Integrin αvß3 Limits Cytokine Production by Plasmacytoid Dendritic Cells and Restricts TLR-Driven Autoimmunity.

Plasmacytoid dendritic cells (pDCs) are strongly implicated as a major source of IFN-I in systemic lupus erythematosus (SLE), triggered through TLR-mediated recognition of nucleic acids released from dying cells. However, relatively little is known about how TLR signaling and IFN-I production are regulated in pDCs. In this article, we describe a role for integrin αvß3 in regulating TLR responses and IFN-I production by pDCs in mouse models. We show that αv and ß3-knockout pDCs produce more IFN-I and inflammatory cytokines than controls when stimulated through TLR7 and TLR9 in vitro and in vivo. Increased cytokine production was associated with delayed acidification of endosomes containing TLR ligands, reduced LC3 conjugation, and increased TLR signaling. This dysregulated TLR signaling results in activation of B cells and promotes germinal center (GC) B cell and plasma cell expansion. Furthermore, in a mouse model of TLR7-driven lupus-like disease, deletion of αvß3 from pDCs causes accelerated autoantibody production and pathology. We therefore identify a pDC-intrinsic role for αvß3 in regulating TLR signaling and preventing activation of autoreactive B cells. Because αvß3 serves as a receptor for apoptotic cells and cell debris, we hypothesize that this regulatory mechanism provides important contextual cues to pDCs and functions to limit responses to self-derived nucleic acids.

TLR2 and TLR7 mediate distinct immunopathological and antiviral plasmacytoid dendritic cell responses to SARS-CoV-2 infection.

Understanding the molecular pathways driving the acute antiviral and inflammatory response to SARS-CoV-2 infection is critical for developing treatments for severe COVID-19. Here, we find decreasing number of circulating plasmacytoid dendritic cells (pDCs) in COVID-19 patients early after symptom onset, correlating with disease severity. pDC depletion is transient and coincides with decreased expression of antiviral type I IFNα and of systemic inflammatory cytokines CXCL10 and IL-6. Using an in vitro stem cell-based human pDC model, we further demonstrate that pDCs, while not supporting SARS-CoV-2 replication, directly sense the virus and in response produce multiple antiviral (interferons: IFNα and IFNλ1) and inflammatory (IL-6, IL-8, CXCL10) cytokines that protect epithelial cells from de novo SARS-CoV-2 infection. Via targeted deletion of virus-recognition innate immune pathways, we identify TLR7-MyD88 signaling as crucial for production of antiviral interferons (IFNs), whereas Toll-like receptor (TLR)2 is responsible for the inflammatory IL-6 response. We further show that SARS-CoV-2 engages the receptor neuropilin-1 on pDCs to selectively mitigate the antiviral interferon response, but not the IL-6 response, suggesting neuropilin-1 as potential therapeutic target for stimulation of TLR7-mediated antiviral protection.

TLR8/TLR7 dysregulation due to a novel TLR8 mutation causes severe autoimmune hemolytic anemia and autoinflammation in identical twins.

Our study presents a novel germline c.1715G>T (p.G572V) mutation in the gene encoding Toll-like receptor 8 (TLR8) causing an autoimmune and autoinflammatory disorder in a family with monozygotic male twins, who suffer from severe autoimmune hemolytic anemia worsening with infections, and autoinflammation presenting as fevers, enteritis, arthritis, and CNS vasculitis. The pathogenicity of the mutation was confirmed by in vitro assays on transfected cell lines and primary cells. The p.G572V mutation causes impaired stability of the TLR8 protein, cross-reactivity to TLR7 ligands and reduced ability of TLR8 to attenuate TLR7 signaling. This imbalance toward TLR7-dependent signaling leads to increased pro-inflammatory responses, such as nuclear factor-κB (NF-κB) activation and production of pro-inflammatory cytokines IL-1ß, IL-6, and TNFα. This unique TLR8 mutation with partial TLR8 protein loss and hyperinflammatory phenotype mediated by TLR7 ligands represents a novel inborn error of immunity with childhood-onset and a good response to TLR7 inhibition.

Nafamostat reduces systemic inflammation in TLR7-mediated virus-like illness.

