Low frequency of the TIRAP S180L polymorphism in Africa, and its potential role in malaria, sepsis, and leprosy

Protective role of TIRAP functional variant against development of coronary artery disease

Coronary artery disease (CAD) is the leading cause of sudden death worldwide. Inflammation is proved to be an important player in development of the CAD. Inflammation is directly regulated by the Toll like receptors (TLRs). Susceptibility of CAD is influenced by genetic variations within TLRs and the proteins involved in its signaling cascade. The TIRAP/MAL {TIR domain containing adaptor protein / MyD88 (myeloid differentiation primary response gene 88) adaptor-like} exhibits maximum genetic variations of all adaptor proteins involved in TLR signaling cascade. Susceptibility to a number of diseases can be influenced due to presence of S180L single nucleotide polymorphism (SNP) of TIRAP/MAL. This study was conducted to investigate the functional role of this well characterized S180L polymorphism on susceptibility to CAD among Pakistani patients. A total of 146 Pakistani CAD patients and 147 controls were genotyped by Amplification Refractory Mutation System-Polymerase Chain Reaction (ARMS-PCR) and the data was analyzed by using 2-tailed Chi square (x2 ) test. The p value ≤ 0.05 was considered to be significant. Significantly high frequency of homozygous L180L genotype was observed among healthy subjects as compared to the CAD patients [24 (16%) vs 7 (5%); x2 11.85; p = 0.003]. Moreover, the allele frequency of the minor allele; 180L was observed to be significantly higher among controls than the CAD patients, having same direction of association [156 (53%) vs 131 (45%); OR (95% CI) = 0.7198 (0.520-0.996); p < 0.05). Our results indicate that protective effect of L180L; a coding variant of TIRAP/MAL against CAD is discernible.

Association of variants in selected genes mediating host immune response with duration of Staphylococcus aureus bacteremia

Host genetic variation may be a contributing factor to variability in Staphylococcus aureus bacteremia duration. We assessed whether 28 single nucleotide polymorphisms (SNPs) in seven genes (TLR2, TLR4, TIRAP, IRAK4, TRAF6, NOD2, and CISH) that mediate host immune response were associated with S. aureus bacteremia duration. Subjects included 158 patients with short-term (≤4 days) and 44 with persistent (>4 days) S. aureus bacteremia from an academic medical center. In single SNP analyses, the minor allele frequencies of three TIRAP SNPs (rs655540, rs563011, and rs8177376) were higher in persistent bacteremia (P < 0.05). A haplotype with all three minor alleles was also associated with persistent bacteremia (P = 0.037). The minor allele frequencies of four other TIRAP SNPs (rs8177342, rs4937114, rs3802813, and rs4937115) were higher in short-term bacteremia (P < 0.05), and a haplotype containing the four minor alleles was associated with short-term bacteremia (P = 0.045). All seven SNPs are located in binding sites for proteins or noncoding RNAs that regulate transcription. None of the associations remained statistically significant after adjustment for multiple comparisons. Further investigation is needed to understand how genetic variation in TIRAP and other host immune genes may influence the duration of S. aureus bacteremia.

Inter-individual variation in health and disease associated with pulmonary infectious agents

Respiratory infectious diseases resulting from bacterial or viral pathogens such as Mycobacterium tuberculosis, Streptococcus pneumoniae, respiratory syncytial virus (RSV), or influenza, are major global public health concerns. Lower respiratory tract infections are leading causes of morbidity and mortality, only behind ischemic heart disease and stroke (GBD 2015 LRI Collaborators in Lancet Infect Dis 17(11):1133–1161, 2017). Developing countries are particularly impacted by these diseases. However, while many are infected with viruses such as RSV (> 90% of all individuals are infected by age 2), only sub-populations develop severe disease. Many factors may contribute to the inter-individual variation in response to respiratory infections, including gender, age, socioeconomic status, nutrition, and genetic background. Association studies with functional single nucleotide polymorphisms in biologically plausible gene candidates have been performed in human populations to provide insight to the molecular genetic contribution to pulmonary infections and disease severity. In vitro cell models and genome-wide association studies in animal models of genetic susceptibility to respiratory infections have also identified novel candidate susceptibility genes, some of which have also been found to contribute to disease susceptibility in human populations. Genetic background may also contribute to differential efficacy of vaccines against respiratory infections. Development of new genetic mouse models such as the collaborative cross and diversity outbred mice should provide additional insight to the mechanisms of genetic susceptibility to respiratory infections. Continued investigation of susceptibility factors should provide insight to novel strategies to prevent and treat disease that contributes to global morbidity and mortality attributed to respiratory infections.

