Toll-Like Receptor 4 Polymorphisms (896A/G and 1196C/T) as an Indicator of COVID-19 Severity in a Convenience Sample of Egyptian Patients

Interferon-Induced Transmembrane Protein-3 Rs12252-G Variant Increases COVID-19 Mortality Potential in Egyptian Population

Coronavirus disease 2019 (COVID-19) represented an international health risk. Variants of the interferon-induced transmembrane protein-3 (IFITM3) gene can increase the risk of developing severe viral infections. This cross-sectional study investigated the association between IFITM3 rs12252A>G single nucleotide polymorphism (SNP) and COVID-19 severity and mortality in 100 Egyptian patients. All participants were subjected to serum interleukin-6 (IL-6) determination by ELISA and IFITM3 rs12252 genotyping by real-time polymerase chain reaction. Of all participants, 85.0% had the IFITM3 rs12252 homozygous AA genotype, whereas 15.0% had the heterozygous AG genotype. None of our participants had the homozygous GG genotype. The IFITM3 rs12252A allele was found in 92.5% and the G allele in only 7.5%. There was no significant association (p > 0.05) between the IFITM3 rs12252 SNP and COVID-19 severity, intensive care unit (ICU) admission, or IL-6 serum levels. The heterozygous AG genotype frequency showed a significant increase among participants who died (32.0%) compared with those who had been cured (9.3%). The mutant G allele was associated with patients' death. Its frequency among cured participants was 8.5%, whereas in those who died was 24.2% (p = 0.024) with 3.429 odds ratio [95% confidence interval: 1.1-10.4]. In conclusion, this study revealed a significant association between the G allele variant of IFITM3 rs12252 and COVID-19 mortality. However, results were unable to establish a significant link between rs12252 polymorphism, disease severity, ICU admission, or serum IL-6 levels.

Impact of IL-6 rs1800795 and IL-17A rs2275913 gene polymorphisms on the COVID-19 prognosis and susceptibility in a sample of Iranian patients

BACKGROUND

From asymptomatic to acute and life-threatening pulmonary infection, the clinical manifestations of COVID-19 are highly variable. Interleukin (IL)-6 and IL-17A are key drivers of hyper inflammation status in COVID-19, and their elevated levels are hallmarks of the infection progression. To explore whether prognosis and susceptibility to COVID-19 are linked to IL-6 rs1800795 and IL-17A rs2275913, these single-nucleotide polymorphisms (SNPs) were assessed in a sample of Iranian COVID-19 patients.

METHODS

This study enrolled two hundred and eighty COVID-19 patients (140 non-severe and 140 severe). Genotyping for IL-6 rs1800795 and IL-17A rs2275913 was performed using tetra primer-amplification refractory mutation system-polymerase chain reaction (tetra-ARMS-PCR). IL-6 and IL-17A circulating levels were measured using enzyme-linked immunosorbent assay (ELISA). Also, mortality predictors of COVID-19 were investigated.

RESULTS

The rs1800795 GG genotype (78/140 (55.7 %)) and G allele (205/280 (73.2 %)) were significantly associated with a positive risk of COVID-19 severe infection (OR = 2.19, 95 %CI: 1.35-3.54, P =.006 and OR = 1.79, 95 %CI: 1.25-2.56, P <.001, respectively). Also, rs1800795 GG genotype was significantly linked to disease mortality (OR = 1.95, 95 %CI: 1.06-3.61, P =.04). The rs2275913 GA genotype was protective against severe COVID-19 (OR = 0.5, 95 %CI: 0.31--0.80, P =.012). However, the present study did not reveal any significant link between rs2275913 genotypes with disease mortality. INR ≥ 1.2 (OR = 2.19, 95 %CI: 1.61-3.78, P =.007), D-dimer ≥ 565.5 ng/mL (OR = 3.12, 95 %CI: 1.27-5.68, P =.019), respiratory rate ≥ 29 (OR = 1.19, 95 %CI: 1.12-1.28, P =.001), IL-6 serum concentration ≥ 28.5 pg/mL (OR = 1.97, 95 %CI: 1.942-2.06, P =.013), and IL-6 rs1800795 GG genotype (OR = 1.95, 95 %CI: 1.06-3.61, P =.04) were predictive of COVID-19 mortality.

