Toll-like receptors in lymphoid malignancies: Double-edged sword

Toll-like receptor-guided therapeutic intervention of human cancers: molecular and immunological perspectives

Toll-like receptors (TLRs) serve as the body's first line of defense, recognizing both pathogen-expressed molecules and host-derived molecules released from damaged or dying cells. The wide distribution of different cell types, ranging from epithelial to immune cells, highlights the crucial roles of TLRs in linking innate and adaptive immunity. Upon stimulation, TLRs binding mediates the expression of several adapter proteins and downstream kinases, that lead to the induction of several other signaling molecules such as key pro-inflammatory mediators. Indeed, extraordinary progress in immunobiological research has suggested that TLRs could represent promising targets for the therapeutic intervention of inflammation-associated diseases, autoimmune diseases, microbial infections as well as human cancers. So far, for the prevention and possible treatment of inflammatory diseases, various TLR antagonists/inhibitors have shown to be efficacious at several stages from pre-clinical evaluation to clinical trials. Therefore, the fascinating role of TLRs in modulating the human immune responses at innate as well as adaptive levels directed the scientists to opt for these immune sensor proteins as suitable targets for developing chemotherapeutics and immunotherapeutics against cancer. Hitherto, several TLR-targeting small molecules (e.g., Pam3CSK4, Poly (I:C), Poly (A:U)), chemical compounds, phytocompounds (e.g., Curcumin), peptides, and antibodies have been found to confer protection against several types of cancers. However, administration of inappropriate doses of such TLR-modulating therapeutics or a wrong infusion administration is reported to induce detrimental outcomes. This review summarizes the current findings on the molecular and structural biology of TLRs and gives an overview of the potency and promises of TLR-directed therapeutic strategies against cancers by discussing the findings from established and pipeline discoveries.

Role of cytokine in malignant T-cell metabolism and subsequent alternation in T-cell tumor microenvironment

T cells are an important component of adaptive immunity and T-cell-derived lymphomas are very complex due to many functional sub-types and functional elasticity of T-cells. As with other tumors, tissues specific factors are crucial in the development of T-cell lymphomas. In addition to neoplastic cells, T- cell lymphomas consist of a tumor micro-environment composed of normal cells and stroma. Numerous studies established the qualitative and quantitative differences between the tumor microenvironment and normal cell surroundings. Interaction between the various component of the tumor microenvironment is crucial since tumor cells can change the microenvironment and vice versa. In normal T-cell development, T-cells must respond to various stimulants deferentially and during these courses of adaptation. T-cells undergo various metabolic alterations. From the stage of quiescence to attention of fully active form T-cells undergoes various stage in terms of metabolic activity. Predominantly quiescent T-cells have ATP-generating metabolism while during the proliferative stage, their metabolism tilted towards the growth-promoting pathways. In addition to this, a functionally different subset of T-cells requires to activate the different metabolic pathways, and consequently, this regulation of the metabolic pathway control activation and function of T-cells. So, it is obvious that dynamic, and well-regulated metabolic pathways are important for the normal functioning of T-cells and their interaction with the microenvironment. There are various cell signaling mechanisms of metabolism are involved in this regulation and more and more studies have suggested the involvement of additional signaling in the development of the overall metabolic phenotype of T cells. These important signaling mediators include cytokines and hormones. The impact and role of these mediators especially the cytokines on the interplay between T-cell metabolism and the interaction of T-cells with their micro-environments in the context of T-cells lymphomas are discussed in this review article.

Integrated network pharmacology and intestinal flora analysis to determine the protective effect of Xuanbai-Chengqi decoction on lung and gut injuries in influenza virus-infected mice

ETHNOPHARMACOLOGICAL RELEVANCE

Xuanbai-Chengqi decoction (XBCQ) is a traditional Chinese medicine (TCM) compound used in the treatment of pulmonary infection in China. Despite the popular usage of XBCQ, its underlying protective roles and the associated molecular mechanisms with the gut-lung axis in influenza remain unclear.

AIM OF THE STUDY

We aimed to explore the protective effects and the underlying mechanism of XBCQ efficacy on lung and intestine injuries induced by influenza A virus as well as to identify the main active components through integrated network pharmacology, intestinal flora analysis and pathway validation.

MATERIALS AND METHODS

The potential active components and therapeutic targets of XBCQ in the treatment of influenza were hypothesized through a series of network pharmacological strategies, including components screening, targets prediction and bioinformatics analysis. Inflammatory cytokines and pathway proteins were assayed to validate the results of network pharmacology. Then the mechanism of XBCQ alleviating lung and intestine injuries was further explored via intestinal flora analysis. The important role of Rhubarb in the formula was verified by removing Rhubarb.

