Sensibilidade do Orthobunyavirus do grupo C, Oriboca (BeAn 17) aos interferons humanos

Abstract

The group C arbovirus Oriboca (genus Orthobunyavirus, family Bunyaviridae) was isolated in the Brazilian amazon during the years 1950. In humans, the disease caused by these viruses is characterized by high fever, mialgy, ocular pain and photophobia, which lasts 4-5 days. The virus from this family present spherical, enveloped, of 100 nm in diameter particles and its genome is formed by three segments of single-stranded RNA of negative polarity. There are still few studies involving this viral family. The interferons are a family of cytokines and are components of the inate immune system, being the first line of defense against a viral infection. The infected cells sinthetize and secrete type I and III interferons, which signal to the neighbor cells to express antiviral proteins in the attempt to hinder the multiplication and avoid this agents diffusion in the cells of the contaminated tissue (antiviral state). Thus, this work had as aims to elucidate some important characteristics involving this member of this importante serogroup of the family Bunyaviridae, such as characterizing its multiplication, comparing its cross reactivity by neutralizing tests and verify the antiviral activity of the types I and III IFNs against this virus. In order to do this, the Oriboca virus sample was multiplied in Vero cells and a plaque cloning was performed to guarantee a homogeneous virus population. The cross reactivity among Oriboca and its clones was investigated by using anti-Apeu serum and antiarbovirus of the group C-1. To evaluate the capacity of the ORIV in inducing IFN in vitro, murine cells L929 were used and the test of the measure of the antiviral activity was used to quantify the IFN present. To assess the action of the IFNs á, â and ë1 on Oriboca virus multiplication, Vero cells were treated with various concentrations of the IFNs and 18 hours later infected with ORIV. To evaluate wheter the use of type III IFN could increase the antiviral effects of the type I IFNs, Vero cells were treated with mixtures of both types of IFN in low or high concentrations. All these samples were posteriorly titled in PFU/mL. Finally, to assess the leves of expression of the ISGs 25OAS, PKR, 6-16 e MxA, human cells A549 were infected in different times and the total cellular RNA extracted and used as a template in real time PCR reactions. We verified that the IFNs á and â were capable of protecting the Vero cells against the ORIV. The antiviral activity verified was dose dependent, and the IFN â was the most efficient in inhibiting ORIV multiplication. Possibly, this differential activity of the IFNs occurs due to the differences in the affinity to cellular receptor chains. The IFN- ë1 (type III) was also capable of protecting these cells from the infection with ORIV, when administrated in doses much higher than the ones of IFNs á/â. The biological activity of the IFNs type III, even when redundant with the IFNs types I activities, are generally less intense and more restrict. We observed that Vero cells treated with a combination of these IFNs in high or low doses did not present an antiviral effect additive on the multiplication of ORIV. The expression of the four ISGs (25OAS, PKR, 6-16 and MxA), quantified by real time PCR was raised in the A549 cells after the infection with ORIV. With this work, we showed that ORIV is sensitive to the IFNs type I and III in higher or lower level and, even though they use different receptors to signal, these two families of IFN share some common characteristics, such as pathways of signal transduction activated and the stimulus required to its production. These results confirm previous data described for other Bunyavirus. The data suggest that the innate immune system has an important role in the control of ORIV and a therapeutic potential of the IFNs types I and III in the control of the arbovirosis. More studies are needed in order to characterize the sensitivity of the IFNs types I and III to other members of the Bunyaviridae family, as well as evaluate other IFNs like the type II (IFN ã) and also the IFN lambda2 for the members of this family.