CONCLUSION

The rs1800795 GG genotype and G allele were associated with disease severity, and INR, D-dimer, respiratory rate, IL-6 serum concentration, and IL-6 rs1800795 GG genotype were predictive of COVID-19 mortality.

Innate Immune Gene Polymorphisms and COVID-19 Prognosis

COVID-19 is characterized by a heterogeneous clinical presentation and prognosis. Risk factors contributing to the development of severe disease include old age and the presence of comorbidities. However, the genetic background of the host has also been recognized as an important determinant of disease prognosis. Considering the pivotal role of innate immunity in the control of SARS-CoV-2 infection, we analyzed the possible contribution of several innate immune gene polymorphisms (including TLR2-rs5743708, TLR4-rs4986790, TLR4-rs4986791, CD14-rs2569190, CARD8-rs1834481, IL18-rs2043211, and CD40-rs1883832) in disease severity and prognosis. A total of 249 individuals were enrolled and further divided into five (5) groups, according to the clinical progression scale provided by the World Health Organization (WHO) (asymptomatic, mild, moderate, severe, and critical). We identified that elderly patients with obesity and/or diabetes mellitus were more susceptible to developing pneumonia and respiratory distress syndrome after SARS-CoV-2 infection, while the IL18-rs1834481 polymorphism was an independent risk factor for developing pneumonia. Moreover, individuals carrying either the TLR2-rs5743708 or the TLR4-rs4986791 polymorphisms exhibited a 3.6- and 2.5-fold increased probability for developing pneumonia and a more severe disease, respectively. Our data support the notion that the host's genetic background can significantly affect COVID-19 clinical phenotype, also suggesting that the IL18-rs1834481, TLR2-rs5743708, and TLR4-rs4986791 polymorphisms may be used as molecular predictors of COVID-19 clinical phenotype.

Role of toll-like receptors in the pathogenesis of COVID-19: Current and future perspectives

The coronavirus disease 2019 (COVID-19) pandemic underlines a persistent threat of respiratory tract infectious diseases and warrants preparedness for a rapid response. At present, COVID-19 has had a serious social impact and imposed a heavy global burden on public health. The exact pathogenesis of COVID-19 has not been fully elucidated. Since the outbreak of COVID-19, a renewed attention has been brought to Toll-like receptors (TLRs). Available data and new findings have demonstrated that the interaction of human TLRs and SARS-CoV-2 is a vital mediator of COVID-19 immunopathogenesis. TLRs such as TLR2, 4, 7 and 8 are potentially important in viral combat and activation of immunity in patients with COVID-19. Therapeutics targeting TLRs are currently considered promising options against the pandemic. A number of TLR-targeting immunotherapeutics are now being investigated in preclinical studies and different phases of clinical trials. In addition, innovative vaccines based on TLRs under development could be a promising approach for building a new generation of vaccines to solve the current challenges. In this review, we summarize recent progress in the role of TLRs in COVID-19, focusing the new candidate drugs targeting TLRs, the current technology and potential paths forward for employing TLR agonists as vaccine adjuvants.

Impact of Toll-Like Receptor 2 and 9 Gene Polymorphisms on COVID-19: Susceptibility, Severity, and Thrombosis

Background

Toll-like receptors (TLRs) play an important role in activation of innate and adaptive immune responses.

Aim

We aimed to detect the association between TLR2 rs5743708 G>A and TLR9 rs5743836 C>T variants and COVID-19 disease susceptibility, severity, and thrombosis by using neutrophil extracellular traps (NETs).

