Antimicrobial peptides in the gonad of European sea bass and gilthead seabream upon infection with nodavirus

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The infection of the gonad by pathogens is the initial step to promote horizontal ltransmission through ovarian fluids and/or vertical transmission through infected gametes. In all vertebrates, the gonad is considered an immunologically privileged site as it triggers lower immune responses in order to avoid germ cell damage. In fish, the implications of this different regulation of the immune functions inside the reproductive organs and its implication on pathogen dissemination through the gonad have very recently been documented (Chaves-Pozo et al., 2010a,b) and deserve further characterization. Nodavirus is a known vertical transmitted pathogen able to infect juveniles of gilthead seabream (Sparus aurata) and European sea bass (Dicentrarchus labrax), however, while he gilthead seabream is an asymptomatic carrier of the nodavirus, the European sea bass develop the viral encephalopathy and retinopathy (VER) disease and suffer high mortalities (Frerichs et al., 1996; Castric et al., 2001). Recent studies have determined the anti-viralactivity of fish anti-microbial peptides (AMPs) against several viruses including nodavirus (Valero et al, 2013). In mammals, the AMPs are expressed in the reproductive tract and probably assume an important role in the innate immune response against pathogens in the reproductive organs (Granz and Lehrer, 1998), however little is known about the presence and role of AMPs in the reproductive organs of teleost fish. In this study we related the functional bactericidal activity (lysozyme and anti-bactericidal activity) in the serum, gonad and brain (target tissue for nodavirus) as well as the expression pattern of AMP-genes in the brain, gonad and head-kidney of control and nodavirus infected fish. Our preliminary results point to the fact that AMPs might have an important role in gonad immune response of European sea bass and gilthead seabream, as both activities and gene expression were sharply altered by nodavirus in both species. However, further studies are needed to understand the regulatory mechanisms in the immune response of the gonad of these species upon nodavirus infection.