Toll-Interleukin 1 Receptor Domain-Containing Adaptor Protein 180L Single-Nucleotide Polymorphism Is Associated With Susceptibility to Recurrent Pneumococcal Lower Respiratory Tract Infections in Children

Lower respiratory tract infections (LRTI) are often caused by Streptococcus pneumoniae (Spn) and can be recurrent in 8% of children older than 2 years of age. Spn is recognized by pattern-recognition receptors (PRRs) of the innate immune system, in particular toll-like receptors (TLRs) 2 and 4. To assess whether a defect somewhere along this TLR signaling pathway increases susceptibility to recurrent pneumococcal LRTI, we conducted a prospective case-control study with 88 healthy individuals and 45 children with recurrent LRTI aged 2-5 years old. We examined cell surface expression of TLR2 and TLR4, as well as eight genetic variants of these receptors or associated co-receptors TLR1 and TLR6. Interleukin-6 production was measured after whole blood stimulation assays with specific agonists and heat-killed Spn. Our findings reveal that single-nucleotide polymorphisms within toll-interleukin 1 receptor domain-containing adaptor protein (TIRAP) alone or in combination with TLR1 N248S, TLR1 I602S, or TLR6 S249P polymorphisms contributes to various degree of susceptibility to recurrent pneumococcal LRTI in children by modulating the inflammatory response. In that respect, carriage of the TIRAP S180L heterozygous trait increases the likelihood to protect against pneumococcal LRTI, whereas children carrying the mutant homozygous TIRAP 180L polymorphism might be more likely susceptible to recurrent pneumococcal LRTI.

The Emerging Role of Pattern Recognition Receptors in the Pathogenesis of Malaria

Despite a global effort to develop an effective vaccine, malaria is still a significant health problem. Much of the pathology of malaria is immune mediated. This suggests that host immune responses have to be finely regulated. The innate immune system initiates and sets the threshold of the acquired immune response and determines the outcome of the disease. Yet, our knowledge of the regulation of innate immune responses during malaria is limited. Theoretically, inadequate activation of the innate immune system could result in unrestrained parasite growth. Conversely, hyperactivation of the innate immune system, is likely to cause excessive production of proinflammatory cytokines and severe pathology. Toll-like receptors (TLRs) have emerged as essential receptors which detect signature molecules and shape the complex host response during malaria infection. This review will highlight the mechanisms by which Plasmodium components are recognized by innate immune receptors with particular emphasis on TLRs. A thorough understanding of the complex roles of TLRs in malaria may allow the delineation of pathological versus protective host responses and enhance the efficacy of anti-malarial treatments and vaccines.

Role of MyD88-adaptor-like gene polymorphism rs8177374 in modulation of malaria severity in the Pakistani population

Introduction

The present study was designed to investigate the association between rs8177374 polymorphism and malaria symptoms due to exposure of Plasmodium vivax and Plasmodium falciparum.

Materials and methods

A total of 454 samples were included in the study (228 malaria patients and 226 healthy individuals). Malaria patients, divided into P. vivax and P. falciparum groups on the basis of the causative species of Plasmodium, were categorized into mild and severe on the basis of clinical outcomes according to WHO criteria. Healthy individuals were used as controls. Allele specific PCR based strategy was used for the identification of rs8177374 SNP.

Results

MyD88-adaptor-like gene polymorphism was associated with susceptibility to malaria (p < 0.001). C allele frequency (0.74) was higher in the population compared to T allele frequency (0.26). CT genotype increased the susceptibility of malaria (OR: 2.661; 95% CI: 1.722–4.113) and was positively associated with mild malaria (OR: 5.609; 95% CI: 3.479–9.044, p = 0.00). On the other hand, CC genotype was associated with severe malaria (OR: 3.116; 95% CI: 1.560–6.224, p = 0.00). P. vivax infection rate was higher in CT genotype carriers compared to other genotypes (OR: 3.616; 95% CI: 2.219–5.894, p < 0.001).

Conclusion

MyD88-adaptor-like/TIR domain containing adaptor protein polymorphism for single nucleotide polymorphism rs8177374 is related with the susceptibility of malaria.

The Role of Host Genetics (and Genomics) in Tuberculosis

Familial risk of tuberculosis (TB) has been recognized for centuries. Largely through studies of mono- and dizygotic twin concordance rates, studies of families with Mendelian susceptibility to mycobacterial disease, and candidate gene studies performed in the 20th century, it was recognized that susceptibility to TB disease has a substantial host genetic component. Limitations in candidate gene studies and early linkage studies made the robust identification of specific loci associated with disease challenging, and few loci have been convincingly associated across multiple populations. Genome-wide and transcriptome-wide association studies, based on microarray (commonly known as genechip) technologies, conducted in the past decade have helped shed some light on pathogenesis but only a handful of new pathways have been identified. This apparent paradox, of high heritability but few replicable associations, has spurred a new wave of collaborative global studies. This review aims to comprehensively review the heritability of TB, critically review the host genetic and transcriptomic correlates of disease, and highlight current studies and future prospects in the study of host genomics in TB. An implicit goal of elucidating host genetic correlates of susceptibility to Mycobacterium tuberculosis infection or TB disease is to identify pathophysiological features amenable to translation to new preventive, diagnostic, or therapeutic interventions. The translation of genomic insights into new clinical tools is therefore also discussed.

