. However, the specific regulatory pathways involved in IgA secretion in the context of PEDV infection have remained elusive. Therefore, in this study, we explore the molecular mechanisms underlying IgA secretion in response to infection, with a particular focus on PEDV, a devastating enteric virus affecting global swine production. Our investigation begins by examining changes in IgA concentrations in both serum and small intestinal contents following PEDV infection in 2- and 4-week-old pigs. Remarkably, a significant increase in IgA levels in these older pigs post-infection were observed. To delve deeper into the regulatory mechanisms governing IgA secretion in response to PEDV infection, isolated porcine intestinal B cells were co-cultured with monocytes derived DCs (Mo-DCs) in vitro. In the intestinal DC-B cell co-cultures, IgA secretion was found to increase significantly after PEDV infection, as well as upregulating the expression of AID, GLTα and PSTα reflecting isotype switching to IgA. In addition, the expression of TLR9 was upregulated in these cultures, as determined by RT-qPCR and western blotting. Moreover, our findings extend to in vivo observations, where we detected higher levels of TLR9 expression in the ileum of pig post PEDV infection. Collectively, our results highlight the ability of PEDV to stimulate the generation of IgA, particularly in elder pigs, and identify TLR9 as a critical mediator of IgA production within the porcine intestinal microenvironment during PEDV infection.

Mitochondrial dysfunction, a weakest link of network of aging, relation to innate intramitochondrial immunity of DNA recognition receptors.

Aging probably is the most complexed process in biology. It is manifested by a variety of hallmarks. These hallmarks weave a network of aging; however, each hallmark is not uniformly strong for the network. It is the weakest link determining the strengthening of the network of aging, or the maximum lifespan of an organism. Therefore, only improvement of the weakest link has the chance to increase the maximum lifespan but not others. We hypothesize that mitochondrial dysfunction is the weakest link of the network of aging. It may origin from the innate intramitochondrial immunity related to the activities of pathogen DNA recognition receptors. These receptors recognize mtDNA as the PAMP or DAMP to initiate the immune or inflammatory reactions. Evidence has shown that several of these receptors including TLR9, cGAS and IFI16 can be translocated into mitochondria. The potentially intramitochondrial presented pathogen DNA recognition receptors have the capacity to attack the exposed second structures of the mtDNA during its transcriptional or especially the replicational processes, leading to the mtDNA mutation, deletion, heteroplasmy colonization, mitochondrial dysfunction, and alterations of other hallmarks, as well as aging. Pre-consumption of the intramitochondrial presented pathogen DNA recognition receptors by medical interventions including development of mitochondrial targeted small molecule which can neutralize these receptors may retard or even reverse the aging to significantly improve the maximum lifespan of the organisms.

A type I interferon regulatory network for human plasmacytoid dendritic cells based on heparin, membrane-bound and soluble BDCA-2.

Plasmacytoid dendritic cells (pDCs) produce type I interferons (IFNs) after sensing viral/bacterial RNA or DNA by toll-like receptor (TLR) 7 or TLR9, respectively. However, aberrant pDCs activation can cause adverse effects on the host and contributes to the pathogenesis of type I IFN-related autoimmune diseases. Here, we show that heparin interacts with the human pDCs-specific blood dendritic cell antigen 2 (BDCA-2) but not with related lectins such as DCIR or dectin-2. Importantly, BDCA-2-heparin interaction depends on heparin sulfation and receptor glycosylation and results in inhibition of TLR9-driven type I IFN production in primary human pDCs and the pDC-like cell line CAL-1. This inhibition is mediated by unfractionated and low-molecular-weight heparin, as well as endogenous heparin from plasma, suggesting that the local blood environment controls the production of IFN-α in pDCs. Additionally, we identified an activation-dependent soluble form of BDCA-2 (solBDCA-2) in human plasma that functions as heparin antagonist and thereby increases TLR9-driven IFN-α production in pDCs. Of importance, solBDCA-2 levels in the serum were increased in patients with scrub typhus (an acute infectious disease caused by Orientia tsutsugamushi) compared to healthy control subjects and correlated with anti-dsDNA antibodies titers. In contrast, solBDCA-2 levels in plasma from patients with bullous pemphigoid or psoriasis were reduced. In summary, this work identifies a regulatory network consisting of heparin, membrane-bound and solBDCA-2 modulating TLR9-driven IFN-α production in pDCs. This insight into pDCs function and regulation may have implications for the treatment of pDCs-related autoimmune diseases.

