Strong association of a tumor necrosis factor-alpha promoter allele with cerebral malaria in Myanmar

Tumor necrosis factor-α (TNF-α) -308G >a promoter polymorphism (rs1800629) promotes Asians in susceptibility to Plasmodium falciparum severe malaria: A meta-analysis

The multifactorial pathogenesis of severe malaria is partly attributed to host genes, such as those encoding cytokines involved in complex inflammatory reactions, namely tumor necrosis factor-alpha (TNF-α). However, the relationship between TNF-α -308G >A gene polymorphism (rs1800629) and the severity of Plasmodium falciparum (P. falciparum) malaria remains unclear, which prompts a meta-analysis to obtain more precise estimates. The present meta-analysis aimed to better understand this correlation and provide insight into its association in populations with different ethnicities. Literature search outcomes included eight eligible articles in which TNF-α -308G >A polymorphism was determined in uncomplicated malaria (UM) and severe malaria (SM) of P. falciparum as represented in the case and control groups. Pooled odds ratios (ORs) and 95% confidence intervals (95% CIs) were estimated in standard homozygous, recessive, dominant, and codominant genetic models. Subgroup analysis was based on ethnicity, i.e., Africans and Asians. The analyses included overall and the modified outcomes; the latter was obtained without the studies that deviated from the Hardy-Weinberg Equilibrium. The significant data also underwent sensitivity treatment but not publication bias tests because the number of studies was less than ten. Interaction tests were applied to differential outcomes between the subgroups. Overall and HWE-compliant analyses showed no significant association between the TNF-α -308G >A polymorphism and susceptibility to P. falciparum SM (ORs = 1.10-1.52, 95%CIs = 0.68-2.79; Pa = 0.24-0.68). Stratification by ethnicity revealed that two significant associations were found only in the Asians favoring SM for dominant (OR = 1.95, 95% CI = 1.06-3.61, Pa = 0.03) and codominant (OR = 1.83, 95% CI = 1.15-2.92, Pa = 0.01) under the random-effects model, but not among the African populations. The two significant Asian associations were improved with a test of interaction with P-value of0.02-0.03. The significant core outcomes were robust. Results of the meta-analysis suggest that TNF-α -308G >A polymorphism might affect the risk of P. falciparum SM, particularly in individuals of Asian descent. This supports ethnicity as one of the dependent factors of the TNF-α -308G >A association with the clinical severity of malaria. Further large and well-designed genetic studies are needed to confirm this conclusion.

Association of TNF-Alpha, MBL2, NOS2, and G6PD with Malaria Outcomes in People in Southern Ghana

Background

One major issue that has set back the gains of the numerous malaria control interventions that national malaria control programs have implemented is asymptomatic malaria. Certain host genetic factors are known to influence symptomatic malaria; however, not much is known about how host genetics influences the acquisition of asymptomatic malaria.

Methods

Genomic DNA was extracted from whole blood collected from 60 symptomatic and 149 nonfebrile (asymptomatic, N = 109, and uninfected, N = 40) volunteers aged between 2 and 69 years from a high (Obom) and a low (Asutsuare) malaria transmission setting in Southern Ghana. Restriction fragment length polymorphism (RFLP) was used to determine polymorphisms at the MBL2 54, TNF-α 308, NOS2 954, and G6PD 202/376 gene loci.

Results

Polymorphisms at the MBL2 54 and TNF-α 308 loci were significantly different amongst the three categories of volunteers in both Asutsuare (p = 0.006) and Obom (p=0.05). In Asutsuare, a low malaria transmission area, the allele G has significantly higher odds (3.15) of supporting asymptomatic malaria as against symptomatic malaria. There were significantly higher odds of TNF-α genotype GA being associated with symptomatic malaria as against asymptomatic malaria in both sites, Obom (p=0.027) and Asutsuare (p=0.027). The allele B of the G6PD gene was more prevalent in symptomatic rather than asymptomatic parasite-infected individuals in both Obom (p=0.001) and Asutsuare (p=0.003).

Conclusion

Individuals in Southern Ghana carrying the TNF-α 308 GA genotype are more likely to exhibit symptoms of malaria when infected with the malaria parasite as opposed to harboring an asymptomatic infection. Also, the B allele of the G6PD gene is likely to prevent a P. falciparum-infected person from exhibiting symptoms and thereby promote asymptomatic parasite carriage.

Association of cerebral malaria and TNF-α levels: a systematic review

Background

Cerebral malaria is the most severe form of infection with Plasmodium falciparum characterized by a highly inflammatory response. This systematic review aimed to investigate the association between TNF-α levels and cerebral malaria.

Methods

This review followed the Preferred Reporting of Systematic Review and Meta-analyses (PRISMA) guidelines. The search was performed at PubMed, LILACS, Scopus, Web of Science, The Cochrane Library, OpenGrey and Google Scholar. We have included studies of P. falciparum-infected humans with or without cerebral malaria and TNF-α dosage level. All studies were evaluated using a risk of bias tool and the GRADE approach.

Results

Our results have identified 2338 studies, and 8 articles were eligible according to this systematic review inclusion criteria. Among the eight articles, five have evaluated TNF- α plasma dosage, while two have evaluated at the blood and one at the brain (post-Morten). Among them, only five studies showed higher TNF-α levels in the cerebral malaria group compared to the severe malaria group. Methodological problems were identified regarding sample size, randomization and blindness, but no risk of bias was detected.

Conclusion

Although the results suggested that that TNF-α level is associated with cerebral malaria, the evidence is inconsistent and imprecise. More observational studies evaluating the average TNF-alpha are needed.

Genetics of Malaria Inflammatory Responses: A Pathogenesis Perspective

Despite significant progress in combating malaria in recent years the burden of severe disease and death due to Plasmodium infections remains a global public health concern. Only a fraction of infected people develops severe clinical syndromes motivating a longstanding search for genetic determinants of malaria severity. Strong genetic effects have been repeatedly ascribed to mutations and allelic variants of proteins expressed in red blood cells but the role of inflammatory response genes in disease pathogenesis has been difficult to discern. We revisited genetic evidence provided by inflammatory response genes that have been repeatedly associated to malaria, namely TNF, NOS2, IFNAR1, HMOX1, TLRs, CD36, and CD40LG. This highlighted specific genetic variants having opposing roles in the development of distinct malaria clinical outcomes and unveiled diverse levels of genetic heterogeneity that shaped the complex association landscape of inflammatory response genes with malaria. However, scrutinizing genetic effects of individual variants corroborates a pathogenesis model where pro-inflammatory genetic variants acting in early infection stages contribute to resolve infection but at later stages confer increased vulnerability to severe organ dysfunction driven by tissue inflammation. Human genetics studies are an invaluable tool to find genes and molecular pathways involved in the inflammatory response to malaria but their precise roles in disease pathogenesis are still unexploited. Genome editing in malaria experimental models and novel genotyping-by-sequencing techniques are promising approaches to delineate the relevance of inflammatory response gene variants in the natural history of infection thereby will offer new rational angles on adjuvant therapeutics for prevention and clinical management of severe malaria.