Heterozygous mutants of TIRAP (S180L) polymorphism protect adult patients with Plasmodium falciparum infection against severe disease and mortality

Toll-interleukin-1 receptor domain containing adapter protein (TIRAP) plays a crucial role in TLR2 and TLR4 signaling pathways. Glycosylphospatidylinositol (GPI), considered a toxin molecule of Plasmodium falciparum, interacts with TLR2 and 4 to induce an immune inflammatory response. A single nucleotide polymorphism at coding region of TIRAP (S180L) has been reported to influence TLRs signaling. In the present study, we investigated the association of TIRAP (S180L) polymorphism with susceptibility/resistance to severe P. falciparum malaria in a cohort of adult patients from India. TIRAP S180L polymorphism was typed in 347 cases of severe malaria (SM), 232 uncomplicated malaria and 150 healthy controls. Plasma levels of TNF-α was quantified by ELISA. Heterozygous mutation (S/L) conferred significant protection against MOD (multi organ dysfunction), NCSM (non-cerebral severe malaria) as well as mortality. Interestingly, homozygous mutants (L/L) had 16 fold higher susceptibility to death. TIRAP mutants (S/L and L/L) were associated with significantly higher plasma TNF-α levels compared to wild type (S/S). The results of the present study demonstrate that TIRAP S180L heterozygous mutation may protect patients against severe malaria and mortality.

Genetic polymorphisms and the development of invasive bacterial infections in children

To evaluate the associations between single nucleotide polymorphisms (SNPs) of factors involved in the development of invasive bacterial disease (IBD) in children, 47 SNPs of 18 candidate genes were analysed in 49 children with IBD and 100 controls. The G/T genotype of TLR2 rs2149356 and the C genotype of LTA rs2229094 were associated with significantly reduced risk of developing IBD (P=0.04 and P=0.05, respectively), whereas the C/T genotype of RFP175 rs1585110 was associated with a significantly higher risk of developing IBD (P=0.02). These results support the evidence that some genetic variants of factors involved in innate immunity may influence IBD risk in children.

The influence of genetic polymorphisms in TLR4 and TIRAP, and their expression levels in peripheral blood, on susceptibility to sepsis

The present study aimed to investigate whether genetic polymorphisms in the Toll-like receptor (TLR)-4 and Toll/interleukin-1 receptor (TIR)-associated protein (TIRAP) genes, and/or their expression levels, influence the susceptibility of a patient to sepsis. A total of 106 patients with sepsis were divided into two groups on the basis of their acute physiology and chronic health evaluation (APACHE) II scores: i) Sepsis group A (APACHE II <20) and ii) Sepsis group B (APACHE II >20). In addition, 100 healthy volunteers were enrolled into the control group. Polymerase chain reaction-restriction fragment length polymorphism assay was used to detect the following genetic polymorphisms: The Ser180Leu allele of the TIRAP gene and the Asp299Gly and Thr399I1e alleles of the TLR4 gene. Furthermore, the protein expression levels of TLR4 and TIRAP were analyzed using an enzyme-linked immunosorbent assay. Genetic polymorphisms were not detected for the TLR4 and TIRAP genes; however, the protein expression levels of TLR4 and TIRAP differed significantly between the control, sepsis A and sepsis B groups (P<0.01). An APACHE II score of 20 was used as a baseline in order to differentiate sepsis severity. Pearson analysis demonstrated that TLR4 and TIRAP protein expression levels were positively correlated with sepsis severity (r=0.931 and 0.972; P<0.05), and TLR4 protein expression levels were positively correlated with those of TIRAP (r=0.936; P<0.05). The results of the present study suggested that the protein expression levels of, but not genetic polymorphisms in, TLR4 and TIRAP were associated with the severity of sepsis.

Role of S180L polymorphism in etiology of malaria caused by Plasmodium falciparum in a small group of Pakistani population

The aim of our study was to investigate the role of S180L polymorphism in modulation of acquisition of malaria caused by Plasmodium falciparum in a small group of Pakistani population. A total of 133 individuals including 60 controls and 73 patients of malaria, caused by Plasmodium falciparum, were genotyped using allele-specific PCR. Ninety-two samples successfully demonstrated the PCR amplification results, while forty-one samples could not be genotyped due to failure in PCR amplification. The allele frequency for S180L polymorphism was deviant from Hardy-Weinberg equilibrium (HWE) of the population under observation. Association was found between the observed polymorphism and the occurrence of malaria caused by Plasmodium falciparum (p = 0.01). Chances of malaria caused by Plasmodium falciparum were low in CC genotype carriers in comparison to other genotypes (Odds ratio: 0.3016; 95% CI: 0.124-0.729). The present findings suggest that S180L polymorphism is important in modulating the probability of acquisition of malaria caused by Plasmodium falciparum in Pakistani population. The CC genotype plays a protective role in local population against this type of malaria.

