The ectodomain of Toll-like receptor 9 is cleaved to generate a functional receptor

Novel quinoline substituted autophagy inhibitors attenuate Zika virus replication in ocular cells

Zika virus (ZIKV) is a re-emerging RNA virus that is known to cause ocular and neurological abnormalities in infants. ZIKV exploits autophagic processes in infected cells to enhance its replication and spread. Thus, autophagy inhibitors have emerged as a potent therapeutic target to combat RNA viruses, with Hydroxychloroquine (HCQ) being one of the most promising candidates. In this study, we synthesized several novel small-molecule quinoline derivatives, assessed their antiviral activity, and determined the underlying molecular mechanisms. Among the nine synthesized analogs, two lead candidates, labeled GL-287 and GL-382, significantly attenuated ZIKV replication in human ocular cells, primarily by inhibiting autophagy. These two compounds surpassed the antiviral efficacy of HCQ and other existing autophagy inhibitors, such as ROC-325, DC661, and GNS561. Moreover, unlike HCQ, these novel analogs did not exhibit cytotoxicity in the ocular cells. Treatment with compounds GL-287 and GL-382 in ZIKV-infected cells increased the abundance of LC3 puncta, indicating the disruption of the autophagic process. Furthermore, compounds GL-287 and GL-382 effectively inhibited the ZIKV-induced innate inflammatory response in ocular cells. Collectively, our study demonstrates the safe and potent antiviral activity of novel autophagy inhibitors against ZIKV.

RNA recognition in toll-like receptor signaling

RNA, either from invading pathogens or within the hosts, is one of the principal PAMPs (pathogen-associated molecular patterns). Toll-like receptors (TLRs) and other receptors of the innate immune system exist that detect immunostimulatory RNA including double and single stranded RNA, and then induce cytokine-mediated antiviral and proinflammatory responses. Recent years have seen remarkable progress in biochemical, immunological, and structural biological studies on TLRs, opening new avenues for TLR signaling. In this review, we highlight our current understanding of RNA- sensing TLRs and discuss the regulatory mechanisms that normally prevent inappropriate responses to self.

Large-scale mutational analysis identifies UNC93B1 variants that drive TLR-mediated autoimmunity in mice and humans

Nucleic acid-sensing Toll-like receptors (TLR) 3, 7/8, and 9 are key innate immune sensors whose activities must be tightly regulated to prevent systemic autoimmune or autoinflammatory disease or virus-associated immunopathology. Here, we report a systematic scanning-alanine mutagenesis screen of all cytosolic and luminal residues of the TLR chaperone protein UNC93B1, which identified both negative and positive regulatory regions affecting TLR3, TLR7, and TLR9 responses. We subsequently identified two families harboring heterozygous coding mutations in UNC93B1, UNC93B1+/T93I and UNC93B1+/R336C, both in key negative regulatory regions identified in our screen. These patients presented with cutaneous tumid lupus and juvenile idiopathic arthritis plus neuroinflammatory disease, respectively. Disruption of UNC93B1-mediated regulation by these mutations led to enhanced TLR7/8 responses, and both variants resulted in systemic autoimmune or inflammatory disease when introduced into mice via genome editing. Altogether, our results implicate the UNC93B1-TLR7/8 axis in human monogenic autoimmune diseases and provide a functional resource to assess the impact of yet-to-be-reported UNC93B1 mutations.

Endolysosomal transient receptor potential mucolipins and two-pore channels: implications for cancer immunity

Past research has identified that cancer cells sustain several cancer hallmarks by impairing function of the endolysosomal system (ES). Thus, maintaining the functional integrity of endolysosomes is crucial, which heavily relies on two key protein families: soluble hydrolases and endolysosomal membrane proteins. Particularly members of the TPC (two-pore channel) and TRPML (transient receptor potential mucolipins) families have emerged as essential regulators of ES function as a potential target in cancer therapy. Targeting TPCs and TRPMLs has demonstrated significant impact on multiple cancer hallmarks, including proliferation, growth, migration, and angiogenesis both in vitro and in vivo. Notably, endosomes and lysosomes also actively participate in various immune regulatory mechanisms, such as phagocytosis, antigen presentation, and the release of proinflammatory mediators. Yet, knowledge about the role of TPCs and TRPMLs in immunity is scarce. This prompts a discussion regarding the potential role of endolysosomal ion channels in aiding cancers to evade immune surveillance and destruction. Specifically, understanding the interplay between endolysosomal ion channels and cancer immunity becomes crucial. Our review aims to comprehensively explore the current knowledge surrounding the roles of TPCs and TRPMLs in immunity, whilst emphasizing the critical need to elucidate their specific contributions to cancer immunity by pointing out current research gaps that should be addressed.

Human and Murine Toll-like Receptor-Driven Disease in Systemic Lupus Erythematosus

The pathogenesis of systemic lupus erythematosus (SLE) is linked to the differential roles of toll-like receptors (TLRs), particularly TLR7, TLR8, and TLR9. TLR7 overexpression or gene duplication, as seen with the Y-linked autoimmune accelerator (Yaa) locus or TLR7 agonist imiquimod, correlates with increased SLE severity, and specific TLR7 polymorphisms and gain-of-function variants are associated with enhanced SLE susceptibility and severity. In addition, the X-chromosome location of TLR7 and its escape from X-chromosome inactivation provide a genetic basis for female predominance in SLE. The absence of TLR8 and TLR9 have been shown to exacerbate the detrimental effects of TLR7, leading to upregulated TLR7 activity and increased disease severity in mouse models of SLE. The regulatory functions of TLR8 and TLR9 have been proposed to involve competition for the endosomal trafficking chaperone UNC93B1. However, recent evidence implies more direct, regulatory functions of TLR9 on TLR7 activity. The association between age-associated B cells (ABCs) and autoantibody production positions these cells as potential targets for treatment in SLE, but the lack of specific markers necessitates further research for precise therapeutic intervention. Therapeutically, targeting TLRs is a promising strategy for SLE treatment, with drugs like hydroxychloroquine already in clinical use.

Differential effects of SORL1 deficiency on the endo-lysosomal network in human neurons and microglia

The endosomal gene SORL1 is a strong Alzheimer's disease (AD) risk gene that harbours loss-of-function variants causative for developing AD. The SORL1 protein SORL1/SORLA is an endosomal receptor that interacts with the multi-protein sorting complex retromer to traffic various cargo through the endo-lysosomal network (ELN). Impairments in endo-lysosomal trafficking are an early cellular symptom in AD and a novel therapeutic target. However, the cell types of the central nervous system are diverse and use the ELN differently. If this pathway is to be effectively therapeutically targeted, understanding how key molecules in the ELN function in various cell types and how manipulating them affects cell-type specific responses relative to AD is essential. Here, we discuss an example where deficiency of SORL1 expression in a human model leads to stress on early endosomes and recycling endosomes in neurons, but preferentially leads to stress on lysosomes in microglia. The differences observed in these organelles could relate to the unique roles of these cells in the brain as neurons are professional secretory cells and microglia are professional phagocytic cells. Experiments to untangle these differences are fundamental to advancing the understanding of cell biology in AD and elucidating important pathways for therapeutic development. Human-induced pluripotent stem cell models are a valuable platform for such experiments. This article is part of a discussion meeting issue 'Understanding the endo-lysosomal network in neurodegeneration'.

