The lack of genetic association of the Toll-like receptor 2 (TLR2) Arg753Gln and Arg677Trp polymorphisms with rheumatic heart disease

Inflammatory Response Genes' Polymorphism Associated with Risk of Rheumatic Heart Disease

Rheumatic heart disease (RHD) caused by group A streptococcus infection is one of the most important reasons of cardiovascular morbidity and mortality in low- and middle-income countries. Aberrant host immune response modulated by polymorphisms in inflammatory response genes plays an important role in RHD pathogenesis. This study aimed to determine risk-associated polymorphic variants in inflammatory response genes in Caucasian RHD patients. A total of 251 Caucasian RHD patients and 300 healthy donors were recruited for this study, and 27 polymorphic sites in 12 genes (TLR1, TLR2, TLR4, TLR6, IL1B, IL6R, IL6, IL10, IL12RB1, IL12B, TNF and CRP) were analyzed using allele-specific PCR. It was demonstrated that the polymorphic variants rs1800871 and rs1800872 in the IL10 gene, rs 1130864, rs3093077 and rs1205 in the CRP gene, rs375947 in the IL12RB1 gene, rs 5743551 and rs5743611 in the TLR1 gene, and rs3775073 in the TLR6 gene can modify RHD risk in a gender- and age-dependent manner. The obtained results can be used to determine the personalized risk of RHD in healthy donors during medical examination or screening, as well as to develop appropriate early prevention strategies targeting RHD in the risk groups.

The microbiome and rheumatic heart disease: current knowledge and future perspectives

Rheumatic heart disease (RHD) is a cardiovascular disease caused by an autoimmune response to group A Streptococcus (GAS) infection resulting in the damage of heart valves. RHD is the most commonly acquired heart disease among children and young adults with a global burden of over 40 million cases accounting for 306,000 deaths annually. Inflammation in the heart valves caused due to molecular mimicry between the GAS antigens and host cardiac proteins is facilitated by cytokines, cross-reactive antibodies and CD4⁺ T cells. The complex interaction between genetic and environmental factors linked with erratic events leads to the loss of immunological tolerance and autoimmunity in RHD. Despite extensive research on the etiopathogenesis of RHD, the precise mechanism underpinning the initiation of acute rheumatic fever (ARF) to the progression of RHD still remains elusive. Mounting evidences support the contribution of the human microbiome in the development of several immune-mediated diseases including rheumatoid arthritis, juvenile idiopathic arthritis, Kawasaki disease, inflammatory bowel disease and type 1 diabetes. The microbiome and their metabolites could play a crucial role in the integrity of the epithelial barrier, development of the immune system, inflammation and differentiation of T cell subsets. Consequently, microbiome dysbiosis might result in autoimmunity by molecular mimicry, epitope spreading and bystander activation. This review discusses various aspects of the interaction between the microbiome and the immune system in order to reveal causative links relating dysbiosis and autoimmune diseases with special emphasis on RHD.

Genetic variants in rheumatic fever and rheumatic heart disease

Genetic association studies in rheumatic heart disease (RHD) have the potential to contribute toward our understanding of the pathogenetic mechanism, and may shed light on controversies about RHD etiology. Furthermore, genetic association studies may uncover biomarkers that can be used to identify susceptible individuals, and contribute toward developing vaccine and novel therapeutic targets. Genetic predisposition to rheumatic fever and RHD has been hypothesized by findings from familial studies and observed associations between genes located in the human leukocyte antigens on chromosome 6p21.3 and elsewhere in the genome. We sought to summarize, from published Genetic association studies in RHD, evidence on genetic variants implicated in RHD susceptibility. Using HuGENet™ systematic review methods, we evaluated 66 studies reporting on 42 genes. Existing meta-analyses of candidate gene studies suggest that TGF-β1 [rs1800469], and IL-1β [rs2853550] single nucleotide polymorphisms (SNPs) contribute to susceptibility to RHD, whereas the TNF-α [rs1800629 and rs361525], TGF-β1 [rs1800470 and rs4803457], IL-6 [rs1800795], IL-10 [rs1800896] were not associated with RHD. However, candidate gene studies in RF/RHD are relatively small, thus lacking statistical power to identify reliable and reproducible findings, emphasizing the need for large-scale multicenter studies with different populations.