On the modelling and analysis of the regulatory network of dengue virus pathogenesis and clearance

Dengue virus can ignite both protective and pathogenic responses in human. The pathogenesis is related with modified functioning of our immune system during infection. Pattern recognition receptors like Toll like receptor 3 is vital for the induction of innate immunity in case of Dengue infection. Toll like receptor 3 induces TRIF mediated activation of Type 1 interferons and Fc receptor mediated induction of cytokines. Interferons have been related with clearance of Dengue virus but it has adopted modified regulatory mechanisms to counter this effect. SOCS protein is also induced due to the interferon and cytokine mediated signalling which can subsequently play its part in the regulation of interferon and cytokine production. Our hypothesis in this study relates the pathogenesis of Dengue virus with the SOCS mediated inhibition of our innate immunity. We used the qualitative formalism of René Thomas to model the biological regulatory network of Toll like receptor 3 mediated signalling pathway in an association with pathogenesis of dengue. Logical parameters for the qualitative modelling were inferred using a model checking approach implemented in SMBioNet. A linear hybrid model, parametric linear hybrid automaton, was constructed to incorporate the activation and inhibition time delays in the qualitative model. The qualitative model captured all the possible expression dynamics of the proteins in the form of paths, some of which were observed as abstract cycles (representing homoeostasis) and diverging paths towards stable states. The analysis of the qualitative model highlighted the importance of SOCS protein in elevating propagation of dengue virus through inhibition of type 1 interferons. Detailed qualitative analysis of regulatory network endorses our hypothesis that elevated levels of cytokine subsequently induce SOCS expression which in turn results into the continuous down-regulation of Toll like receptor 3 and interferon. This may result into the Dengue pathogenesis during the stage of immunosuppression. Further analysis with HyTech (HYbrid TECHnology) tool provided us with the real-time constraints (delay constraints) of the proteins involved in the cyclic paths of the regulatory network backing the evidence provided by the qualitative analysis. The HyTech results also suggest that the role of SOCS is vital in homoeostasis.

The genetics of innate immunity sensors and human disease

Since their discovery, innate immunity microbial sensors have been increasingly studied and shown to play a critical role in innate responses to microbes in several experimental in vitro, ex vivo, and animal models. However, their role in the human response to infection in natural conditions has just started to be deciphered, by means of clinical studies of primary immunodeficiencies and epidemiological genetic studies. Here, we summarize the major findings concerning the genetic diversity of the various families of microbial sensors in humans, and of other molecules involved in the signaling pathways they trigger. Specifically, we review the genetic associations, revealed by both clinical and epidemiological genetics studies, of microbial sensors from five different families: Toll-like receptors, C-type lectin receptors, NOD-like receptors, RIG-I-like receptors, and cytosolic DNA sensors. In particular, we consider the relationships between variation at the genes encoding these molecules and susceptibility to and the severity of infectious diseases and other clinical conditions associated with immune dysfunction, including autoimmunity, inflammation, allergy, and cancer. Despite the fact that the genetic links between innate immunity sensors and human disorders remain still limited, human genetics studies are increasingly improving our understanding of the genuine functions of microbial sensors and downstream signaling molecules in the natural setting.

Neither microbial translocation nor TLR responsiveness are likely explanations for preexisting immune activation in women who subsequently acquired HIV in CAPRISA 004

Innate immune activation was a strong predictor of HIV acquisition in women at risk for HIV in CAPRISA 004. Identifying the cause(s) of activation could enable targeted prevention interventions. In this study, plasma concentrations of lipopolysaccharide, soluble CD14, and intestinal fatty acid-binding protein did not differ between subjects who did or did not subsequently acquire HIV nor were these levels correlated with plasma cytokines or natural killer cell activation. There was no difference between HIV acquirers and non-acquirers in the chemokine and cytokine responses of peripheral blood mononuclear cells stimulated with TLR2, 4, or 7/8 agonists. Further studies are required.

Genetic variation in the TNF gene is associated with susceptibility to severe sepsis, but not with mortality

Background

Tumor necrosis factor (TNF) and TNF receptor superfamily (TNFR)-mediated immune response play an essential role in the pathogenesis of severe sepsis. Studies examining associations of TNF and lymphotoxin-α (LTA) single nucleotide polymorphisms (SNPs) with severe sepsis have produced conflicting results. The objective of this study was to investigate whether genetic variation in TNF, LTA, TNFRSF1A and TNFRSF1B was associated with susceptibility to or death from severe sepsis in Chinese Han population.