Hydroxychloroquine in obstetrics: potential implications of the prophylactic use of hydroxychloroquine for placental insufficiency during pregnancy

Proper placentation during early pregnancy is a key factor for maintaining a healthy pregnancy. Placental insufficiency leads to critical complications such as preeclampsia, fetal growth restriction, and fetal demise. These complications are often associated with pathological findings of restricted remodeling and obstructive lesions of the myometrial spiral arteries, which have high recurrence rates during subsequent pregnancies. Currently, there are no pharmacological interventions other than aspirin for the prevention of preeclampsia. Hydroxychloroquine (HCQ), a well-known antimalarial drug, reduces inflammatory and thrombotic changes in vessels. For decades, the use of HCQ for autoimmune diseases has resulted in the successful prevention of both arterial and venous thrombotic events and has been extended to the treatment of lupus and antiphospholipid antibody syndrome during pregnancy. HCQ reduces the risk of preeclampsia with lupus by up to 90%. Several recent studies have investigated whether HCQ improves pregnancy outcomes in women with a history of poor outcomes. In addition, in vitro and animal studies have demonstrated the beneficial effects of HCQ in improving endothelial dysfunction and alleviating hypertension and proteinuria. Therefore, we hypothesized that HCQ has the potential to attenuate the vascular inflammatory and thrombogenic pathways associated with placental insufficiency and conducted a multicenter clinical trial on the efficacy of combining aspirin with HCQ for pregnancies at high risk for preeclampsia in Korea. This study summarizes the potential effects of HCQ on pregnancies with placental insufficiency and the implications of HCQ treatment in the field of obstetrics.

Non-biologic immunosuppressive drugs for inflammatory and autoimmune skin diseases

Non-biologic immunosuppressive drugs, such as azathioprine, dapsone or methotrexate are fundamental treatment options for a wide range of autoimmune and chronic inflammatory skin diseases. Some of these drugs were initially used for malignancies (e.g., azathioprine or methotrexate) or infectious diseases (e.g., hydroxychloroquine or dapsone) but are nowadays mostly used for their immunosuppressive/immunomodulating action. Although dermatologists have years of clinical experience with these drugs, some of the mechanisms of action are not fully understood and are the subject of research. Although these drugs are commonly used, lack of experience or knowledge regarding their safety profiles and management leads to skepticism among physicians. Here, we summarize the mechanism of action and detailed management of adverse effects of the most commonly used immunosuppressive drugs for skin diseases. Furthermore, we discuss the management of these drugs during pregnancy and breastfeeding, as well as their interaction and handling during vaccination.

Nicht-Biologika-Immunsuppressiva bei entzündlichen und autoimmunen Hautkrankheiten: Non-biologic immunosuppressive drugs for inflammatory and autoimmune skin diseases

Nicht‐Biologika‐Immunsuppressiva wie Azathioprin, Dapson oder Methotrexat sind grundlegende Behandlungsmöglichkeiten für ein breites Spektrum von Autoimmunerkrankungen und chronisch‐entzündlichen Hauterkrankungen. Einige dieser Medikamente wurden ursprünglich bei malignen Erkrankungen (zum Beispiel Azathioprin oder Methotrexat) oder Infektionskrankheiten (zum Beispiel Hydroxychloroquin oder Dapson) eingesetzt, werden aber heute hauptsächlich wegen ihrer immunsuppressiven/immunmodulierenden Wirkung verwendet. Obwohl Dermatologen über jahrelange klinische Erfahrung mit diesen Arzneimitteln verfügen, sind einige der Wirkmechanismen noch nicht vollständig geklärt und noch Gegenstand der Forschung. Obwohl diese Medikamente häufig eingesetzt werden, führen mangelnde Erfahrung oder fehlendes Wissen über ihre Sicherheitsprofile und ihr Management zu einer skeptischen Haltung bei den Ärzten. Hier fassen wir den Wirkmechanismus und das detaillierte Management der Nebenwirkungen der am häufigsten verwendeten immunsuppressiven Medikamente für Hautkrankheiten zusammen. Darüber hinaus diskutieren wir den Umgang mit diesen Medikamenten während der Schwangerschaft und Stillzeit sowie ihre Wechselwirkung und Handhabung im Zusammenhang mit Impfungen.

Disrupted degradative sorting of TLR7 is associated with human lupus

Hyperactive TLR7 signaling has long been appreciated as driver of autoimmune disease in mouse models. Recently, gain-of-function mutations in TLR7 were identified as a monogenic cause of human lupus. TLR7 is an intracellular transmembrane receptor, sensing RNA breakdown products within late endosomes. Here, we show that endosome dysfunction leads to unrestricted TLR7 signaling and is associated with human lupus. The late endosomal BORC complex together with the small GTPase Arl8b controls intracellular TLR7 levels by regulating receptor turnover. This requires a direct interaction between the TLR7-associated trafficking factor Unc93b1 and Arl8b. We identified an UNC93B1 mutation in a patient with childhood-onset lupus, which results in reduced BORC interaction and endosomal TLR7 accumulation. Therefore, a failure to control TLR7 turnover is sufficient to break immunological tolerance to nucleic acids. Our results highlight the importance of an intact endomembrane system in preventing pathological TLR7 signaling and autoimmune disease.

Deciphering the immunological interactions: targeting preeclampsia with Hydroxychloroquine's biological mechanisms

Preeclampsia (PE) is a complex pregnancy-related disorder characterized by hypertension, followed by organ dysfunction and uteroplacental abnormalities. It remains a major cause of maternal and neonatal morbidity and mortality worldwide. Although the pathophysiology of PE has not been fully elucidated, a two-stage model has been proposed. In this model, a poorly perfused placenta releases various factors into the maternal circulation during the first stage, including pro-inflammatory cytokines, anti-angiogenic factors, and damage-associated molecular patterns into the maternal circulation. In the second stage, these factors lead to a systemic vascular dysfunction with consecutive clinical maternal and/or fetal manifestations. Despite advances in feto-maternal management, effective prophylactic and therapeutic options for PE are still lacking. Since termination of pregnancy is the only curative therapy, regardless of gestational age, new treatment/prophylactic options are urgently needed. Hydroxychloroquine (HCQ) is mainly used to treat malaria as well as certain autoimmune conditions such as systemic lupus and rheumatoid arthritis. The exact mechanism of action of HCQ is not fully understood, but several mechanisms of action have been proposed based on its pharmacological properties. Interestingly, many of them might counteract the proposed processes involved in the development of PE. Therefore, based on a literature review, we aimed to investigate the interrelated biological processes of HCQ and PE and to identify potential molecular targets in these processes.

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.