Subjects and Methods

We included 100 adult COVID-19 patients as well as 100 age- and gender-matched normal controls. Participants were genotyped for TLR2 rs5743708 and TLR9 rs5743836. Citrullinated Histone (H3) was detected as an indicator of NETs.

Results

The mutant (G/A and C/C) genotypes and (A and C) alleles of TLR2 rs5743708 and TLR9 rs5743836, respectively, have been significantly related to a higher risk of COVID-19 infection, representing a significant risk factor for the severity of COVID-19. There was no significant association between the two variants and citrullinated histone (H3).

Conclusion

TLR2 rs5743708 and TLR9 rs5743836 variants have been significantly related to a higher risk and severity of COVID-19 infection but had no effect on thrombus formation.

Association of Toll-like receptor-4 polymorphism with SARS CoV-2 infection in Kurdish Population

Genetic variations are critical for understanding clinical outcomes of infections including server acute respiratory syndrome coronavirus 2 (SARS CoV-2). The immunological reactions of human immune genes with SARS CoV-2 have been under investigation. Toll-like receptors (TLRs), a group of proteins, are important for microbial detections including bacteria and viruses. TLR4 can sense both bacterial lipopolysaccharides (LPS) and endogenous oxidized phospholipids triggered by Covid-19 infection. Two TLR4 single nucleotide polymorphisms (SNPs), Asp299Gly and Thr399Ile have been linked to infectious diseases. No studies have focused on these SNPs in association with Covid-19. This study aims to reveal the association between Covid-19 infection with these SNPs by comparing a group of patients and a general population. Restriction fragment length polymorphisms (RFLP) were used to identify the TLR4 SNPs in both the general population (n = 114) and Covid-19 patient groups (n = 125). The results found no association between the TLR4 polymorphisms and Covid-19 infections as the data showed no statistically significant difference between the compared groups. This suggested that these TLR4 SNPs may not be associated with Covid-19 infections.

Systematic review and meta-analysis of human genetic variants contributing to COVID-19 susceptibility and severity

The COVID-19 pandemic has spawned global health crisis of unprecedented magnitude, claiming millions of lives and pushing healthcare systems in many countries to the brink. Among several factors that contribute to an increased risk of COVID-19 and progression to exacerbated manifestations, host genetic landscape is increasingly being recognized as a critical determinant of susceptibility/resistance to infection and a prognosticator of clinical outcomes in infected individuals. Recently, several case-control association studies investigated the influence of human gene variants on COVID-19 susceptibility and severity to identify the culpable mutations. However, a comprehensive synthesis of the recent advances in COVID-19 host genetics research was lacking, and the inconsistent findings of the association studies required reliable evaluation of the strength of association with greater statistical power. In this study, we embarked on a systematic search of all possible reports of genetic association with COVID-19 till April 07, 2022, and performed meta-analyses of all the genetic polymorphisms that were examined in at least three studies. After identifying a total of 84 studies that investigated the association of 130 polymorphisms in 61 genes, we performed meta-analyses of all the eligible studies. Seven genetic polymorphisms involving 15,550 cases and 444,007 controls were explored for association with COVID-19 susceptibility, of which, ACE1 I/D rs4646994/rs1799752, APOE rs429358, CCR5 rs333, and IFITM3 rs12252 showed increased risk of infection. Meta-analyses of 11 gene variants involving 6702 patients with severe COVID-19 and 8640 infected individuals with non-severe manifestations revealed statistically significant association of ACE2 rs2285666, ACE2 rs2106809, ACE2 rs2074192, AGTR1 rs5186, and TNFA rs1800629 with COVID-19 severity. Overall, our study presents a synthesis of evidence on all the genetic determinants implicated in COVID-19 to date, and provides evidence of correlation between the above polymorphisms with COVID-19 susceptibility and severity.