Streptococcal pharyngitis and rheumatic heart disease: the superantigen hypothesis revisited

Streptococcus pyogenes is a human-specific and globally prominent bacterial pathogen that despite causing numerous human infections, this bacterium is normally found in an asymptomatic carrier state. This review provides an overview of both bacterial and human factors that likely play an important role in nasopharyngeal colonization and pharyngitis, as well as the development of acute rheumatic fever and rheumatic heart disease. Here we highlight a recently described role for bacterial superantigens in promoting acute nasopharyngeal infection, and discuss how these immune system activating toxins could be crucial to initiate the autoimmune process in rheumatic heart disease.

A normal polymorphism site of TLR2 3′ untranslated region is related to rheumatic heart disease by up-regulating TLR2 expression

Background

The worldwide incidence of rheumatic heart disease is at least 15.6 million cases and is responsible for around 233,000 deaths per year. The pathogenesis of rheumatic heart disease is complex and involves genetic factors that predispose a person to the development of autoimmune reactions. Although Arg753Gln polymorphism of the TLR2 gene was considered to be related to acute rheumatic fever susceptibility in child, two groups have identified that there were no relations between this Arg753Gln polymorphism and rheumatic heart disease susceptibility.

Methods

In this study, we scanned the full length 826 bp of 3′ untranslated region of TLR2 in a Chinese-Han population and found that the rare allele G of rs35514500 was highly related to rheumatic heart disease.

Results

Results of dual-luciferase assay indicated that this T->G variation weakens the interaction between miR-340 and TLR2 3′ untranslated region and up-regulated firefly luciferase expression. Further results about the patients’ serum cytokines concentration detection constructed a relationship between G allele of rs35514550 and up-regulated serum IL-6 and TNFα.

Conclusions

These findings may give insight into understanding of rheumatic heart disease development and create an opportunity to approach the diagnosis and treatment of rheumatic heart disease.

Different patterns of Toll-like receptor 2 polymorphisms in populations of various ethnic and geographic origins

Upon the invasion of the host by microorganisms, innate immunity is triggered through pathogen recognition by pattern recognition receptors (PRRs). Toll-like receptors (TLRs) are the best-studied class of PRRs, and they recognize specific pathogen-associated molecular patterns (PAMPs) from various microorganisms. A large number of studies have shown that genetic variation in TLRs may influence susceptibility to infections. We assessed the genetic variation of TLR2, which encodes one of the most important TLRs, in various populations around the globe and correlated it with changes in the function of the molecule. The three best-known nonsynonymous TLR2 polymorphisms (1892C>A, 2029C>T, and 2258G>A) were assessed in different populations from the main continental masses: Romanians, Vlax-Roma, Dutch (European populations), Han Chinese (East Asia), Dogon, Fulani (Africa), and Trio Indians (America). The 2029C>T polymorphism was absent in both European and non-European populations, with the exception of the Vlax-Roma, suggesting that this polymorphism most likely arose in Indo-Aryan people after migration into South Asia. The 1892C>A polymorphism that was found exclusively in European populations, but not in Asian, African, or American volunteers, probably occurred in proto-Indo-Europeans. Interestingly, 2258G>A was present only in Europeans, including Vlax-Roma, but at a very low frequency. The differential pattern of the TLR2 polymorphisms in various populations may explain some of the differences in susceptibility to infections between these populations.

Very low frequencies of Toll-like receptor 2 supposed-2029T and 2258A (RS5743708) mutant alleles in southern Brazilian critically ill patients: would it be a lack of worldwide-accepted clinical applications of Toll-like receptor 2 variants?

