Figures
Abstract
Background
Plasmodium vivax malaria (Pv-malaria) is still considered a neglected disease despite an alarming number of individuals being infected annually. Malaria pathogenesis occurs with the onset of the vector-parasite-host interaction through the binding of pathogen-associated molecular patterns (PAMPs) and receptors of innate immunity, such as toll-like receptors (TLRs). The triggering of the signaling cascade produces an elevated inflammatory response. Genetic polymorphisms in TLRs are involved in susceptibility or resistance to infection, and the identification of genes involved with Pv-malaria response is important to elucidate the pathogenesis of the disease and may contribute to the formulation of control and elimination tools.
Methodology/Principal findings
A retrospective case-control study was conducted in an intense transmission area of Pv-malaria in the state of Amazonas, Brazil. Genetic polymorphisms (SNPs) in different TLRs, TIRAP, and CD14 were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis in 325 patients infected with P. vivax and 274 healthy individuals without malaria history in the prior 12 months from the same endemic area. Parasite load was determined by qPCR. Simple and multiple logistic/linear regressions were performed to investigate association between the polymorphisms and the occurrence of Pv-malaria and parasitemia. The C/T (TLR5 R392StopCodon) and T/T (TLR9 -1486C/T) genotypes appear to be risk factors for infection by P. vivax (TLR5: C/C vs. C/T [OR: 2.116, 95% CI: 1.054–4.452, p = 0.031]; TLR9: C/C vs. T/T [OR: 1.919, 95% CI: 1.159–3.177, p = 0.010]; respectively). Fever (COEF = 7599.46, 95% CI = 3063.80–12135.12, p = 0.001) and the C/C genotype of TLR9 -1237C/T (COEF = 17006.63, 95% CI = 3472.83–30540.44, p = 0.014) were independently associated with increased parasitemia in patients with Pv-malaria.
Citation: Costa AG, Ramasawmy R, Ibiapina HNS, Sampaio VS, Xábregas LA, Brasil LW, et al. (2017) Association of TLR variants with susceptibility to Plasmodium vivax malaria and parasitemia in the Amazon region of Brazil. PLoS ONE 12(8): e0183840. https://doi.org/10.1371/journal.pone.0183840
Editor: Luzia Helena Carvalho, Centro de Pesquisas Rene Rachou, BRAZIL
Received: May 5, 2017; Accepted: August 11, 2017; Published: August 29, 2017
Copyright: © 2017 Costa et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: Data are available from by Ethics Committee for researchers from Fundação de Medicina Tropical Dr. Heitor Vieira Dourado (CEP/FMT-HVD - cep@fmt.am.gov.br), who meet the criteria for access to confidential data. Due to ethical restrictions regarding patient privacy, data are available upon request. Requests for the data may be sent to the corresponding author or coauthors [Allyson G. Costa (allyson.gui.costa@gmail.com), Rajendranath Ramasawmy (ramasawm@gmail.com), Marcus V.G. Lacerda (marcuslacerda.br@gmail.com) and Adriana Malheiro (malheiroadriana@yahoo.com.br)].
Funding: This study was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (Grant number 575788/2008-9), Fundació Cellex (P. vivax Consortium) and Bill & Mellinda Gates Foundation (TransEPI Consortium). MVGL is a level 1 research fellow from CNPq. AM is a level 2 research fellow from CNPq. RR is a research fellow from FAPEAM (PVS Program - PECTI-AM/PG#019/2013). AGC, VSS, AMT, LWB, ACGA, HNSI and LAX have fellowship from CAPES, CNPq and FAPEAM (PhD, Master´s and SI students). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Introduction
Approximately 214 million cases of malaria were diagnosed in 2015, with 438,000 deaths [1]. In Brazil, 140,000 cases were reported, representing 41.7% of cases in the Americas [2,3]. The Amazon region contributes nearly 99.9% of the malaria notifications, and Plasmodium vivax is responsible for 83.7% of cases [4,5].
Malaria results in a wide spectrum of clinical manifestations that occur during the vector-parasite-host interaction, and the first asexual reproduction process occurs in the liver [6,7]. Febrile episodes of malaria start after the interaction between the toxins that are produced by the schizont and released during the rupture of red blood cells and the phagocytic cells of the innate immune system [8]. These toxins, also called pathogen associated molecular patterns (PAMPs) are mainly recognized by toll-like receptors (TLRs) [9]. The Plasmodium PAMPs such as the glycosylphosphatidylinositol anchors (GPI), hemozoin linked to DNA are recognized by TLR-1/TLR-2, TLR-4, TLR-2/TLR-6, and TLR-9, respectively, producing an intense inflammatory response and activating dendritic cells, monocyte subtypes, and macrophages [10–16].
The inflammatory response resulting from the pathogenesis of the disease is closely related to the parasite load and the genetic background of the host [17]. Inflammation and cytokine production were reported to be higher in P. vivax infection than that in other species such as Plasmodium falciparum [18–20]. Deletion of TLRs and co-stimulatory molecules in murine models showed decreased production of proinflammatory cytokines and increased susceptibility to infection by different species of Plasmodium and other protozoans [11,21–23].