Inducible nitric oxide synthase 2 promoter polymorphism and malaria disease severity in children in Southern Ghana

Objective

We assessed the association of mutant allele frequencies of nitric oxide synthase 2 (NOS2) gene at two SNPs (-954 and -1173) with malaria disease severity in children from a malaria endemic area in Southern Ghana.

Method

Using children recruited at the hospital, assigned into clinical subgroups of uncomplicated and severe malaria and matching with their “healthy control” counterparts, we designed a case control study. Genomic DNA was extracted and genotyping using Restriction Fragment Polymorphism was done.

Result

A total of 123 malaria cases (91 uncomplicated, 32 severe) and 100 controls were sampled. Their corresponding mean Hbs were 9.6, 9.3 and 11.2g/dl and geometric mean parasite densities of 32097, 193252 and 0 parasites/ml respectively. Variant allele frequencies varied from 0.09 through 0.03 to 0.12 for G-954C and 0.06 through 0.03 to 0.07 for C-1173T in the uncomplicated, severe and healthy control groups respectively. There was a strong linkage disequilibrium between the two alleles (p<0.001). For the -954 position, the odds of developing severe malaria was found to be 2.5 times lower with the carriage of a C allele compared to those without severe malaria (χ²; p< 0.05) though this isn’t the case with -1173.

Conclusion

The carriage of a mutant allele in the -954 NOS2 gene may have a protective effect on malaria among Southern Ghanaian children.

Genetic variants of tumor necrosis factor-α -308G/A (rs1800629) but not Toll-interacting proteins or vitamin D receptor genes enhances susceptibility and severity of malaria infection

Susceptibility to malaria infection has been associated with host genetic polymorphisms that differs between groups. We hypothesize that Toll-interacting proteins (TOLLIP), vitamin D receptor (VDR) and tumor necrosis factor-α (TNF) genes are significant contributors to susceptibility and disease severity in Plasmodium falciparum (Pf) infection. Our aim is to explore the genomic diversity and haplotype frequency of these genes, as well as extrapolate possible association with markers of severity, between malaria-infected and healthy controls. Genomic DNA samples extracted from the blood of 107 malaria-infected patients and 190 uninfected controls were analyzed, with no difference in genotypic or allelic frequencies of TOLLIP and VDR polymorphisms. However, a significant difference in the genotypic (p = 2.20E-16) and allelic frequencies (p = 2.20E-16) of the TNF-α (snp rs1800629) polymorphism was found. The preponderance of the mutant variant among the malaria-infected show a possible impaired capacity to mount an effective immune response, potentially confirmed by our association results. This result calls for analysis of clearly delineated uncomplicated versus severe disease groups, including serum assays, providing a basis to conclude that susceptibility to malaria infection and potential contribution to disease severity is significantly associated with polymorphisms of the tumor necrosis factor-α but not TOLLIP or VDR genes.

Overview of human genetic susceptibility to malaria: From parasitemia control to severe disease

Malaria is a life-threatening blood disease caused by the protozoan Plasmodium. Infection may lead to several different patterns of symptoms in the host: asymptomatic state, uncomplicated disease or severe disease. Severe malaria occurs mostly in young children and is a major cause of death. Disease is thought to result from the sequestration of parasites in the small blood vessels of the brain and the deregulation of key immune system elements. The cellular and molecular regulatory mechanisms underlying the pathogenesis of disease are however not fully understood. What is known it is that the genetic determinants of the host play an important role in the severity of the disease and the outcome of infection. Here we review the most convincing results obtained through genetic epidemiology studies concerning the genetic control of malaria in human caused by Plasmodium falciparum infection. The identification of genes conferring susceptibility or resistance to malaria might improve diagnosis and treatment.

Lack of inflammatory gene expression in bats: a unique role for a transcription repressor

In recent years viruses similar to those that appear to cause no overt disease in bats have spilled-over to humans and other species causing serious disease. Since pathology in such diseases is often attributed to an over-active inflammatory response, we tested the hypothesis that bat cells respond to stimulation of their receptors for viral ligands with a strong antiviral response, but unlike in human cells, the inflammatory response is not overtly activated. We compared the response of human and bat cells to poly(I:C), a viral double-stranded RNA surrogate. We measured transcripts for several inflammatory, interferon and interferon stimulated genes using quantitative real-time PCR and observed that human and bat cells both, when stimulated with poly(I:C), contained higher levels of transcripts for interferon beta than unstimulated cells. In contrast, only human cells expressed robust amount of RNA for TNFα, a cell signaling protein involved in systemic inflammation. We examined the bat TNFα promoter and found a potential repressor (c-Rel) binding motif. We demonstrated that c-Rel binds to the putative c-Rel motif in the promoter and knocking down c-Rel transcripts significantly increased basal levels of TNFα transcripts. Our results suggest bats may have a unique mechanism to suppress inflammatory pathology.

Frequency of TNFA, INFG, and IL10 Gene Polymorphisms and Their Association with Malaria Vivax and Genomic Ancestry

Polymorphisms in cytokine genes can alter the production of these proteins and consequently affect the immune response. The trihybrid heterogeneity of the Brazilian population is characterized as a condition for the use of ancestry informative markers. The objective of this study was to evaluate the frequency of -1031T>C, -308G>A and -238G>A TNFA, +874 A>T IFNG and -819C>T, and -592C>A IL10 gene polymorphisms and their association with malaria vivax and genomic ancestry. Samples from 90 vivax malaria-infected individuals and 51 noninfected individuals from northern Brazil were evaluated. Genotyping was carried out by using ASO-PCR or PCR/RFLP. The genomic ancestry of the individuals was classified using 48 insertion/deletion polymorphism biallelic markers. There were no differences in the proportions of African, European, and Native American ancestry between men and women. No significant association was observed for the allele and genotype frequencies of the 6 SNPs between malaria-infected and noninfected individuals. However, there was a trend toward decreasing the frequency of individuals carrying the TNF-308A allele with the increasing proportion of European ancestry. No ethnic-specific SNPs were identified, and there was no allelic or genotype association with susceptibility or resistance to vivax malaria. Understanding the genomic mechanisms by which ancestry influences this association is critical and requires further study.