Methodology/Principal Findings

Ten SNPs in TNF, LTA, TNFRSF1A and TNFRSF1B were genotyped in samples of patients with severe sepsis (n = 432), sepsis (n = 384) and healthy controls (n = 624). Our results showed that rs1800629, a SNP in the promoter region of TNF, was significantly associated with risk for severe sepsis. The minor allele frequency of rs1800629 was significantly higher in severe sepsis patients than that in both healthy controls (P_adj = 0.00046, odds ratio (OR)_adj = 1.92) and sepsis patients (P_adj = 0.002, OR_adj = 1.56). Further, we investigated the correlation between rs1800629 genotypes and TNF-α concentrations in peripheral blood mononuclear cells (PBMCs) of healthy volunteers exposed to lipopolysaccharides (LPS) ex vivo, and the association between rs1800629 and TNF-α serum levels in severe sepsis patients. After exposure to LPS, the TNF-α concentration in culture supernatants of PBMCs was significantly higher in the subjects with AA+AG genotypes than that with GG genotype (P = 0.007). Moreover, in patients with severe sepsis, individuals with AA+AG genotypes had significantly higher TNF-α serum concentrations than those with GG genotype (P_adj = 0.02). However, there were no significant associations between SNPs in the four candidate genes and 30 day mortality for patients with severe sepsis.

Conclusions/Significance

Our findings suggested that the functional TNF gene SNP rs1800629 was strongly associated with susceptibility to severe sepsis, but not with lethality in Chinese Han population.

Toll-like receptor kinetics in septic shock patients: a preliminary study

The aim of this study is to evaluate some inflammatory parameter changes in septic shock patients and their possible correlation with clinical outcome, in particular when continuous veno-venous hemofiltration (CVVH) treatment is required. Considering the objective difficulty in enrolling this kind of patient, a preliminary study was initiated on seventeen septic shock patients admitted to a medical and surgical ICU. The mRNA expression of Toll-like receptor (TLR)-1, TLR-2, TLR-4, TLR-5, TLR-9, TNFα, IL-8 and IL-1β was assessed, the plasmatic concentrations of IL-18, IL-2, IL-10 and TNFα were measured on the day of sepsis diagnosis and after 72 h. In those patients who developed acute renal failure unresponsive to medical treatment and who underwent CVVH treatment the same parameters were measured every 24 h during CVVH and after completion of the treatment. On sepsis diagnosis, gene expression of TLRs was up-regulated compared to the housekeeping gene in all the patients. After 72 h, in 35% of the patients a down-regulation of these genes was found compared to day 1, but it was not associated with a reduction of cytokine serum levels or improved clinical signs, better outcome or reduced mortality. After high volume hemofiltration treatment, cytokine serum levels and TLR expression were not significantly modified. In conclusion, considering the not numerous number of cases, from our preliminary study, we cannot certainly correlate TLR over-expression in septic shock patients with severity or outcome scores.

Role of polymorphisms of toll-like receptor (TLR) 4, TLR9, toll-interleukin 1 receptor domain containing adaptor protein (TIRAP) and FCGR2A genes in malaria susceptibility and severity in Burundian children

Background

Malaria caused by Plasmodium falciparum is one of the leading causes of human morbidity and mortality from infectious diseases, predominantly in tropical and sub-tropical countries. As genetic variations in the toll-like receptors (TLRs)-signalling pathway have been associated with either susceptibility or resistance to several infectious and inflammatory diseases, the supposition is that single nucleotide polymorphisms (SNPs) of TLR2, TLR4, TLR9, Toll-interleukin 1 receptor domain containing adaptor protein (TIRAP) and FCGR2A could modulate malaria susceptibility and severity.

Methods

This study was planned to make a further contribution to solving the problem of the real role of the most common polymorphisms of TLR4, TLR9, TIRAP and FCGR2A genes in modulating the risk of malaria and disease severity in children from Burundi, Central Africa. All the paediatric patients aged six months to 10 years admitted to the hospital of Kiremba, Burundi, between February 2011 and September 2011, for fever and suspicion of acute malaria were screened for malaria parasitaemia by light microscopy of thick and thin blood smears. In children with malaria and in uninfected controls enrolled during the study period in the same hospital, blood samples were obtained on filter paper and TLR4 Asp299Gly rs4986790, TLR9 G1174A rs352139, T-1486 C rs187084 TLR9 T-1237 C rs5743836, TIRAP Ser180Leu rs8177374 and the FCGR2A His131Arg rs1801274 polymorphisms were studied using an ABI PRISM 7900 HT Fast Real-time instrument.