Genetic polymorphisms in TLRs are involved in cytokine activation pathways and may play a role in resistance or susceptibility to Plasmodium infection. The variant TLR1 I602S was associated with the development of symptomatic malaria and high parasitemia in P. falciparum malaria (Pf-malaria) [24,25]. Single nucleotide polymorphisms (SNPs) in TLR4 (A299G and T399I) were shown to be associated with the onset of clinical manifestations of severe Pf-malaria in African children and pregnant women, and in adults with non-severe symptomatic malaria [26–28]. Individuals with the SNP R392StopCodon (TLR5) are unable to induce the intracellular signaling cascade in bacterial diseases, producing lower concentrations of inflammatory cytokines such as IL-6 and TNF-α [29,30]. Cytokines are important for parasite load control and Plasmodium clearance in humans [15,31]
The TLR6 S249P polymorphism may be a risk factor for the development of malaria [24]. Allelic variants in the promoter region of TLR9 -1237C/T and -1486C/T are associated with parasitemia in Pf-infected individuals and placental malaria [24,27]. The SNP of TIR domain-containing adaptor protein (TIRAP) S180L appears to confer protection against malaria, tuberculosis, and bacterial diseases [32]. CD14–159 is associated with the incidence and mortality of septic shock [33,34].
P. vivax has several PAMPs that are recognized by TLRs, and studies have shown that polymorphisms in the TLR genes may be associated with Pf-malaria. In this study, SNPs in the TLRs, TIRAP, and CD14 genes were investigated in P. vivax infected individuals from the Amazon region of Brazil. Association of the polymorphisms TLR5 R392StopCodon and TLR9 -1486C/T with Pv-malaria and the C/C genotype of the SNP TLR9 -1237C/T with increased parasitemia was observed.
Materials and methods
Study area and sampling
The study was conducted with biological samples collected from individuals of two areas of the state of Amazonas, based on the low intra-regional migration of its inhabitants and similar profiles of malaria transmission. The regions chosen were followed in two cohort studies, entitled "The epidemiology of malaria in the municipality of Careiro", and "The comparative epidemiology of P. falciparum and P. vivax transmission in Papua New Guinea, Thailand and Brazil", carried out in rural and peri-urban areas of the cities of Careiro and Manaus from 2008 to 2011 and 2013 to 2014, respectively.
The Careiro municipality, which is 110 km from the Amazonas state capital Manaus, has access to a federal highway (BR-319), and has an estimated population of 30,000. Most inhabitants live in rural areas and are supported by federal programs that encourage the practice of agriculture. The Panelão and Sítio Castanho communities comprise an estimated population of 1,200, and were chosen for the study due to the observation of intense transmission of Pv-malaria [35].
The communities Brasileirinho, Ipiranga, and Puraquequara, located in the peri-urban area east of Manaus, had an estimated population of 2,500 at the end of 2012, according to a census conducted by the FMT-HVD team shortly before our sample collection. There is uncontrolled deforestation in these areas. The economy is mainly based on agricultural and extraction activities, and is at high risk of Pv-infection [36].
A retrospective case-control study was conducted from the two cohorts. A total of 325 patients with Pv-malaria diagnosed by thick blood smear examination [37] and confirmed by qPCR [38] were included in the study, along with 274 healthy individuals with no malaria history in the prior 12 months and confirmed negative by qPCR for Plasmodium spp. during the cohort studies (Fig 1). All study participants were from the same endemic area, sharing similar environments and risk of exposure to the parasite.
We included 599 eligible participants from two cohort studies conducted in Amazonas. Of these, 274 healthy individuals without malaria history in the prior 12 months were included in the “Healthy Group” and 325 patients diagnosed with Pv-malaria infection were included in the “Pv-malaria Cases”. Parasitemia analysis was performed for 208 patients.
Ethics statement
The studies were approved by the Comitê de Ética em Pesquisa da Fundação de Medicina Tropical Dr. Heitor Vieira Dourado (CEP/FMT-HVD process #51536/2012), and by the Comissão Nacional de Ética em Pesquisa (CONEP) linked to the Conselho Nacional de Saúde (CONEP process #15197/2008, #349211/2013). All participants read and signed the written informed consent form. Malaria cases detected in longitudinal studies were treated in accordance with the recommendations of the Brazilian Ministry of Health [39].
Genomic DNA extraction
Samples of 300 μL of blood were collected via finger puncture from each participant for genomic DNA purification. The QIAmp DNA kit (QIAGEN, Chatsworth, CA, USA) was used for the Careiro study, and the FavorPrepTM 96-well Genomic DNA Kit (Favorgen, Ping-Tung, Taiwan) was used for the Manaus study. DNA samples were quantified with a NanoDrop 2000c (Thermo Fisher Scientific, Waltham, MA, USA) to evaluate the concentration, and purity of nucleic acids.
Quantification of P. vivax DNA by qPCR assay
Parasitemia of Pv-malaria was determined by amplifying the 18S rRNA gene using the 7500 Fast qPCR System (Applied Biosystems, Foster, CA, USA) as described previously [40,41], and is expressed as number of copies/μL. The primers/probes, qPCR cycling conditions, qPCR efficiency and detection limit are shown in S1 Table. Parasitemia was obtained for only 208 Pv-malaria patients (Fig 1).