Molecular basis of human cerebral malaria development

Cerebral malaria is still a deleterious health problem in tropical countries. The wide spread of malarial drug resistance and the lack of an effective vaccine are obstacles for disease management and prevention. Parasite and human genetic factors play important roles in malaria susceptibility and disease severity. The malaria parasite exerted a potent selective signature on the human genome, which is apparent in the genetic polymorphism landscape of genes related to pathogenesis. Currently, much genomic data and a novel body of knowledge, including the identification of microRNAs, are being increasingly accumulated for the development of laboratory testing cassettes for cerebral malaria prevention. Therefore, understanding of the underlying complex molecular basis of cerebral malaria is important for the design of strategy for cerebral malaria treatment and control.

Tumour necrosis factor allele variants and their association with the occurrence and severity of malaria in African children: a longitudinal study

Background

Tumour necrosis factor (TNF) is central to the immune response to Plasmodium infection. Its plasma concentration is influenced by allele variants in the promoter region of TNF. The study’s objectives were to assess TNF allele variants (TNF₋₁₀₃₁, TNF₋₃₀₈): (1) modulation of malaria rates in young Tanzanian children; (2) modulation of the severity of malaria as indicated by haemoglobin concentrations at the time of presentation with febrile episodes; and (3) the association between Plasmodium infection and haemoglobin concentration in symptomless parasite carriers.

Methods

Data from a placebo-controlled trial in which 612 Tanzanian children aged 6–60 months with height-for-age z-score in the range −3 SD to 1.5 SD was utilised. Those with Plasmodium infection at baseline were treated with artemether-lumefantrine. An episode of malaria was predefined as current Plasmodium infection with an inflammatory response (axillary temperature ≥37.5°C or whole blood C-reactive protein concentration ≥8 mg/L) in children reported sick. Linkage disequilibrium (LD) pattern assessment as well as haplotype analysis was conducted using HAPLOVIEW. Cox regression models used in the primary analysis accounted for multiple episodes per child.

Results

Genotyping of 94.9% (581/612) children for TNF₋₁₀₃₁ (TNF₋₁₀₃₁T>C); allele frequency was 0.39. Corresponding values for rs1800629 (TNF₋₃₀₈G>A) were 95.4% (584/612) and 0.17. Compared to the wild type genotype (TT), malaria rates were increased in the TNF₋₁₀₃₁CC genotype (hazard ratio, HR [95% CI]: 1.41 [1.01‒1.97] and 1.31 [0.97‒1.76] for crude analysis and adjusting for pre-specified baseline factors, respectively) but decreased in those with the TNF₋₃₀₈AA genotype (corresponding HR: 0.13 [0.02‒0.63] and 0.16 [0.04‒0.67]). These associations were weaker when analysing first episodes of malaria (P value −0.59 and 0.38, respectively). No evidence that allele variants of TNF₋₁₀₃₁ and TNF₋₃₀₈ affected haemoglobin concentration at first episode of malaria, or that they modified the association between Plasmodium infection and haemoglobin concentrations at baseline was observed.

Conclusion

In this cohort of Tanzanian children, the TNF₋₁₀₃₁CC genotype was associated with increased rates of malarial episodes, whereas the TNF₋₃₀₈AA genotype was associated with decreased rates.

IFN-gamma and TNF associated with severe falciparum malaria infection in Saudi pregnant women

Background

Tumour necrosis factor (TNF) and interferon gamma (IFN-γ), encoded by TNF-836 C/A (rs 1800630) and IFN-γ -1616 C/T (rs2069705) genes, are key immunological mediators that are believed to both play protective and pathological roles in malaria. The aim of this study was to investigate the relationship between TNF-836 C/A and IFN-γ-1616 C/T polymorphism and susceptibility to severe malaria in pregnant women.

Methods

A prospective cohort (cross-sectional) study was conducted in pregnant women attending the out-patient clinic in King Fahad Specialist Hospital in Jazan (KFSHJ), with a clinical diagnosis of malaria. A total of one hundred and eighty six pregnant women were genotyped for single nucleotide polymorphism (SNP) for TNF and IFN-γ using Taqman® MGB Probes. Serum cytokine concentrations were measured by sandwich ELISA method.

Results

A hospital case–control study of severe malaria in a Saudi population identified strong associations with individual single-nucleotide polymorphisms in the TNF and IFN-γ genes, and defined TNF-836 C and IFN-γ-1616 T genotypes and alleles which were statistically significantly associated with severe malaria infection. Furthermore, TNF-836 CC and IFN-γ-1616 TT genotypes were associated with higher serum concentration of TNF and IFN-γ, respectively, and with susceptibility to severe malaria.

Conclusions

This data provides a starting point for functional and genetic analysis of the TNF and IFN-γ genomic region in malaria infection affecting Saudi populations.

Host susceptibility to malaria in human and mice: compatible approaches to identify potential resistant genes

There is growing evidence for human genetic factors controlling the outcome of malaria infection, while molecular basis of this genetic control is still poorly understood. Case-control and family-based studies have been carried out to identify genes underlying host susceptibility to malarial infection. Parasitemia and mild malaria have been genetically linked to human chromosomes 5q31-q33 and 6p21.3, and several immune genes located within those regions have been associated with malaria-related phenotypes. Association and linkage studies of resistance to malaria are not easy to carry out in human populations, because of the difficulty in surveying a significant number of families. Murine models have proven to be an excellent genetic tool for studying host response to malaria; their use allowed mapping 14 resistance loci, eight of them controlling parasitic levels and six controlling cerebral malaria. Once quantitative trait loci or genes have been identified, the human ortholog may then be identified. Comparative mapping studies showed that a couple of human and mouse might share similar genetically controlled mechanisms of resistance. In this way, char8, which controls parasitemia, was mapped on chromosome 11; char8 corresponds to human chromosome 5q31-q33 and contains immune genes, such as Il3, Il4, Il5, Il12b, Il13, Irf1, and Csf2. Nevertheless, part of the genetic factors controlling malaria traits might differ in both hosts because of specific host-pathogen interactions. Finally, novel genetic tools including animal models were recently developed and will offer new opportunities for identifying genetic factors underlying host phenotypic response to malaria, which will help in better therapeutic strategies including vaccine and drug development.