RESULTS

XBCQ could significantly improve the survival rate in IAV-infected mice. The network pharmacology results demonstrated that JUN, mitogen-activated protein kinase (MAPK), and tumor necrosis factor (TNF) are the key targets of XBCQ that can be useful in influenza treatment as it contains the core components luteolin, emodin, and aloe-emodin, which are related to the pathways of TNF, T-cell receptor (TCR), and NF-κB. Verification experiments demonstrated that XBCQ could significantly alleviate the immune injury of the lungs and the gut of the mice, which is attributable to the inhibition of the release of inflammatory cytokines (such as TNF-α, IL-6, and IL-1β), the downregulation of the protein expression levels of Toll-like receptors-7 (TLR7), MyD88, and p-NF-κB65, and the reduction in the relative abundance of Enterobacteriaceae and Proteus, while an increase in that of Firmicutes and Lachnospiraceae. The overall protective role of XBCQ contributing to the treatment of the lungs and the gut was impaired when Rhubarb was removed from XBCQ.

CONCLUSIONS

Our results suggest that the efficacy of XBCQ is related to the inhibition of the immune injury and remodeling of the intestinal flora, wherein Rhubarb plays an important role, which cumulatively provide the evidence applicable for the treatment of viral pneumonia induced by a different respiratory virus with XBCQ.

Toll-like receptor (TLRs) agonists and antagonists for COVID-19 treatments

Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) rapidly infects humans and animals which make coronavirus disease 2019 (COVID-19) a grievous epidemic worldwide which broke out in 2020. According to data analysis of the other coronavirus family, for instance severe acute respiratory syndrome SARS coronavirus (SARS-CoV), can provide experience for the mutation of SARS-CoV-2 and the prevention and treatment of COVID-19. Toll-like receptors (TLRs) as a pattern recognition receptor (PRRs), have an indispensable function in identifying the invader even activate the innate immune system. It is possible for organism to activate different TLR pathways which leads to secretion of proinflammatory cytokines such as Interleukin 1 (IL-1), Interleukin 6 (IL-6), Tumor necrosis factor α (TNFα) and type Ⅰ interferon. As a component of non-specific immunity, TLRs pathway may participate in the SARS-CoV-2 pathogenic processes, due to previous works have proved that TLRs are involved in the invasion and infection of SARS-CoV and MERS to varying degrees. Different TLR, such as TLR2, TLR4, TLR7, TLR8 and TLR9 probably have a double-sided in COVID-19 infection. Therefore, it is of great significance for a correctly acknowledging how TLR take part in the SARS-CoV-2 pathogenic processes, which will be the development of treatment and prevention strategies.

Association of Toll-like receptors polymorphisms with the risk of acute lymphoblastic leukemia in the Brazilian Amazon

Acute lymphoblastic leukemia (ALL) is the most common hematologic malignancy in children in childhood. Single-nucleotide polymorphism (SNPs) in key molecules of the immune system, such as Toll-like receptors (TLRs) and CD14 molecules, are associated with the development of several diseases. However, their role in ALL is unknown. A case–control study was performed with 152 ALL patients and 187 healthy individuals to investigate the role of SNPs in TLRs and the CD14 gene in ALL. In this study, TLR6 C > T rs5743810 [OR: 3.20, 95% CI: 1.11–9.17, p = 0.003) and TLR9 C > T rs187084 (OR: 2.29, 95% CI: 1.23–4.26, p = 0.000) seems to be a risk for development of ALL. In addition, the TLR1 T > G rs5743618 and TLR6 C > T rs5743810 polymorphisms with protection against death (OR: 0.17, 95% IC: 0.04–0.79, p = 0.008; OR: 0.48, 95% IC: 0.24–0.94, p = 0.031, respectively). Our results show that SNPs in TLRs genes may be involved in the pathogenesis of ALL and may influence clinical prognosis; however, further studies are necessary to elucidate the role of TLR1, TLR4, TLR5, TLR6, TLR9 and CD14 polymorphisms in this disease.