ECDD-S16 targets vacuolar ATPase: A potential inhibitor compound for pyroptosis-induced inflammation

BACKGROUND

Cleistanthin A (CA), extracted from Phyllanthus taxodiifolius Beille, was previously reported as a potential V-ATPase inhibitor relevant to cancer cell survival. In the present study, ECDD-S16, a derivative of cleistanthin A, was investigated and found to interfere with pyroptosis induction via V-ATPase inhibition.

OBJECTIVE

This study examined the ability of ECDD-S16 to inhibit endolysosome acidification leading to the attenuation of pyroptosis in Raw264.7 macrophages activated by both surface and endosomal TLR ligands.

METHODS

To elucidate the activity of ECDD-S16 on pyroptosis-induced inflammation, Raw264.7 cells were pretreated with the compound before stimulation with surface and endosomal TLR ligands. The release of lactate dehydrogenase (LDH) was determined by LDH assay. Additionally, the production of cytokines and the expression of pyroptosis markers were examined by ELISA and immunoblotting. Moreover, molecular docking was performed to demonstrate the binding of ECDD-S16 to the vacuolar (V-)ATPase.

RESULTS

This study showed that ECDD-S16 could inhibit pyroptosis in Raw264.7 cells activated with surface and endosomal TLR ligands. The attenuation of pyroptosis by ECDD-S16 was due to the impairment of endosome acidification, which also led to decreased Reactive Oxygen Species (ROS) production. Furthermore, molecular docking also showed the possibility of inhibiting endosome acidification by the binding of ECDD-S16 to the vacuolar (V-)ATPase in the region of V0.

CONCLUSION

Our findings indicate the potential of ECDD-S16 for inhibiting pyroptosis and prove that vacuolar H+ ATPase is essential for pyroptosis induced by TLR ligands.

Mitochondrial Impairment: A Link for Inflammatory Responses Activation in the Cardiorenal Syndrome Type 4

Cardiorenal syndrome type 4 (CRS type 4) occurs when chronic kidney disease (CKD) leads to cardiovascular damage, resulting in high morbidity and mortality rates. Mitochondria, vital organelles responsible for essential cellular functions, can become dysfunctional in CKD. This dysfunction can trigger inflammatory responses in distant organs by releasing Damage-associated molecular patterns (DAMPs). These DAMPs are recognized by immune receptors within cells, including Toll-like receptors (TLR) like TLR2, TLR4, and TLR9, the nucleotide-binding domain, leucine-rich-containing family pyrin domain-containing-3 (NLRP3) inflammasome, and the cyclic guanosine monophosphate (cGMP)-adenosine monophosphate (AMP) synthase (cGAS)-stimulator of interferon genes (cGAS-STING) pathway. Activation of these immune receptors leads to the increased expression of cytokines and chemokines. Excessive chemokine stimulation results in the recruitment of inflammatory cells into tissues, causing chronic damage. Experimental studies have demonstrated that chemokines are upregulated in the heart during CKD, contributing to CRS type 4. Conversely, chemokine inhibitors have been shown to reduce chronic inflammation and prevent cardiorenal impairment. However, the molecular connection between mitochondrial DAMPs and inflammatory pathways responsible for chemokine overactivation in CRS type 4 has not been explored. In this review, we delve into mechanistic insights and discuss how various mitochondrial DAMPs released by the kidney during CKD can activate TLRs, NLRP3, and cGAS-STING immune pathways in the heart. This activation leads to the upregulation of chemokines, ultimately culminating in the establishment of CRS type 4. Furthermore, we propose using chemokine inhibitors as potential strategies for preventing CRS type 4.

The show and tell of cross-presentation

Cross-presentation is the culmination of complex subcellular processes that allow the processing of exogenous proteins and the presentation of resultant peptides on major histocompatibility class I (MHC-I) molecules to CD8 T cells. Dendritic cells (DCs) are a cell type that uniquely specializes in cross-presentation, mainly in the context of viral or non-viral infection and cancer. DCs have an extensive network of endovesicular pathways that orchestrate the biogenesis of an ideal cross-presentation compartment where processed antigen, MHC-I molecules, and the MHC-I peptide loading machinery all meet. As a central conveyor of information to CD8 T cells, cross-presentation allows cross-priming of T cells which carry out robust adaptive immune responses for tumor and viral clearance. Cross-presentation can be canonical or noncanonical depending on the functional status of the transporter associated with antigen processing (TAP), which in turn influences the vesicular route of MHC-I delivery to internalized antigen and the cross-presented repertoire of peptides. Because TAP is a central node in MHC-I presentation, it is targeted by immune evasive viruses and cancers. Thus, understanding the differences between canonical and noncanonical cross-presentation may inform new therapeutic avenues against cancer and infectious disease. Defects in cross-presentation on a cellular and genetic level lead to immune-related disease progression, recurrent infection, and cancer progression. In this chapter, we review the process of cross-presentation beginning with the DC subsets that conduct cross-presentation, the signals that regulate cross-presentation, the vesicular trafficking pathways that orchestrate cross-presentation, the modes of cross-presentation, and ending with disease contexts where cross-presentation plays a role.

Three-Dimensional Modeling of CpG DNA Binding with Matrix Lumican Shows Leucine-Rich Repeat Motif Involvement as in TLR9-CpG DNA Interactions

Lumican is an extracellular matrix proteoglycan known to regulate toll-like receptor (TLR) signaling in innate immune cells. In experimental settings, lumican suppresses TLR9 signaling by binding to and sequestering its synthetic ligand, CpG-DNA, in non-signal permissive endosomes. However, the molecular details of lumican interactions with CpG-DNA are obscure. Here, the 3-D structure of the 22 base-long CpG-DNA (CpG ODN_2395) bound to lumican or TLR9 were modeled using homology modeling and docking methods. Some of the TLR9-CpG ODN_2395 features predicted by our model are consistent with the previously reported TLR9-CpG DNA crystal structure, substantiating our current analysis. Our modeling indicated a smaller buried surface area for lumican-CpG ODN_2395 (1803 Å2) compared to that of TLR9-CpG ODN_2395 (2094 Å2), implying a potentially lower binding strength for lumican and CpG-DNA than TLR9 and CpG-DNA. The docking analysis identified 32 amino acids in lumican LRR1-11 interacting with CpG ODN_2395, primarily through hydrogen bonding, salt-bridges, and hydrophobic interactions. Our study provides molecular insights into lumican and CpG-DNA interactions that may lead to molecular targets for modulating TLR9-mediated inflammation and autoimmunity.

The resolution of phagosomes

Phagocytosis is a fundamental immunobiological process responsible for the removal of harmful particulates. While the number of phagocytic events achieved by a single phagocyte can be remarkable, exceeding hundreds per day, the same phagocytic cells are relatively long-lived. It should therefore be obvious that phagocytic meals must be resolved in order to maintain the responsiveness of the phagocyte and to avoid storage defects. In this article, we discuss the mechanisms involved in the resolution process, including solute transport pathways and membrane traffic. We describe how products liberated in phagolysosomes support phagocyte metabolism and the immune response. We also speculate on mechanisms involved in the redistribution of phagosomal metabolites back to circulation. Finally, we highlight the pathologies owed to impaired phagosome resolution, which range from storage disorders to neurodegenerative diseases.