The relationship between 896A/G (rs4986790) polymorphism of TLR4 and infectious diseases: A meta-analysis

Toll-like Receptors (TLRs), such as the TLR4, are genes encoding transmembrane receptors of the same name, which induce a pro- or anti-inflammatory response according to their expression as the host's first line of defense against pathogens, such as infectious ones. Single nucleotide polymorphisms (SNPs) are the most common type of mutation in the human genome and can generate functional modification in genes. The aim of this article is to review in which infectious diseases there is an association of susceptibility or protection by the TLR4 SNP rs4986790. A systematic review and meta-analysis of the literature was conducted in the Science Direct, PUBMED, MEDLINE, and SciELO databases between 2011 and 2021 based on the dominant genotypic model of this SNP for general and subgroup analysis of infectious agent type in random effect. Summary odds ratios (ORs) and corresponding 95% confidence intervals (CIs) were calculated for genotypic comparison. I² statistics were calculated to assess the presence of heterogeneity between studies and funnel plots were inspected for indication of publication bias. A total of 27 articles were included, all in English. Among the results achieved, the categories of diseases that were most associated with the SNP studied were in decreasing order of number of articles: infections by bacteria (29.63%); caused by viruses (22.23%); urinary tract infection-UTI (7.4%), while 11 studies (40.74%) demonstrated a nonsignificant association. In this meta-analysis, a total of 5599 cases and 5871 controls were finalized. The present meta-analysis suggests that there is no significant association between TLR4-rs4986790 SNP and infections (OR = 1,11; 95% CI: 0,75-1,66; p = 0,59), but in the virus subgroup it was associated with a higher risk (OR = 2,16; 95% CI: 1,09-4,30; p = 0,03). The subgroups of bacteria and parasites did not show statistical significance (OR = 0,86; 95% CI: 0,56-1,30; p = 0,47, and no estimate of effects, respectively). Therefore, it has been shown that a diversity of infectious diseases is related to this polymorphism, either by susceptibility or even severity to them, and the receptor generated is also crucial for the generation of cell signaling pathways and immune response against pathogens.

Innate immunity, cytokine storm, and inflammatory cell death in COVID-19

The innate immune system serves as the first line of defense against invading pathogens; however, dysregulated innate immune responses can induce aberrant inflammation that is detrimental to the host. Therefore, careful innate immune regulation is critical during infections. The coronavirus disease 2019 (COVID-19) pandemic is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and has resulted in global morbidity and mortality as well as socio-economic stresses. Innate immune sensing of SARS-CoV-2 by multiple host cell pattern recognition receptors leads to the production of various pro-inflammatory cytokines and the induction of inflammatory cell death. These processes can contribute to cytokine storm, tissue damage, and acute respiratory distress syndrome. Here, we discuss the sensing of SARS-CoV-2 to induce innate immune activation and the contribution of this innate immune signaling in the development and severity of COVID-19. In addition, we provide a conceptual framework for innate immunity driving cytokine storm and organ damage in patients with severe COVID-19. A better understanding of the molecular mechanisms regulated by innate immunity is needed for the development of targeted modalities that can improve patient outcomes by mitigating severe disease.

Genetic variants determine intrafamilial variability of SARS-CoV-2 clinical outcomes in 19 Italian families

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection results in a wide range of outcomes characterized by a high heterogeneity in both symptomatology and susceptibility to the disease. In such a perspective, COVID-19 may be considered as a multifactorial disease featured by the interaction between the environment, which is the virus itself, and the genetic profile of the host. Our analysis aimed at investigating the transmission dynamics of SARS-CoV-2 within families whose members responded in different ways to the infection, although the exposure was common to the entire group and occurred before the availability of any vaccine. The goal was to understand how the genetic background of each subject can influence the viral infection outcome and hence the above-mentioned clinical variability. We performed a segregation analysis in 19 Italian families with a designed custom panel of 42 genes involved in immunity and virus entry and which have also been shown to be related to SARS-CoV-2 host response. We carried out both a familial segregation analysis and a global statistical analysis. In the former we identified eighteen risk variants co-segregating with a COVID-positive status and six variants with a possible protective effect. In addition, sixteen variants showed a trend of association to a severe phenotype. Together with common SNPs, we detected private rare variants that may also provide insight into the observed clinical COVID-19 heterogeneity. The global statistical analysis confirmed statistically significant positive associations between SARS-CoV-2 individual response and some specific gene variants identified in familial analysis. In conclusion our data confirm that the clinical expression of COVID-19 is markedly influenced by the host genetic profile both with a mendelian transmission pattern and a polygenic architecture.

