Análise da influência de polimorfismos nos genes TLR1, TLR4, TLR7, TLR8, TLR9 e TIRAP na severidade de infecções por Plasmodium vivax

Abstract

Malaria is a widespread infectious disease caused by protozoa of the genus Plasmodium. The parasite is transmitted to the human host through the bite of a female Anopheles mosquito. Malaria caused by P. vivax is characterized by mild initial symptoms that begin between 7 and 10 days after vector ransmission. The immune response to infection by this pathogen releases pro-inflammatory cytokines during the blood phase of infection in the host. The release of these cytokines at the beginning of the disease is essential for controlling and eliminating the parasite. Toll-like receptors (TLRs) are transmembrane proteins present in epithelial, endothelial, natural killer, monocyte, macrophage, neutrophil, and dendritic cells. TLRs induce the production of pro-inflammatory cytokines by activating the transcription factor NF-κB in individuals infected with P. vivax. The study aimed to evaluate the association between the rs4833095, rs1927911, rs179008, rs3764880, rs352140, and rs8177374 polymorphisms in the TLR1, TLR4, TLR7, TLR8, TLR9, and TIRAP genes of the immune system and the clinical manifestations of malaria caused by P. vivax in a population from the Amazon region of the state of Pará, Brazil. The study consisted of samples from 148 individuals infected with P. vivax. The study participants were diagnosed using the blood smear microscopy technique, and the levels of parasitemia and gametocytaemia were estimated. The clinical symptoms of the individuals were assessed by the doctors and recorded. DNA samples from the patients were genotyped by allelic discrimination using TaqMan™ probes in an Applied Biosystems StepOne™ real-time PCR thermal cycler. Individuals were genotyped by a validated set of 48 ancestry-informative molecular markers for genomic control in statistical analyses. The SPSS 21.0 statistical package for Windows® was used for statistical analyses. Statistical significance was defined as a two tailed p value < 0.05. A principal component analysis was performed to group the patients' symptoms into a clinical severity index. TLR genotypes were analyzed for association with parasitemia levels, gametocytaemia, and clinical index in generalized linear models, considering sex, age, African and European genetic ancestry, exposure period, infections history, and parasitemia as covariates. Individuals homozygous for the T allele of the rs352140 polymorphism of the TLR9 gene had an increased average level of parasitemia compared to those with the C allele (TC+CC) (p = 0.034). The GG homozygotes for SNP rs1927911 in the TLR4 gene had the highest clinical index compared to A allele carriers (p = 0.030). There was no association between the polymorphisms studied and gametocytaemia levels in individuals with malaria caused by P. vivax. The polymorphisms rs352140 in the TLR9 gene and rs1927911 in the TLR4 gene may be molecular markers of malaria caused by P. vivax in the Amazonian population. Further studies replicating our results are needed to confirm the potential of these markers.