The role of the antigen processing machinery in the regulation and trafficking of intracellular -Toll-like receptor molecules

Intracellular Toll-like receptors (TLRs) are key components of the innate immune system. Their expression in antigen-presenting cells (APCs), and in particular dendritic cells (DCs), makes them critical in the induction of the adaptive immune response. In DCs, they interact with the chaperone UNC93B1 that mediates their trafficking from the endoplasmic reticulum (ER) to endosomes where they are cleaved by proteases and activated. All these different steps are also shared by major histocompatibility complex class-II (MHCII) molecules. Here, we will discuss the tight relationship intracellular TLRs have with the antigen processing machinery in APCs for their trafficking and activation.

Surface toll-like receptor 9 on immune cells and its immunomodulatory effect

Toll like receptor 9 (TLR9) has been considered as a crucial intracellular pattern recognition receptor in the immune system, which can directly or indirectly mediate innate and adaptive immune responses by recognizing CpG DNA in endosomes to initiate its downstream signaling. However, TLR9 can also be expressed on the membrane surface of some immune and non-immune cells, called surface TLR9 (sTLR9), which covers the TLR9 and its immunomodulatory role with a mysterious veil. In this review, we mainly focus on the sTLR9 expressed on neutrophils, B cells and erythrocytes, and its immunomodulatory roles displayed alone or in coordination with endosomal TLR9 (eTLR9), providing a theoretical reference for the application of its modulators.

3D modeling of CpG DNA binding with matrix lumican shows leucine-rich repeat motif involvement as in TLR9-CpG DNA interactions

Lumican is an extracellular matrix proteoglycan, known to regulate toll-like receptor (TLR) signaling in innate immune cells. In experimental settings, lumican suppresses TLR9 signaling by binding to, and sequestering its synthetic ligand, CpG-DNA, in non-signal permissive endosomes. However, the molecular details of lumican interactions with CpG-DNA are obscure. Here, the 3-D structure of the 22 base-long CpG-DNA (CpG ODN_2395) bound to lumican or TLR9 were modeled using homology modeling and docking methods. Some of the TLR9-CpG ODN_2395 features predicted by our model are consistent with the previously reported TLR9-CpG DNA crystal structure, substantiating our current analysis. Our modeling indicated a smaller buried surface area for lumican-CpG ODN_2395 (1803 Å2) compared to that of TLR9-CpG ODN_2395 (2094 Å2), implying a potentially lower binding strength for lumican and CpG-DNA than TLR9 and CpG-DNA. The docking analysis identified 32 amino acids in lumican LRR1-11 interacting with CpG ODN_2395, primarily through hydrogen bonding, salt-bridges and hydrophobic interactions. Our study provides molecular insights into lumican and CpG-DNA interactions that may lead to molecular targets for modulating TLR9 mediated inflammation and autoimmunity.

The Src-ZNRF1 axis controls TLR3 trafficking and interferon responses to limit lung barrier damage

Type I interferons are important antiviral cytokines, but prolonged interferon production is detrimental to the host. The TLR3-driven immune response is crucial for mammalian antiviral immunity, and its intracellular localization determines induction of type I interferons; however, the mechanism terminating TLR3 signaling remains obscure. Here, we show that the E3 ubiquitin ligase ZNRF1 controls TLR3 sorting into multivesicular bodies/lysosomes to terminate signaling and type I interferon production. Mechanistically, c-Src kinase activated by TLR3 engagement phosphorylates ZNRF1 at tyrosine 103, which mediates K63-linked ubiquitination of TLR3 at lysine 813 and promotes TLR3 lysosomal trafficking and degradation. ZNRF1-deficient mice and cells are resistant to infection by encephalomyocarditis virus and SARS-CoV-2 because of enhanced type I interferon production. However, Znrf1-/- mice have exacerbated lung barrier damage triggered by antiviral immunity, leading to enhanced susceptibility to respiratory bacterial superinfections. Our study highlights the c-Src-ZNRF1 axis as a negative feedback mechanism controlling TLR3 trafficking and the termination of TLR3 signaling.

Comparison between hydroxychloroquine and systemic corticosteroids in IgA nephropathy: a two-year follow-up study

BACKGROUND

Hydroxychloroquine (HCQ) is recommended as a treatment for IgA nephropathy (IgAN) to control proteinuria. The long-term effects of HCQ compared to systemic corticosteroid therapy remain unclear.

METHODS

We conducted a retrospective case‒control study at Peking University First Hospital. Thirty-nine patients with IgAN who received HCQ for at least 24 months without corticosteroids (CSs) or other immunosuppressive agents were included. Thirty-nine matched patients who received systemic CS therapy were selected using propensity score matching. Clinical data over a 24-month period were compared.

RESULTS

In the HCQ group, the level of proteinuria decreased from 1.72 [1.44, 2.35] to 0.97 [0.51, 1.37] g/d (-50.5 [-74.0, -3.4] %, P < 0.001) at 24 months. A significant decline in proteinuria was also found in the CS group, but no significant differences were found between the HCQ group and CS group in the levels of proteinuria (0.97 [0.51, 1.37] vs. 0.53 [0.25, 1.81] g/d, P = 0.707) and change rates (-50.5% [-74.0%, -3.4%] vs. -63.7% [-78.5%, -24.2%], P = 0.385) at 24 months. In addition, the decline rates of eGFR between the HCQ and CS groups were comparable (-7.9% [-16.1%, 5.8%] vs. -6.6% [-14.9%, 5.3%], P = 0.758). More adverse events were observed in the CS group.

CONCLUSIONS

Long-term use of HCQ can maintain stable renal function with minimal side effects. In patients who cannot tolerate corticosteroids, HCQ might be an effective and safe supportive therapy for IgAN.

Cathepsins in oral diseases: mechanisms and therapeutic implications

Cathepsins are a type of lysosomal globulin hydrolase and are crucial for many physiological processes, including the resorption of bone matrix, innate immunity, apoptosis, proliferation, metastasis, autophagy, and angiogenesis. Findings regarding their functions in human physiological processes and disorders have drawn extensive attention. In this review, we will focus on the relationship between cathepsins and oral diseases. We highlight the structural and functional properties of cathepsins related to oral diseases, as well as the regulatory mechanisms in tissue and cells and their therapeutic uses. Elucidating the associated mechanism between cathepsins and oral diseases is thought to be a promising strategy for the treatment of oral diseases and may be a starting point for further studies at the molecular level.

