O papel de receptores do Tipo Toll (TLRS) na resposta às infecções por Zika virus, Dengue virus e SARS-COV-2

Abstract

Viral infections are a global public health problem and a severe social and economic burden. In viral infections, the immune system protects the body, with the innate immune system being the first line of defense to be activated. The detection of viruses can be done by toll-like receptors (TLRs), which are responsible for recognizing pathogens and stimulating the production of cytokines. The objective of this work was to evaluate the innate immune response, mainly via the TLRs, biologically differentiate two samples of Zika virus (ZIKV) isolated in Brazil and evaluate the single nucleotide polymorphisms (SNPs) of genes of the innate immune system of children with manifestations of the central nervous system (CNS) caused by ZIKV, dengue virus (DENV) and children with severe Covid-19. Two ZIKV strains isolated in Brazil (PE243 and SPH) and an African strain adapted in mice (MR766), used as control, were used to study the TLRs induction in CHO cells stably transfected with TLR2 and TLR4. The results confirmed the activation of TLR2, with reduced differential response of the ZIKV SPH. The strains were also used for infection in immunocompetent and knockout mice. C57BL/6 mice infected by the subcutaneous route showed no signs of weight loss, but they showed less significant weight gain when infected by the intracranial route (IC) with ZIKV PE243. In C57BL/6 mice infected via IC with ZIKV SPH, a significant increase in interferon-γ (IFN-γ) was detected in the brain, liver, and spleen. Knockout mice for the myeloid differentiation factor 88 (myd88) and tlr2/9 genes infected via IC showed significantly less weight gain, and an increased monocyte chemoattractant protein-1 (MCP-1) was identified in the brain of myd88-/- mice infected with ZIKV PE243. Viral RNA was detected in the brains, livers, spleens, kidneys, and testes of C57BL/6 and myd88-/- mice infected via IC. Knockout mice for the nitric oxide synthase 2 gene (nos2) showed no signs or weight reduction. These results confirm the biological differences between the ZIKV isolates from Brazil and the importance of the innate immune system in ZIKV infection. The evaluation of SNPs rs3775291 and rs5743316 (tlr3), rs179008 (tlr7), rs8177374 (TIR domain -containing adapter protein - tirap), rs387907272 (myd88), rs61942233 (2',5'-oligoadenylate synthetase - oas3) and rs1024611 (mcp- 1) was performed in 19 children with CNS manifestations and ZIKV genomic RNA in the cerebrospinal fluid (CSF). Eighteen had SNPs in at least one of the genes studied, and a 0.21 frequency of the mutated allele of SNP rs8177374 was detected while, the mean of the database populations is 0.11. In 39 children with CNS manifestations and DENV genomic RNA in CSF, SNP rs8177374 was analyzed, and a 0.29 mutated allele frequency was detected. Analysis of 59 children with Covid-19, showed a 0.17 frequency for the SNP rs3775291, while the mean of the populations in the database was 0.27. A case study observed an association between SNP rs179008 and hepatitis by SARS-CoV-2 and SNPs rs179008 and rs8177374 and severe Covid- 19 in 3 children with sickle cell anemia. These results demonstrate the importance of mutations in genes related to the immune system in ZIKV, DENV, and SARS-CoV-2 infections.