Association of TLR4 Rs4986791 Polymorphism and TLR9 Haplotypes with Acute Myeloid Leukemia Susceptibility: A Case-Control Study of Adult Patients

Toll-like receptors (TLRs) have an important role in innate immunity, and single nucleotide polymorphisms (SNPs) of TLR genes influence the risk of developing hematological malignancies. We aimed to evaluate the effect of TLR2 (rs5743708), TLR4 (rs11536889, rs4986790, rs4986791), TLR9 (rs187084, rs352140, rs5743836) on AML risk, the relation between investigated SNPs and somatic mutations, clinical features, and the overall survival of adult AML patients. All mentioned SNPs were genotyped in 511 AML cases and 503 healthy controls. DNMT3A (R882), FLT3 (D835, ITD), and NPM1 mutations’ status were investigated in AML patients. TLR4 rs4986791 was associated with an increased risk of AML under the dominant model (OR = 1.61, 95% CI: 1.001–2.59). Variant genotypes of the TLR4 rs4986790 or rs4986791 were associated with the odds of developing AML in the codominant model (OR = 3.14; 95% CI: 1.12–8.84; p = 0.032). The TLR9 rs5743836 variant genotype was associated with the NPM1 mutation (p = 0.002). The investigated SNPs were not associated with the DNMT3A, FLT3 mutations and had no significant contribution to the hazard of death after adjusting for covariates. Our findings suggest that TLR4 rs4986791 is associated with AML susceptibility. The combined variant genotypes of TLR4 rs4986790 and rs4986791 increase AML risk, the TLR9 C-G-A haplotype may represent a promising approach to predict a person’s risk for developing AML.

Aberrant Expression of TLR2, TLR7, TLR9, Splicing Variants of TLR4 and MYD88 in Chronic Lymphocytic Leukemia Patients

Functional toll-like receptors (TLRs) could modulate anti-tumor effects by activating inflammatory cytokines and the cytotoxic T-cells response. However, excessive TLR expression could promote tumor progression, since TLR-induced inflammation might stimulate cancer cells expansion into the microenvironment. Myd88 is involved in activation NF-κB through TLRs downstream signaling, hence in the current study we provided, for the first time, a complex characterization of expression of TLR2, TLR4, TLR7, TLR9, and MYD88 as well as their splicing forms in two distinct compartments of the microenvironment of chronic lymphocytic leukemia (CLL): peripheral blood and bone marrow. We found correlations between MYD88 and TLRs expressions in both compartments, indicating their relevant cooperation in CLL. The MYD88 expression was higher in CLL patients compared to healthy volunteers (HVs) (0.1780 vs. 0.128, p < 0.0001). The TLRs expression was aberrant in CLL compared to HVs. Analysis of survival curves revealed a shorter time to first treatment in the group of patients with low level of TLR4(3) expression compared to high level of TLR4(3) expression in bone marrow (13 months vs. 48 months, p = 0.0207). We suggest that TLRs expression is differentially regulated in CLL but is similarly shared between two distinct compartments of the microenvironment.

Microbial sensing by haematopoietic stem and progenitor cells: Vigilance against infections and immune education of myeloid cells

Bone marrow haematopoietic stem and progenitor cells (HSPCs) express pattern recognition receptors such as Toll-like receptors (TLRs) to sense microbial products and activation of these innate immune receptors induces cytokine expression and redirects bone marrow haematopoiesis towards the increased production of myeloid cells. Secreted cytokines by HSPCs in response to TLR ligands can act in an autocrine or paracrine manner to regulate haematopoiesis. Moreover, tonic activation of HSPCs by microbiota-derived compounds might educate HSPCs to produce superior myeloid cells equipped with innate memory responses to combat pathogens. While haematopoietic stem cell activation through TLRs meets the increased demand for blood leucocytes to protect the host against infection, persistent exposure to inflammatory cytokines or microbial products might impair their function and even induce malignant transformation. This review highlights the potential outcomes of HSPCs in response to TLR ligands.

Diffuse large B-cell lymphoma in Southeast Asian cohort: expression patterns of B-cell receptor (BCR) repertoire and its linkage with molecular subtypes and response to R-CHOP therapy

AIMS

Heightened B-cell receptor (BCR) activity in diffuse large B-cell lymphoma (DLBCL) is well established, and a subset of patients with relapsed DLBCL can benefit from BCR-targeted therapies. Universal outreach of such emerging therapies mandates forming a global landscape of BCR molecular signalling in DLBCL, including Southeast Asia.

METHODS

79 patients with DLBCL (nodal, 59% and extranodal, 41%) treated with rituximab combined with cyclophosphamide, doxorubicin, vincristine and prednisone (R-CHOP) therapy were selected. Expression levels of BCR and linked signalling pathway molecules were inter-related with Lymph2Cx-based cell of origin (COO) types and overall survival (OS).