The host genetic diversity in malaria infection

Populations exposed to Plasmodium infection develop genetic mechanisms of protection against severe disease. The clinical manifestation of malaria results primarily from the lysis of infected erythrocytes and subsequent immune and inflammatory responses. Herein, we review the genetic alterations associated with erythrocytes or mediators of the immune system, which might influence malaria outcome. Moreover, polymorphisms in genes related to molecules involved in mechanisms of cytoadherence and their influence on malaria pathology are also discussed. The results of some studies have suggested that the combinatorial effects of a set of genetic factors in the erythrocyte-immunology pathway might be relevant to host resistance or susceptibility against Plasmodium infection. However, these results must be interpreted with caution because of the differences observed in the functionality and frequency of polymorphisms within different populations. With the recent advances in molecular biology techniques, more robust studies with reliable data have been reported, and the results of these studies have identified individual genetic factors for consideration in preventing severe disease and the individual response to treatment.

Protective human leucocyte antigen haplotype, HLA-DRB1*01-B*14, against chronic Chagas disease in Bolivia

BACKGROUND

Chagas disease, caused by the flagellate parasite Trypanosoma cruzi affects 8-10 million people in Latin America. The mechanisms that underlie the development of complications of chronic Chagas disease, characterized primarily by pathology of the heart and digestive system, are not currently understood. To identify possible host genetic factors that may influence the clinical course of Chagas disease, Human Leucocyte Antigen (HLA) regional gene polymorphism was analyzed in patients presenting with differing clinical symptoms.

METHODOLOGY

Two hundred and twenty nine chronic Chagas disease patients in Santa Cruz, Bolivia, were examined by serological tests, electrocardiogram (ECG), and Barium enema colon X-ray. 31.4% of the examinees showed ECG alterations, 15.7% megacolon and 58.1% showed neither of them. A further 62 seropositive megacolon patients who had undergone colonectomy due to acute abdomen were recruited. We analyzed their HLA genetic polymorphisms (HLA-A, HLA-B, MICA, MICB, DRB1 and TNF-alpha promoter region) mainly through Sequence based and LABType SSO typing test using LUMINEX Technology.

PRINCIPAL FINDINGS

The frequencies of HLA-DRB1*01 and HLA-B*14:02 were significantly lower in patients suffering from megacolon as well as in those with ECG alteration and/or megacolon compared with a group of patients with indeterminate symptoms. The DRB1*0102, B*1402 and MICA*011 alleles were in strong Linkage Disequilibrium (LD), and the HLA-DRB1*01-B*14-MICA*011 haplotype was associated with resistance against chronic Chagas disease.

CONCLUSIONS

This is the first report of HLA haplotype association with resistance to chronic Chagas disease.

Tumour necrosis factor gene polymorphism and disease prevalence

Tumour necrosis factor (TNF), an important proinflammatory cytokine, plays a role in the regulation of cell differentiation, proliferation and death, as well as in inflammation, innate and adaptive immune responses, and also implicated in a wide variety of human diseases. The presence of DNA sequence variations in regulatory region might interfere with transcription of TNF gene, influencing the circulating level of TNF and thus increases the susceptibility to human diseases (infectious, cancer, autoimmune, neurodegenerative and other diseases). In this review, we have comprehensively analysed various published case-control studies of different types of human diseases, in which TNF gene polymorphism played a role, and computationally predicted several single nucleotide polymorphisms (SNPs) lie in transcription factor-binding sites (TFBS) of transcription factors (TFs). It has been observed that TNF enhancer polymorphism is implicated in several diseases, and TNF rs1800629 and rs361525 SNPs are the most important in human disease susceptibility as these might influence the transcription of TNF gene. Thirty-two SNPs lies in TFBS of 20 TFs have been detected in the TNF upstream region. It has been found that TNF enhancer polymorphism influences the serum level of TNF in different human diseases and thus affects the susceptibility to diseases. The presence of DNA sequence variation in TNF gene causes the modification of transcriptional regulation and thus responsible for association of susceptibility/resistance with human diseases.

Human leukocyte antigen class I polymorphisms influence the mild clinical manifestation of Plasmodium falciparum infection in Ghanaian children

A prospective study that included 429 children for active detection of mild malaria was conducted in a coastal region of Ghana to reveal whether the incidence of malaria is affected by human leukocyte antigen (HLA) polymorphism. During 12 months of follow-up, 85 episodes of mild clinical malaria in 74 individuals were observed, and 34 episodes among them were accompanied with significant parasitemia at >5000 infected red blood cells per cubic millimeter. Attributable and relative risks conferred by genetic factors in the HLA region were evaluated by comparison of the incidence in children, stratified by carrier status, of a given allele of HLA-A, -B, -DRB1 and TNFA promoter polymorphism. HLA-B*35:01 reduced the incidence by 0.178 events per person per year (0.060 versus 0.239 for B*35:01-positive and -negative subpopulations, respectively), and a relative risk of 0.25, which remained statistically significant after Bonferroni's correction for multiple testing (p(c) = 8.2 × 10(-5)). Further, HLA-B*35:01 and -B*53:01 exhibited opposite effects on the incidence of malaria with significant parasitemia. When parasite densities in different HLA carriers status were compared, HLA-A*01 conferred an increase in parasite load (p = 6.0 × 10(-7)). In addition, we found a novel DRB1 allele that appears to have emerged from DRB1*03:02 by single nucleotide substitution.

Cytokine gene haplotypes with a potential effect on susceptibility to malaria in sympatric ethnic groups in Mali

Cytokines are important players in the immune responses, and an unbalance in pro- and anti-inflammatory cytokine responses may affect parasitemia and pathology in a Plasmodium falciparum infection. Polymorphisms in cytokine genes may affect not only the levels of the protein, but many down-stream functions, such as production of C-reactive protein and immunoglobulin isotype switching. Susceptibility to malaria has been shown to differ between individuals with different genetic backgrounds, as indicated by studies in Fulani and non-Fulani ethnic groups. The aim of this study was to investigate possible interethnic differences in totally twelve single nucleotide polymorphisms (SNPs) in the genes encoding the cytokines IL-1β, IL-6, IL-10 and TNF. These SNPs are present in the promoter region of the genes, and have previously been associated with cytokine expression and with disease outcome in malaria. The results from the present study suggest that the Fulani ethnic group has a more pro-inflammatory response, due to high frequencies of high-producing alleles of IL1β and low-producing alleles of IL10. IL-6 could potentially also contribute to the relatively lower susceptibility to malaria in the Fulani ethnic group, whereas the TNF polymorphisms analysed in this study rather seem to associate with the severity of the infection and not the susceptibility for the infection itself. We therefore suggest that the polymorphisms analysed in this study all show a potential to influence the relatively lower susceptibility to malaria seen in the Fulani ethnic group as compared to the other sympatric ethnic groups.

