Toll-like receptors and Streptococcus mutans: An updated review article

It has been reported that toll-like receptors (TLRs) are the main innate immune receptors that recognize gram-positive pathogen-associated molecular patterns (PAMPs). The molecules can induce expression of the innate immune-related molecules that are essential against the bacteria. Streptococcus mutans (S. mutans) is a potential caries-associated pathogen, and innate immunity plays a key role in inhibiting its development and the progression of inflammatory responses. Recently, the roles played by TLRs against S. mutans and the induction of inflammatory responses were evaluated by several investigations. This review article discusses updated information regarding the roles played by TLRs and their potential therapeutic effects against S. mutans (AU)

Influenza vaccination reveals sex dimorphic imprints of prior mild COVID-19.

Acute viral infections can have durable functional impacts on the immune system long after recovery, but how they affect homeostatic immune states and responses to future perturbations remain poorly understood1-4. Here we use systems immunology approaches, including longitudinal multimodal single-cell analysis (surface proteins, transcriptome and V(D)J sequences) to comparatively assess baseline immune statuses and responses to influenza vaccination in 33 healthy individuals after recovery from mild, non-hospitalized COVID-19 (mean, 151 days after diagnosis) and 40 age- and sex-matched control individuals who had never had COVID-19. At the baseline and independent of time after COVID-19, recoverees had elevated T cell activation signatures and lower expression of innate immune genes including Toll-like receptors in monocytes. Male individuals who had recovered from COVID-19 had coordinately higher innate, influenza-specific plasmablast, and antibody responses after vaccination compared with healthy male individuals and female individuals who had recovered from COVID-19, in part because male recoverees had monocytes with higher IL-15 responses early after vaccination coupled with elevated prevaccination frequencies of 'virtual memory'-like CD8+ T cells poised to produce more IFNγ after IL-15 stimulation. Moreover, the expression of the repressed innate immune genes in monocytes increased by day 1 to day 28 after vaccination in recoverees, therefore moving towards the prevaccination baseline of the healthy control individuals. By contrast, these genes decreased on day 1 and returned to the baseline by day 28 in the control individuals. Our study reveals sex-dimorphic effects of previous mild COVID-19 and suggests that viral infections in humans can establish new immunological set-points that affect future immune responses in an antigen-agnostic manner.

Design of a multi-epitope Zika virus vaccine candidate - an in-silico study.

Zika virus (ZIKV), an RNA virus, rapidly spreads Aedes mosquito-borne sickness. Currently, there are neither effective vaccines nor therapeutics available to prevent or treat ZIKV infection. In this study, to address these unmet medical needs, we aimed to design B- and T-cell candidate multi-epitope-based subunit against ZIKV using an in silico approach. In this study we applied immunoinformatics, molecular docking, and dynamic simulation assessments targeting the most immunogenic proteins; the capsid (C), envelope (E) proteins and the non-stuctural protein (NS1), described in our previous study, and which predicted immunodominant B and T cell epitopes. The final non-allergenic and highly antigenic multi-epitope was constituted of immunogenic screened-epitopes (3 CTL and 3 HTL) and the ß-defensin as an adjuvant that have been linked using EAAAK, AAY, and GPGPG linkers, respectively. The final construct containing 143 amino acids was characterized for its allergenicity, antigenicity, and physiochemical properties; and found to be safe and immunogenic with a good prediction of solubility. The existence of IFN-γ epitopes asserts the capacity to trigger strong immune responses. Subsequently, the molecular docking among vaccine and immune receptors (TLR2/TLR4) was revealed with a good binding affinity with and stable molecular interactions. Molecular dynamics simulation confirmed the stability of the complexes. Finally, the construct was subjected to in silico cloning demonstrating the efficiently of its expression in E.coli. However, this study needs the experimental validation to demonstrate vaccine safety and efficacy.Communicated by Ramaswamy H. Sarma.

Cyclic nucleotide-induced helical structure activates a TIR immune effector.