Polymorphism genotyping
The following polymorphisms, TLR1 I602S, (rs5743618), TLR4 A299G (rs4986790), TLR4 T399I (rs4986791), TLR5 R392StopCodon (rs5744105), TLR6 S249P (rs5743810), TLR9 -1237C/T (rs187084), TLR9 -1486C/T (rs5743836), TIRAP S180L (rs8177374), and CD14–159 (rs2569191) were investigated. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis was used for allelic discrimination as described previously [24,42,43]. Briefly, the PCR reaction for each SNP consisted of 1 μL genomic DNA (~ 20ng) added to 24 μL amplification mix containing 0.2 μL (2 U) Platinum™ Taq polymerase (Thermo Fisher Scientific), 2.5 μL 10x buffer (100 mmol/L Tris-HCl [pH 8.3] and 500 mmol/L KCl), 1 μL MgCl2 (1.5 mmol/L), 1 μL dNTPs (40 mmol/L), 0.5 μL each of forward and reverse primer (0.25 pmol/L) and 18.3 μL ultrapure dH2O. A total of 10 μL of PCR product was digested with 5 U of respective restriction endonuclease (New England Biolabs, Ipswich, MA, USA) in enzyme buffer according to the manufacturer’s instructions. The primers, PCR cycling conditions, and restriction endonucleases are shown in S2 Table. The fragments generated by PCR-RFLP were separated by electrophoresis in either a 2% or 4% agarose gel stained with GelRed™ Nucleic Acid Gel Stain (Biotium, Hayward, CA, USA), and visualized with the UV light Gel Doc™ XR+ System (Bio-Rad Corporation, Hercules, CA, USA) with a photo documentation system.
Statistical and data analysis
Comparison between groups was performed with the chi-squared (χ2) or Fisher’s exact test with 95% confidence interval [CI]. The Hardy-Weinberg equilibrium (HWE) was determined by comparing the frequency of the observed and expected number of genotypes. Simple and multiple logistic regressions were performed to investigate association between the polymorphisms and the occurrence and recurrence of Pv-malaria and parasitemia. For both regression analyses, the variables age, gender, fever, and hemoglobin levels were included as confounders. A backward stepwise technique was applied. Variables with p-values less than or equal to 0.2 in the simple linear regression were selected for the multivariate model analysis. The final model considered all variables that were statistically significant (p<0.05). The analysis of haplotypes and linkage disequilibrium (LD) was carried out by Haploview software (v4.2). Tests for Hardy-Weinberg equilibrium were performed by an online application (https://ihg.gsf.de/cgi-bin/hw/hwa1.pl). Regression models were performed by Stata software (v13).
Results
Baseline characteristics of the study population
Baseline characteristics of the study population are shown in Table 1. The median age of the healthy control and Pv-malaria cases were 39 and 37 years, respectively (p = 0.744). In both groups, male subjects were predominant (55% and 62%). The average parasite load was 188 copies/uL. A median of 2 malarial episodes was reported by the patients. Approximately 27% of the Pv-malaria cases were primary infections. Patients reported fever (54%), headache (31%), chills (29%), myalgia (28%) and sweating (16%). The median hemoglobin level was 13.7 g/dL.
Association of the genotypes and alleles of polymorphisms in TLR5 R392StopCodon and TLR9 -1486C/T with P. vivax malaria
Of all the SNPs studied, only TLR9 -1486C/T slightly deviated from the HWE in Pv-malaria cases (p = 0.006). TIRAP S180L was null in the population studied. The genotypic and allelic frequencies for all the SNPs are shown in Table 2. The genotype distributions for TLR5 R392StopCodon and TLR9 -1486C/T were significantly different between the groups (p = 0.03 and p = 0.01, respectively). The genotypes C/T (TLR5 R392StopCodon) and T/T (TLR9 -1486C/T) appear to be risk factors for Pv-infection (TLR5: C/C vs. C/T OR = 2.1 [95% CI: 1.1–4.5, p = 0.031]; TLR9: C/C vs. T/T OR = 1.9, [95% CI: 1.2–3.2, p = 0.01]; TLR9: C/C vs. C/T+T/T OR = 1.6, [95% CI: 1.1–2.5, p = 0.024]). Similar trends were observed at the allele levels for both SNPs. Carriers of the T allele were at higher risk for developing Pv-malaria (TLR5 OR = 2.1, [95% CI: 1.0–4.3, p = 0.034]; TLR9 OR = 1.3, [95% CI: 1.0–1.7, p = 0.02]).
The TLR9 -1237C/C genotype is associated with increased parasitemia in Pv-malaria
Table 3 summarizes the univariable and multivariable linear regression analyses for parasitemia association with the different variables. Fever (COEF = 7599.46, 95% CI = 3063.80–12135.12, p = 0.001) and the C/C genotype of TLR9 -1237C/T (COEF = 17006.63, 95% CI = 3472.83–30540.44, p = 0.014) were independently associated with increased parasitemia.
Linkage disequilibrium of the TLR polymorphisms
Linkage disequilibrium (LD) between polymorphisms in receptors TLR1 and TLR6 (I602S vs. S249P), TLR4 (A299G vs. T399I), and TLR9 (-1237C/T vs. -1486C/T) was very low, as calculated by Haploview 4.2 software. The R2 and D' of the LD were 0.38 and 0.83 for TLR1 and TLR6, 0.18 and 0.44 for TLR4, 0.006 and 0.20 for TLR9.