Impact of Toll-Like Receptors (TLRs) and TLR Signaling Proteins in Trigeminal Ganglia Impairing Herpes Simplex Virus 1 (HSV-1) Progression to Encephalitis: Insights from Mouse Models.

Herpes simplex virus 1 (HSV-1) or simplexvirus humanalpha 1 is a neurotropic virus that is responsible for orofacial infections in humans. More than 70% of the world's population may have seropositivity for HSV-1, and this virus is a leading cause of sporadic lethal encephalitis in humans. The role of toll-like receptors (TLRs) in defending against HSV-1 infection has been explored, including the consequences of lacking these receptors or other proteins in the TLR pathway. Cell and mouse models have been used to study the importance of these receptors in combating HSV-1, how they relate to the innate immune response, and how they participate in the orchestration of the adaptive immune response. Myeloid differentiation factor 88 (MyD88) is a protein involved in the downstream activation of TLRs and plays a crucial role in this signaling. Mice with functional MyD88 or TLR2 and TLR9 can survive HSV-1 infection. However, they can develop encephalitis and face a 100% mortality rate in a dose-dependent manner when MyD88 or TLR2 plus TLR9 proteins are non-functional. In TLR2/9 knockout mice, an increase in chemokines and decreases in nitric oxide (NO), interferon (IFN) gamma, and interleukin 1 (IL-1) levels in the trigeminal ganglia (TG) have been correlated with mortality.

Formation of memory assemblies through the DNA-sensing TLR9 pathway.

As hippocampal neurons respond to diverse types of information1, a subset assembles into microcircuits representing a memory2. Those neurons typically undergo energy-intensive molecular adaptations, occasionally resulting in transient DNA damage3-5. Here we found discrete clusters of excitatory hippocampal CA1 neurons with persistent double-stranded DNA (dsDNA) breaks, nuclear envelope ruptures and perinuclear release of histone and dsDNA fragments hours after learning. Following these early events, some neurons acquired an inflammatory phenotype involving activation of TLR9 signalling and accumulation of centrosomal DNA damage repair complexes6. Neuron-specific knockdown of Tlr9 impaired memory while blunting contextual fear conditioning-induced changes of gene expression in specific clusters of excitatory CA1 neurons. Notably, TLR9 had an essential role in centrosome function, including DNA damage repair, ciliogenesis and build-up of perineuronal nets. We demonstrate a novel cascade of learning-induced molecular events in discrete neuronal clusters undergoing dsDNA damage and TLR9-mediated repair, resulting in their recruitment to memory circuits. With compromised TLR9 function, this fundamental memory mechanism becomes a gateway to genomic instability and cognitive impairments implicated in accelerated senescence, psychiatric disorders and neurodegenerative disorders. Maintaining the integrity of TLR9 inflammatory signalling thus emerges as a promising preventive strategy for neurocognitive deficits.

The interactions between CpG oligodeoxynucleotides and Toll-like receptors in Pacific white shrimp Litopenaeus vannamei.