Cyclic nucleotide signalling is a key component of antiviral defence in all domains of life. Viral detection activates a nucleotide cyclase to generate a second messenger, resulting in activation of effector proteins. This is exemplified by the metazoan cGAS-STING innate immunity pathway1, which originated in bacteria2. These defence systems require a sensor domain to bind the cyclic nucleotide and are often coupled with an effector domain that, when activated, causes cell death by destroying essential biomolecules3. One example is the Toll/interleukin-1 receptor (TIR) domain, which degrades the essential cofactor NAD+ when activated in response to infection in plants and bacteria2,4,5 or during programmed nerve cell death6. Here we show that a bacterial antiviral defence system generates a cyclic tri-adenylate that binds to a TIR-SAVED effector, acting as the 'glue' to allow assembly of an extended superhelical solenoid structure. Adjacent TIR subunits interact to organize and complete a composite active site, allowing NAD+ degradation. Activation requires extended filament formation, both in vitro and in vivo. Our study highlights an example of large-scale molecular assembly controlled by cyclic nucleotides and reveals key details of the mechanism of TIR enzyme activation.

Toll-like receptor-mediated innate immunity orchestrates adaptive immune responses in HBV infection.

Chronic hepatitis B virus (HBV) infection remains to be a substantial global burden, especially for end-stage liver diseases. It is well accepted that HBV-specific T and B cells are essential for controlling HBV infection. Toll-like receptors (TLRs) represent one of the major first-line antiviral defenses through intracellular signaling pathways that induce antiviral inflammatory cytokines and interferons, thereby shaping adaptive immunity. However, HBV has evolved strategies to counter TLR responses by suppressing the expression of TLRs and blocking the downstream signaling pathways, thus limiting HBV-specific adaptive immunity and facilitating viral persistence. Recent studies have stated that stimulation of the TLR signaling pathway by different TLR agonists strengthens host innate immune responses and results in suppression of HBV replication. In this review, we will discuss how TLR-mediated responses shape HBV-specific adaptive immunity as demonstrated in different experimental models. This information may provide important insight for HBV functional cure based on TLR agonists as immunomodulators.

Cryo-EM structure of an active bacterial TIR-STING filament complex.

Stimulator of interferon genes (STING) is an antiviral signalling protein that is broadly conserved in both innate immunity in animals and phage defence in prokaryotes1-4. Activation of STING requires its assembly into an oligomeric filament structure through binding of a cyclic dinucleotide4-13, but the molecular basis of STING filament assembly and extension remains unknown. Here we use cryogenic electron microscopy to determine the structure of the active Toll/interleukin-1 receptor (TIR)-STING filament complex from a Sphingobacterium faecium cyclic-oligonucleotide-based antiphage signalling system (CBASS) defence operon. Bacterial TIR-STING filament formation is driven by STING interfaces that become exposed on high-affinity recognition of the cognate cyclic dinucleotide signal c-di-GMP. Repeating dimeric STING units stack laterally head-to-head through surface interfaces, which are also essential for human STING tetramer formation and downstream immune signalling in mammals5. The active bacterial TIR-STING structure reveals further cross-filament contacts that brace the assembly and coordinate packing of the associated TIR NADase effector domains at the base of the filament to drive NAD+ hydrolysis. STING interface and cross-filament contacts are essential for cell growth arrest in vivo and reveal a stepwise mechanism of activation whereby STING filament assembly is required for subsequent effector activation. Our results define the structural basis of STING filament formation in prokaryotic antiviral signalling.

Standardized Whole Blood Assay and Bead-Based Cytokine Profiling Reveal Commonalities and Diversity of the Response to Bacteria and TLR Ligands in Cattle.