RESULTS

Activated B-cell (ABC) type DLBCL constituted 49% (39/79) compared with germinal centre B-cell (GCB) type DLBCL (29/79; 37%) and revealed poor prognosis (p=0.013). In ABC-DLBCL, high BTK expression exerted poor response to R-CHOP, while OS in ABC-DLBCL with low BTK expression was similar to GCB-DLBCL subtype (p=0.004). High LYN expression coupled with a poor OS for ABC-DLBCL as well as GCB-DLBCL subtypes (p=0.001). Furthermore, high coexpression of BTK/LYN (BTK ^high/LYN ^high) showed poor OS (p=0.019), which linked with upregulation of several genes associated with BCR repertoire and nuclear factor-kappa B pathway (p<0.01). In multivariate analysis, high BTK and LYN expression retained prognostic significance against established clinical predictive factors such as age, International Prognostic Index and COO (p<0.05).

CONCLUSIONS

Our data provide a clear association between high BCR activity in DLBCL and response to therapy in a distinct population. Molecular data provided here will pave the pathway for the provision of promising novel-targeted therapies to patients with DLBCL in Southeast Asia.

Effects of Gui Zhi Ma Huang Ge Ban Tang on the TLR7 Pathway in Influenza Virus Infected Mouse Lungs in a Cold Environment

OBJECTIVE

We wished to investigate the effects of the traditional Chinese medicine Gui Zhi Ma Huang Ge Ban Tang on controlling influenza A virus (IAV) infection and improving inflammation in mouse lungs.

METHOD

Mice were maintained in normal and cold environments and infected with IAV by intranasal application, respectively. Real-time quantitative polymerase chain reaction was used to measure mRNA expression of TLR7, myeloid differentiation primary response 88 (MyD88), and nuclear factor-kappa B (NF-κB)p65 in the TLR7 signaling pathway and virus replication in lungs. Western blotting was used to measure expression levels of TLR7, MyD88, and NF-κB p65 proteins. Flow cytometry was used to detect the proportion of T-helper (Th)1/Th2 and Th17/T-regulatory (Treg) cells.

RESULTS

Application of Gui Zhi Ma Huang Ge Ban Tang in influenza-infected mice in a cold environment showed (i) downregulation of TLR7, MyD88, and NF-κBp65; (ii) inhibition of transcriptional activities of promoters coding for TLR7, MyD88, and NF-κBp65; (iii) reduction in the proportion of Th1/Th2 and Th17/Treg cells.

CONCLUSIONS

Gui Zhi Ma Huang Ge Ban Tang had a good therapeutic effect on mice infected with IAV, especially in the cold environment. It could reduce lung inflammation in mice significantly and elicit an anti-influenza effect by downregulating expression of the key factors in TLR7 signaling pathway.

Synergy of purine-scaffold TLR7 agonist with doxorubicin on systemic inhibition of lymphoma in mouse model

Chemo- and radio-therapy suffer from certain well-recognized drawbacks for lymphoma therapy. Passive immunotherapy with monoclonal antibody has improved outcome for patients with CD20⁺ B cell lymphoma, but not for T cell lymphoma. Therefore, novel treatment approaches are clearly required for T cell lymphoma. To date, the combined application targeting TLR7, 8 and 9 has established long-term antitumor immunity. We previously synthesized a purine-scaffold TLR7 agonist named GD5. Here, we report that the intratumoral administration of GD5 combined with doxorubicin (DOX), a conventional chemotherapeutic agent in T cell lymphoma. This combined treatment made mice to produce more cytokines in blood, and generate more potent cytotoxic T lymphocyte response, then result in effective eradication of both local and distant tumors in tumor-bearing mice. Our findings demonstrate the potential for enhancing the efficacy of the current standard DOX therapy through combination with TLR7 agonist GD5 to improve antitumor immune responses and provide durable remissions for T cell lymphoma.