Results

A total of 602 patients and 337 controls were enrolled. Among the malaria cases, 553 (91.9 %) were considered as suffering from uncomplicated and 49 (8.1 %) from severe malaria. TLR9 T1237C rs5743836CC was associated with an increased risk of developing malaria (p = 0.03), although it was found with the same frequency in uncomplicated and severe malaria cases. No other differences were found in all alleles studied and in genotype frequencies between malaria cases and uninfected controls as well as between uncomplicated and severe malaria cases.

Conclusions

TLR9 T1237C seems to condition susceptibility to malaria in Burundian children but not its severity, whereas none of the assessed SNPs of TLR4, TIRAP and FCGR2A seem to influence susceptibility to malaria and disease severity in this population.

Genetic variation in Toll-like receptors and disease susceptibility

Toll-like receptors (TLRs) are key initiators of the innate immune response and promote adaptive immunity. Much has been learned about the role of TLRs in human immunity from studies linking TLR genetic variation with disease. First, monogenic disorders associated with complete deficiency in certain TLR pathways, such as MyD88-IRAK4 or TLR3-Unc93b-TRIF-TRAF3, have demonstrated the specific roles of these pathways in host defense against pyogenic bacteria and herpesviruses, respectively. Second, common polymorphisms in genes encoding several TLRs and associated genes have been associated with both infectious and autoimmune diseases. The study of genetic variation in TLRs in various populations combined with information on infection has demonstrated complex interaction between genetic variation in TLRs and environmental factors. This interaction explains the differences in the effect of TLR polymorphisms on susceptibility to infection and autoimmune disease in various populations.

Formal modeling and analysis of the MAL-associated biological regulatory network: insight into cerebral malaria

The discrete modeling formalism of René Thomas is a well known approach for the modeling and analysis of Biological Regulatory Networks (BRNs). This formalism uses a set of parameters which reflect the dynamics of the BRN under study. These parameters are initially unknown but may be deduced from the appropriately chosen observed dynamics of a BRN. The discrete model can be further enriched by using the model checking tool HyTech along with delay parameters. This paves the way to accurately analyse a BRN and to make predictions about critical trajectories which lead to a normal or diseased response. In this paper, we apply the formal discrete and hybrid (discrete and continuous) modeling approaches to characterize behavior of the BRN associated with MyD88-adapter-like (MAL)--a key protein involved with innate immune response to infections. In order to demonstrate the practical effectiveness of our current work, different trajectories and corresponding conditions that may lead to the development of cerebral malaria (CM) are identified. Our results suggest that the system converges towards hyperinflammation if Bruton's tyrosine kinase (BTK) remains constitutively active along with pre-existing high cytokine levels which may play an important role in CM pathogenesis.

Polymorphisms of innate immunity receptors in infection by parasites

The innate immune system is the first line of defence against infection by pathogenic bacteria, virus and parasites and is also responsible for initiating an adaptive immune response. In contrast to the receptors of adaptive immunity (TCRs and antibodies) which are generated by gene recombination, receptors of the innate immune system are encoded in the germline and are thus inherited from generation to generation. Although evolutionarily selected, the genes encoding the innate recognition receptors show variations among individuals, and these polymorphisms may have an impact on the ability of an individual to deal with an infection. In recent years, several polymorphisms have been identified in innate recognition receptors, and efforts are being made to determine whether these polymorphisms are associated with a higher or lower susceptibility to infectious diseases. These studies will allow a better understanding of the role of innate receptors in specific diseases and are valuable in the design of preventive or therapeutic interventions to fight the disease. In this review, we summarize studies aimed at determining the influence of polymorphisms in innate recognition receptors on the susceptibility to diseases caused by parasites.

Human polymorphisms as clinical predictors in leprosy

Genetic and serum markers in human host can predict leprosy susceptibility per se as well as be useful in classification and/or prediction of clinical variants and immunological responses in leprosy. Adequate and timely assessment of potential risks associated with these 38 host leprosy genes could diminish epidemiological burden and improve life quality of patients with this still prevalent mycobacterial disease.

Polymorphisms of toll-like receptors and their pathways in viral hepatitis

Toll-like receptors (TLRs) are an important part of the innate immune response to a variety of pathogens including hepatic viral infections. Activation of TLRs stimulates a complex intracellular signalling cascade that results in production of proinflammatory cytokines and interferons important for antiviral responses as well as induction of the adaptive arm of the immune system. There is substantial evidence for an important role for TLRs and TLR-mediated signalling in the pathogenesis and outcomes of hepatitis B and C in particular, but it might also influence responses to other viral hepatitis infections. Several single nucleotide polymorphisms (SNPs) of TLRs, relevant adaptor molecules and cytokines mediated by TLR signalling have been described that alter innate immune responses and have been implicated in a variety of human diseases including viral and other infections. There is now significant evidence that a number of TLR SNPs can affect various clinical outcomes in Caucasian patients with chronic HCV. However, the role of these polymorphisms in acute and other chronic hepatitis infections, including HBV as well as in non-Caucasian populations, has not been elucidated. In addition, results for SNPs downstream of TLR activation, such as in relevant cytokines, are inconsistent and their influence requires further investigation to determine the clinical significance of genetic variations in these mediators.

