Background/Aims: The innate immune response is remarkably important for controlling infections. Information about the participation of antimicrobial peptides (AMPs) in response to dengue virus (DENV) is scarce. The aim of this study was to examine the AMP response to DENV-2 in human THP-1 cells and neutrophils. Methods: Protein and mRNA levels of two AMPs - hBD-1 and cathelicidin LL-37 - were assessed in DENV-infected macrophage-like THP-1 cells using qRT-PCR and indirect immunofluorescence. Also, mRNA levels of α-defensins (hDEFAs) and LL-37 were examined by qRT-PCR in human neutrophils taken from peripheral blood and treated with DENV-2. Results: mRNA expression of hBD-1 rose in THP-1 cells at 24-72 h, while protein expression increased later, from 48 to 72 h after infection. Cathelicidin LL-37 mRNA expression of DENV-infected THP-1 cells was observed at 6-48 h after infection, while protein levels increased importantly up to 72 h after infection. Regarding neutrophils, the mRNA expression of hDEFAs and LL-37 increased slightly at 2 and 5 h after the contact with DENV-2. Conclusion: THP-1 cells and human neutrophils strongly respond to DENV by producing AMPs: hBD-1 and LL-37 for the THP-1 cells and hDEFAs and LL-37 for neutrophils. However, the direct effect of these molecules on DENV particles remains unclear.

Nucleotide-binding domain (NBD) leucine-rich repeat (LRR)-containing receptors or NLRs are a family of receptors that detect both, molecules associated to pathogens and alarmins, and are located mainly in the cytoplasm. NOD2 belongs to the NLR family and is a dynamic receptor capable of interacting with multiple proteins and modulate immune responses in a stimuli-dependent manner. The experimental evidence shows that interaction between NOD2 structural domains and the effector proteins shape the overall response against bacterial or viral infections. Other reports have focused on the importance of NOD2 not only in infection but also in maintaining tissue homeostasis. However, not only protein interactions relate to function but also certain polymorphisms in the gene that encodes NOD2 have been associated with inflammatory diseases, such as Crohn's disease. Here, we review the importance and general characteristics of NOD2, discussing its participation in infections caused by bacteria and viruses as well as its interaction with other pathogen recognition receptors or effectors to induce antibacterial and antiviral responses. Finally, the role of NOD2 in chronic inflammatory conditions and its potential to be targeted therapeutically are examined.

No abstract

The nucleotide-binding domain (NBD) and leucine-rich repeat receptors, such as NOD-like receptors (NLRs), have pivotal functions in the innate immune response to various viral infections participating during the recognition of pathogens and activation of signaling pathways. One NLR, NOD2, is a dynamic protein that is activated in the presence of viral genomes and metabolites. However, its participation in combating a dengue virus (DENV) infection remains unclear. The aim of this study was to determine the role of NOD2 in macrophage-like THP-1 cells during an in vitro infection with DENV type 2 (DENV2). The interactions of NOD2 with RIP2 and MAVS was examined in DENV2-infected and agonist-stimulated cells. The effects of downregulating NOD2 expression or signaling on virus loads was also evaluated. The cellular mRNA expression and protein levels of NOD2 on cells under the stimuli were quantified with RT-PCR, Western blot and indirect immunofluorescence. Both the mRNA and protein expression of NOD2 was enhanced in response to DENV-2 infection. Interactions of NOD2 with RIP2 and MAVS, analyzed with confocal microscopy and co-immunoprecipitation assays, were time-dependent and increased in the post-infection period, between 6 and 24 h. After silencing NOD2 expression, DENV2-infected cells displayed greater viral loads and decreased expression of IL-8 and IFN-α (measured in supernatants obtained from the cells), compared to the uninfected (mock control) cells or those transfected with irrelevant-siRNA. Thus, in response to a DENV2 infection, NOD2 was activated in THP-1 human macrophage-like cells, the production of IL-8 and IFN-α was enhanced, and viral replication was limited.