Therapeutic targeting of Toll-like receptors: a review of Toll-like receptors and their signaling pathways in psoriasis

INTRODUCTION

Expression of various Toll-like receptors (TLR) in keratinocytes (KCs) has offered new insights into the pathogenesis of psoriasis. When plasmacytoid dendritic cells (pDCs) are scarce in established psoriatic lesions, KCs take the responsibility to secrete IFN type 1 through TLR9 activation. Antagonists of TLR7 and TLR8 and anti-IL-12/IL-23 substances have shown promising results in treating psoriasis. Areas covered: References in this study were extracted from Scopus, PubMed and Embase databases by the search term: ('Toll-Like Receptors' OR 'TLR') AND ('Psoriasis' OR 'Arthritis, Psoriatic' OR 'PsA'). Expert commentary: As the prevailing cell type, KCs play a major role in the maintenance of psoriatic lesions. By specific upregulation of IL-36 R, KCs can start the IL-23/IL-12 axis, leading to production of major culprits of psoriatic phenotype IL-17 and IL-22. Targeting IL-36 R could be considered as a new therapeutic target to eliminate cutaneous manifestations of psoriasis.

Low expression of Toll-like receptors in peripheral blood mononuclear cells of pediatric patients with acute lymphoblastic leukemia

Cancer is the second most common cause of death among children aged 1-14 years. Leukemia accounts for one-third of all childhood cancers, 78% of which is acute lymphoblastic leukemia (ALL). The development of cancer has been associated with malignant cells that express low levels of immunogenic molecules, which facilitates their escape from the antineoplastic immune response. It is thought that it may be possible to rescue the antineoplastic immune response through the activation of recognition receptors, such as Toll-like receptors (TLRs), which activate the innate immune system. TLRs are type I membrane glycoproteins expressed mainly in immune system cells such as monocytes, neutrophils, macrophages, dendritic cells, T, B and natural killer cells. The aim of the present study was to evaluate the expression of TLR1, TLR3, TLR4, TLR7 and TLR9 in peripheral blood mononuclear cells (PBMCs) in patients with ALL and prior to any treatment. PBMCs were obtained from 50 pediatric patients diagnosed with ALL and from 20 children attending the ophthalmology and orthopedics services. The mean fluorescence intensity was obtained by analysis of immunofluorescence. We found lower expression levels of TLR1, TLR3, TLR4, TLR7 and TLR9 in PBMCs from patients with ALL compared with those from control patients. We also observed that the PBMCs from patients with Pre-B and B ALL had lower TLR4 expression than controls and patients with Pro-B, Pre-B, B and T ALL had lower TLR7 expression than controls. The present study is the first to demonstrate reduced expression of TLRs in PBMCs from pediatric patients with ALL. This finding is of great relevance and may partly explain the reduction in the antineoplastic immune response in patients with ALL.

Targeting immune checkpoints in lymphoma

PURPOSE OF REVIEW

The purpose of this article is to discuss the tumor microenvironment in lymphoma, and to review potential immune targets that are now becoming relevant because of clinical responses seen with the use of immune checkpoint inhibitors.

RECENT FINDINGS

Recent data have shown that cells within the immune microenvironment in lymphoma express programmed death ligand-1 (PD-L1) and many of the intratumoral T cells with an exhausted immune phenotype express programmed cell death-1 (PD-1). This provides a novel opportunity to inhibit the immune checkpoints and initial clinical trials utilizing antibodies that block the interaction between PD-1 and PD-L1 have demonstrated significant clinical responses in various lymphomas, including Hodgkin lymphoma.

SUMMARY

The use of immune checkpoint inhibitors, including nivolumab and pembrolizumab, in relapsed and refractory patients with lymphoma is proving highly successful. Patients with Hodgkin lymphoma, in particular, have a very high response rate to PD-1 blockade and responses in these patients appear durable.

The role of toll-like receptors in B-cell development and immunopathogenesis of common variable immunodeficiency

Common variable immunodeficiency (CVID) is the most frequent symptomatic primary immune deficiency and is characterized by hypogammaglobulinemia, defect in specific antibody response and increased susceptibility to recurrent infections, malignancy and autoimmunity. Patients with CVID often have defects in post-antigenic B-cell differentiation, with fewer memory B cells and impaired isotype switching. Toll-like receptors (TLRs) are expressed on various immune cells as key elements of innate and adaptive immunity. TLR signaling in B cells plays multiple roles in cell differentiation and activation, class-switch recombination and cytokine and antibody production. Moreover, recent studies have shown functional alteration of TLRs responses in CVID patients including poor cell proliferation, impaired upregulation of co-stimulatory molecules and failure in cytokine and immunoglobulin production. The purpose of the present review is to discuss the role of TLRs in B-cell development and function as well as their role in the immunopathogenesis of CVID.