Genetic polymorphisms linked to susceptibility to malaria

The influence of host genetics on susceptibility to Plasmodium falciparum malaria has been extensively studied over the past twenty years. It is now clear that malaria parasites have imposed strong selective forces on the human genome in endemic regions. Different genes have been identified that are associated with different malaria related phenotypes. Factors that promote severity of malaria include parasitaemia, parasite induced inflammation, anaemia and sequestration of parasitized erythrocytes in brain microvasculature.

Recent advances in human genome research technologies such as genome-wide association studies (GWAS) and fine genotyping tools have enabled the discovery of several genetic polymorphisms and biomarkers that warrant further study in host-parasite interactions. This review describes and discusses human gene polymorphisms identified thus far that have been shown to be associated with susceptibility or resistance to P. falciparum malaria. Although some polymorphisms play significant roles in susceptibility to malaria, several findings are inconclusive and contradictory and must be considered with caution. The discovery of genetic markers associated with different malaria phenotypes will help elucidate the pathophysiology of malaria and enable development of interventions or cures. Diversity in human populations as well as environmental effects can influence the clinical heterogeneity of malaria, thus warranting further investigations with a goal of developing new interventions, therapies and better management against malaria.

Human TLRs and IL-1Rs in host defense: natural insights from evolutionary, epidemiological, and clinical genetics

Toll-like receptors (TLRs) and interleukin-1 receptors (IL-1Rs) have TIR intracellular domains that engage two main signaling pathways, via the TIR-containing adaptors MyD88 (which is not used by TLR3) and TRIF (which is used only by TLR3 and TLR4). Extensive studies in inbred mice in various experimental settings have attributed key roles in immunity to TLR- and IL-1R-mediated responses, but what contribution do human TLRs and IL-1Rs actually make to host defense in the natural setting? Evolutionary genetic studies have shown that human intracellular TLRs have evolved under stronger purifying selection than surface-expressed TLRs, for which the frequency of missense and nonsense alleles is high in the general population. Epidemiological genetic studies have yet to provide convincing evidence of a major contribution of common variants of human TLRs, IL-1Rs, or their adaptors to host defense. Clinical genetic studies have revealed that rare mutations affecting the TLR3-TRIF pathway underlie herpes simplex virus encephalitis, whereas mutations in the TIR-MyD88 pathway underlie pyogenic bacterial diseases in childhood. A careful reconsideration of the contributions of TLRs and IL-1Rs to host defense in natura is required.

Genetic variation of TLR-4, TLR-9 and TIRAP genes in Iranian malaria patients

Background

Toll-like receptors (TLRs) recognize pathogen-associated molecular patterns and their activation leads to the induction of effector genes involving inflammatory cytokines that may have contribute to controlling parasite growth and disease pathogenesis. The current immunogenetic study was designed to analyse the key components of innate immunity, TLRs and TIRAP (Toll-interleukin-1 receptor domain-containing adaptor protein), also known as MAL (MYD88 adaptor-like), in Iranian patients with mild malaria.

Methods

The tlr-4 (D299G and T399I), tlr-9 (T-1486C and T-1237C) and tirap (S180L) genes were assessed in 640 Baluchi individuals (320 Plasmodium falciparum-infected and 320 non-infected, median age of 28 years) from malaria-endemic regions using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) methods.

Results

Common tlr-4 SNPs and promoter SNPs of tlr-9 were distributed among P. falciparum-infected and non-infected groups (P > 0.05) that showed no association of these variants with mild clinical manifestation. The comparison of the tirap S180L genotypes between patients with mild malaria and those healthy individuals showed that the frequency of heterozygosity was significantly higher in infected than non-infected individuals (33.8 vs. 25.6; OR, 1.479; 95% CI, 1.051-2.081; P = 0.024). The result also revealed a significant association of tirap S180L (P < 0.05) with development of mild malaria, which is common in Baluchi populations, who are living in malaria hypoendemic region of Iran but not in African populations (0%-6%).

Conclusion

These data point towards the need for addressing the exact role of TLRs in contributing to human genetic factors in malaria susceptibility/resistance/severity within different malaria settings in the world.