CpG oligodeoxynucleotides (ODNs), as a novel type of adjuvant with immunomodulatory effects, are recognized by Toll-like receptors (TLRs) in Litopenaeus vannamei. In the present study, eleven LvTLRs-pCMV recombinants (rLvTLRs) were constructed to investigate the relationships between various CpG ODNs and different LvTLRs in human embryonic kidney 293T (HEK293T) cells, which was further confirmed by bio-layer interferometry (BLI) technique. The results of dual luciferase reporter assay showed that every LvTLR could activate multiple downstream genes, mainly including NF-κB, CREB, ISRE, IL-6-promoter, TNF-α-promoter and Myc, thereby inducing main signaling pathways in shrimps. Most CpG ODNs possessed affinities to more than one LvTLR, while each LvTLR could recognize multiple CpG ODNs, and the widely recognized ligands within CpG ODNs are A-class and B-class. Moreover, BLI analysis showed that CpG 2216, Cpg 2006, CpG 2143 and CpG 21425 exhibited dose-dependent affinity to the expressed TLR protein, which were consistent with the results in HEK293T cells. It suggested that the interactions of CpG ODNs with LvTLRs were indispensable for the immune regulation triggered by CpG ODNs, and these findings would lay foundations for studying the activations of LvTLRs to immune signaling pathways and shedding lights on the immune functions and mechanisms of CpG ODNs.

Granulin in renal tubular epithelia is associated with interstitial inflammation and activates the TLR9-IFN-α pathway in lupus nephritis.

OBJECTIVE: This study aimed to investigate the possible role of granulin (GRN) in activating the TLR9-IFN-α pathway in renal tubular epithelial cells (RTECs) and explore clues that RTECs regulate the micro-environment of inflammatory response in lupus nephritis (LN). METHODS: Renal sections from 57 LN patients and 30 non-LN patients were sampled for histological study, and GRN overexpression RTECs were applied for cytological study. RESULTS: In the histological study, GRN is highly expressed in LN RTECs with tubulointerstitial inflammation (TII) and well co-localized with TLR9. ROC analysis suggested a potential relationship between GRN expression in RTECs and therapeutic response. Moreover, IFN-α also highly expressed in LN RTECs with TII, and the intensity of IFN-α is positively correlated with the co-localization intensity of GRN and TLR9. In the cytological study, LN serum, especially serum from LN with TII, activates the expression of TLR9 in RTECs, and GRN engages the interaction of TLR9 to activate the expression of IFN-α in RTECs. While TLR9 inhibitors can suppress the expression of IFN-α in RTECs, the degree of inhibition is dose-dependent. CONCLUSION: The expression of GRN in RTECs is associated with interstitial inflammation and therapeutic response. GRN may mediate the activation of the TLR9-IFN-α pathway in RTECs and involve in the micro-environment of inflammatory response in LN.

TLR9 Knockdown Alleviates Sepsis via Disruption of MyD88/NF-κB Pathway Activation.

Sepsis is a life-threatening organ dysfunction due to dysregulated host response to infection, accompanied by a high rate of mortality worldwide. During sepsis progression, toll-like receptors (TLRs) play essential roles in the aberrant inflammatory response that contributes to sepsis-related mortality. Here, we demonstrated a critical role of TLR9 in the progression of sepsis. A septic mouse model was established by cecal ligation and puncture (CLP), then administered with lentivirus encoding si-TLR9/LY294002. TLR9 protein expression and p65 nuclear translocation level/TLR9 protein positive expression/interaction between TLR9 and myeloid differentiation primary response protein 88 (MyD88) in the cecal tissues were examined by Western blot/immunohistochemistry/co-immunoprecipitation assays. Serum levels of pro-inflammatory factors [e.g., interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α)] as well as bacterial contents in the liver/spleen/mesenteric lymph nodes (MLN) were measured by ELISA and bacterial mobility assay. TLR9 expression was augmented in the cecal tissues, TLR9 and MyD88 interaction was enhanced, nuclear p65 protein level was increased, cytoplasmic p65 protein level was decreased, and the nuclear factor kappa B (NF-κB) pathway was activated in CLP-induced septic mice, while TLR9 knockout protected against CLP-induced sepsis via the MyD88/NF-κB pathway inactivation. Briefly, TLR9 inhibition-mediated protection against CLP-induced sepsis was associated with a reduction in pro-inflammatory cytokine release and a promotion of bacterial clearance via a mechanism involving the MyD88/NF-κB pathway inactivation.

Activation of innate immune receptor TLR9 by mitochondrial DNA plays essential roles in the chemical long-term depression of hippocampal neurons.