BACKGROUND: The serine protease inhibitor nafamostat has been proposed as a treatment for COVID-19, by inhibiting TMPRSS2-mediated viral cell entry. Nafamostat has been shown to have other, immunomodulatory effects, which may be beneficial for treatment, however animal models of ssRNA virus infection are lacking. In this study, we examined the potential of the dual TLR7/8 agonist R848 to mimic the host response to an ssRNA virus infection and the associated behavioural response. In addition, we evaluated the anti-inflammatory effects of nafamostat in this model. METHODS: CD-1 mice received an intraperitoneal injection of R848 (200 µg, prepared in DMSO, diluted 1:10 in saline) or diluted DMSO alone, and an intravenous injection of either nafamostat (100 µL, 3 mg/kg in 5% dextrose) or 5% dextrose alone. Sickness behaviour was determined by temperature, food intake, sucrose preference test, open field and forced swim test. Blood and fresh liver, lung and brain were collected 6 h post-challenge to measure markers of peripheral and central inflammation by blood analysis, immunohistochemistry and qPCR. RESULTS: R848 induced a robust inflammatory response, as evidenced by increased expression of TNF, IFN-γ, CXCL1 and CXCL10 in the liver, lung and brain, as well as a sickness behaviour phenotype. Exogenous administration of nafamostat suppressed the hepatic inflammatory response, significantly reducing TNF and IFN-γ expression, but had no effect on lung or brain cytokine production. R848 administration depleted circulating leukocytes, which was restored by nafamostat treatment. CONCLUSIONS: Our data indicate that R848 administration provides a useful model of ssRNA virus infection, which induces inflammation in the periphery and CNS, and virus infection-like illness. In turn, we show that nafamostat has a systemic anti-inflammatory effect in the presence of the TLR7/8 agonist. Therefore, the results indicate that nafamostat has anti-inflammatory actions, beyond its ability to inhibit TMPRSS2, that might potentiate its anti-viral actions in pathologies such as COVID-19.

TLR7 agonism accelerates disease in a mouse model of primary Sjögren's syndrome and drives expansion of T-bet+ B cells.

Primary Sjögren's syndrome (pSS) is a systemic autoimmune disease characterized by chronic inflammation of exocrine tissue, resulting in loss of tears and saliva. Patients also experience many extra-glandular disease manifestations. Treatment for pSS is palliative, and there are currently no treatments available that target disease etiology. Previous studies in our lab demonstrated that MyD88 is crucial for pSS pathogenesis in the NOD.B10Sn-H2b (NOD.B10) pSS mouse model, although the way in which MyD88-dependent pathways become activated in disease remains unknown. Based on its importance in other autoimmune diseases, we hypothesized that TLR7 activation accelerates pSS pathogenesis. We administered the TLR7 agonist Imiquimod (Imq) or sham treatment to pre-disease NOD.B10 females for 6 weeks. Parallel experiments were performed in age and sex-matched C57BL/10 controls. Imq-treated pSS animals exhibited cervical lymphadenopathy, splenomegaly, and expansion of TLR7-expressing B cells. Robust lymphocytic infiltration of exocrine tissues, kidney and lung was observed in pSS mice following treatment with Imq. TLR7 agonism also induced salivary hypofunction in pSS mice, which is a hallmark of disease. Anti-nuclear autoantibodies, including Ro (SSA) and La (SSB) were increased in pSS mice following Imq administration. Cervical lymph nodes from Imq-treated NOD.B10 animals demonstrated an increase in the percentage of activated/memory CD4+ T cells. Finally, T-bet+ B cells were expanded in the spleens of Imq-treated pSS mice. Thus, activation of TLR7 accelerates local and systemic disease and promotes expansion of T-bet-expressing B cells in pSS.

Hydroxychloroquine inhibits proteolytic processing of endogenous TLR7 protein in human primary plasmacytoid dendritic cells.