Evidence for epistasis between hemoglobin C and immune genes in human P. falciparum malaria: a family study in Burkina Faso

Hemoglobin C (HbC) has been recently associated with protection against Plasmodium falciparum malaria. It is thought that HbC influences the development of immune responses against malaria, suggesting that the variation at the HbC locus (rs33930165) may interact with polymorphic sites in immune genes. We investigated, in 198 individuals belonging to 34 families living in Burkina Faso, statistical interactions between HbC and 11 polymorphisms within interleukin-4 (IL4), IL12B, NCR3, tumor necrosis factor (TNF) and lymphotoxin-α (LTA), which have been previously associated with malaria-related phenotypes. We searched for multilocus interactions by using the pedigree-based generalized multifactor dimensionality reduction approach. We detected 29 multilocus interactions for mild malaria, maximum parasitemia or asymptomatic parasitemia after correcting for multiple tests. All the single-nucleotide polymorphisms studied are included in several multilocus models. Nevertheless, most of the significant multilocus models included IL12B 3' untranslated region, IL12Bpro or LTA+80, suggesting that those polymorphisms play a particular role in the interactions detected. Moreover, we identified six multilocus models involving NCR3 that encodes the activating natural killer (NK) receptor NKp30, suggesting an interaction between HbC and genes involved in the activation of NK cells. More generally, our findings suggest an interaction between HbC and genes influencing the activation of effector cells for phenotypes related to mild malaria.

A study of the TNF/LTA/LTB locus and susceptibility to severe malaria in highland papuan children and adults

BACKGROUND

Severe malaria (SM) syndromes caused by Plasmodium falciparum infection result in major morbidity and mortality each year. However, only a fraction of P. falciparum infections develop into SM, implicating host genetic factors as important determinants of disease outcome. Previous studies indicate that tumour necrosis factor (TNF) and lymphotoxin alpha (LTα) may be important for the development of cerebral malaria (CM) and other SM syndromes.

METHODS

An extensive analysis was conducted of single nucleotide polymorphisms (SNPs) in the TNF, LTA and LTB genes in highland Papuan children and adults, a population historically unexposed to malaria that has migrated to a malaria endemic region. Generated P-values for SNPs spanning the LTA/TNF/LTB locus were corrected for multiple testing of all the SNPs and haplotype blocks within the region tested through 10,000 permutations. A global P-value of < 0.05 was considered statistically significant.

RESULTS

No associations between SNPs in the TNF/LTA/LTB locus and susceptibility to SM in highland Papuan children and adults were found.

CONCLUSIONS

These results support the notion that unique selective pressure on the TNF/LTA/LTB locus in different populations has influenced the contribution of the gene products from this region to SM susceptibility.

Study on association between genetic polymorphisms of haem oxygenase-1, tumour necrosis factor, cadmium exposure and malaria pathogenicity and severity

Background

Malaria is the most important public health problems in tropical and sub-tropical countries. Haem oxygenase (HO) enzyme and the pro-inflammatory cytokine tumour necrosis factor (TNF) have been proposed as one of the factors that may play significant role in pathogenicity/severity of malaria infection. HO is the enzyme of the microsomal haem degradation pathway that yields biliverdin, carbon monoxide, and iron. In this study, the association between malaria disease pathogenicity/severity and (GT)_n repeat polymorphism in the promoter region of the inducible HO-1 including the effect of cadmium exposure (potent inducer of HO-1 transcription) as well as polymorphism of TNF were investigated.

Methods

Blood samples were collected from 329 cases non-severe malaria with acute uncomplicated Plasmodium falciparum malaria (UM) and 80 cases with Plasmodium vivax malaria (VM), and 77 cases with severe or cerebral malaria (SM) for analysis of genetic polymorphisms of HO-1 and TNF and cadmium levels. These patients consisted of 123 (25.3%) Thai, 243 (50.0%) Burmese and 120 (24.7%) Karen who were present at Mae Sot General Hospital, Mae Sot, Tak Province, Thailand.

Results

The number of (GT)_n repeats of the HO-1 gene in all patients varied between 16 and 39 and categorized to short (S), medium (M) and long (L) GT_n repeats. The genotype of (GT)_n repeat of HO-1 was found to be significantly different among the three ethnic groups of patients. Significantly higher frequency of S/L genotype was found in Burmese compared with Thai patients, while significantly lower frequencies of S/S and M/L but higher frequency of M/M genotype was observed in Burmese compared with Karen patients. No significant association between HO-1 and TNF polymorphisms including the inducing effect of cadmium and malaria pathogenicity/severity was observed.

Conclusions

Difference in the expression of HO-1 genotype in different ethnic groups may contribute to different severity of malaria disease. With this limited sample size, the finding of the lack of association between malaria disease pathogenicity/severity genetic polymorphisms of HO-1 (GT)_n repeat as well as TNF observed in this study may not entirely exclude their possible link with malaria disease pathogenicity/severity. Further study in larger sample size is required.

TNF family members and malaria: old observations, new insights and future directions

Tumor necrosis factor (TNF) has long been recognized to promote malaria parasite killing, but also to contribute to the development of severe malaria disease. The precise molecular mechanisms that influence these different outcomes in malaria patients are not well understood, but the virulence and drug-resistance phenotype of malaria parasites and the genetic background and age of patients are likely to be important determinants. In the past few years, important roles for other TNF family members in host immune responses to malaria parasites and the induction of disease pathology have been discovered. In this review, we will summarize these more recent findings and highlight major gaps in our current knowledge. We will also discuss future research strategies that may allow us to better understand the sometimes subtle and intricate effects of TNF family molecules during malaria infection.

Genomic Approaches to the Host Response to Pathogens

The need to better understand host–pathogen interactions has risen with the expansion in genomics and related technologies. This chapter focuses on two aspects of the host response to pathogens where major advances are being made using genomic approaches. The availability of complete genomic sequences of an expanding number of pathogens, the human and mouse genome sequences, and the advent of genome-wide genotyping and gene expression profiling has opened up new avenues of investigation in the field. The genotype of the pathogen plays a major role in the response of the host to infection with more virulent pathogenic strains possessing the capability to interfere with the host immune response. In addition, different individuals in a population can have very different responses to a genetically identical pathogen. Part of the differential response is governed by the underlying genetic differences between individuals. The advent of genome-wide genotyping using single nucleotide polymorphisms or microsatellite markers is leading to major advances in molecular epidemiology. The future impact of genomic approaches on the development of diagnostics and therapeutics is discussed for infectious diseases. This includes defining the basis of genetic susceptibility to infection and system-wide molecular response to a pathogen.