Discussion
Pv-malaria is still considered a neglected disease despite various efforts directed to its control and elimination [44–46]. P. vivax presents biological complexity due to the interplay between environmental factors, parasite load, and the immunological status and genetic background of the human host [17,47]. The hypnozoite stage in the liver can cause clinical episodes of relapse with lower parasite load. These are often associated with mild or asymptomatic clinical display and contribute to the transmission of the disease [48,49]. The molecular mechanisms influencing these characteristics remain poorly understood. Knowledge of the host genetic factors in malaria may contribute to the elucidation of the molecular mechanisms involved in the development of the disease, as not all individuals exposed to the parasites develop symptoms. The identification of genes involved in susceptibility or resistance to infection by P. vivax is important to understand the pathogenesis of the disease and may contribute to the designing of control and elimination tools, as well as the development of an effective vaccine.
Innate immunity plays a key role in infectious processes. The discovery of pattern recognition receptors (PRRs) such as TLRs, Nod-like receptors (NLRs), RIG-I-like receptors (RLRs), and scavenger receptors has contributed to the understanding of infectious disease [50,51]. TLRs are key mediators in the response to malaria, playing an important role in the bridge between innate and adaptive immunity, mainly by activation of transcription factor NF-κB and inducing production of proinflammatory cytokines [52]. SNPs in TLRs and adapter molecules that influence the inflammatory process and proinflammatory cytokine production may be associated with susceptibility to infections [34,53,54]. Changes in the production of these cytokines may influence the control of parasitemia and clinical manifestations of the disease, since a fine balance in the inflammatory process is essential for parasite clearance [15,16,55,31]. The data presented in this study suggest an association of polymorphisms TLR5 and TLR9 with Pv-malaria. Furthermore, the SNP TLR9 -1237C/T was associated with increased parasitemia.
Allelic variants of TLR1 I602S and TLR6 S249P showed no association with Pv-malaria. An association of polymorphisms in TLR1 and TLR6 with mild malaria in patients infected with different Plasmodium species was recently demonstrated. Variants in TLR1 may predispose patients with Pf-malaria complications and increased parasitemia [24,25]. In addition, SNPs I602S (TLR1) and S249P (TLR6) were associated with severe malaria in Indian patients, showing the genetic contribution of these variants to the onset of cerebral malaria [56]. TLR-1 and -6 form heterodimers with TLR-2 and recognize the GPI anchor of the parasite. Mutations in these receptors can impair recognition and subsequent elimination of Plasmodium [12,24].
SNPs in TLR4 were not associated with Pv-malaria in our study. These polymorphisms have been associated with severe manifestations of malaria in children and mild symptoms in pregnant African women infected with P. falciparum [26,27]. Furthermore, T399I and A299G in TLR4 were associated with increased parasitemia in Indian patients with Pf-malaria, indicating that this receptor is important in inducing immune response to malaria [57]. In addition, these SNPs appeared to modulate the susceptibility to severe anemia and malaria in Nigerian children [58,59]. Moreover, there was no correlation between these polymorphisms and complications of malaria in adult patients and in other parasitic diseases, such as chronic Chagas disease [28,60,61], and this study corroborates this lack of association. The TLR4/CD14 complex is responsible for cytokine production via NF-κB, and the SNP CD14–159 in the promoter region has been associated with susceptibility to tuberculosis, and was shown to influence the production of IFN-γ [62–64]. Our data does not show any association of this SNP with Pv-malaria or parasitemia.
Flagellin (FliC), present in bacteria and parasites, is a ligand of TLR-5. Activation of TLR-5 leads to the production of proinflammatory cytokines such as IL-6 [65]. To our knowledge, this is the first report of an association of the SNP R392StopCodon in TLR5 with susceptibility to Pv-malaria. TLR-5 was shown to be a promising alternative to enhance the immunogenicity of the proteins to specific P. vivax, such as the 19 kDa C-terminal fragment of merozoite surface protein 1 (MSP119) after combination with Salmonella enterica serovar Typhimurium FliC [66,67]. Thus, we suggest that individuals with this mutation may not react favorably to this vaccine design. Alternative vaccines for carriers of this mutation must be sought.
The association of the -1486C/T variant present in the promoter region of TLR9 with Pv-malaria in this study corroborated other observations of association of this SNP with susceptibility to symptomatic and placental malaria caused by P. falciparum [24,27]. Interestingly, this SNP has been shown to correlate with high Plasmodium parasitemia and low production of IFN-γ and TNF-α [24,68,69]. We show the genotype C/C of the SNP TLR9 -1237C/T was associated with high parasite load. Together, these data confirm recent studies with Pf-malaria and suggest that TLR9 may play a key role in controlling parasitemia [24,69]. TLR9-depleted mice showed loss in control of parasitic infections compared to wild type mice [23,70]. SNPs in TLR9 appear to predispose Indian individuals to severe malaria [71] and these findings were confirmed in a meta-analysis study with 665 severe malaria patients and 1,187 uncomplicated malaria individuals from India and Africa, with an association of variants -1486C/T and -1237C/T of TLR9 with severe malaria [72].
This study has some limitations. Although the levels of associations with Pv-malaria and parasitemia are high, the study population is small. It needs validation with a larger sample size to confirm the importance of TLR9 and TLR5 in Pv-malaria. The small sample size does not allow intra-comparison of the genotypes and alleles studied with clinical manifestations of Pv-malaria, including in asymptomatic, mild, and severe malaria.