Recent developments in multiplex technologies enable the determination of a large nu\mber of soluble proteins such as cytokines in various biological samples. More than a one-by-one determination of the concentration of immune mediators, they permit the establishment of secretion profiles for a more accurate description of conditions related to infectious diseases or vaccination. Cytokine profiling has recently been made available for bovine species with the development of a Luminex® technology-based 15-plex assay. Independently from the manufacturer, we evaluated the bovine cytokine/chemokine multiplex assay for limits of detection, recovery rate, and reproducibility. Furthermore, we assessed cytokine secretion in blood samples from 107 cows upon stimulation with heat-killed bacteria and TLR2/4 ligands compared to a null condition. Secretion patterns were analyzed either using the absolute concentration of cytokines or using their relative concentration with respect to the overall secretion level induced by each stimulus. Using Partial Least Square-Discriminant Analysis, we show that the 15-cytokine profile is different under Escherichia coli, Staphylococcus aureus, and Streptococcus uberis conditions, and that IFN-γ, IL-1ß, and TNF-α contribute the most to differentiate these conditions. LPS and E. coli induced largely overlapping biological responses, but S. aureus and S. uberis were associated with distinct cytokine profiles than their respective TLR ligands. Finally, results based on adjusted or absolute cytokine levels yielded similar discriminative power, but led to different stimuli-related signatures.

Innate Immune Response to Dengue Virus: Toll-like Receptors and Antiviral Response.

Dengue is a mosquito-borne viral disease caused by the dengue virus (DENV1-4). The clinical manifestations range from asymptomatic to life-threatening dengue hemorrhagic fever (DHF) and/or Dengue Shock Syndrome (DSS). Viral and host factors are related to the clinical outcome of dengue, although the disease pathogenesis remains uncertain. The innate antiviral response to DENV is implemented by a variety of immune cells and inflammatory mediators. Blood monocytes, dendritic cells (DCs) and tissue macrophages are the main target cells of DENV infection. These cells recognize pathogen-associated molecular patterns (PAMPs) through pattern recognition receptors (PRRs). Pathogen recognition is a critical step in eliciting the innate immune response. Toll-like receptors (TLRs) are responsible for the innate recognition of pathogens and represent an essential component of the innate and adaptive immune response. Ten different TLRs are described in humans, which are expressed in many different immune cells. The engagement of TLRs with viral PAMPs triggers downstream signaling pathways leading to the production of inflammatory cytokines, interferons (IFNs) and other molecules essential for the prevention of viral replication. Here, we summarize the crucial TLRs' roles in the antiviral innate immune response to DENV and their association with viral pathogenesis.

Chemokines form nanoparticles with DNA and can superinduce TLR-driven immune inflammation.

Chemokines control the migratory patterns and positioning of immune cells to organize immune responses to pathogens. However, many chemokines have been associated with systemic autoimmune diseases that have chronic IFN signatures. We report that a series of chemokines, including CXCL4, CXCL10, CXCL12, and CCL5, can superinduce type I IFN (IFN-I) by TLR9-activated plasmacytoid DCs (pDCs), independently of their respective known chemokine receptors. Mechanistically, we show that chemokines such as CXCL4 mediate transcriptional and epigenetic changes in pDCs, mostly targeted to the IFN-I pathways. We describe that chemokines physically interact with DNA to form nanoparticles that promote clathrin-mediated cellular uptake and delivery of DNA in the early endosomes of pDCs. Using two separate mouse models of skin inflammation, we observed the presence of CXCL4 associated with DNA in vivo. These data reveal a noncanonical role for chemokines to serve as nucleic acid delivery vectors to modulate TLR signaling, with implications for the chronic presence of IFN-I by pDCs in autoimmune diseases.

Fish-specific Toll-like receptor 14 (TLR14) from Asian swamp eel (Monopterus albus) is involved in immune response to bacterial infection.

