Conservation and Divergence of Ligand Recognition and Signal Transduction Mechanisms in Toll-Like Receptors

Association of TLR8 Variants in Sex-Based Clinical Differences in Patients with COVID-19

The host immune response might confer differential vulnerability to SARS-CoV-2 infection. The Toll-like receptor 8 (TLR8), could participated for severe COVID-19 outcomes. To investigated the relationship of TLR8 rs3764879-C/G, rs3764880-A/G, and rs3761624-A/G with COVID-19 outcomes and with biochemical parameters. A cross-sectional study of 830 laboratory-confirmed COVID-19 patients was performed, and classified into mild, severe, critical, and deceased outcomes. The TLR8 rs3764879-C/G, rs3764880-A/G, and rs3761624-A/G polymorphisms were genotyped. A logistic regression analysis was performed to determinate the association with COVID-19. A stratified analysis was by alleles was done with clinical and metabolic markets. In all outcomes, men presented the highest ferritin levels compared to women (P < 0.001). LDH levels were significantly different between sex in mild (P = 0.003), severe (P < 0.001) and deceased (P = 0.01) COVID-19 outcomes. The GGG haplotype showed an Odds Ratio of 1.55 (Interval Confidence 95% 1.05-2.32; P = 0.03) in men. Among patients with severe outcome, we observed that the carriers of the GGG haplotype had lower Ferritin, C-reactive protein and LDH levels than the CAA carriers (P < 0.01). After further stratified by sex, these associations were also seen in the male patients, except for D-dimer. Interestingly, among men patients, we could observe associations between TLR8 haplotypes and Ferritin (P < 0.001), D-dimer (P = 0.04), C-reactive protein, and Lactate dehydrogenase in mild (P = 0.04) group. Our results suggest that even though TLR8 haplotypes show a significant association with COVID-19 outcomes, they are associated with clinical markers in COVID-19 severity.

Cryo-electron Microscopic Analysis of Single-Pass Transmembrane Receptors

Single-pass transmembrane receptors (SPTMRs) represent a diverse group of integral membrane proteins that are involved in many essential cellular processes, including signal transduction, cell adhesion, and transmembrane transport of materials. Dysregulation of the SPTMRs is linked with many human diseases. Despite extensive efforts in past decades, the mechanisms of action of the SPTMRs remain incompletely understood. One major hurdle is the lack of structures of the full-length SPTMRs in different functional states. Such structural information is difficult to obtain by traditional structural biology methods such as X-ray crystallography and nuclear magnetic resonance (NMR). The recent rapid development of single-particle cryo-electron microscopy (cryo-EM) has led to an exponential surge in the number of high-resolution structures of integral membrane proteins, including SPTMRs. Cryo-EM structures of SPTMRs solved in the past few years have tremendously improved our understanding of how SPTMRs function. In this review, we will highlight these progresses in the structural studies of SPTMRs by single-particle cryo-EM, analyze important structural details of each protein involved, and discuss their implications on the underlying mechanisms. Finally, we also briefly discuss remaining challenges and exciting opportunities in the field.

The Association Between Gut Microbiota, Toll-Like Receptors, and Colorectal Cancer

The large number of microbes found in the gut are involved in various critical biological processes in the human body and have dynamic and complex interactions with the immune system. Disruptions in the host’s gut microbiota and the metabolites produced during fermentation promote the development of intestinal inflammation and colorectal cancer (CRC). Toll-like receptors (TLRs) recognize specific microbial-associated molecular patterns specific to microorganisms whose signaling is involved in maintaining intestinal homeostasis or, under certain conditions, mediating dysbiosis-associated intestinal inflammation. The signaling pathways of TLRs are described first, followed by a discussion of the interrelationship between gut microbes and TLRs, including the activation of TLRs by gut microbes and the effect of TLRs on the distribution of gut microbiota, particularly the role of microbes in colorectal carcinogenesis via TLRs. Finally, we discuss the potential roles of various TLRs in colorectal cancer.

Molecular Mechanisms of the Toll-Like Receptor, STING, MAVS, Inflammasome, and Interferon Pathways

Pattern recognition receptors (PRRs) form the front line of defense against pathogens. Many of the molecular mechanisms that facilitate PRR signaling have been characterized in detail, which is critical for the development of accurate PRR pathway models at the molecular interaction level. These models could support the development of therapeutics for numerous diseases, including sepsis and COVID-19. This review describes the molecular mechanisms of the principal signaling interactions of the Toll-like receptor, STING, MAVS, and inflammasome pathways. A detailed molecular mechanism network is included as Data Set S1 in the supplemental material.

Thymic stromal lymphopoietin participates in the TLR2-and TLR4-dependent immune response triggered by Aspergillus fumigatus in human corneal cells

Fungal keratitis constitutes a serious vision-threatening disease. Toll-like receptors (TLRs) comprise key mediators of innate immunity triggered by Aspergillus fumigatus (AF) in the cornea, but the messenger between innate and adaptive immunity remained unknown. Thymic stromal lymphopoietin (TSLP) represents a critical factor of adaptive immunity. Here we investigated the expression of TSLP in corneal epithelial and stromal cells challenged by AF and its relationship with TLRs. We stimulated corneal cells with TLR ligands zymosan or lipopolysaccharide (LPS), human recombinant TSLP, or AF hyphae for various periods, with or without prior TLR2, TLR4, or TSLP inhibition. TLR2, TLR4, TSLP, IL-8, and TNF-α release and expression were measured via enzyme-linked immunosorbent analysis, quantitative polymerase chain reaction, or western blot. Corneal cell stimulation with zymosan or LPS induced up-regulated TSLP expression. Enhanced TSLP expression was associated with AF treatment in human corneal cells; TLR2 or TLR4 inhibition impaired the AF-induced TSLP levels. Human recombinant TSLP augmented TLR2 and TLR4 expression; RNA interference of TSLP attenuated TLR, IL-8, and TNF-α expression stimulated by AF hyphae. These findings indicated that TSLP participates in the immune response of corneal cells triggered by AF, which is closely related to TLR function, and the innate immunity mediated by TLRs could be enhanced by TSLP. Innate immunity may therefore transmit inflammatory signals to adaptive immunity through activation of TSLP; in turn, adaptive immunity likely exerts certain regulatory effects on innate immunity via TSLP. That is, TSLP could interact with innate immunity mediated by TLR2 and TLR4 in human corneal cells challenged by AF and thus may serve as a messenger between the innate and adaptive immune responses in AF keratitis.