Unexpected Need of the Epidermal Growth Factor Receptor Tyrosine Kinase Activity for Signaling by Intracellular Pattern Recognition Receptors of Nucleic Acids

Many pattern recognition receptors in mammalian cells initiate signaling processes that culminate in mounting an innate protective response mediated by induced synthesis of a large number of proteins including type I interferons and other cytokines. Many of these receptors are not located on the plasma membrane but on the membranes of intracellular organelles such as endosomes, mitochondria, and the endoplasmic reticulum; they primarily recognize microbial or cellular nucleic acids. In the course of biochemical analyses of the signaling pathways triggered by these receptors, we discovered that they require tyrosine phosphorylation by the protein kinase activity of the epidermal growth factor receptor (EGFR), which is located not only on the plasma membrane but also on the intracellular membranes. Here, we discuss how specific members of this family of receptors, such as TLR3, TLR9, or STING, interact with EGFR and other protein tyrosine kinases and what are the functional consequences of their post-translational modifications. The article highlights an unexpected functional link between a growth factor receptor and cellular innate immune response.

TLR9 and Glioma: Friends or Foes?

Toll-like receptor 9 (TLR9) is an intracellular innate immunity receptor that plays a vital role in chronic inflammation and in recognizing pathogenic and self-DNA in immune complexes. This activation of intracellular signaling leads to the transcription of either immune-related or malignancy genes through specific transcription factors. Thus, it has been hypothesized that TLR9 may cause glioma. This article reviews the roles of TLR9 in the pathogenesis of glioma and its related signaling molecules in either defending or promoting glioma. TLR9 mediates the invasion-induced hypoxia of brain cancer cells by the activation of matrix metalloproteinases (2, 9, and 13) in brain tissues. In contrast, the combination of the TLR9 agonist CpG ODN to radiotherapy boosts the role of T cells in antitumor effects. The TLR9 agonist CpG ODN 107 also enhances the radiosensitivity of human glioma U87 cells by blocking tumor angiogenesis. CpG enhances apoptosis in vitro and in vivo. Furthermore, it can enhance the antigen-presenting capacity of microglia, switch immune response toward CD8 T cells, and reduce the number of CD4CD25 Treg cells. CpG ODN shows promise as a potent immunotherapeutic drug against cancer, but specific cautions should be taken when activating TLR9, especially in the case of glioblastoma.

The subversion of toll-like receptor signaling by bacterial and viral proteases during the development of infectious diseases

Toll-like receptors (TLRs) are pattern recognition receptors (PRRs) that respond to pathogen-associated molecular patterns (PAMPs). The recognition of specific microbial ligands by TLRs triggers an innate immune response and also promotes adaptive immunity, which is necessary for the efficient elimination of invading pathogens. Successful pathogens have therefore evolved strategies to subvert and/or manipulate TLR signaling. Both the impairment and uncontrolled activation of TLR signaling can harm the host, causing tissue destruction and allowing pathogens to proliferate, thus favoring disease progression. In this context, microbial proteases are key virulence factors that modify components of the TLR signaling pathway. In this review, we discuss the role of bacterial and viral proteases in the manipulation of TLR signaling, highlighting the importance of these enzymes during the development of infectious diseases.

Toll-like receptor 9 agonists and combination therapies: strategies to modulate the tumour immune microenvironment for systemic anti-tumour immunity

Over the past decade, tremendous progress has taken place in tumour immunotherapy, relying on the fast development of combination therapy strategies that target multiple immunosuppressive signaling pathways in the immune system of cancer patients to achieve a high response rate in clinical practice. Toll-like receptor 9 (TLR9) agonists have been extensively investigated as therapeutics in monotherapy or combination therapies for the treatment of cancer, infectious diseases and allergies. TLR9 agonists monotherapy shows limited efficacy in cancer patients; whereas, in combination with other therapies including antigen vaccines, radiotherapies, chemotherapies and immunotherapies exhibit great potential. Synthetic unmethylated CpG oligodeoxynucleotide (ODN), a commonly used agonist for TLR9, stimulate various antigen-presenting cells in the tumour microenvironment, which can initiate innate and adaptive immune responses. Novel combination therapy approaches, which co-deliver immunostimulatory CpG-ODN with other therapeutics, have been tested in animal models and early human clinical trials to induce anti-tumour immune responses. In this review, we describe the basic understanding of TLR9 signaling pathway; the delivery methods in most studies; discuss the key challenges of each of the above mentioned TLR9 agonist-based combination immunotherapies and provide an overview of the ongoing clinical trial results from CpG-ODN based combination therapies in cancer patients.

Modulating Macrophage Clearance of Nanoparticles: Comparison of Small-Molecule and Biologic Drugs as Pharmacokinetic Modifiers of Soft Nanomaterials

Nanomedicines show benefits in overcoming the limitations of conventional drug delivery systems by reducing side effects, toxicity, and exhibiting enhanced pharmacokinetic (PK) profiles to improve the therapeutic window of small-molecule drugs. However, upon administration, many nanoparticles (NPs) prompt induction of host innate immune responses, which in combination with other clearance pathways such as renal and hepatic, eliminate up to 99% of the administered dose. Here, we explore a drug predosing strategy to transiently suppress the mononuclear phagocyte system (MPS), subsequently improving the PK profile and biological behaviors exhibited by a model NP system [hyperbranched polymers (HBPs)] in an immunocompetent mouse model. In vitro assays allowed the identification of five drug candidates that attenuated cellular association. Predosing of lead compounds chloroquine (CQ) and zoledronic acid (ZA) further showed increased HBP retention within the circulatory system of mice, as shown by both fluorescence imaging and positron emission tomography-computed tomography. Flow cytometric evaluation of spleen and liver tissue cells following intravenous administration further demonstrated that CQ and ZA significantly reduced HBP association with myeloid cells by 23 and 16%, respectively. The results of this study support the use of CQ to pharmacologically suppress the MPS to improve NP PKs.

Structure and dynamics of Toll immunoreceptor activation in the mosquito Aedes aegypti

Aedes aegypti has evolved to become an efficient vector for arboviruses but the mechanisms of host-pathogen tolerance are unknown. Immunoreceptor Toll and its ligand Spaetzle have undergone duplication which may allow neofunctionalization and adaptation. Here we present cryo-EM structures and biophysical characterisation of low affinity Toll5A complexes that display transient but specific interactions with Spaetzle1C, forming asymmetric complexes, with only one ligand clearly resolved. Loop structures of Spaetzle1C and Toll5A intercalate, temporarily bridging the receptor C-termini to promote signalling. By contrast unbound receptors form head-to-head homodimers that keep the juxtamembrane regions far apart in an inactive conformation. Interestingly the transcriptional signature of Spaetzle1C differs from other Spaetzle cytokines and controls genes involved in innate immunity, metabolism and tissue regeneration. Taken together our results explain how upregulation of Spaetzle1C in the midgut and Toll5A in the salivary gland shape the concomitant immune response.

Spatial localization of cathepsins: Implications in immune activation and resolution during infections

Cathepsins were first described, as endolysosomal proteolytic enzymes in reference to the organelles where they degrade the bulk of endogenous and exogenous substrates in a slightly acidic environment. These substrates include pathogens internalized via endocytosis and/or marked for destruction by autophagy. However, the role of cathepsins during infection far exceeds that of direct digestion of the pathogen. Cathepsins have been extensively investigated in the context of tumour associated immune cells and chronic inflammation. Several cathepsin-dependent immune responses develop in the endocytic pathway while others take place in the cytosol, the nucleus, or in the extracellular space. In this review we highlight the spatial localization of cathepsins and their implications in immune activation and resolution pathways during infection.

