Evolutionary interplay of single nucleotide polymorphisms at the promoter region of TNF-α gene in different clinical outcomes of malaria in India

An elevated level of interleukin-17A in a Senegalese malaria cohort is associated with rs8193038 IL-17A genetic variant

Malaria infection is a multifactorial disease partly modulated by host immuno-genetic factors. Recent evidence has demonstrated the importance of Interleukin-17 family proinflammatory cytokines and their genetic variants in host immunity. However, limited knowledge exists about their role in parasitic infections such as malaria. We aimed to investigate IL-17A serum levels in patients with severe and uncomplicated malaria and gene polymorphism's influence on the IL-17A serum levels. In this research, 125 severe (SM) and uncomplicated (UM) malaria patients and 48 free malaria controls were enrolled. IL-17A serum levels were measured with ELISA. PCR and DNA sequencing were used to assess host genetic polymorphisms in IL-17A. We performed a multivariate regression to estimate the impact of human IL-17A variants on IL-17A serum levels and malaria outcomes. Elevated serum IL-17A levels accompanied by increased parasitemia were found in SM patients compared to UM and controls (P < 0.0001). Also, the IL-17A levels were lower in SM patients who were deceased than in those who survived. In addition, the minor allele frequencies (MAF) of two IL-17A polymorphisms (rs3819024 and rs3748067) were more prevalent in SM patients than UM patients, indicating an essential role in SM. Interestingly, the heterozygous rs8193038 AG genotype was significantly associated with higher levels of IL-17A than the homozygous wild type (AA). According to our results, it can be concluded that the IL-17A gene rs8193038 polymorphism significantly affects IL-17A gene expression. Our results fill a gap in the implication of IL-17A gene polymorphisms on the cytokine level in a malaria cohort. IL-17A gene polymorphisms also may influence cytokine production in response to Plasmodium infections and may contribute to the hyperinflammatory responses during severe malaria outcomes.

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.

TNF-α promoter variant (G-308A) is associated with susceptibility to P. falciparum infection and severe malaria: a meta-analysis and trial sequential analysis

Tumor necrosis factor-alpha (TNF-α) plays an essential role in Plasmodium falciparum infection, with lower levels associated with susceptibility to infection and higher levels linked with organ failure in severe malaria. Genetic polymorphisms in the promoter region of the TNF-α gene (G-308A and G-238A) affect plasma TNF-α levels. Numerous case-control studies have been conducted to determine the possible association between TNF-α polymorphisms and susceptibility to malaria infection and clinical severity; however, the results are inconsistent. Various databases such as Google Scholar, Science Direct, PubMed, and Scopus were searched for relevant articles for the present meta-analysis. Data were extracted from the eligible studies based on inclusion and exclusion criteria. Meta-analysis was carried out with CMA v.3.3.070 software, and combined odds ratio, 95% confidence interval, and p values were calculated. Further, a trial sequential analysis was also performed to test whether enough number of case and controls have been enrolled to date to draw a valid conclusion. Allele (OR = 9.757, p value=.049) and heterozygous (OR = 8.98, p value=.016) comparison model revealed the TNF-α G-308A variant as a susceptible genetic factor for P. falciparum infection. Similarly, a significant association of TNF-α G-308A polymorphism with P. falciparum malarial severity was also observed (A versus G: OR = 1.761, p value = .000; and GG + GA versus GG: OR = 1.769, p value = .000). However, no association of TNF-α (G-238A) polymorphism was observed with infection and severity of P. falciparum or Plasmodium vivax malaria. TNF-α G-308A variant is associated with susceptibility to P. falciparum infection and clinical severity. However, further studies on different populations are required.

Genetics of cerebral malaria: pathogenesis, biomarkers and emerging therapeutic interventions

Background

Cerebral malaria (CM) is a preeminent cause of severe disease and premature deaths in Sub-Saharan Africa, where an estimated 90% of cases occur. The key features of CM are a deep, unarousable coma that persists for longer than 1 h in patients with peripheral Plasmodium falciparum and no other explanation for encephalopathy. Significant research efforts on CM in the last few decades have focused on unravelling the molecular underpinnings of the disease pathogenesis and the identification of potential targets for therapeutic or pharmacologic intervention. These efforts have been greatly aided by the generation and study of mouse models of CM, which have provided great insights into key events of CM pathogenesis, revealed an interesting interplay of host versus parasite factors that determine the progression of malaria to severe disease and exposed possible targets for therapeutic intervention in severe disease.

Main Body

This paper reviews our current understanding of the pathogenic and immunologic factors involved in CM. We present the current view of the roles of certain gene products e.g., the var gene, ABCA-1, ICAM-1, TNF-alpha, CD-36, PfEMP-1 and G6PD, in CM pathogenesis. We also present alterations in the blood–brain barrier as a consequence of disease proliferation as well as complicated host and parasite interactions, including the T-cell immune reaction, reduced deformation of erythrocytes and cytoadherence. We further looked at recent advances in cerebral malaria treatment interventions by emphasizing on biomarkers, new diagnostic tools and emerging therapeutic options.

Conclusion

Finally, we discuss how the current understanding of some of these pathogenic and immunologic factors could inform the development of novel therapeutic interventions to fight CM.

Pathophysiology and neurologic sequelae of cerebral malaria

Cerebral malaria (CM), results from Plasmodium falciparum infection, and has a high mortality rate. CM survivors can retain life-long post CM sequelae, including seizures and neurocognitive deficits profoundly affecting their quality of life. As the Plasmodium parasite does not enter the brain, but resides inside erythrocytes and are confined to the lumen of the brain's vasculature, the neuropathogenesis leading to these neurologic sequelae is unclear and under-investigated. Interestingly, postmortem CM pathology differs in brain regions, such as the appearance of haemorragic punctae in white versus gray matter. Various host and parasite factors contribute to the risk of CM, including exposure at a young age, parasite- and host-related genetics, parasite sequestration and the extent of host inflammatory responses. Thus far, several proposed adjunctive treatments have not been successful in the treatment of CM but are highly needed. The region-specific CM neuro-pathogenesis leading to neurologic sequelae is intriguing, but not sufficiently addressed in research. More attention to this may lead to the development of effective adjunctive treatments to address CM neurologic sequelae.