Toll-like receptor 2 (TLR2) is a recognition receptor for the widest repertoire of pathogen-associated molecular patterns. Two polymorphisms of TLR2 could be linked to reduced nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) activation and to increased risk of infection (supposed-2029C>T and 2258G>A). We investigated the supposed-2029C>T and 2258G>A TLR2 polymorphisms in 422 critically ill patients of European origin from southern Brazil (295 with sepsis and 127 without sepsis) and reviewed 33 studies on these polymorphisms, conducting a quality assessment with a score system. Among our patients we found only one heterozygote (1/422) for the supposed-2029C>T and none for the 2258G>A (0/422) single nucleotide polymorphism (SNP). We were unable to find a clinical application of supposed-2029T and 2258A allele analyses in our southern Brazilian population. Our review detected that current TLR2 SNP assays had very controversial and contradictory results derived from reports with a variety of investigation quality criteria. We suggest that, if analyzed alone, the supposed-2029C>T and 2258G>A TLR2 SNP are not good candidates for genetic markers in studies that search for direct or indirect clinical applications between genotype and phenotype. Future efforts to improve the knowledge and to provide other simultaneous genetic markers might reveal a more effective TLR2 effect on the susceptibility to infectious diseases.

Lack of association of Toll-Like Receptor 2 Arg753Gln with cutaneous leishmaniasis

The aim of the present study was to investigate the frequency of Arg753Gln and Arg677Trp polymorphisms of TLR2 in patients with cutaneous leishmaniasis (CL) compared to healthy controls. The polymorphisms were genotyped by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) and amplification refractory mutation system assay (ARMS-PCR). The results showed that the frequency of Arg753Gln genotype was 14.3% and 10.1% in CL patients and normal controls, respectively. No one in either group was homozygous for the mutation. There was no significant difference in the genotype frequency. In contrast to the results for Arg753Gln polymorphism, we did not detect any case with Arg677Trp polymorphism in either control or patient group. In conclusion the TLR2 mutations are found equally in CL patients and healthy subjects.

Toll-like receptor polymorphisms and susceptibility to human disease

Although several lines of evidence suggest that variation in human inflammation is genetically controlled, the genes which regulate these responses are largely unknown. TLRs (Toll-like receptors) mediate recognition of microbes, regulate activation of the innate immune response and influence the formation of adaptive immunity. Cellular and molecular studies over the past several years have identified a number of common TLR polymorphisms that modify the cellular immune response and production of cytokines in vitro. In addition, human genetic studies suggest that some of these polymorphisms are associated with susceptibility to a spectrum of diseases. In this review, we summarize studies of common TLR polymorphisms and how this work is beginning to illuminate the influence of human variation on inflammation and disease susceptibility.

Rheumatic fever and rheumatic heart disease: genetics and pathogenesis

Molecular mimicry between streptococcal and human proteins is considered as the triggering factor leading to autoimmunity in rheumatic fever (RF) and rheumatic heart disease (RHD). Here, we present a review of the genetic susceptibility markers involved in the development of RF/RHD and the major immunopathological events underlying the pathogenesis of RF and RHD. Several human leucocyte antigen (HLA) class II alleles are associated with the disease. Among these alleles, HLA-DR7 is predominantly observed in different ethnicities and is associated with the development of valvular lesions in RHD patients. Cardiac myosin is one of the major autoantigens involved in rheumatic heart lesions and several peptides from the LMM (light meromyosin) region were recognized by peripheral and intralesional T-cell clones from RF and RHD patients. The production of TNF-alpha and IFN-gamma from heart-infiltrating mononuclear cells suggests that Th-1 type cytokines are the mediators of RHD heart lesions while the presence of few interleukin-4 producing cells in the valve tissue contributes to the maintenance and progression of the valvular lesions.