Genetic variants in the TIRAP gene are associated with increased risk of sepsis-associated acute lung injury

Background

Toll like receptors (TLRs) signaling pathways, including the adaptor protein Mal encoded by the TIRAP gene, play a central role in the development of acute lung injury (ALI). Recently, the TIRAP variants have been described association with susceptibility to inflammatory diseases. The aim of this study was to investigate whether genetic variants in TIRAP are associated with the development of ALI.

Methods

A case-control collection from Han Chinese of 298 healthy subjects, 278 sepsis-associated ALI and 288 sepsis alone patients were included. Three tag single nucleotide polymorphisms (SNPs) of the TIRAP gene and two additional SNPs that have previously showed association with susceptibility to other inflammatory diseases were genotyped by direct sequencing. The differences of allele, genotype and haplotype frequencies were evaluated between three groups.

Results

The minor allele frequencies of both rs595209 and rs8177375 were significantly increased in ALI patients compared with both healthy subjects (odds ratio (OR) = 1.47, 95% confidence interval (CI):1.15-1.88, P = 0.0027 and OR = 1.97, 95% CI: (1.38-2.80), P = 0.0001, respectively) and sepsis alone patients (OR = 1.44, 95% CI: 1.12-1.85, P = 0.0041 and OR = 1.82, 95% CI: 1.28-2.57, P = 0.00079, respectively). Haplotype consisting of these two associated SNPs strengthened the association with ALI susceptibility. The frequency of haplotype AG (rs595209A, rs8177375G) in the ALI samples was significantly higher than that in the healthy control group (OR = 2.13, 95% CI: 1.46-3.09, P = 0.00006) and the sepsis alone group (OR = 2.24, 95% CI: 1.52-3.29, P = 0.00003). Carriers of the haplotype CA (rs595209C, rs8177375A) had a lower risk for ALI compared with healthy control group (OR = 0.69, 95% CI: 0.54-0.88, P = 0.0003) and sepsis alone group (OR = 0.71, 95% CI: 0.55-0.91, P = 0.0006). These associations remained significant after adjustment for covariates in multiple logistic regression analysis and for multiple comparisons.

Conclusions

These results indicated that genetic variants in the TIRAP gene might be associated with susceptibility to sepsis-associated ALI in Han Chinese population. However, the association needs to be replicated in independent studies.

Influence of genetic variations in TLR4 and TIRAP/Mal on the course of sepsis and pneumonia and cytokine release: an observational study in three cohorts

Introduction

It has been proposed that individual genetic variation contributes to the course of severe infections and sepsis. Recent studies of single nucleotide polymorphisms (SNPs) within the endotoxin receptor and its signaling system showed an association with the risk of disease development. This study aims to examine the response associated with genetic variations of TLR4, the receptor for bacterial LPS, and a central intracellular signal transducer (TIRAP/Mal) on cytokine release and for susceptibility and course of severe hospital acquired infections in distinct patient populations.

Methods

Three intensive care units in tertiary care university hospitals in Greece and Germany participated. 375 and 415 postoperative patients and 159 patients with ventilator associated pneumonia (VAP) were included. TLR4 and TIRAP/Mal polymorphisms in 375 general surgical patients were associated with risk of infection, clinical course and outcome. In two prospective studies, 415 patients following cardiac surgery and 159 patients with newly diagnosed VAP predominantly caused by Gram-negative bacteria were studied for cytokine levels in-vivo and after ex-vivo monocyte stimulation and clinical course.

Results

Patients simultaneously carrying polymorphisms in TIRAP/Mal and TLR4 and patients homozygous for the TIRAP/Mal SNP had a significantly higher risk of severe infections after surgery (odds ratio (OR) 5.5; confidence interval (CI): 1.34 - 22.64; P = 0.02 and OR: 7.3; CI: 1.89 - 28.50; P < 0.01 respectively). Additionally we found significantly lower circulating cytokine levels in double-mutant individuals with ventilator associated pneumonia and reduced cytokine production in an ex-vivo monocyte stimulation assay, but this difference was not apparent in TIRAP/Mal-homozygous patients. In cardiac surgery patients without infection, the cytokine release profiles were not changed when comparing different genotypes.

Conclusions

Carriers of mutations in sequential components of the TLR signaling system may have an increased risk for severe infections. Patients with this genotype showed a decrease in cytokine release when infected which was not apparent in patients with sterile inflammation following cardiac surgery.

The innate immune response in leprosy

Investigation into the innate immune response in leprosy has provided insight into immunoregulation in human infectious disease. Key advances include the role of pattern recognition receptors in recognizing pathogen-associated molecular patterns of Mycobacterium leprae, cytokine release by innate immune cells, macrophage and dendritic cell differentiation, as well as antimicrobial effector pathways. These insights provide targets for therapeutic intervention in modulating the course of leprosy and other chronic infectious diseases.