N-glycosylation of UNC93B1 at a Specific Asparagine Residue Is Required for TLR9 Signaling

Toll-like receptors (TLRs) play critical roles in the first line of host defense against pathogens through recognition of pathogen-associated molecular patterns and initiation of the innate immune responses. The proper localization of TLRs in specific subcellular compartments is crucial for their ligand recognition and downstream signaling to ensure appropriate responses against pathogens while avoiding erroneous or excessive activation. Several TLRs, including TLR7 and TLR9 but not TLR4, depend on UNC93B1 for their proper intracellular localization and signaling. Accumulating evidence suggest that UNC93B1 differentially regulates its various client TLRs, but the specific mechanisms by which UNC93B1 controls individual TLRs are not well understood. Protein N-glycosylation is one of the most frequent and important post-translational modification that occurs in membrane-localized or secreted proteins. UNC93B1 was previously shown to be glycosylated at Asn251 and Asn272 residues. In this study, we investigated whether N-glycosylation of UNC93B1 affects its function by comparing wild type and glycosylation-defective mutant UNC93B1 proteins. It was found that glycosylation of Asn251 and Asn272 residues can occur independently of each other and mutation of neither N251Q or N272Q in UNC93B1 altered expression and localization of UNC93B1 and TLR9. In contrast, CpG DNA-stimulated TLR9 signaling was severely inhibited in cells expressing UNC93B1(N272Q), but not in cells with UNC93B1(N251Q). Further, it was found that glycosylation at Asn272 of UNC93B1 is essential for the recruitment of MyD88 to TLR9 and the subsequent downstream signaling. On the other hand, the defective glycosylation at Asn272 did not affect TLR7 signaling. Collectively, these data demonstrate that the glycosylation at a specific asparagine residue of UNC93B1 is required for TLR9 signaling and the glycosylation status of UNC93B1 differently affects activation of TLR7 and TLR9.

The NCF1 variant aggravates autoimmunity by facilitating the activation of plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) are a professional type I IFN producer that play critical roles in the pathogenesis of autoimmune diseases. However, both genetic regulation of the function of pDCs and their relationships with autoimmunity are largely undetermined. Here, we investigated the causality of the neutrophil cytosolic factor 1 (NCF1) missense variant, which is one of the most significant associated risk variants for lupus, and found that the substitution of arginine (R) for histidine (H) at position 90 in the NCF1 protein (NCF1 p.R90H) led to excessive activation of pDCs. A mechanism study demonstrated that p.R90H reduced the affinity of NCF1 for phospholipids, thereby impairing endosomal localization of NCF1. As NCF1 is a subunit of the NADPH oxidase 2 (NOX2) complex, this impairment led to an acidified endosomal pH and facilitated downstream TLR signaling. Consistently, the homozygous knockin mice manifested aggravated lupus progression in a pDC-dependent lupus model. More important, pharmaceutical intervention revealed that hydroxychloroquine (HCQ) could antagonize the detrimental function of NCF1 p.R90H in the lupus model and systemic lupus erythematosus samples, supporting the idea that NCF1 p.R90H could be identified as a genetic biomarker for HCQ application. Therefore, our study provides insights into the genetic control of pDC function and a paradigm for applying genetic variants to improve targeted therapy for autoimmune diseases.

Targeting DAMPs with nucleic acid scavengers to treat lupus

Systemic lupus erythematosus (SLE) is a chronic and often progressive autoimmune disorder marked clinically by a variable constellation of symptoms including fatigue, rash, joint pains, and kidney damage. The lungs, heart, gastrointestinal system, and brain can also be impacted, and individuals with lupus are at higher risk for atherosclerosis, thrombosis, thyroid disease, and other disorders associated with chronic inflammation . Autoimmune diseases are marked by erroneous immune responses in which the target of the immune response is a "self"-antigen, or autoantigen, driven by the development of antigen-specific B or T cells that have overcome the normal systems of self-tolerance built into the development of B and T cells. SLE is specifically characterized by the production of autoantibodies against nucleic acids and their binding proteins, including anti-double stranded DNA, anti-Smith (an RNA binding protein), and many others . These antibodies bind their nuclear-derived antigens to form immune complexes that cause injury and scarring through direct deposition in tissues and activation of innate immune cells . In over 50% of SLE patients, immune complex aggregation in the kidneys drives intrarenal inflammation and injury and leads to lupus nephritis, a progressive destruction of the glomeruli that is one of the most common causes of lupus-related death . To counter this pathology increasing attention has turned to developing approaches to reduce the development and continued generation of such autoantibodies. In particular, the molecular and cellular events that lead to long term, continuous activation of such autoimmune responses have become the focus of new therapeutic strategies to limit renal and other pathologies in lupus patients. The focus of this review is to consider how the innate immune system is involved in the development and progression of lupus nephritis and how a novel approach to inhibit innate immune activation by neutralizing the activators of this response, called Damage Associated Molecular Patterns, may represent a promising approach to treat this and other autoimmune disorders.

Bioactivity of orange-spotted grouper (Epinephelus coioides) cathepsin L: Proteolysis of bacteria and regulation of the innate immune response

Cathepsin L (CTSL) is a cysteine endopeptidase involved in protein degradation mainly in lysosomes. Following activation in an acidic environment, it plays a key role in a variety of physiological, immunological, and pathological processes. The biological function of CTSL in teleost remains unclear. Immunohistochemical analysis revealed that CTSL was expressed mainly in lymphoid organs, head kidney, trunk kidney, and liver, which particularly was expressed in leukocyte-like cells. We performed two forms of recombinant CTSL (rCTSL and rTCTSL) derived from orange-spotted grouper (Epinephelus coioides) to elucidate the role of CTSL in teleost innate immunity, based on differences in immune-related gene expression. We determined that rCTSL has a proteolytic function whereas rTCTSL does not. Under CTSL activation, we observed increases in IL-1β, IL-6, IL-12, IFNγ, CCL-1, CCL-3, epinecidin-1, lysozyme, and IgM. The bacteriolytic activity of rCTSL was more pronounced against Gram-positive bacteria than Gram-negative bacteria. Our findings indicate CTSL plays multiple roles in the reactions of innate immunity.

Lysosomes and lysosome‐related organelles in immune responses

The catabolic, degradative capacity of the endo‐lysosome system is put to good use in mammalian immune responses as is their recently established status as signaling platforms. From the ‘creative destruction’ of antigenic and ‘self’ material for antigen presentation to T cells to the re‐purposing of lysosomes as toxic exocytosable lysosome‐related organelles (granules) in leukocytes such as CD8 T cells and eosinophils, endo‐lysosomes are key players in host defense. Signaled responses to some pathogen products initiate in endo‐lysosomes and these organelles are emerging as important in distinct ways in the unique immunobiology of dendritic cells. Potential self‐inflicted toxicity from lysosomal and granule proteases is countered by expression of serpin and cystatin family members.