Activation of TLR4 by viral glycoproteins: A double-edged sword?

Recognition of viral infection by pattern recognition receptors is paramount for a successful immune response to viral infection. However, an unbalanced proinflammatory response can be detrimental to the host. Recently, multiple studies have identified that the SARS-CoV-2 spike protein activates Toll-like receptor 4 (TLR4), resulting in the induction of proinflammatory cytokine expression. Activation of TLR4 by viral glycoproteins has also been observed in the context of other viral infection models, including respiratory syncytial virus (RSV), dengue virus (DENV) and Ebola virus (EBOV). However, the mechanisms involved in virus-TLR4 interactions have remained unclear. Here, we review viral glycoproteins that act as pathogen-associated molecular patterns to induce an immune response via TLR4. We explore the current understanding of the mechanisms underlying how viral glycoproteins are recognized by TLR4 and discuss the contribution of TLR4 activation to viral pathogenesis. We identify contentious findings and research gaps that highlight the importance of understanding viral glycoprotein-mediated TLR4 activation for potential therapeutic approaches.

Individual genetic variability mainly of Proinflammatory cytokines, cytokine receptors, and toll-like receptors dictates pathophysiology of COVID-19 disease

Innate and acquired immunity responses are crucial for viral infection elimination. However, genetic variations in coding genes may exacerbate the inflammation or initiate devastating cytokine storms which poses severe respiratory conditions in coronavirus disease-19 (COVID-19). Host genetic variations in particular those related to the immune responses determine the patients' susceptibility and COVID-19 severity and pathophysiology. Gene polymorphisms such as single nucleotide polymorphisms (SNPs) of interferons, TNF, IL1, IL4, IL6, IL7, IL10, and IL17 predispose patients to the severe form of COVID-19 or severe acute respiratory syndrome coronavirus-2 (SARS-COV-2). These variations mainly alter the gene expression and cause a severe response by B cells, T cells, monocytes, neutrophils, and natural killer cells participating in a cytokine storm. Moreover, cytokines and chemokines SNPs are associated with the severity of COVID-19 and clinical outcomes depending on the corresponding effect. Additionally, genetic variations in genes encoding toll-like receptors (TLRs) mainly TLR3, TLR7, and TLR9 have been related to the COVID-19 severe respiratory symptoms. The specific relation of these mutations with the novel variants of concern (VOCs) infection remains to be elucidated. Genetic variations mainly within genes encoding proinflammatory cytokines, cytokine receptors, and TLRs predispose patients to COVID-19 disease severity. Understanding host immune gene variations associated with the SARS-COV-2 infection opens insights to control the pathophysiology of emerging viral infections.

The Remarkable Roles of the Receptor for Advanced Glycation End Products (RAGE) and Its Soluble Isoforms in COVID-19: The Importance of RAGE Pathway in the Lung Injuries