Toll-like receptors (TLRs) are a class of pattern recognition receptors (PRRs) that play a critical role in innate immune responses against pathogens. In the present study, a fish-specific TLR14 was identified and characterized from Monopterus albus (named MaTLR14), which consisted of a 2658 bp open reading frame encoding a protein of 885 amino acids. Phylogenetic analysis revealed that MaTLR14 belong to the TLR1 subfamily and shared the highest similarity to Paralichthys olivaceus TLR14. Immunohistochemistry assay showed that MaTLR14 mainly located in intestinal epithelial cells of hindgut. Immunofluorescence revealed that MaTLR14 largely localized to the intracellular region and partially co-localized with cell membrane of HeLa cells. The expression levels of MaTLR14 were upregulated in the liver, spleen, foregut and hindgut post infection with Aeromonas hydrophila. When stimulated with LPS and Flagellin, the MaTLR14 expression was elevated in isolated peripheral blood leukocytes. Further studies showed that recombinant MaTLR14-LRR could bind to both the gram-negative and gram-positive bacteria and cause agglutination. Subsequently, the signaling pathway of MaTLR14 was investigated. Confocal microscopy and co-immunoprecipitation assay demonstrated that MaTLR14 recruited MyD88 as adaptor. When overexpressed, MaTLR14 augmented the expression of TRAF6 and phosphorylation of ERK and p65, activated NF-κB and AP-1 and elicited the expression of il-6 and tnf-α. Collectively, MaTLR14 plays an important role in the microorganism recognition and signaling transduction.

Innate immunity: the first line of defense against SARS-CoV-2.

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus (SARS-CoV)-2, continues to cause substantial morbidity and mortality. While most infections are mild, some patients experience severe and potentially fatal systemic inflammation, tissue damage, cytokine storm and acute respiratory distress syndrome. The innate immune system acts as the first line of defense, sensing the virus through pattern recognition receptors and activating inflammatory pathways that promote viral clearance. Here, we discuss innate immune processes involved in SARS-CoV-2 recognition and the resultant inflammation. Improved understanding of how the innate immune system detects and responds to SARS-CoV-2 will help identify targeted therapeutic modalities that mitigate severe disease and improve patient outcomes.

Innate Immune Responses of Vaccinees Determine Early Neutralizing Antibody Production After ChAdOx1nCoV-19 Vaccination.

Background: Innate immunity, armed with pattern recognition receptors including Toll-like receptors (TLR), is critical for immune cell activation and the connection to anti-microbial adaptive immunity. However, information regarding the impact of age on the innate immunity in response to SARS-CoV2 adenovirus vector vaccines and its association with specific immune responses remains scarce. Methods: Fifteen subjects between 25-35 years (the young group) and five subjects between 60-70 years (the older adult group) were enrolled before ChAdOx1 nCoV-19 (AZD1222) vaccination. We determined activation markers and cytokine production of monocyte, natural killer (NK) cells and B cells ex vivo stimulated with TLR agonist (poly (I:C) for TLR3; LPS for TLR4; imiquimod for TLR7; CpG for TLR9) before vaccination and 3-5 days after each jab with flow cytometry. Anti-SARS-CoV2 neutralization antibody titers (surrogate virus neutralization tests, sVNTs) were measured using serum collected 2 months after the first jab and one month after full vaccination. Results: The older adult vaccinees had weaker vaccine-induced sVNTs than young vaccinees after 1st jab (47.2±19.3% vs. 21.2±22.2%, p value<0.05), but this difference became insignificant after the 2nd jab. Imiquimod, LPS and CpG strongly induced CD86 expression in IgD+CD27- naïve and IgD-CD27+ memory B cells in the young group. In contrast, only the IgD+ CD27- naïve B cells responded to these TLR agonists in the older adult group. Imiquimode strongly induced the CD86 expression in CD14+ monocytes in the young group but not in the older adult group. After vaccination, the young group had significantly higher IFN-γ expression in CD3- CD56dim NK cells after the 1st jab, whilst the older adult group had significantly higher IFN-γ and granzyme B expression in CD56bright NK cells after the 2nd jab (all p value <0.05). The IFN-γ expression in CD56dim and CD56bright NK cells after the first vaccination and CD86 expression in CD14+ monocyte and IgD-CD27-double-negative B cells after LPS and imiquimod stimulation correlated with vaccine-induced antibody responses. Conclusions: The innate immune responses after the first vaccination correlated with the neutralizing antibody production. Older people may have defective innate immune responses by TLR stimulation and weak or delayed innate immune activation profile after vaccination compared with young people.