Toll-like receptor 7 (TLR7) triggers antiviral immune responses through its capacity to recognize ssRNA. Proteolytic cleavage of TLR7 protein is required for its functional maturation in the endosomal compartment. Structural studies demonstrated that the N- and C-terminal domains of TLR7 are connected and involved in ligand binding after cleavage. Hydroxychloroquine (HCQ), an antimalarial drug, has been studied for its antiviral effects. HCQ increases pH in acidic organelles and has been reported to potently inhibit endosomal TLR activation. Whether HCQ can prevent endogenous TLR7 cleavage in primary immune cells, such as plasmacytoid DCs (pDCs), had never been examined. Here, using a validated anti-TLR7 antibody suitable for biochemical detection of native TLR7 protein, we show that HCQ treatment of fresh PBMCs, CAL-1 leukemic, and primary human pDCs inhibits TLR7 cleavage and results in accumulation of full-length protein. As a consequence, we observe an inhibition of pDC activation in response to TLR7 stimulation with synthetic ligands and viruses including inactivated SARS-CoV2, which we show herein activates pDCs through TLR7-signaling. Together, our finding suggests that the major pathway by which HCQ inhibits ssRNA sensing by pDCs may rely on its capacity to inhibit endosomal acidification and the functional maturation of TLR7 protein.

Mesenchymal Stem Cell-Derived Exosomes Attenuate TLR7-Mediated Mast Cell Activation.

BACKGROUND: Mast cells are immune sentinels in the skin that respond to a wide range of pathological and environmental stimuli; they owe their function to the expression of Toll-like receptors (TLRs). We previously found that tonsil-derived mesenchymal stem cells (T-MSCs) were able to effectively attenuate TLR7-mediated skin inflammation in mice, which was accompanied by an increase in mast cell number. The present study investigated whether T-MSC extracellular vesicles, such as exosomes, are able to regulate mast cell activation in response to TLR7 stimulation. METHODS: The HMC-1 human mast cell line was treated with a TLR7 agonist in the presence or absence of T-MSC exosomes, and the levels of expressed inflammatory cytokines were assessed. Additionally, mice were repeatedly injected with a TLR7 agonist with or without interval treatments with T-MSC exosomes and assessed dermal distribution of mast cells and related immune cells. RESULTS: We showed that T-MSC exosomes containing microRNAs that target inflammatory cytokines significantly reduced the expression of inflammatory cytokines in TLR7 agonist-treated HMC-1 cells. In addition, T-MSC exosomes inhibited the increase in the number of both dermal mast cells and CD14-positive cells in TLR7 agonist-treated mice. CONCLUSION: Our data suggest that T-MSC exosomes have regulatory effects on mast cell activation under inflammatory conditions, including TLR7 stimulation.

Distinct trans-placental effects of maternal immune activation by TLR3 and TLR7 agonists: implications for schizophrenia risk.

Exposure to infection in utero predisposes towards psychiatric diseases such as autism, depression and schizophrenia in later life. The mechanisms involved are typically studied by administering mimetics of double-stranded (ds) virus or bacterial infection to pregnant rats or mice. The effect of single-stranded (ss) virus mimetics has been largely ignored, despite evidence linking prenatal ss virus exposure with psychiatric disease. Understanding the effects of gestational ss virus exposure has become even more important with recent events. In this study, in pregnant mice, we compare directly the effects, on the maternal blood, placenta and the embryonic brain, of maternal administration of ds-virus mimetic poly I:C (to activate Toll-like receptor 3, TLR3) and ss-virus mimetic resiquimod (to activate TLR7/8). We find that, 4 h after the administration, both poly I:C and resiquimod elevated the levels of IL-6, TNFα, and chemokines including CCL2 and CCL5, in maternal plasma. Both agents also increased placental mRNA levels of IL-6 and IL-10, but only resiquimod increased placental TNFα mRNA. In foetal brain, poly I:C produced no detectable immune-response-related increases, whereas pronounced increases in cytokine (e.g. Il-6, Tnfα) and chemokine (e.g. Ccl2, Ccl5) expression were observed with maternal resiquimod administration. The data show substantial differences between the effect of maternal exposure to a TLR7/8 activator as compared to a TLR3 activator. There are significant implications for future modelling of diseases where maternal ss virus exposure contributes to environmental disease risk in offspring.

Anti-TLR7 Antibody Protects Against Lupus Nephritis in NZBWF1 Mice by Targeting B Cells and Patrolling Monocytes.