Toll-like receptor stimulation in splenic marginal zone lymphoma can modulate cell signaling, activation and proliferation

Recent studies on splenic marginal zone lymphoma identified distinct mutations in genes belonging to the B-cell receptor and Toll-like receptor signaling pathways, thus pointing to their potential implication in the biology of the disease. However, limited data is available regarding the exact role of TLRs. We aimed at characterizing the expression pattern of TLRs in splenic marginal zone lymphoma cells and their functional impact on the activation, proliferation and viability of malignant cells in vitro. Cells expressed significant levels of TLR1, TLR6, TLR7, TLR8, TLR9 and TLR10 mRNA; TLR2 and TLR4 showed a low, variable pattern of expression among patients whereas TLR3 and TLR5 mRNAs were undetectable; mRNA specific for TLR signaling molecules and adapters was also expressed. At the protein level, TLR1, TLR6, TLR7, TLR9 and TLR10 were detected. Stimulation of TLR1/2, TLR2/6 and TLR9 with their respective ligands triggered the activation of IRAK kinases, MAPK and NF-κB signaling pathways, and the induction of CD86 and CD25 activation molecules, although in a heterogeneous manner among different patient samples. TLR-induced activation and cell viability were also inhibited by a specific IRAK1/4 inhibitor, thus strongly supporting the specific role of TLR signaling in these processes. Furthermore, TLR2/6 and TLR9 stimulation also significantly increased cell proliferation. In conclusion, we demonstrate that splenic marginal zone lymphoma cells are equipped with functional TLR and signaling molecules and that the stimulation of TLR1/2, TLR2/6 and TLR9 may play a role in regulating disease pathobiology, likely promoting the expansion of the neoplastic clone.

Innate adjuvant receptor Toll-like receptor 3 can promote breast cancer through cell surface

Toll-like receptor 3 has been targeted in different cancers for adjuvant therapy. The ligand-mediated effects of TLR-3 on cancer cells are discordant. In the present work, we have addressed the hypothesis possibility of cell membrane-bound action of TLR-3 in breast cancer to justify its pro-tumor effect. TLR-3 was stimulated by Poly (I:C) on the surface of human breast cancer cells MCF-7 and MDA-MB-231 for up to 72 h. To check the cell survival and growth, thiazol blue tetrazolium bromide (MTT) assay, apoptosis assay, and cell cycle analysis were carried out. For changes in the metastatic properties, in vitro colony formation assay, scratch-wound healing assay and adhesion assay were also done. Using real-time PCR and immunocytochemistry, expression of E-cadherin, was studied. To determine the affect of cytoplasmic stimulation, Poly (I:C) was delivered with lipid transfection reagent. The results of the aforesaid experiments showed that there was a gradual increase of cellular survivability, growth, and metastasis after the cell surface stimulation of TLR-3 with Poly (I:C). Interestingly, E-cadherin expression was increased both at transcriptional and translational level. On the other hand, when Poly (I:C) was delivered in the cytoplasm by lipid transfecting medium, the cells survivability was decreased. For the first time, in the present work, we are convincingly reporting the functional evidence that TLR-3 induces cell survivability and metastasis through cell surface. The present work may help for the proper understanding of the adjuvant therapy of breast cancer.

Epigenetically modulated LRRC33 acts as a negative physiological regulator for multiple Toll-like receptors

The members of a LRR family play crucial roles in the activation of innate and adaptive immune responses. We reported previously that LRRC33, a transmembrane protein of the LRR family, might potentially affect TLR-mediated activity. Here, we demonstrate that LRRC33 is a negative physiological regulator for multiple TLRs. Lrrc33(-/-) and Lrrc33(+/-) mice were more susceptible to TLR ligand challenges. The macrophages and DCs from Lrrc33(-/-) mice produced more proinflammatory cytokines than those of WT mice through increased activation of MAPK and NF-κB. Silencing LRRC33 also promoted multiple TLR-mediated activation in human moDCs. Notably, LRRC33 expression could be down-regulated by TLR ligands LPS, poly I:C, or PGN through H3K4me3 and H3K27me3 modification. In LPS-conditioned moDCs, reduced enrichment of H3K4me3 and increased H3K27me3 could be observed at the promoter region of LRRC33. Furthermore, silencing H3K4me3-associated factors MLL and RBBP5 not only decreased the enrichment of H3K4me3 but also down-regulated expression of LRRC33, whereas the expression of LRRC33 was up-regulated after silencing H3K27me3-associated factors EZH2 and EED. Thus, our results suggest that LRRC33 and TLRs may form a negative-feedback loop, which is important for the maintenance of immune homeostasis.