Synaptic plasticity is believed to be the cellular basis for experience-dependent learning and memory. Although long-term depression (LTD), a form of synaptic plasticity, is caused by the activity-dependent reduction of cell surface α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-type glutamate receptors (AMPA receptors) at postsynaptic sites, its regulation by neuronal activity is not completely understood. In this study, we showed that the inhibition of toll-like receptor-9 (TLR9), an innate immune receptor, suppresses N-methyl-d-aspartate (NMDA)-induced reduction of cell surface AMPA receptors in cultured hippocampal neurons. We found that inhibition of TLR9 also blocked NMDA-induced activation of caspase-3, which plays an essential role in the induction of LTD. siRNA-based knockdown of TLR9 also suppressed the NMDA-induced reduction of cell surface AMPA receptors, although the scrambled RNA had no effect on the NMDA-induced trafficking of AMPA receptors. Overexpression of the siRNA-resistant form of TLR9 rescued the AMPA receptor trafficking abolished by siRNA. Furthermore, NMDA stimulation induced rapid mitochondrial morphological changes, mitophagy, and the binding of mitochondrial DNA (mtDNA) to TLR9. Treatment with dideoxycytidine and mitochondrial division inhibitor-1, which block mtDNA replication and mitophagy, respectively, inhibited NMDA-dependent AMPA receptor internalization. These results suggest that mitophagy induced by NMDA receptor activation releases mtDNA and activates TLR9, which plays an essential role in the trafficking of AMPA receptors during the induction of LTD.

Cyclical palmitoylation regulates TLR9 signalling and systemic autoimmunity in mice.

Toll-like receptor 9 (TLR9) recognizes self-DNA and plays intricate roles in systemic lupus erythematosus (SLE). However, the molecular mechanism regulating the endosomal TLR9 response is incompletely understood. Here, we report that palmitoyl-protein thioesterase 1 (PPT1) regulates systemic autoimmunity by removing S-palmitoylation from TLR9 in lysosomes. PPT1 promotes the secretion of IFNα by plasmacytoid dendritic cells (pDCs) and TNF by macrophages. Genetic deficiency in or chemical inhibition of PPT1 reduces anti-nuclear antibody levels and attenuates nephritis in B6.Sle1yaa mice. In healthy volunteers and patients with SLE, the PPT1 inhibitor, HDSF, reduces IFNα production ex vivo. Mechanistically, biochemical and mass spectrometry analyses demonstrated that TLR9 is S-palmitoylated at C258 and C265. Moreover, the protein acyltransferase, DHHC3, palmitoylates TLR9 in the Golgi, and regulates TLR9 trafficking to endosomes. Subsequent depalmitoylation by PPT1 facilitates the release of TLR9 from UNC93B1. Our results reveal a posttranslational modification cycle that controls TLR9 response and autoimmunity.

Emerging nanoparticle platforms for CpG oligonucleotide delivery.

Unmethylated cytosine-phosphate-guanine (CpG) oligodeoxynucleotides (ODNs), which were therapeutic DNA with high immunostimulatory activity, have been applied in widespread applications from basic research to clinics as therapeutic agents for cancer immunotherapy, viral infection, allergic diseases and asthma since their discovery in 1995. The major factors to consider for clinical translation using CpG motifs are the protection of CpG ODNs from DNase degradation and the delivery of CpG ODNs to the Toll-like receptor-9 expressed human B-cells and plasmacytoid dendritic cells. Therefore, great efforts have been devoted to the advances of efficient delivery systems for CpG ODNs. In this review, we outline new horizons and recent developments in this field, providing a comprehensive summary of the nanoparticle-based CpG delivery systems developed to improve the efficacy of CpG-mediated immune responses, including DNA nanostructures, inorganic nanoparticles, polymer nanoparticles, metal-organic-frameworks, lipid-based nanosystems, proteins and peptides, as well as exosomes and cell membrane nanoparticles. Moreover, future challenges in the establishment of CpG delivery systems for immunotherapeutic applications are discussed. We expect that the continuously growing interest in the development of CpG-based immunotherapy will certainly fuel the excitement and stimulation in medicine research.