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by autoantibody production and multiple organ damage. Toll-like receptor 7 (TLR7), an innate immune RNA sensor expressed in monocytes/macrophages, dendritic cells (DCs), and B cells, promotes disease progression. However, little is known about the cellular mechanisms through which TLR7 drives lupus nephritis. Here, we show that the anti-mouse TLR7 mAb, but not anti-TLR9 mAb, protected lupus-prone NZBWF1 mice from nephritis. The anti-TLR7 mAb reduced IgG deposition in glomeruli by inhibiting the production of autoantibodies to the RNA-associated antigens. We found a disease-associated increase in Ly6Clow patrolling monocytes that expressed high levels of TLR7 and had upregulated expression of lupus-associated IL-10, CD115, CD31, and TNFSF15 in NZBWF1 mice. Anti-TLR7 mAb abolished this lupus-associated increase in patrolling monocytes in the circulation, spleen, and glomeruli. These results suggested that TLR7 drives autoantibody production and lupus-associated monocytosis in NZBWF1 mice and, that anti-TLR7 mAb is a promising therapeutic tool targeting B cells and monocytes/macrophages.

TLR7 modulating B-cell immune responses in the spleen of C57BL/6 mice infected with Schistosoma japonicum.

B cells played an important role in Schistosoma infection-induced diseases. TLR7 is an intracellular member of the innate immune receptor. The role of TLR7 on B cells mediated immune response is still unclear. Here, C57BL/6 mice were percutaneously infected by S. japonicum for 5-6 weeks. The percentages and numbers of B cells increased in the infected mice (p < 0.05), and many activation and function associated molecules were also changed on B cells. More splenic cells of the infected mice expressed TLR7, and B cells were served as the main cell population. Moreover, a lower level of soluble egg antigen (SEA) specific antibody and less activation associated molecules were found on the surface of splenic B cells from S. japonicum infected TLR7 gene knockout (TLR7 KO) mice compared to infected wild type (WT) mice (p < 0.05). Additionally, SEA showed a little higher ability in inducing the activation of B cells from naive WT mice than TLR7 KO mice (p < 0.05). Finally, the effects of TLR7 on B cells are dependent on the activation of NF-κB p65. Altogether, TLR7 was found modulating the splenic B cell responses in S. japonicum infected C57BL/6 mice.

SARS-CoV-2-associated ssRNAs activate inflammation and immunity via TLR7/8.

The inflammatory and IFN pathways of innate immunity play a key role in the resistance and pathogenesis of coronavirus disease 2019 (COVID-19). Innate sensors and SARS-CoV-2-associated molecular patterns (SAMPs) remain to be completely defined. Here, we identified single-stranded RNA (ssRNA) fragments from the SARS-CoV-2 genome as direct activators of endosomal TLR7/8 and MyD88 pathway. The same sequences induced human DC activation in terms of phenotype and function, such as IFN and cytokine production and Th1 polarization. A bioinformatic scan of the viral genome identified several hundreds of fragments potentially activating TLR7/8, suggesting that products of virus endosomal processing potently activate the IFN and inflammatory responses downstream of these receptors. In vivo, SAMPs induced MyD88-dependent lung inflammation characterized by accumulation of proinflammatory and cytotoxic mediators and immune cell infiltration, as well as splenic DC phenotypical maturation. These results identified TLR7/8 as a crucial cellular sensor of ssRNAs encoded by SARS-CoV-2 involved in host resistance and the disease pathogenesis of COVID-19.

Genetic Screening for TLR7 Variants in Young and Previously Healthy Men With Severe COVID-19.

Introduction: Loss-of-function TLR7 variants have been recently reported in a small number of males to underlie strong predisposition to severe COVID-19. We aimed to determine the presence of these rare variants in young men with severe COVID-19. Methods: We prospectively studied males between 18 and 50 years-old without predisposing comorbidities that required at least high-flow nasal oxygen to treat COVID-19. The coding region of TLR7 was sequenced to assess the presence of potentially deleterious variants. Results: TLR7 missense variants were identified in two out of 14 patients (14.3%). Overall, the median age was 38 (IQR 30-45) years. Both variants were not previously reported in population control databases and were predicted to be damaging by in silico predictors. In a 30-year-old patient a maternally inherited variant [c.644A>G; p.(Asn215Ser)] was identified, co-segregating in his 27-year-old brother who also contracted severe COVID-19. A second variant [c.2797T>C; p.(Trp933Arg)] was found in a 28-year-old patient, co-segregating in his 24-year-old brother who developed mild COVID-19. Functional testing of this variant revealed decreased type I and II interferon responses in peripheral mononuclear blood cells upon stimulation with the TLR7 agonist imiquimod, confirming a loss-of-function effect. Conclusions: This study supports a rationale for the genetic screening for TLR7 variants in young men with severe COVID-19 in the absence of other relevant risk factors. A diagnosis of TLR7 deficiency could not only inform on treatment options for the patient, but also enables pre-symptomatic testing of at-risk male relatives with the possibility of instituting early preventive and therapeutic interventions.