Antiviral Toll-like Receptor Signaling in Non-Parenchymal Liver Cells Is Restricted to TLR3.

The role of non-parenchymal liver cells as part of the hepatic, innate immune system in the defense against hepatotropic viruses is not well understood. Here, primary human Kupffer cells, liver sinusoidal endothelial cells and hepatic stellate cells were isolated from liver tissue obtained after tumor resections or liver transplantations. Cells were stimulated with Toll-like receptor 1-9 ligands for 6-24 h. Non-parenchymal liver cells expressed and secreted inflammatory cytokines (IL6, TNF and IL10). Toll-like receptor- and cell type-specific downstream signals included the phosphorylation of NF-κB, AKT, JNK, p38 and ERK1/2. However, only supernatants of TLR3-activated Kupffer cells, liver sinusoidal endothelial cells and hepatic stellate cells contained type I and type III interferons and mediated an antiviral activity in the interferon-sensitive subgenomic hepatitis C virus replicon system. The antiviral effect could not be neutralized by antibodies against IFNA, IFNB nor IFNL, but could be abrogated using an interferon alpha receptor 2-specific neutralization. Interestingly, TLR3 responsiveness was enhanced in liver sinusoidal endothelial cells isolated from hepatitis C virus-positive donors, compared to uninfected controls. In conclusion, non-parenchymal liver cells are potent activators of the hepatic immune system by mediating inflammatory responses. Furthermore, liver sinusoidal endothelial cells were identified to be hyperresponsive to viral stimuli in chronic hepatitis C virus infection.

Train the Trainer: Hematopoietic Stem Cell Control of Trained Immunity.

Recent evidence shows that innate immune cells, in addition to B and T cells, can retain immunological memory of their encounters and afford long-term resistance against infections in a process known as 'trained immunity'. However, the duration of the unspecific protection observed in vivo is poorly compatible with the average lifespan of innate immune cells, suggesting the involvement of long-lived cells. Accordingly, recent studies demonstrate that hematopoietic stem and progenitor cells (HSPCs) lay at the foundation of trained immunity, retaining immunological memory of infections and giving rise to a "trained" myeloid progeny for a long time. In this review, we discuss the research demonstrating the involvement of HSPCs in the onset of long-lasting trained immunity. We highlight the roles of specific cytokines and Toll-like receptor ligands in influencing HSPC memory phenotypes and the molecular mechanisms underlying trained immunity HSPCs. Finally, we discuss the potential benefits and drawbacks of the long-lasting trained immune responses, and describe the challenges that the field is facing.

Differential Effects of Toll-Like Receptor Signaling on the Activation of Immune Responses in the Upper Respiratory Tract.

Vaccination through the upper respiratory tract (URT) is highly effective for the prevention of respiratory infectious diseases. Toll-like receptor (TLR)-based adjuvants are immunostimulatory and considered potential adjuvant candidates. However, the patterns of immune response to different TLRs at the URT have not been revealed. In this study, SPF mice were preexposed to TLR agonists intranasally to simulate the status of humans. Inflammatory response to TLR agonists and TLR signal-mediated adaptive immune responses were analyzed. The results revealed that similar to human tonsils, inflammatory response to stimulation with TLR4 or TLR2 agonist was attenuated in agonist-exposed mice but not in mice without this exposure. In contrast, TLR9 or TLR3 agonist preexposure did not affect the inflammatory response to restimulation by matching agonists. For the adaptive immune response, after agonist preexposure the antibody response to antigens adjuvanted with TLR4 or TLR2 agonist was substantially restricted, whereas, both antibody and T cell responses to antigens adjuvanted with TLR9 or TLR3 agonist were activated as robustly as in mice without agonist exposure. Moreover, we demonstrate that the mechanisms underlying the differential activation of TLRs are regulated at the level of TLR expression in innate and adaptive immune cells. These results indicate that TLRs on the cell surface (TLR4 and 2) and in the endolysosomal compartments (TLR9 and 3) display distinct immune response patterns. The findings provide important information for the use of TLR agonists as mucosal adjuvants and enhance our understanding of immune responses to bacterial and viral infections in the respiratory mucosa. IMPORTANCE Agonists of TLRs are potential adjuvant candidates for mucosal vaccination. We demonstrated that the TLR-mediated inflammatory and antibody responses in the URT of SPF mice exposed to extracellular TLR agonists were substantially restricted. In contrast, inflammatory and adaptive immune responses, including B and T cell activation, were not desensitized in mice exposed to intracellular TLR agonists. The distinct responsive patterns of extra and intracellular TLRs regulated at TLR expression in immune cells. The results indicated that TLRs differentially impact the innate and adaptive immune response in the URT, which contributes to the selection of TLR-based mucosal adjuvants and helps understand the difference between the immune response in bacterial and viral infections.

