Immune gene expression in gilthead seabream (Sparus aurata) after Lymphocystis disease virus (LCDV-Sa) challenge resulting in asymptomatic infection.

AIMS: To determine the immune gene expression response of gilthead seabream (Sparus aurata) that is experimentally infected with the lymphocystivirus LCDV-Sa. METHODS AND RESULTS: Viral DNA and transcripts were detected by qPCR in all samples from fish injected with LCDV-Sa, demonstrating that the virus establish a systemic and asymptomatic infection. The expression of 23 immune-related genes was also analysed by RT-qPCR in the head kidney (HK) and intestine at several times post-infection (dpi). In HK, the expression of five type I interferon (IFN)-related genes (ifn, irf3, mx2, mx3 and isg15), il10 and ck10 was upregulated at 1-3 dpi, while genes related to the inflammation process (tnfα, il1ß, il6, casp1) were not differentially expressed or even downregulated. The expression profile in the intestine was different regarding type I INF-related genes. An upregulated c3 and ighm expression was observed in both HK and intestine at 3-8 dpi. Finally, the transcription of nccrp1 and mhcIIα was induced in HK, whereas tcrß expression was downregulated in both organs. CONCLUSIONS: LCDV-Sa seems to trigger an immune response in gilthead seabream characterized by a partial activation of type I IFN system and a lack of systemic inflammatory response which may be related to viral persistence. SIGNIFICANCE AND IMPACT OF THE STUDY: The immune response observed in gilthead seabream infected by LCDV-Sa could be implicated in the establishment of an asymptomatic persistent infection.