Large, Anionic Liposomes Enable Targeted Intraperitoneal Delivery of a TLR 7/8 Agonist To Repolarize Ovarian Tumors' Microenvironment.

Ovarian cancer is the most lethal gynecological malignancy in the United States. Current standard of treatment includes surgical debulking and chemotherapy, such as cisplatin and paclitaxel. However, the patients' response rate for chemotherapy in ovarian cancer is not optimal, and they often develop chemoresistance and suffer from side effects. Current clinical trials make extensive use of immune checkpoint blockade (ICB) as a novel cancer immunotherapeutic strategy against ovarian tumors. However, the response rates for ICB antibodies remain limited to 10-20% of treated ovarian cancer patients despite the success of this approach in melanoma, renal, head and neck, and nonsmall cell lung cancers. This lack of efficacy is often attributed to the "cold" immune status of ovarian tumors, as these tumors often have a low number of tumor-infiltrating lymphocytes (TILs) but a high number of suppressive immune cells, including tumor-associated macrophages (TAMs), myeloid-derived suppressor cells (MDSCs), or regulatory T cells (Tregs). Repolarizing TAMs could be a promising strategy to reshape the tumor immune microenvironment and promote antitumor activity when combined with ICBs. Toll-like receptor (TLR) 7 and 8 agonists, such as imiquimod and resiquimod, are potent immunostimulatory molecules with potential to repolarize macrophages. However, these small molecules have poor pharmacokinetic profiles and can induce severe side effects when administered systemically. Previously, our group demonstrated that various large, anionic nanomaterials (silica, PLGA, and polystyrene) specifically target TAMs when administered intraperitoneally (IP) to ovarian tumor-bearing mice. In the present study, we demonstrate that large, anionic liposomes administered IP also efficiently localize to TAMs and can be used to target the delivery of resiquimod. Resiquimod delivered in this targeted fashion promoted activation of M1 macrophages and T cell infiltration, while reducing the percentage of Tregs in the tumor microenvironment. Finally, liposome-formulated resiquimod significantly enhanced the efficacy of PD1 blockade against syngeneic ovarian tumors. We anticipate that further optimization of our liposomal delivery strategy can generate a clinically relevant strategy for more effective and safer immunotherapy for ovarian cancer patients.

ATF6-DGAT pathway is involved in TLR7-induced innate immune response in Ctenopharyngodon idellus kidney cells.

DGAT1 and DGAT2 are two acyl-CoA:diacylglycerol O-acyltransferase (DGAT) enzymes that catalyze the final step in triglyceride (TG) synthesis. TGs are the primary constituents of lipid droplets (LDs). Although it has been demonstrated that LDs modulate immune and inflammatory responses in CIK cells, little is known about whether DGAT1 and DGAT2 involve in this process. Firstly, grass carp DGAT2 was isolated and characterized, encoding 361 amino acids, and all DGAT2 proteins in genomic structures are conserved in vertebrates. Then, using TLR7 agonist, we induced LDs accumulation in CIK cells. Only DGAT1b and DGAT2 were upregulated in forming TLR7 agonist induced-LDs. Next, we utilized small-molecule inhibitors of DGAT1 and DGAT2. The results indicated that DGAT1 inactivation attenuated TG content and the relative expressions of IFNα3, NF-κB, IL-1ß, and TNFα genes, whereas DGAT2 inhibition decreased TG content and the relative expressions of MyD88, IRF7, IFNα3, NF-κB, IL-1ß, and TNFα genes, implying that DGAT1-generated LDs and DGAT2-generated LDs contribute to TLR7-induced immune response via different signaling pathways. Finally, inhibiting ATF6 effectively decreased DGAT-generated LDs accumulation and the expression of TLR7 signaling-related genes induced by TLR7 agonist, implying that ATF6 UPR pathway may mediate the role of DGAT-generated LDs in TLR7 signaling. Overall, we demonstrate that DGAT1 and DGAT2-catalyzed TAG synthesis may generate different LDs to provide distinct signaling platforms for innate TLR7 signaling.