Regulatory strategies limiting endosomal Toll-like receptor activation in B cells

The recognition of pathogen-associated nucleic acid (NA) promotes effective immunity against invading pathogens. However, endosomal Toll-like receptor (TLR) activation by self-NA also underlies the pathogenesis of systemic autoimmune diseases, such as systemic lupus erythematosus (SLE). For this reason, the activation thresholds of NA-sensing TLRs must be tightly regulated to balance protective and pathogenic immune responses. In this study, we will provide an overview of the evolutionary mechanisms designed to limit the aberrant activation of endosomal TLRs by self-ligands, focusing on four broad strategies. These include the following: 1) the production of nucleases able to degrade self-DNA and RNA; 2) the cell-specific regulation of endosomal TLR expression; 3) the spatial and temporal control of TLR positioning at a sub-cellular level; and 4) the modulation of downstream TLR signaling cascades. Given the critical role of B cells in lupus pathogenesis, where possible, we will describe evidence for B cell-specific induction of these regulatory mechanisms. We will also highlight our own work showing how modulation of B cell endolysosomal flux tunes NA-sensing TLR activation signals. In the face of inevitable generation of self-NA during normal cellular turnover, these parallel mechanisms are vital to protect against pathogenic inflammation.

Progranulin as a Potential Therapeutic Target in Immune-Mediated Diseases

Progranulin (PGRN), a secretory glycoprotein consisting of 593 amino acid residues, is a key actor and regulator of multiple system functions such as innate immune response and inflammation, as well as tissue regeneration. Recently, there is emerging evidence that PGRN is protective in the development of a variety of immune-mediated diseases, including rheumatoid arthritis (RA), inflammatory bowel disease (IBD), type 1 diabetes mellitus (T1DM) and multiple sclerosis (MS) by regulating signaling pathways known to be critical for immunology, particularly the tumor necrosis factor alpha/TNF receptor (TNF-α/TNFR) signaling pathway. Whereas, the role of PGRN in psoriasis, systemic lupus erythematosus (SLE) and systemic sclerosis (SSc) is controversial. This review summarizes the immunological functions of PGRN and its role in the pathogenesis of several immune-mediated diseases, in order to provide new ideas for developing therapeutic strategies for these diseases.

Toll-Like Receptors (TLRs), NOD-Like Receptors (NLRs), and RIG-I-Like Receptors (RLRs) in Innate Immunity. TLRs, NLRs, and RLRs Ligands as Immunotherapeutic Agents for Hematopoietic Diseases

The innate immune system plays a pivotal role in the first line of host defense against infections and is equipped with patterns recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). Several classes of PRRS, including Toll-like receptors (TLRs), NOD-like receptors (NLRs), and RIG-I-like receptors (RLRs) recognize distinct microbial components and directly activate immune cells. TLRs are transmembrane receptors, while NLRs and RLRs are intracellular molecules. Exposure of immune cells to the ligands of these receptors activates intracellular signaling cascades that rapidly induce the expression of a variety of overlapping and unique genes involved in the inflammatory and immune responses. The innate immune system also influences pathways involved in cancer immunosurveillance. Natural and synthetic agonists of TLRs, NLRs, or RLRs can trigger cell death in malignant cells, recruit immune cells, such as DCs, CD8+ T cells, and NK cells, into the tumor microenvironment, and are being explored as promising adjuvants in cancer immunotherapies. In this review, we provide a concise overview of TLRs, NLRs, and RLRs: their structure, functions, signaling pathways, and regulation. We also describe various ligands for these receptors and their possible application in treatment of hematopoietic diseases.

Therapeutic Interventions Targeting Innate Immune Receptors: A Balancing Act

The innate immune system is an organism's first line of defense against an onslaught of internal and external threats. The downstream adaptive immune system has been a popular target for therapeutic intervention, while there is a relative paucity of therapeutics targeting the innate immune system. However, the innate immune system plays a critical role in many human diseases, such as microbial infection, cancer, and autoimmunity, highlighting the need for ongoing therapeutic research. In this review, we discuss the major innate immune pathways and detail the molecular strategies underpinning successful therapeutics targeting each pathway as well as previous and ongoing efforts. We will also discuss any recent discoveries that could inform the development of novel therapeutic strategies. As our understanding of the innate immune system continues to develop, we envision that therapies harnessing the power of the innate immune system will become the mainstay of treatment for a wide variety of human diseases.

Hydroxychloroquine in IgA nephropathy: a systematic review

Background

Hydroxychloroquine (HCQ) has recently been reported to be a promising and safe anti-proteinuric agent for IgA nephropathy (IgAN) patients. In the present systematic review, we aimed to summarize the evidence concerning the benefits and risks of HCQ therapy in IgAN.

Methods

Electronic databases were searched for randomized, cohort, or case-control studies with IgAN biopsy-proven patients comparing the effects of HCQ with angiotensin-converting enzyme inhibitors/angiotensin receptor blockers or immunosuppression on proteinuria reduction.

Results

Five studies, one randomized and three observational, involving a total of 504 patients, were eligible for inclusion. Overall, there was a tendency of HCQ treatment to reduce proteinuria. In the studies where the control arm was supportive therapy, HCQ significantly reduced proteinuria at 6 months. However, in the studies that compared HCQ to immunosuppressive therapy, we found no difference in proteinuria reduction. HCQ had no impact on eGFR.

Conclusion

HCQ seems to be an efficient alternative therapy for patients with IgAN who insufficiently respond to conventional therapy. However, ethnically diverse randomized controlled studies with long-term follow-up are needed.

Mycobacterium tuberculosis canonical virulence factors interfere with a late component of the TLR2 response

For many intracellular pathogens, the phagosome is the site of events and interactions that shape infection outcome. Phagosomal membrane damage, in particular, is proposed to benefit invading pathogens. To define the innate immune consequences of this damage, we profiled macrophage transcriptional responses to wild-type Mycobacterium tuberculosis (Mtb) and mutants that fail to damage the phagosomal membrane. We identified a set of genes with enhanced expression in response to the mutants. These genes represented a late component of the TLR2-dependent transcriptional response to Mtb, distinct from an earlier component that included Tnf. Expression of the later component was inherent to TLR2 activation, dependent upon endosomal uptake, and enhanced by phagosome acidification. Canonical Mtb virulence factors that contribute to phagosomal membrane damage blunted phagosome acidification and undermined the endosome-specific response. Profiling cell survival and bacterial growth in macrophages demonstrated that the attenuation of these mutants is partially dependent upon TLR2. Further, TLR2 contributed to the attenuated phenotype of one of these mutants in a murine model of infection. These results demonstrate two distinct components of the TLR2 response and identify a component dependent upon endosomal uptake as a point where pathogenic bacteria interfere with the generation of effective inflammation. This interference promotes tuberculosis (TB) pathogenesis in both macrophage and murine infection models.