Malaria: mechanisms of erythrocytic infection and pathological correlates of severe disease

Malaria is an ancient disease that continues to cause enormous human morbidity and mortality. The life cycle of the causative parasite involves multiple tissues in two distinct host organisms, mosquitoes and humans. However, all the clinical symptoms of malaria are a consequence of infection of human erythrocytes. An understanding of the basic mechanisms that govern parasite invasion, remodeling, growth, and reinvasion of erythrocytes and the complex events leading to tissue pathology may yield new diagnostics and treatments for malaria. This approach is revealing a more complete picture of the most serious syndrome associated with this infection-cerebral malaria. We focus on the most recent understanding of the molecular basis of infection, summarize our finding from an ongoing pediatric cerebral malaria autopsy study in Malawi, and integrate these insights to malarial pathology.

The severity of malarial anaemia in Plasmodium chabaudi infections of BALB/c mice is determined independently of the number of circulating parasites

BACKGROUND

Severe malarial anaemia is a major complication of malaria infection and is multi-factorial resulting from loss of circulating red blood cells (RBCs) from parasite replication, as well as immune-mediated mechanisms. An understanding of the causes of severe malarial anaemia is necessary to develop and implement new therapeutic strategies to tackle this syndrome of malaria infection.

METHODS

Using analysis of variance, this work investigated whether parasite-destruction of RBCs always accounts for the severity of malarial anaemia during infections of the rodent malaria model Plasmodium chabaudi in mice of a BALB/c background. Differences in anaemia between two different clones of P. chabaudi were also examined.

RESULTS

Circulating parasite numbers were not correlated with the severity of anaemia in either BALB/c mice or under more severe conditions of anaemia in BALB/c RAG2 deficient mice (lacking T and B cells). Mice infected with P. chabaudi clone CB suffered more severe anaemia than mice infected with clone AS, but this was not correlated with the number of parasites in the circulation. Instead, the peak percentage of parasitized RBCs was higher in CB-infected animals than in AS-infected animals, and was correlated with the severity of anaemia, suggesting that the availability of uninfected RBCs was impaired in CB-infected animals.

CONCLUSION

This work shows that parasite numbers are a more relevant measure of parasite levels in P. chabaudi infection than % parasitaemia, a measure that does not take anaemia into account. The lack of correlation between parasite numbers and the drop in circulating RBCs in this experimental model of malaria support a role for the host response in the impairment or destruction of uninfected RBC in P. chabaudi infections, and thus development of acute anaemia in this malaria model.

HLA-B27 and ankylosing spondylitis geographic distribution as the result of a genetic selection induced by malaria endemic? A review supporting the hypothesis

The geographic distribution of HLA-B27 shows a latitude-related gradient inverse to that of malaria endemic. An apparent exception occurs in New Guinea, a region where malaria is present, but where HLA-B27 frequency shows, however, an orographic gradient antithetic to that of malaria incidence. We therefore suggest that Plasmodium falciparum may have exerted a negative selection on this gene. This might be due to a higher susceptibility to severe forms of malaria, associated with HLA-B27 or other close gene(s). In addition, we suggest here that the same selective pressure that has contributed to reduce the HLA-B27 frequency in some regions has favoured the fixing of newly generated B27 subtypes included in more advantageous HLA haplotypes. In some cases, as for B*2709 in Sardinia and B*2706 in Southeast Asia, these haplotypes may harbour factors that protect from Ankylosing Spondylitis, an autoimmune disease strongly associated with HLA-B27, thus offering a novel, powerful tool to dissect disease pathogenesis, and to identify additional genetic factors of susceptibility.

Polymorphisms of TNF-enhancer and gene for FcgammaRIIa correlate with the severity of falciparum malaria in the ethnically diverse Indian population

BACKGROUND

Susceptibility/resistance to Plasmodium falciparum malaria has been correlated with polymorphisms in more than 30 human genes with most association analyses having been carried out on patients from Africa and south-east Asia. The aim of this study was to examine the possible contribution of genetic variants in the TNF and FCGR2A genes in determining severity/resistance to P. falciparum malaria in Indian subjects.

METHODS

Allelic frequency distribution in populations across India was first determined by typing genetic variants of the TNF enhancer and the FCGR2A G/A SNP in 1871 individuals from 55 populations. Genotyping was carried out by DNA sequencing, single base extension (SNaPshot), and DNA mass array (Sequenom). Plasma TNF was determined by ELISA. Comparison of datasets was carried out by Kruskal-Wallis and Mann-Whitney tests. Haplotypes and LD plots were generated by PHASE and Haploview, respectively. Odds ratio (OR) for risk assessment was calculated using EpiInfotrade mark version 3.4.

RESULTS

A novel single nucleotide polymorphism (SNP) at position -76 was identified in the TNF enhancer along with other reported variants. Five TNF enhancer SNPs and the FCGR2A R131H (G/A) SNP were analyzed for association with severity of P. falciparum malaria in a malaria-endemic and a non-endemic region of India in a case-control study with ethnically-matched controls enrolled from both regions. TNF -1031C and -863A alleles as well as homozygotes for the TNF enhancer haplotype CACGG (-1031T>C, -863C>A, -857C>T, -308G>A, -238G>A) correlated with enhanced plasma TNF levels in both patients and controls. Significantly higher TNF levels were observed in patients with severe malaria. Minor alleles of -1031 and -863 SNPs were associated with increased susceptibility to severe malaria. The high-affinity IgG2 binding FcgammaRIIa AA (131H) genotype was significantly associated with protection from disease manifestation, with stronger association observed in the malaria non-endemic region. These results represent the first genetic analysis of the two immune regulatory molecules in the context of P. falciparum severity/resistance in the Indian population.

CONCLUSION

Association of specific TNF and FCGR2A SNPs with cytokine levels and disease severity/resistance was indicated in patients from areas with differential disease endemicity. The data emphasizes the need for addressing the contribution of human genetic factors in malaria in the context of disease epidemiology and population genetic substructure within India.

