Dengue virus infection by any one of the 4 serotypes results in a clinical sings spectrum that ranges from an asymptomatic state, or moderate fever, to a classical fever (DF), or a more severe illness, the hemorrhagic fever (DHF). The global prevalence of dengue infections has grown dramatically in recent decades. Over 2,5 billion people are now at risk to get dengue. Recent studies reported the occurrence of high plasmatic levels of cytokines and chemokines in DHF patients, suggesting a central role of these immune mediators in DHF. In this context, the role of viral proteins and its influence in imunopathogenic processes has been extensively studied. The ability of dengue virus to manipulate the interferon signaling pathway has also been reported. Another study, using two hybrid system technology, showed the interaction of NS1 with STA3-beta protein, a protein involved in the expression of various inflammatory genes. NS1 protein is expressed in the cytoplasm as in the external face of the plasmatic membrane as a dimmer. Moreover, NS1 can be secreted in a hexameric form. A recent work reported that hexamers of NS1, when injected in mouse blood vessels, are delivered to hepatic cells. However, the role of secreted and membrane-anchored NS1 protein is still unknown and needs further investigations. In order to study the involvement of NS1 in cytokine gene regulation the coding sequence of NS1 of Dengue1 was amplified through RT-PCR. After sequencing, the fragment was cloned in the eukaryotic expression vector pCDNA3, for stable transfection of HepG2 cells, and in pQE9 prokaryotic expression vector, for expression and purification of NS1, to be used in immunization of animals to raise polyclonal antibodies. Antibody was raised and then analyzed for specific binding properties and used for characterization of stably-expressing NS1 cells as well. We have previously shown a strong reduction in the expression of some proinflammatory proteins in the supernatant of culture of cells constitutively expressing NS1. We are now searching for differential activation of transcription factors (i.e. AP-1; NF-kB) that could be involved in this process. These observations suggest that this viral protein can be involved in a protective mechanism of Dengue virus during the infection of hepatic cells. The role played by NS1 protein in the regulation of proinflammatory genes can be an important step towards the understanding of pathologies associated with dengue virus.