To our knowledge, this is the first study to show that variants in the TLR pathway may be involved in the pathogenesis of P. vivax malaria. TLRs are key mediators in response to malaria as they trigger the expression of proinflammatory cytokines to inhibit parasite growth. TLR5 R392StopCodon and TLR9 -1486C/T may predispose individuals to P. vivax malaria, while TLR9 -1237C/T was associated with Pv-malaria with high parasitemia. However, additional studies should be conducted in other endemic areas to confirm the role of host genetics in infection and pathogenesis of Pv-malaria.
Supporting information
S1 Table. Description of assay, primer/probe sequences, qPCR protocol, qPCR efficiency and detection limit for quantification of P. vivax DNA.
https://doi.org/10.1371/journal.pone.0183840.s001
(DOCX)
S2 Table. Description of polymorphisms, primer sequences, PCR protocols, restriction enzymes, and fragments generated during the SNP identification study.
https://doi.org/10.1371/journal.pone.0183840.s002
(DOCX)
References
- 1.
World Health Organization (WHO). World Malaria Report. World Heal Organ. 2015; 238.
- 2.
Pan American Health Organization. Situation of malaria in the region of the Americas, 2000–2013. Geneva: World Health Organization; 2014.
- 3. Brazilian Ministry of Health. Secretaria de Vigilância em Saúde. Boletim Epidemiológico. 2015;46: 1–5.
- 4. Oliveira-ferreira J, Lacerda MVG, Brasil P, Ladislau JLB, Tauil PL, Daniel-ribeiro CT. Malaria in Brazil: an overview Review. Malar J. 2010;9: 1–15.
- 5. Sampaio VS, Siqueira AM, Alecrim M das GC, Mourão MPG, Marchesini PB, Albuquerque BC, et al. Malaria in the state of amazonas: A typical brazilian tropical disease infl uenced by waves of economic development. Rev Soc Bras Med Trop. scielo; 2015;48: 4–11. pmid:26061365
- 6. Mayor A, Aponte JJ, Fogg C, Saúte F, Greenwood B, Dgedge M, et al. The epidemiology of malaria in adults in a rural area of southern Mozambique. Malar J. 2007;6: 3. pmid:17233881
- 7. Schofield L, Grau GE. Immunological processes in malaria pathogenesis. Nat Rev Immunol. 2005;5: 722–35. pmid:16138104
- 8. Oakley MS, Gerald N, McCutchan TF, Aravind L, Kumar S. Clinical and molecular aspects of malaria fever. Trends Parasitol. Elsevier Ltd; 2011;27: 442–9. pmid:21795115
- 9. Gowda DC. TLR-mediated cell signaling by malaria GPIs. Trends Parasitol. 2007;23: 596–604. pmid:17980663
- 10. Pichyangkul S, Yongvanitchit K, Kum-arb U, Hemmi H, Akira S, Krieg AM, et al. Malaria blood stage parasites activate human plasmacytoid dendritic cells and murine dendritic cells through a Toll-like receptor 9-dependent pathway. J Immunol. 2004;172: 4926–33. Available: http://www.ncbi.nlm.nih.gov/pubmed/15067072 pmid:15067072
- 11. Coban C, Ishii KJ, Kawai T, Hemmi H, Sato S, Uematsu S, et al. Toll-like receptor 9 mediates innate immune activation by the malaria pigment hemozoin. J Exp Med. 2005;201: 19–25. pmid:15630134
- 12. Krishnegowda G, Hajjar AM, Zhu J, Douglass EJ, Uematsu S, Akira S, et al. Induction of proinflammatory responses in macrophages by the glycosylphosphatidylinositols of Plasmodium falciparum: cell signaling receptors, glycosylphosphatidylinositol (GPI) structural requirement, and regulation of GPI activity. J Biol Chem. 2005;280: 8606–16. pmid:15623512
- 13. Nebl T, De Veer MJ, Schofield L. Stimulation of innate immune responses by malarial glycosylphosphatidylinositol via pattern recognition receptors. Parasitology. 2005;130 Suppl: S45–62. pmid:16281992
- 14. Parroche P, Lauw FN, Goutagny N, Latz E, Monks BG, Visintin A, et al. Malaria hemozoin is immunologically inert but radically enhances innate responses by presenting malaria DNA to Toll-like receptor 9. Proc Natl Acad Sci U S A. 2007;104: 1919–24. pmid:17261807
- 15. Gazzinelli RT, Kalantari P, Fitzgerald K a, Golenbock DT. Innate sensing of malaria parasites. Nat Rev Immunol. 2014;14: 744–757. pmid:25324127
- 16. Antonelli LR V, Leoratti FMS, Costa PAC, Rocha BC, Diniz SQ, Tada MS, et al. The CD14+CD16+ inflammatory monocyte subset displays increased mitochondrial activity and effector function during acute Plasmodium vivax malaria. PLoS Pathog. 2014;10: e1004393. pmid:25233271
- 17. Costa AG, Ramasawmy R, Malheiro A, Lacerda MVG. Implications of SNPs on toll-like receptor genes in malaria: what do we know? Rev Soc Bras Med Trop. 2017;50: 151–152. pmid:28562748