Sialic acid blockade in dendritic cells enhances CD8+ T cell responses by facilitating high-avidity interactions.

Sialic acids are negatively charged carbohydrates that cap the glycans of glycoproteins and glycolipids. Sialic acids are involved in various biological processes including cell-cell adhesion and immune recognition. In dendritic cells (DCs), the major antigen-presenting cells of the immune system, sialic acids emerge as important regulators of maturation and interaction with other lymphocytes including T cells. Many aspects of how sialic acids regulate DC functions are not well understood and tools and model systems to address these are limited. Here, we have established cultures of murine bone marrow-derived DCs (BMDCs) that lack sialic acid expression using a sialic acid-blocking mimetic Ac53FaxNeu5Ac. Ac53FaxNeu5Ac treatment potentiated BMDC activation via toll-like receptor (TLR) stimulation without affecting differentiation and viability. Sialic acid blockade further increased the capacity of BMDCs to induce antigen-specific CD8+ T cell proliferation. Transcriptome-wide gene expression analysis revealed that sialic acid mimetic treatment of BMDCs induces differential expression of genes involved in T cell activation, cell-adhesion, and cell-cell interactions. Subsequent cell clustering assays and single cell avidity measurements demonstrated that BMDCs with reduced sialylation form higher avidity interactions with CD8+ T cells. This increased avidity was detectable in the absence of antigens, but was especially pronounced in antigen-dependent interactions. Together, our data show that sialic acid blockade in BMDCs ameliorates maturation and enhances both cognate T cell receptor-MHC-dependent and independent T cell interactions that allow for more robust CD8+ T cell responses.

ß(2→6)-Type fructans attenuate proinflammatory responses in a structure dependent fashion via Toll-like receptors.

Graminan-type fructans (GTFs) have demonstrated immune benefits. However, mechanisms underlying these benefits are unknown. We studied GTFs interaction with Toll-like receptors (TLRs), performed molecular docking and determined their impact on dendritic cells (DCs). Effects of GTFs were compared with those of inulin-type fructans (ITFs). Whereas ITFs only contained ß(2→1)-linked fructans, GTFs showed higher complexity as it contains additional ß(2→6)-linkages. GTFs activated NF-κB/AP-1 through MyD88 and TRIF pathways. GTFs stimulated TLR3, 7 and 9 while ITFs activated TLR2 and TLR4. GTFs strongly inhibited TLR2 and TLR4, while ITFs did not inhibit any TLR. Molecular docking demonstrated interactions of fructans with TLR2, 3, and 4 in a structure dependent fashion. Moreover, ITFs and GTFs attenuated pro-inflammatory cytokine production of stimulated DCs. These findings demonstrate immunomodulatory effects of GTFs via TLRs and attenuation of cytokine production in dendritic cells by GTFs and long-chain ITF.

A novel toll-like receptor from Crassostrea gigas is involved in innate immune response to Vibrio alginolyticus.