Sequence-specific extracellular microRNAs activate TLR7 and induce cytokine secretion and leukocyte migration.

Toll-like receptors (TLRs) can contribute to central nervous system disease pathologies via recognition of microRNAs (miRNAs); however, it remains to be determined which miRNAs are able to activate this signaling. Here we report that numerous miRNAs induced the production of tumor necrosis factor alpha in multiple myeloid cell types, including microglia, and that this effect was abolished in cells deficient in TLR7. Examination of closely related miRNAs that differed in their ability to activate TLR7 resulted in the identification of a motif (UGCUUAU) in miR-20a-5p and specific nucleotides (all the uridines and surprisingly the cytosine as well) in a key area of miR-20a-5p and miR-148b-3p that were vital for the secretion of cytokines via TLR7 stimulation. A 10-nucleotide sequence including this motif was identified to be the shortest single-stranded RNA to signal via TLR7. An miRNA containing this motif induced the secretion of multiple proinflammatory molecules, which was dependent on the phosphoinositide 3-kinase, mitogen-activated protein kinase, and nuclear factor kappa-light-chain-enhancer of activated B cell signaling pathways. Wild-type mice administered miR-20a-5p, which contained this motif, demonstrated increased leukocyte migration. This effect was significantly ameliorated in TLR7-knockout mice, and mice administered miR-20b-5p, in which the motif was mutated, did not exhibit leukocyte migration. We provide a detailed analysis of miRNAs that activate endosomal TLR7 and identify key nucleotide features of a sequence motif recognized by TLR7.

Neutralizing interferon-α blocks inflammation-mediated vascular injury via PI3K and AMPK in systemic lupus erythematosus.

Plasmacytoid dendritic cells (pDCs) play a key role in the initiation and amplification of systemic lupus erythematosus (SLE)-associated vascular injury. In this study, we found that dsDNA induced dose- and time-dependent increase in IFN-α and Toll-like receptor 7 (TLR7), TLR9 and IRF7 expression in pDCs. Co-cultured circulating endothelial cells (ECs) with activated pDCs significantly decreased proliferation, tube formation and migration in ECs. The elevated level of cellular IFN-α increased cell adhesion, promoted cell apoptosis, induced cell senescence and arrested cells at G0/G1 phase of endothelial progenitor cells (EPCs). Additionally, the co-culture system activated MAPK and inactivated PI3K. Pristane was used to establish a in vivo SLE-like mouse model. Importantly, we showed that INF-α-neutralizing antibody (IFN-α-NA) rescued all the changes induced by IFN-α in vitro and prevented vascular injury in pristane-induced SLE model in vivo. In conclusion, we confirmed that activated pDCs promoted vascular damage and the dysfunction of ECs/EPCs via IFN-α production. IFN-α-neutralizing antibody may be a clinical implication for preventing vascular injury. PI3K signalling and AMPK signalling were associated with SLE-associated vascular functions.

TLR7 Ligation Inhibits TLR8 Responsiveness in IL-27-Primed Human THP-1 Monocytes and Macrophages.

Regulation of proinflammatory cytokine expression is critical in the face of single-stranded RNA (ssRNA) virus infections. Many viruses, including coronavirus and influenza virus, wreak havoc on the control of cytokine expression, leading to the formation of detrimental cytokine storms. Understanding the regulation and interplay between inflammatory cytokines is critical to the identification of targets involved in controlling the induction of cytokine expression. In this study, we focused on how the antiviral cytokine interleukin-27 (IL-27) regulates signal transduction downstream of Toll-like receptor 7 (TLR7) and TLR8 ligation, which recognize endosomal single-stranded RNA. Given that IL-27 alters bacterial-sensing TLR expression on myeloid cells and can inhibit replication of single-stranded RNA viruses, we investigated whether IL-27 affects expression and function of TLR7 and TLR8. Analysis of IL-27-treated THP-1 monocytic cells and THP-1-derived macrophages revealed changes in mRNA and protein expression of TLR7 and TLR8. Although treatment with IL-27 enhanced TLR7 expression, only TLR8-mediated cytokine secretion was amplified. Furthermore, we demonstrated that imiquimod, a TLR7 agonist, inhibited cytokine and chemokine production induced by a TLR8 agonist, TL8-506. Delineating the immunomodulatory role of IL-27 on TLR7 and TLR8 responses provides insight into how myeloid cell TLR-mediated responses are regulated during virus infection.