- 18. Anstey NM, Handojo T, Pain MCF, Kenangalem E. Lung Injury in Vivax Malaria: Pathophysiological Evidence for Pulmonary Vascular Sequestration and Posttreatment Alveolar- Capillary Inflammation. 2007;195: 589–596. pmid:17230420
- 19. Price RN, Tjitra E, Guerra C a, Yeung S, White NJ, Anstey NM. Vivax malaria: neglected and not benign. Am J Trop Med Hyg. 2007;77: 79–87. 77/6_Suppl/79 [pii pmid:18165478
- 20. Tjitra E, Anstey NM, Sugiarto P, Warikar N, Kenangalem E, Karyana M, et al. Multidrug-resistant Plasmodium vivax associated with severe and fatal malaria: A prospective study in Papua, Indonesia. PLoS Medicine. 2008. pp. 0890–0899. pmid:18563962
- 21. Adachi K, Tsutsui H, Kashiwamura S, Seki E, Nakano H, Takeuchi O, et al. Plasmodium berghei infection in mice induces liver injury by an IL-12- and toll-like receptor/myeloid differentiation factor 88-dependent mechanism. J Immunol. 2001;167: 5928–34. pmid:11698470
- 22. Franklin BS, Rodrigues SO, Antonelli LR, Oliveira R V, Goncalves AM, Sales-Junior P a, et al. MyD88-dependent activation of dendritic cells and CD4(+) T lymphocytes mediates symptoms, but is not required for the immunological control of parasites during rodent malaria. Microbes Infect. 2007;9: 881–90. pmid:17537666
- 23. Bafica A, Santiago HC, Goldszmid R, Ropert C, Gazzinelli RT, Sher A. Cutting edge: TLR9 and TLR2 signaling together account for MyD88-dependent control of parasitemia in Trypanosoma cruzi infection. J Immunol. 2006;177: 3515–3519. pmid:16951309
- 24. Leoratti FMS, Farias L, Alves FP, Suarez-Mútis MC, Coura JR, Kalil J, et al. Variants in the toll-like receptor signaling pathway and clinical outcomes of malaria. J Infect Dis. 2008;198: 772–780. pmid:18662133
- 25. Hahn WO, Harju-Baker S, Erdman LK, Krudsood S, Kain KC, Wurfel MM, et al. A common TLR1 polymorphism is associated with higher parasitaemia in a Southeast Asian population with Plasmodium falciparum malaria. Malar J. BioMed Central; 2016;15: 12. pmid:26738805
- 26. Mockenhaupt FP, Cramer JP, Hamann L, Stegemann MS, Eckert J, Oh N-R, et al. Toll-like receptor (TLR) polymorphisms in African children: common TLR-4 variants predispose to severe malaria. J Commun Dis. 2006;38: 230–45. pmid:17373355
- 27. Mockenhaupt FP, Hamann L, von Gaertner C, Bedu-Addo G, von Kleinsorgen C, Schumann RR, et al. Common polymorphisms of toll-like receptors 4 and 9 are associated with the clinical manifestation of malaria during pregnancy. J Infect Dis. 2006;194: 184–8. pmid:16779724
- 28. Greene J a Moormann AM, Vulule J Bockarie MJ, Zimmerman P a Kazura JW. Toll-like receptor polymorphisms in malaria-endemic populations. Malar J. 2009;8: 50. pmid:19317913
- 29. Hawn TR, Verbon A, Lettinga KD, Zhao LP, Li SS, Laws RJ, et al. A common dominant TLR5 stop codon polymorphism abolishes flagellin signaling and is associated with susceptibility to legionnaires’ disease. J Exp Med. 2003;198: 1563–72. pmid:14623910
- 30. Gu L, Huang J, Tan J, Wei Q, Jiang H, Shen T, et al. Impact of TLR5 rs5744174 on stroke risk, gene expression and on inflammatory cytokines, and lipid levels in stroke patients. Neurol Sci. 2016;37: 1537–1544. pmid:27262705
- 31. Guimarães da Costa A, do Valle Antonelli LR, Augusto Carvalho Costa P, Paulo Diniz Pimentel J, Garcia NP, Monteiro Tarragô A, et al. The Robust and Modulated Biomarker Network Elicited by the Plasmodium vivax Infection Is Mainly Mediated by the IL-6/IL-10 Axis and Is Associated with the Parasite Load. J Immunol Res. 2014;2014: 1–11. pmid:24741587
- 32. Khor CC, Chapman SJ, Vannberg FO, Dunne A, Murphy C, Ling EY, et al. A Mal functional variant is associated with protection against invasive pneumococcal disease, bacteremia, malaria and tuberculosis. Nat Genet. 2007;39: 523–8. pmid:17322885
- 33. Schröder NWJ, Morath S, Alexander C, Hamann L, Hartung T, Zähringer U, et al. Lipoteichoic acid (LTA) of Streptococcus pneumoniae and Staphylococcus aureus activates immune cells via Toll-like receptor (TLR)-2, lipopolysaccharide-binding protein (LBP), and CD14, whereas TLR-4 and MD-2 are not involved. J Biol Chem. 2003;278: 15587–15594. pmid:12594207
- 34. Schröder NWJ, Schumann RR. Single nucleotide polymorphisms of Toll-like receptors and susceptibility to infectious disease. Lancet Infect Dis. 2005;5: 156–64. pmid:15766650
- 35. Silva SV, Siqueira AM, Sampaio VDS, Guinovart C, Carlos R, Lecca R, et al. Declining malaria transmission in rural Amazon: changing epidemiology and challenges to achieve elimination. Malar J. BioMed Central; 2016; 1–14.