Based on previous reports，toll-like receptors (TLRs) are recognition molecules common in various aquatic animals and play a vital role in innate immunity. In this study, a novel TLR CgToll-3 with leucine-rich repeats (LRRs) and a TIR (Toll-interleukin 1-resistance) domain was cloned in Crassostrea gigas. CgToll-3 with sixteen potential extracellular N-linked glycosylation sites and shares the closest phylogenic relationship with molluscan TLRs. Alignment of LRRs and TIR domains indicated that CgToll-3 was highly conserved compared to other LRRs of mollusks which could respond against Vibrio or other bacterial molecules, and contained three conserved functionally important motifs (Box 1, Box 2, and Box 3). The Hex Molecular Docking result showed that CgToll-3 could interact with CgMyd88 via the TIR domain. Subcellular Co-localization and BiFC Assay confirmed this interaction, and they could induce NF-κB activation. CgToll-3 was moderately expressed in the digestive gland, and its expression level was significantly up-regulated after Vibrio alginolyticus challenge. Taken together, CgToll-3 might be involved in the innate immune response to V. alginolyticus for C. gigas through a MyD88-dependent TLR mediated signaling pathway.

Toll-Like Receptors in Adaptive Immunity.

The immune (innate and adaptive) system has evolved to protect the host from any danger present in the surrounding outer environment (microbes and associated MAMPs or PAMPs, xenobiotics, and allergens) and dangers originated within the host called danger or damage-associated molecular patterns (DAMPs) and recognizing and clearing the cells dying due to apoptosis. It also helps to lower the tissue damage during trauma and initiates the healing process. The pattern recognition receptors (PRRs) play a crucial role in recognizing different PAMPs or MAMPs and DAMPs to initiate the pro-inflammatory immune response to clear them. Toll-like receptors (TLRs) are first recognized PRRs and their discovery proved milestone in the field of immunology as it filled the gap between the first recognition of the pathogen by the immune system and the initiation of the appropriate immune response required to clear the infection by innate immune cells (macrophages, neutrophils, dendritic cells or DCs, and mast cells). However, in addition to their expression by innate immune cells and controlling their function, TLRs are also expressed by adaptive immune cells. We have identified 10 TLRs (TLR1-TLR10) in humans and 12 TLRs (TLR1-TLR13) in laboratory mice till date as TLR10 in mice is present only as a defective pseudogene. The present chapter starts with the introduction of innate immunity, timing of TLR evolution, and the evolution of adaptive immune system and its receptors (T cell receptors or TCRs and B cell receptors or BCRs). The next section describes the role of TLRs in the innate immune function and signaling involved in the generation of inflammation. The subsequent sections describe the expression and function of different TLRs in murine and human adaptive immune cells (B cells and different types of T cells, including CD4+T cells, CD8+T cells, CD4+CD25+Tregs, and CD8+CD25+Tregs, etc.). The modulation of TLRs expressed on T and B cells has a great potential to develop different vaccine candidates, adjuvants, immunotherapies to target various microbial infections, including current COVID-19 pandemic, cancers, and autoimmune and autoinflammatory diseases.

Update on the aetiology and mechanisms of generalized pustular psoriasis.

Generalized pustular psoriasis (GPP) is a chronic disease characterized by non-bacterial pustules. Variants in several genes, such as IL36RN, AP1S3, and CARD14, are involved in the pathogenesis of GPP. The prevalence of different gene variants varies among ethnicities, and some variants are related to concurrent psoriasis vulgaris or age at onset. Flares can be triggered by medications (most commonly corticosteroids), infections (possibly due to Toll-like receptor [TLR] and antimicrobial peptides), pregnancy (the onset of GPP has been attributed to endocrine abnormalities such as hypoparathyroidism and hypocalcaemia), hypocalcaemia (presumably due to low levels of calcium and vitamin D regulating the proliferation and differentiation of keratinocytes), and other factors including stress and sun exposure. The mechanisms of pustule formation involve: 1) the LL37/TLR pathway, in which LL37 acts as an alarmin, interacting with TLR and activating the NF-κB and MAPK pathways; 2) the balance between calcium and 1,25(OH)2D levels, and 3) neutrophils and the complement system.