The respiratory symptoms of acute respiratory distress syndrome (ARDS) in the coronavirus disease 2019 (COVID-19) patients is associated with accumulation of pre-inflammatory molecules such as advanced glycation end-products (AGES), calprotectin, high mobility group box family-1 (HMGB1), cytokines, angiotensin converting enzyme 2 (ACE2), and other molecules in the alveolar space of lungs and plasma. The receptor for advanced glycation end products (RAGEs), which is mediated by the mitogen-activated protein kinase (MAPK), plays a critical role in the severity of chronic inflammatory diseases such as diabetes mellitus (DM) and ARDS. The RAGE gene is most expressed in the alveolar epithelial cells (AECs) of the pulmonary system. Several clinical trials are now being conducted to determine the possible association between the levels of soluble isoforms of RAGE (sRAGE and esRAGE) and the severity of the disease in patients with ARDS and acute lung injury (ALI). In the current article, we reviewed the most recent studies on the RAGE/ligands axis and sRAGE/esRAGE levels in acute respiratory illness, with a focus on COVID-19–associated ARDS (CARDS) patients. According to the research conducted so far, sRAGE/esRAGE measurements in patients with CARDS can be used as a powerful chemical indicator among other biomarkers for assessment of early pulmonary involvement. Furthermore, inhibiting RAGE/MAPK and Angiotensin II receptor type 1 (ATR1) in CARDS patients can be a powerful strategy for diminishing cytokine storm and severe respiratory symptoms.

TLR Signaling Pathway Gene Polymorphisms, Gene-Gene and Gene-Environment Interactions in Allergic Rhinitis

Background

Allergic rhinitis (AR) is a nasal inflammatory disease resulting from a complex interplay between genetic and environmental factors. The association between Toll-like receptor (TLR) signaling pathway and environmental factors in AR pathogenesis remains to be explored. This study aims to assess the genetic association of AR with single nucleotide polymorphisms (SNPs) in TLR signaling pathway, and investigate the roles of gene–gene and gene–environment interactions in AR.

Methods

A total of 452 AR patients and 495 healthy controls from eastern China were enrolled in this hospital-based case–control study. We evaluated putatively functional genetic polymorphisms in TLR2, TLR4 and CD14 genes for their association with susceptibility to AR and related clinical phenotypes. Interactions between environmental factors (such as traffic pollution, residence, pet keeping) and polymorphisms with AR were examined using logistic regression. Models were stratified by genotype and interaction terms, and tested for the significance of gene–gene and gene–environment interactions.

Results

In the single-locus analysis, two SNPs in CD14, rs2563298 (A/C) and rs2569191 (C/T) were associated with a significantly decreased risk of AR. Compared with the GG genotype, the GT and GT/TT genotypes of TLR2 rs7656411 (G/T) were associated with a significantly increased risk of AR. Gene–gene interactions (eg, TLR2 rs7656411, TLR4 rs1927914, and CD14 rs2563298) was associated with AR. Gene–environment interactions (eg, TLR4 or CD14 polymorphisms and certain environmental exposures) were found in AR cases, but they were not significant after Bonferroni correction.

Conclusion

The genetic polymorphisms of TLR2 and CD14 and gene–gene interactions in TLR signaling pathway were associated with susceptibility to AR in this Han Chinese population. However, the present results were limited to support the association between gene–environment interactions and AR.

Viral and Host Genetic and Epigenetic Biomarkers Related to SARS-CoV-2 Cell Entry, Infection Rate, and Disease Severity

The rapid spread of COVID-19 outbreak lead to a global pandemic declared in March 2020. The common features of corona virus family helped to resolve structural characteristics and entry mechanism of SARS-CoV-2. However, rapid mutagenesis leads to the emergence of new strains that may have different reproduction rates or infectivity and may impact the course and severity of the disease. Host related factors may also play a role in the susceptibility for infection as well as the severity and outcomes of the COVID-19. We have performed a literature and database search to summarize potential viral and host-related genomic and epigenomic biomarkers, such as genetic variability, miRNA, and DNA methylation in the molecular pathway of SARS-CoV-2 entry into the host cell, that may be related to COVID-19 susceptibility and severity. Bioinformatics tools may help to predict the effect of mutations in the spike protein on the binding to the ACE2 receptor and the infectivity of the strain. SARS-CoV-2 may also target several transcription factors and tumour suppressor genes, thus influencing the expression of different host genes and affecting cell signalling. In addition, the virus may interfere with RNA expression in host cells by exploiting endogenous miRNA and its viral RNA. Our analysis showed that numerous human miRNA may form duplexes with different coding and non-coding regions of viral RNA. Polymorphisms in human genes responsible for viral entry and replication, as well as in molecular damage response and inflammatory pathways may also contribute to disease prognosis and outcome. Gene ontology analysis shows that proteins encoded by such polymorphic genes are highly interconnected in regulation of defense response. Thus, virus and host related genetic and epigenetic biomarkers may help to predict the course of the disease and the response to treatment.