- 36. Brasil LW, Barbosa LRA, de Araujo FJ, da Costa AG, da Silva LDO, Pinheiro SK, et al. TOLLIP gene variant is associated with Plasmodium vivax malaria in the Brazilian Amazon. Malar J. BioMed Central; 2017;16: 116. pmid:28288644
- 37.
Brazilian Ministry of Health. Manual de diagnóstico laboratorial da malária. Brasília: Ministério da Saúde; 2005. http://portal.saude.gov.br/portal/arquivos/pdf/manual_diag_malaria.pdf.
- 38. Perandin F, Manca N, Calderaro A, Piccolo G, Galati L, Ricci L, et al. Development of a Real-Time PCR Assay for Detection of Plasmodium falciparum, Plasmodium vivax, and Plasmodium ovale for Routine Clinical Diagnosis. J Clin Microbiol. 2004;42: 1214–1219. pmid:15004078
- 39.
Brazilian Ministry of Health. Guia prático de tratamento da Malária no Brasil. Brasília: Ministério da Saúde; 2010. http://bvsms.saude.gov.br/bvs/publicacoes/guia_pratico_malaria.pdf.
- 40. Rosanas-Urgell A, Mueller D, Betuela I, Barnadas C, Iga J, Zimmerman PA, et al. Comparison of diagnostic methods for the detection and quantification of the four sympatric Plasmodium species in field samples from Papua New Guinea. Malar J. 2010;9: 361. pmid:21156052
- 41. Wampfler R, Mwingira F, Javati S, Robinson L, Betuela I, Siba P, et al. Strategies for Detection of Plasmodium species Gametocytes. Paul RE, editor. PLoS One. 2013;8: e76316. pmid:24312682
- 42. Heinzmann A, Dietrich H, Jerkic SP, Kurz T, Deichmann KA. Promoter polymorphisms of the CD14 gene are not associated with bronchial asthma in Caucasian children. Eur J Immunogenet. 2003;30: 345–348. pmid:14641542
- 43. Ramasawmy R, Cunha-Neto E, Fae KC, Borba SCP, Teixeira PC, Ferreira SCP, et al. Heterozygosity for the S180L variant of MAL/TIRAP, a gene expressing an adaptor protein in the Toll-like receptor pathway, is associated with lower risk of developing chronic Chagas cardiomyopathy. J Infect Dis. 2009;199: 1838–45. pmid:19456234
- 44. Mueller I, Galinski MR, Baird JK, Carlton JM, Kochar DK, Alonso PL, et al. Key gaps in the knowledge of Plasmodium vivax, a neglected human malaria parasite. Lancet Infect Dis. Elsevier Ltd; 2009;9: 555–66. pmid:19695492
- 45. Val FF, Sampaio VS, Cassera MB, Andrade RT, Tauil PL, Monteiro WM, et al. Plasmodium vivax malaria elimination: should innovative ideas from the past be revisited? Mem Inst Oswaldo Cruz. 2014;109: 522–524. pmid:25184997
- 46. Siqueira AM, Mesones-Lapouble O, Marchesini P, de Souza Sampaio V, Brasil P, Tauil PL, et al. Plasmodium vivax Landscape in Brazil: Scenario and Challenges. Am J Trop Med Hyg. 2016;16: 1–21.
- 47. Mackinnon MJ, Mwangi TW, Snow RW, Marsh K, Williams TN. Heritability of malaria in Africa. PLoS Med. 2005;2: 1253–1259. pmid:16259530
- 48. Gething PW, Elyazar IRF, Moyes CL, Smith DL, Battle KE, Guerra CA, et al. A long neglected world malaria map: Plasmodium vivax endemicity in 2010. PLoS Negl Trop Dis. 2012;6: e1814. pmid:22970336
- 49. Miller LH, Ackerman HC, Su X, Wellems TE. Malaria biology and disease pathogenesis: insights for new treatments. Nat Med. 2013;19: 156–167. pmid:23389616
- 50. Akira S, Uematsu S, Takeuchi O. Pathogen recognition and innate immunity. Cell. 2006;124: 783–801. pmid:16497588
- 51. Kawai T, Akira S. The role of pattern-recognition receptors in innate immunity: update on Toll-like receptors. Nat Immunol. Nature Publishing Group; 2010;11: 373–84. pmid:20404851
- 52. Kawai T, Akira S. Toll-like receptors and their crosstalk with other innate receptors in infection and immunity. Immunity. 2011;34: 637–50. pmid:21616434
- 53. Giribaldi G, Valente E, Khadjavi A, Polimeni M, Prato M. Macrophage inflammatory protein-1alpha mediates matrix metalloproteinase-9 enhancement in human adherent monocytes fed with malarial pigment. Asian Pac J Trop Med. Hainan Medical College; 2011;4: 925–30. pmid:22118025
- 54. Netea MG, Wijmenga C, O’Neill L a J. Genetic variation in Toll-like receptors and disease susceptibility. Nat Immunol. 2012;13: 535–42. pmid:22610250
- 55. Mendonça VRR, Queiroz ATL, Lopes FM, Andrade BB, Barral-Netto M. Networking the host immune response in Plasmodium vivax malaria. Malar J. 2013;12: 69. pmid:23433077
- 56. Panigrahi S, Kar A, Tripathy S, Mohapatra MK, Dhangadamajhi G. Genetic predisposition of variants in TLR2 and its co-receptors to severe malaria in Odisha, India. Immunol Res. Springer US; 2016;64: 291–302. pmid:26621243
- 57. Basu M, Maji AK, Chakraborty A, Banerjee R, Mullick S, Saha P, et al. Genetic association of Toll-like-receptor 4 and tumor necrosis factor-α polymorphisms with Plasmodium falciparum blood infection levels. Infect Genet Evol. Elsevier B.V.; 2010;10: 686–696. pmid:20307689
- 58. Iwalokun BA, Oluwadun A, Iwalokun SO, Agomo P. Toll-like receptor (TLR4) Asp299Gly and Thr399Ile polymorphisms in relation to clinical falciparum malaria among Nigerian children: a multisite cross-sectional immunogenetic study in Lagos. Genes Environ. Genes and Environment; 2015;37: 3. pmid:27350800
- 59. Iwalokun BA, Iwalokun SO, Udoh BE, Balogun M. Assessment of co-segregated TLR4 genotypes among Nigerian children with asymptomatic and clinical malaria. Asian Pac J Trop Biomed. Elsevier B.V.; 2017;7: 96–102.
