Poly I:C induces Mx transcription and promotes an antiviral state against sole aquabirnavirus in the flatfish Senegalese sole (Solea senegalensis Kaup) A. Fernandez-Trujillo a , P. Ferro b , E. Garcia-Rosado b , C. Infante c , M.C. Alonso b , J. Bejar a , J.J. Borrego b , M. Manchado c, * a Department of Genetics, Faculty of Sciences, University of Ma´laga, 29071 Ma´laga, Spain b Department of Microbiology, Faculty of Sciences, University of Ma´laga, 29071 Ma´laga, Spain c IFAPA CentroEl Torun˜o, CICE,Junta de Andalucı´a, Camino tiro de picho´n s/n11500 El Puerto Santa Marı´a (Ca´diz), Spain Received 27 September 2007; revised 15 November 2007; accepted 18 November 2007 Available online 4 December 2007 KEYWORDS Mx; Innate immunity; Poly I:C; Sole aquabirnavirus; Antiviral state; Senegalese sole Abstract Mx is an interferon-induced protein that protects against viral infections. In this study the absolute number of Mx transcripts after poly I:C injection (a synthetic dsRNA) or sole aquabirnavirus (solevirus) inoculation in Senegalese sole (Solea senegalensis Kaup) has been quantified. Mx expression profiles differed clearly in both experimental conditions; the induc- tion response was faster and more intense after poly I:C injection than after solevirus inocu- lation. Moreover, pre-injection of soles with poly I:C prior to solevirus infection eliminated the induction of Mx expression associated with this virus. To evaluate the possible interference of poly I:C treatments on solevirus replication, the mRNA levels of the virus capsid protein (VP2) were determined by RT-PCR. VP2 transcripts were hardly detected in poly I:C pre-injected animals from 12 to 72 h after solevirus inoculation. All these data suggest that poly I:C is able to induce an antiviral state that interferes with solevirus replication, and support the suitabil- ity of Mx expression analysis as a marker to study the defensive response against solevirus. ª 2007 Elsevier Ltd. All rights reserved. Introduction The innate immune system represents the first defence barrier against microbial pathogens. This system undergoes an immediate response against infection using different mechanisms such as physical barriers (i.e. skin), cells and molecules that become active within minutes after a micro- bial infection [1]. Interferons (IFN) are key components of the innate immunity against viral infection [2]. These mole- cules are cytokines that are divided into two categories: type I and type II [2e4]. Type I IFN includes different sub- types the most predominant being IFN-a and IFN-b, which are induced by viruses in most cells. IFN-g represents the type II IFN and it is produced by natural killer cells (NK cells) and T lymphocytes [2,5]. Type I IFN promotes an antiviral state in neighbouring cells by inducing the expression of * Corresponding author. Tel.: þ34 956011315; fax: þ34 956011324. E-mail address: manuel.manchado.ext@juntadeandalucia.es (M. Manchado). 1050-4648/$ - see front matter ª 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.fsi.2007.11.008 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/fsi Fish & Shellfish Immunology (2008) 24, 279e285