Cryo-EM structures of Toll-like receptors in complex with UNC93B1

Nucleic acid-sensing Toll-like receptors (TLRs) play a pivotal role in innate immunity by recognizing foreign DNA and RNA. Compartmentalization of these TLRs in the endosome limits their activation by self-derived nucleic acids and reduces the possibility of autoimmune reactions. Although chaperone Unc-93 homolog B1, TLR signaling regulator (UNC93B1) is indispensable for the trafficking of TLRs from the endoplasmic reticulum to the endosome, mechanisms of UNC93B1-mediated TLR regulation remain largely unknown. Here, we report two cryo-EM structures of human and mouse TLR3-UNC93B1 complexes and a human TLR7-UNC93B1 complex. UNC93B1 exhibits structural similarity to the major facilitator superfamily transporters. Both TLRs interact with the UNC93B1 amino-terminal six-helix bundle through their transmembrane and luminal juxtamembrane regions, but the complexes of TLR3 and TLR7 with UNC93B1 differ in their oligomerization state. The structural information provided here should aid in designing compounds to combat autoimmune diseases.

Isorhamnetin Has Potential for the Treatment of Escherichia coli-Induced Sepsis

Isorhamnetin is a flavonoid that is abundant in the fruit of Hippophae rhamnoides L. It is widely studied for its ability to modulate inflammatory responses. In this study, we evaluated the potential of isorhamnetin to prevent gram-negative sepsis. We investigated its efficacy using an Escherichia coli-induced sepsis model. Our study reveals that isorhamnetin treatment significantly enhances survival and reduces proinflammatory cytokine levels in the serum and lung tissue of E. coli-infected mice. Further, isorhamnetin treatment also significantly reduces the levels of aspartate aminotransferase, alanine amino transferase and blood urea nitrogen, suggesting that it can improve liver and kidney function in infected mice. Docking studies reveal that isorhamnetin binds deep in the hydrophobic binding pocket of MD-2 via extensive hydrophobic interactions and hydrogen bonding with Tyr102, preventing TLR4/MD-2 dimerization. Notably, binding and secreted alkaline phosphatase reporter gene assays show that isorhamnetin can interact directly with the TLR4/MD-2 complex, thus inhibiting the TLR4 cascade, which eventually causes systemic inflammation, resulting in death due to cytokine storms. We therefore presume that isorhamnetin could be a suitable therapeutic candidate to treat bacterial sepsis.

Associations between genetic polymorphisms of TLRs and susceptibility to tuberculosis: A meta-analysis

Some genetic association studies have tried to investigate potential associations between TLR polymorphisms and tuberculosis. However, the results of these studies have not been consistent. Thus, we performed the present meta-analysis to explore associations between TLR polymorphisms and tuberculosis in a larger combined population. A systematic literature research of PubMed, Web of Science and Embase was performed to identify eligible studies for combined analyses. I² statistics were employed to assess between-study heterogeneities. If I² was >50%, random-effects models were used to combine the data. Otherwise, fixed-effects models were applied for synthetic analyses. A total of 39 genetic association studies were included in the analyses. The combined analyses showed that TLR1 rs4833095, TLR1 rs5743557, TLR1 rs5743596, TLR2 rs3804099, TLR2 rs5743704, TLR2 rs5743708, TLR6 rs5743810 and TLR8 rs3764879 polymorphisms were significantly associated with susceptibility to TB in the overall population. Further subgroup analyses revealed similar significant findings for TLR1 rs4833095, TLR1 rs5743557, TLR1 rs5743596, TLR1 rs5743618, TLR2 rs3804099, TLR2 rs5743704, TLR2 rs5743708, TLR4 rs4986790 and TLR4 rs4986791 polymorphisms in certain ethnicities. In conclusion, our findings support that these TLR polymorphisms may be used to identify individuals at high risk of developing tuberculosis.

Roles of Host Immunity in Viral Myocarditis and Dilated Cardiomyopathy

The pathogenesis of viral myocarditis includes both the direct damage mediated by viral infection and the indirect lesion resulted from host immune responses. Myocarditis can progress into dilated cardiomyopathy that is also associated with immunopathogenesis. T cell-mediated autoimmunity, antibody-mediated autoimmunity (autoantibodies), and innate immunity, working together, contribute to the development of myocarditis and dilated cardiomyopathy.

Viruses Seen by Our Cells: The Role of Viral RNA Sensors

The role of the innate immune response in detecting RNA viruses is crucial for the establishment of proper inflammatory and antiviral responses. Different receptors, known as pattern recognition receptors (PRRs), are present in the cytoplasm, endosomes, and on the cellular surface. These receptors have the capacity to sense the presence of viral nucleic acids as pathogen-associated molecular patterns (PAMPs). This recognition leads to the induction of type 1 interferons (IFNs) as well as inflammatory cytokines and chemokines. In this review, we provide an overview of the significant involvement of cellular RNA helicases and Toll-like receptors (TLRs) 3, 7, and 8 in antiviral immune defenses.