Significant association between TNF-alpha (TNF) promoter allele (-1031C, -863C, and -857C) and cerebral malaria in Thailand

We examined a possible association of three single nucleotide polymorphisms (SNPs) of the tumor necrosis factor alpha (TNF) promoter -1031T>C (rs1799964), -863C>A (rs1800630), and -857C>T (rs1799724) with severe malaria in 466 adult patients having Plasmodium falciparum malaria in northwest Thailand. Four TNF promoter alleles comprising these three SNPs were detected in the studied population. The frequency of the TNF U04 allele designated -1031C, -863C, and -857C was found to be significantly greater in patients with cerebral malaria than in patients with mild malaria (12.6%, cerebral malaria vs 5.6%, mild malaria; odds ratio =2.5; P=0.002). The association of U04 with susceptibility to cerebral malaria was not caused by linkage disequilibrium with any specific HLA-B and -DRB1 alleles.

Human malarial disease: a consequence of inflammatory cytokine release

Malaria causes an acute systemic human disease that bears many similarities, both clinically and mechanistically, to those caused by bacteria, rickettsia, and viruses. Over the past few decades, a literature has emerged that argues for most of the pathology seen in all of these infectious diseases being explained by activation of the inflammatory system, with the balance between the pro and anti-inflammatory cytokines being tipped towards the onset of systemic inflammation. Although not often expressed in energy terms, there is, when reduced to biochemical essentials, wide agreement that infection with falciparum malaria is often fatal because mitochondria are unable to generate enough ATP to maintain normal cellular function. Most, however, would contend that this largely occurs because sequestered parasitized red cells prevent sufficient oxygen getting to where it is needed. This review considers the evidence that an equally or more important way ATP deficiency arises in malaria, as well as these other infectious diseases, is an inability of mitochondria, through the effects of inflammatory cytokines on their function, to utilise available oxygen. This activity of these cytokines, plus their capacity to control the pathways through which oxygen supply to mitochondria are restricted (particularly through directing sequestration and driving anaemia), combine to make falciparum malaria primarily an inflammatory cytokine-driven disease.

TNF as a malaria candidate gene: polymorphism-screening and family-based association analysis of mild malaria attack and parasitemia in Burkina Faso

We have previously obtained strong evidence for linkage of mild malaria attack to the MHC region, with a peak close to the tumor necrosis factor (TNF) gene. We screened, for polymorphisms, the entire TNF gene in the same sample of 34 families comprising 197 individuals living in a Plasmodium falciparum endemic area and we found 17 polymorphisms. In a longitudinal study, we investigated whether the 11 most frequent and informative polymorphisms were associated with mild malaria attack and maximum parasitemia, which was the highest parasitemia in each individual over 2 years. Mild malaria attack and maximum parasitemia were positively correlated. Transmission disequilibrium tests showed nominal evidence for association between TNF-1031, TNF-308, TNF851 and TNF1304 polymorphisms, and mild malaria attack on the one hand, and between TNF-238, TNF851 and TNF1304 polymorphisms, and maximum parasitemia on the other hand. After accounting for multiple tests, we confirmed the association of TNF-238 with maximum parasitemia and the association of TNF1304 and TNF851 with maximum parasitemia and mild malaria attack. The association tests with mild malaria attack suggest a moderate effect of TNF-308 polymorphism. In conclusion, our study suggests that several TNF variants may be part of the genetic determinants for maximum parasitemia and/or mild malaria attack.

Associations between frequencies of a susceptible TNF-alpha promoter allele and protective alpha-thalassaemias and malaria parasite incidence in Vanuatu

Tumour necrosis factor-alpha (TNF-alpha) is one of the key cytokines that influence the pathology of microbial infections. The genetic susceptibility to severe forms of falciparum malaria is differentially associated with TNF-alpha promoter gene polymorphisms (TNFP alleles). In a previous study, we identified a TNFP-allele characterized by a C to T transition at position -857 (TNFP-D allele) as a marker for susceptibility to cerebral malaria in Myanmar. The frequencies of TNFP alleles on six islands of Vanuatu, Melanesia (South-west Pacific) were estimated to investigate whether malaria selection pressure on this susceptibility marker has influenced its prevalence. Within the archipelago of Vanuatu there is a decreasing cline of parasite incidence from North to South. Of the four alleles of the TNFP gene detected in Vanuatu, the TNFP-D allele frequencies were inversely correlated with the parasite incidence of islands; TNFP-D varied from 0.55 on the island with the lowest parasite incidence to 0.26 on the island with the highest parasite incidence (r = -0.855, P = 0.03). We also observed a significant correlation between the frequencies of alpha-thalassaemia alleles, thought to protect against malaria and parasite incidence in the same populations. These data are consistent with a previously reported correspondence between the frequencies of glucose 6-phosphate dehydrogenase (G6PD) deficiency and parasite incidences on the islands of Vanuatu (Kaneko et al. 1998) and indicate that the degree of malaria endemicity has influenced the allele frequencies of at least three loci that confer both susceptibility (TNFP-D) and protection (alpha-thalassaemias and G6PD deficiency).

Is there a future for TNF promoter polymorphisms?

The in vitro study of TNF promoter polymorphism (SNP) function was stimulated by the numerous case-control (association) studies of the polymorphisms in relation to human disease and the appearance of several studies claiming to show a functional role for these SNPs provided a further impetus to researchers interested in the role of TNF in their disease of interest. In this review we consider case-control studies, concentrating on the autoimmune and inflammatory diseases rheumatoid arthritis, multiple sclerosis, ankylosing spondylitis, and asthma, and on infectious diseases including malaria, hepatitis B and C infection, leprosy and sepsis/septic shock. We also review the available evidence on the functional role of the various TNF promoter polymorphisms. In general, case-control studies have produced mixed results, with little consensus in most cases on whether any TNF polymorphisms are actually associated with disease, although results have been more consistent in the case of infectious diseases, particularly malaria. Functional studies have also produced mixed results but recent work suggests that the much studied -308G/A polymorphism is not functional, while the function of other TNF polymorphisms remains controversial. Studies of the TNF region are increasingly using extended haplotypes that can better capture the variation of the MHC region.

Tumor necrosis factor-alpha gene promoter polymorphisms in chronic schizophrenia

BACKGROUND

Alterations in cytokine levels in patients with schizophrenia have been documented. Polymorphisms in these cytokine genes are thus potential genetic markers for schizophrenia. The aim of this study was to investigate four biallelic polymorphisms in the tumor necrosis factor-alpha (TNFalpha) gene promoter in relation to susceptibility to schizophrenia.