Context-Dependent miR-21 Regulation of TLR7-Mediated Autoimmune and Foreign Antigen-Driven Antibody-Forming Cell and Germinal Center Responses.

MicroRNAs (miRNAs) are involved in healthy B cell responses and the loss of tolerance in systemic lupus erythematosus (SLE), although the role of many miRNAs remains poorly understood. Dampening miR-21 activity was previously shown to reduce splenomegaly and blood urea nitrogen levels in SLE-prone mice, but the detailed cellular responses and mechanism of action remains unexplored. In this study, using the TLR7 agonist, imiquimod-induced SLE model, we observed that loss of miR-21 in Sle1b mice prevented the formation of plasma cells and autoantibody-producing Ab-forming cells (AFCs) without a significant effect on the magnitude of the germinal center (GC) response. We further observed reduced dendritic cell and monocyte numbers in the spleens of miR-21-deficient Sle1b mice that were associated with reduced IFN, proinflammatory cytokines, and effector CD4+ T cell responses. RNA sequencing analysis on B cells from miR-21-deficient Sle1b mice revealed reduced activation and response to IFN, and cytokine and target array analysis revealed modulation of numerous miR-21 target genes in response to TLR7 activation and type I IFN stimulation. Our findings in the B6.Sle1bYaa (Sle1b Yaa) spontaneous model recapitulated the miR-21 role in TLR7-induced responses with an additional role in autoimmune GC and T follicular helper responses. Finally, immunization with T-dependent Ag revealed a role for miR-21 in foreign Ag-driven GC and Ab, but not AFC, responses. Our data suggest a potential multifaceted, context-dependent role for miR-21 in autoimmune and foreign Ag-driven AFC and GC responses. Further study is warranted to delineate the cell-intrinsic requirements and mechanisms of miR-21 during infection and SLE development.

A tractable covalent linker strategy for the production of immunogenic antigen-TLR7/8L bioconjugates.

Despite the ease of production and improved safety profiles of recombinant vaccines, the inherently low immunogenicity of unadjuvanted proteins remains an impediment to their widespread adoption. The covalent tethering of TLR agonists to antigenic proteins offers a unique approach to co-deliver both constituents to the same cell-enhancing vaccine efficacy while minimizing reactogenicity. However, the paucity of simple and effective linker chemistries continues to hamper progress. Here, we present a modular, PEG-based linker system compatible with even extremely lipophilic and challenging TLR7/8 agonists. To advance the field and address previous obstacles, we offer the most straightforward and antigen-preserving linker system to date. These antigen-adjuvant conjugates enhance antigen-specific immune responses in mice, demonstrating the power of our approach within the context of modern vaccinology.

Absence of Toll-like receptor 7 protects mice against Pseudomonas aeruginosa pneumonia.

Toll-like receptor 7 (TLR7) is a sensor of microbial ssRNA that participates in the immune response process in many diseases. We herein sought to establish the role of TLR7 in Pseudomonas aeruginosa pneumonia. Pneumonia model was created by intratracheally injecting Pseudomonas aeruginosa and the effects of TLR7 on survival, bacterial burden, lung pathology, cytokine and chemokine production, and pulmonary leukocyte recruitment were measured after Pseudomonas aeruginosa challenge. TLR7 expression was significantly elevated in WT mice after Pseudomonas aeruginosa infection. TLR7-/- mice demonstrated enhanced survival, bacterial clearance, leukocyte infiltration, and macrophages phagocytic activity, and decreased pathology and capillary leakage. Besides, improved survival and bacterial clearance were observed in WT mice treated with TLR7 antagonist IRS661. More importantly, lack of TLR7 suppressed pro-inflammatory cytokine production and induced anti-inflammatory cytokine production in mice lungs. Finally, neutralized IL-10 damaged the bacterial clearance ability of TLR7 deficient mice, leading to decreased survival. Collectively, absence of TLR7 provided protective effects during Pseudomonas aeruginosa pneumonia and suggested that TLR7 could act as a novel immune target to treat clinical cases with Pseudomonas aeruginosa pneumonia.