- 60. Zafra G, Flórez O, Morillo C a, Echeverría LE, Martín J, González CI. Polymorphisms of toll-like receptor 2 and 4 genes in Chagas disease. Mem Inst Oswaldo Cruz. 2008;103: 27–30. Available: http://www.ncbi.nlm.nih.gov/pubmed/18368233 pmid:18368233
- 61. Zakeri S, Pirahmadi S, Mehrizi A a, Djadid ND. Genetic variation of TLR-4, TLR-9 and TIRAP genes in Iranian malaria patients. Malar J. 2011;10: 77. pmid:21457584
- 62. Pugin J, Heumann D, Tomasz A. CD14 is a pattern recognition receptor. Immunity. 1994;1: 509–16. pmid:7534618
- 63. Rosas-Taraco AG, Revol A, Salinas-Carmona MC, Rendon A, Caballero-Olin G, Arce-Mendoza AY. CD14 C(-159)T polymorphism is a risk factor for development of pulmonary tuberculosis. J Infect Dis. 2007;196: 1698–706. pmid:18008256
- 64. Areeshi MY, Mandal RK, Panda AK, Bisht SC, Haque S. CD14–159 C>T Gene Polymorphism with Increased Risk of Tuberculosis: Evidence from a Meta-Analysis. PLoS One. 2013;8: 1–6. pmid:23741383
- 65. Hayashi F, Smith KD, Ozinsky A, Hawn TR, Yi EC, Goodlett DR, et al. The innate immune response to bacterial flagellin is mediated by Toll- like receptor 5. Nature. 2001;410: 1099–103. pmid:11323673
- 66. Bargieri DY, Rosa DS, Braga CJM, Carvalho BO, Costa FTM, Espíndola NM, et al. New malaria vaccine candidates based on the Plasmodium vivax Merozoite Surface Protein-1 and the TLR-5 agonist Salmonella Typhimurium FliC flagellin. Vaccine. 2008;26: 6132–42. pmid:18804504
- 67. Bargieri DY, Leite JA, Lopes SCP, Sbrogio-Almeida ME, Braga CJM, Ferreira LCS, et al. Immunogenic properties of a recombinant fusion protein containing the C-terminal 19 kDa of Plasmodium falciparum merozoite surface protein-1 and the innate immunity agonist FliC flagellin of Salmonella Typhimurium. Vaccine. Elsevier Ltd; 2010;28: 2818–2826. pmid:20170765
- 68. Sam-Agudu N a, Greene J a, Opoka RO, Kazura JW, Boivin MJ, Zimmerman P a, et al. TLR9 polymorphisms are associated with altered IFN-gamma levels in children with cerebral malaria. Am J Trop Med Hyg. 2010;82: 548–55. pmid:20348497
- 69. Omar AH, Yasunami M, Yamazaki A, Shibata H, Ofori MF, Akanmori BD, et al. Toll-like receptor 9 (TLR9) polymorphism associated with symptomatic malaria: a cohort study. Malar J. 2012;11: 168. pmid:22594374
- 70. Hisaeda H, Tetsutani K, Imai T, Moriya C, Tu L, Hamano S, et al. Malaria parasites require TLR9 signaling for immune evasion by activating regulatory T cells. J Immunol. 2008;180: 2496–2503. pmid:18250459
- 71. Kar A, Panigrahi S, Tripathy S, Mohapatra MK, Tayung K, Dhangadamajhi G. Influence of common variants of TLR4 and TLR9 on clinical outcomes of Plasmodium falciparum malaria in Odisha, India. Infect Genet Evol. Elsevier B.V.; 2015;36: 356–362. pmid:26462624
- 72. Dhangadamajhi G, Kar A, Rout R, Dhangadamajhi P. A meta-analysis of TLR4 and TLR9 SNPs implicated in severe malaria. Rev Soc Bras Med Trop. 2017;50: 153–160. pmid:28562749