Comparison of COVID-19 characteristics in Egyptian patients according to their Toll-Like Receptor-4 (Asp299Gly) polymorphism

BACKGROUND

Toll-like receptor (TLR)-4 plays a vital role in recognizing viral particles, activating the innate immune system, and producing pro-inflammatory cytokines.

OBJECTIVES

This cross-sectional study aimed to compare COVID-19 severity, progression, and fate according to TLR-4 (Asp299Gly) polymorphism in Egyptian patients.

METHODS

A total of 145 COVID-19 patients were included in this study. TLR-4 (Asp299Gly) genotyping was done using the PCR restriction fragment length polymorphism (PCR-RFLP) approach.

RESULTS

The most commonly encountered TLR-4 genotype in relation to the amino acid at position 299 was the wild-type AA (73.1%); meanwhile, the homozygous mutant GG genotype (8.3%) was the least encountered. At hospital admission, 85.8% of the AA group had free (with no ground glass opacities) chest computed tomography (CT) examination, and 16.0% were asymptomatic. On the other hand, of the AG and GG groups, 81.5% and 83.3%, respectively showed bilateral ground-glass opacities in chest CT, as well as 25.9% and 75.0%, respectively were dyspneic. Values of the total leucocytic count, C-reactive protein (CRP), ferritin, and D dimer increased in the AA<AG<GG sequence. In contrast, hemoglobin values and the absolute lymphocyte counts decreased in the AA>AG>GG sequence. ICU admission (83.3%) and in-hospital death (33.3%) rates were significantly higher in the GG group.

CONCLUSIONS

In COVID-19 patients, the TLR-4 mutant G allele may be associated with a more aggressive disease course and in-hospital death. New therapeutic alternatives could be aimed at this area.

Toll-Like Receptors (TLRs) in Health and Disease: An Overview

Toll-like receptors were discovered as proteins playing a crucial role in the dorsoventral patterning during embryonic development in the Drosophila melanogaster (D. melanogaster) almost 40 years ago. Subsequently, further research also showed a role of the Toll protein or Toll receptor in the recognition of Gram-positive bacterial and fungal pathogens infecting D. melanogaster. In 1997, the human homolog was reported and the receptor was named the Toll-like receptor 4 (TLR4) that recognizes lipopolysaccharide (LPS) of the Gram-negative bacteria as a pathogen-associated molecular pattern (PAMP). Identification of TLR4 in humans filled the long existing gap in the field of infection and immunity, addressing the mystery surrounding the recognition of foreign pathogens/microbes by the immune system. It is now known that mammals (mice and humans) express 13 different TLRs that are expressed on the outer cell membrane or intracellularly, and which recognize different PAMPs or microbe-associated molecular patterns (MAMPs) and death/damage-associated molecular patterns (DAMPs) to initiate the protective immune response. However, their dysregulation generates profound and prolonged pro-inflammatory immune responses responsible for different inflammatory and immune-mediated diseases. This chapter provides an overview of TLRs in the control of the immune response, their association with different diseases, including TLR single nucleotide polymorphisms (SNPs), interactions with microRNAs (miRs), use in drug development and vaccine design, and expansion in neurosciences to include pain, addiction, metabolism, reproduction, and wound healing.