METHODS

Three hundred two patients and 152 control subjects were genotyped and frequencies of genotypes and alleles were compared for the -1031T/C, -863C/A, -857C/T, and -308G/A polymorphisms. Genotype and allele frequencies were compared between controls and patients.

RESULTS

There were statistically significant differences in genotype distribution and allele frequencies for the -308 polymorphism (p <.001). Genotype distribution and allele frequencies of the other three polymorphisms were not different between patients and reference controls.

CONCLUSIONS

The -308 polymorphism or another genetic variant in linkage disequilibrium with it could be a susceptibility factor for chronic schizophrenia.

Novel polymorphisms and the definition of promoter ‘alleles’ of the tumor necrosis factor and lymphotoxin α loci: inclusion in HLA haplotypes

Tumor necrosis factor (TNF) and lymphotoxin alpha (LTA) influence a variety of cellular responses and play a complex role in the immune response. Several single nucleotide polymorphisms (SNPs) have been reported in these major histocompatibility complex (MHC)-linked loci; however, a comprehensive examination of polymorphisms in the promoter regions of TNF and LTA has not been carried out and was undertaken here. Seven novel SNPs in LTA were identified by sequence analysis of 69 samples. Eight novel TNF alleles and 16 novel LTA alleles were designated. The TNF alleles clustered into two closely related groups, while the LTA alleles clustered into three distinct groups using phylogenetic and percentage difference analyses. A total of 52 unique TNF-LTA-HLA haplotypes are reported. There appear to be some associations between TNF/LTA alleles and HLA haplotypes, but not with specific HLA alleles. The majority of the SNPs appear to be randomly associated within and between the two loci except for the LTA SNPs at -293, +81 and +369. These observations may provide an explanation for the oftentimes contradictory results of studies associating individual cytokine gene SNPs with expression level phenotypes, HLA and disease.

No evidence for a major effect of tumor necrosis factor alpha gene polymorphisms in periportal fibrosis caused by Schistosoma mansoni infection

Hepatic periportal fibrosis (PPF), associated with portal hypertension, is a major pathological consequence of infections with Schistosoma mansoni and Schistosoma japonicum. Indeed, affected subjects may die from portal hypertension. Previous studies have indicated that tumor necrosis factor alpha (TNF-alpha) may aggravate fibrosis. We therefore investigated whether PPF was associated with certain polymorphisms of the TNF-alpha gene. Four polymorphisms (TNF-alpha -376 G/A, -308 G/A, -238 G/A, and +488 G/A) were investigated in two Sudanese populations living in an area in which S. mansoni is endemic. These polymorphisms were analyzed for 105 Sudanese subjects with various grades of PPF, from mild to advanced; all subjects were from two neighboring villages (Taweela and Umzukra). They were then analyzed for 70 subjects with advanced liver disease and for 345 matched controls from the Gezira region. We found no evidence of associations between these four polymorphisms and PPF in both of these studies. Thus, these four polymorphisms, two of which (TNF-alpha -376 and -308) were found to increase TNF-alpha gene transcription, are unlikely to have a major effect on PPF progression in these populations. However, this result does not exclude the possibility that these polymorphisms have a minor effect on PPF development.

Cytokines: accelerators and brakes in the pathogenesis of cerebral malaria

Cerebral malaria (CM) is a major life-threatening complication of Plasmodium falciparum infection. The nature of the pathogenetic processes leading to the cerebral complications is poorly understood. Mouse models of this condition have provided insight into the key events in pathogenesis, including those that occur before clinical symptoms are seen. Some T helper 1 (Th1) cytokines (e.g. interferon-gamma, lymphotoxin and tumour necrosis factor) have been implicated in driving the immunopathological process leading to CM, whereas some Th2 cytokines (e.g. interleukin-10, transforming growth factor-beta) appear to oppose this process. Upregulation of leukocyte adhesion molecules on the cerebral microvascular endothelium appears to be an important component of the proinflammatory actions of the cytokines. Activation of platelets in the cerebral microcirculation could also be a key event in CM. Furthermore, recent evidence has emerged indicating that cytokines might influence biochemical pathways in the brain that, in turn, could determine the outcome of CM.

Genetic factors associated with development of cerebral malaria and fibrotic schistosomiasis

Collaborative studies have identified some genetic factors contributing to the development of severe forms of malaria and schistosomiasis. In Thailand, the TNF-alpha 5'-flanking region shows biallelic polymorphic sites at nucleotides -238, -308, -857, -863, and -1031, and seven alleles have been identified in patients from Myanmar. We found that the TNF promoter (TNFP)-D allele was significantly associated with cerebral malaria in populations from Karen (P < 0.0001, OR = 124.86) and ethnic Burma (P < 0.0001, OR = 34.50). In China, we have identified two major genes related to the severity of liver fibrosis, one an HLA class II gene, and the other the IL-13 gene. The frequency of the HLA-DRB5*0101 allele and that of the IL-13 promoter A/A (IL-13P- A/A) genotype were elevated in fibrotic patients, although the two genes are located on different chromosomes, chromosomes 6p and 5q, respectively. Subjects with both genotypes had odds ratios (OR = 24.5) much higher than the sum of the ratios for each individual genotype (OR = 5.1, 95% Confidence Interval 1.3-24.7 for HLA-DRB5*0101, OR = 3.1 95% CI 1.5 - 6.5 for IL-13P- A/A). That the effects of the two susceptibility markers are synergistic rather than additive, strongly suggests that the pathogenic Th2 response directly influences the prognosis of post-schistosomal liver fibrosis.

Tumor necrosis factor-alpha in normal and diseased brain: Conflicting effects via intraneuronal receptor crosstalk?

Tumor necrosis factor-alpha (TNF-alpha) is pleiotropic mediator of a diverse array of physiological and neurological functions, including both normal regulatory functions and immune responses to infectious agents. Its role in the nervous system is prominent but paradoxical. Studies on uninflamed or "normal" brain have generally attributed TNF-alpha a neuromodulatory effect. In contrast, in inflamed or diseased brain, the abundance of evidence suggests that TNF-alpha has an overall neurotoxic effect, which may be particularly pronounced for virally mediated neurological disease. Still others have found TNF-alpha to be protective under some conditions of neurological insult. It is still uncertain exactly how TNF-alpha is able to induce these opposing effects through receptor activation of only a limited set of cell signaling pathways. In this paper, we provide support from the literature to advance our hypothesis that one mechanism by which TNF-alpha can exert its paradoxical effects in the brain is via crosstalk with signaling pathways of growth factors or other cytokines.