The antiviral and immunomodulatory activities of propolis: An update and future perspectives for respiratory diseases

Propolis is a complex natural product that possesses antioxidant, anti‐inflammatory, immunomodulatory, antibacterial, and antiviral properties mainly attributed to the high content in flavonoids, phenolic acids, and their derivatives. The chemical composition of propolis is multifarious, as it depends on the botanical sources from which honeybees collect resins and exudates. Nevertheless, despite this variability propolis may have a general pharmacological value, and this review systematically compiles, for the first time, the existing preclinical and clinical evidence of propolis activities as an antiviral and immunomodulatory agent, focusing on the possible application in respiratory diseases. In vitro and in vivo assays have demonstrated propolis broad‐spectrum effects on viral infectivity and replication, as well as the modulatory actions on cytokine production and immune cell activation as part of both innate and adaptive immune responses. Clinical trials confirmed propolis undeniable potential as an effective therapeutic agent; however, the lack of rigorous randomized clinical trials in the context of respiratory diseases is tangible. Since propolis is available as a dietary supplement, possible use for the prevention of respiratory diseases and their deleterious inflammatory drawbacks on the respiratory tract in humans is considered and discussed. This review opens up new perspectives on the clinical investigation of neglected propolis biological properties which, now more than ever, are particularly relevant with respect to the recent outbreaks of pandemic respiratory infections.

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.

Regulation of the nucleic acid-sensing Toll-like receptors

Many of the ligands for Toll-like receptors (TLRs) are unique to microorganisms, such that receptor activation unequivocally indicates the presence of something foreign. However, a subset of TLRs recognizes nucleic acids, which are present in both the host and foreign microorganisms. This specificity enables broad recognition by virtue of the ubiquity of nucleic acids but also introduces the possibility of self-recognition and autoinflammatory or autoimmune disease. Defining the regulatory mechanisms required to ensure proper discrimination between foreign and self-nucleic acids by TLRs is an area of intense research. Progress over the past decade has revealed a complex array of regulatory mechanisms that ensure maintenance of this delicate balance. These regulatory mechanisms can be divided into a conceptual framework with four categories: compartmentalization, ligand availability, receptor expression and signal transduction. In this Review, we discuss our current understanding of each of these layers of regulation.

Activation of nucleic acid-sensing Toll-like receptors is finely tuned to limit self-reactivity while maintaining recognition of foreign microorganisms. The authors describe recent progress made in defining the regulatory mechanisms that facilitate this delicate balance.

What makes (hydroxy)chloroquine ineffective against COVID-19: insights from cell biology

Since chloroquine (CQ) and hydroxychloroquine (HCQ) can inhibit the invasion and proliferation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in cultured cells, the repurposing of these antimalarial drugs was considered a promising strategy for treatment and prevention of coronavirus disease (COVID-19). However, despite promising preliminary findings, many clinical trials showed neither significant therapeutic nor prophylactic benefits of CQ and HCQ against COVID-19. Here, we aim to answer the question of why these drugs are not effective against the disease by examining the cellular working mechanisms of CQ and HCQ in prevention of SARS-CoV-2 infections.

Molecular mechanisms of nonself nucleic acid recognition by the innate immune system

Nucleic acids (NAs) represent one of the most important classes of molecules recognized by the innate immune system. However, NAs are not limited to pathogens, but are also present within the host. As such, the immune system has evolved an elaborate set of pathogen recognition receptors (PRRs) that employ various strategies to recognize distinct types of NAs, while reliably distinguishing between self and nonself. The here-employed strategies encompass the positioning of NA-sensing PRRs in certain subcellular compartments that potentially come in contact with pathogens but not host NAs, the existence of counterregulatory measures that keep endogenous NAs below a certain threshold, and also the specific identification of certain nonself patterns. Here, we review recent advances in the molecular mechanisms of NA recognition by TLRs, RLRs, and the cGAS-STING axis. We highlight the differences in NA-PRR interfaces that confer specificity and selectivity toward an NA ligand, as well as the NA-dependent induced conformational changes required for signal transduction.

Immunomodulatory Responses Of Toll Like Receptors Against 2019nCoV

The present review discusses the immune signals via toll like receptors (TLRs) against 2019nCoV. We researched using different database, up to June 18th, 2020. All the included articles were published in English language. The outcome of this review, that some TLRs agonists or antagonists are progressed as drugs to combat and down regulating TLRs immune signals respectively. TLRs 3 and 4 recognized 2019nCoV spike protein through immune and molecular signals that leading to immune stimulation of pro-inflammatory cytokines and even the immune fever. While the TLRs7 and 8 recognized single-stranded ribonucleic acids (ssRNAs) leading to elevation of the tumour necrosis factor α (TNF-α), interleukin (IL)-6 and -12 levels. TLRs agonists or antagonists utilized as immunotherapeutic targets against 2019nCoV via TLRs signals. Chloroquine and hydroxychloroquine; the approval compounds for 2019nCoV therapy can be inhibiting the class II major histocompatibility complex molecules expression and antigen presentation and even immune suppressions of the pro-inflammatory cytokines profile.

TLR9 expression in chronic lymphocytic leukemia identifies a promigratory subpopulation and novel therapeutic target

Chronic lymphocytic leukemia (CLL) remains incurable despite B-cell receptor-targeted inhibitors revolutionizing treatment. This suggests that other signaling molecules are involved in disease escape mechanisms and resistance. Toll-like receptor 9 (TLR9) is a promising candidate that is activated by unmethylated cytosine guanine dinucleotide-DNA. Here, we show that plasma from patients with CLL contains significantly more unmethylated DNA than plasma from healthy control subjects (P < .0001) and that cell-free DNA levels correlate with the prognostic markers CD38, β2-microglobulin, and lymphocyte doubling time. Furthermore, elevated cell-free DNA was associated with shorter time to first treatment (hazard ratio, 4.0; P = .003). We also show that TLR9 expression was associated with in vitro CLL cell migration (P < .001), and intracellular endosomal TLR9 strongly correlated with aberrant surface expression (sTLR9; r = 0.9). In addition, lymph node-derived CLL cells exhibited increased sTLR9 (P = .016), and RNA-sequencing of paired sTLR9hi and sTLR9lo CLL cells revealed differential transcription of genes involved in TLR signaling, adhesion, motility, and inflammation in sTLR9hi cells. Mechanistically, a TLR9 agonist, ODN2006, promoted CLL cell migration (P < .001) that was mediated by p65 NF-κB and STAT3 transcription factor activation. Importantly, autologous plasma induced the same effects, which were reversed by a TLR9 antagonist. Furthermore, high TLR9 expression promoted engraftment and rapid disease progression in a NOD/Shi-scid/IL-2Rγnull mouse xenograft model. Finally, we showed that dual targeting of TLR9 and Bruton's tyrosine kinase (BTK) was strongly synergistic (median combination index, 0.2 at half maximal effective dose), which highlights the distinct role for TLR9 signaling in CLL and the potential for combined targeting of TLR9 and BTK as a more effective treatment strategy in this incurable disease.