Differential gene expression in White Spot Syndrome Virus (WSSV)-infected naïve and previously challenged Pacific white shrimp Penaeus (Litopenaeus) vannamei

White Spot Syndrome Virus (WSSV) is the most devastating viral disease affecting cultivated shrimp around the world. The CENIACUA breeding programme included host resistance as strategy to control WSSV. Since 1999, all families were subjected to WSSV challenge tests and up to 5% of the animals survived. We suspect that a unique genetic profile could be responsible for survival. By Subtractive Suppression Hybridization improved with Mirror Orientation Selection we compared gene expression in haemocytes of WSSV-infected shrimp; seven were previously challenged (pre-challenged) and 10 naive. Out of 1167 clones, 993 (85%) were obtained from the WSSV-infected pre-challenged library, while 174 (15%) were from the WSSV-infected naive library. Differential expression was confirmed by hybridization using PCR DIG-labelled probes from unsubtracted cDNA. The 216 (18.5%) clones differentially expressed in the WSSV-infected pre-challenged library and 23 (2%) in the WSSV-infected naive animals were sequenced. Relative expression of relevant gene products from both libraries was confirmed by reverse transcription real time PCR. Genes related to shrimp immune response, such as the antimicrobial peptide penaeidin, crustin, C-type lectin, protease inhibitor and chitin binding domain-containing protein were found in the library of pre-challenged shrimp. On the other hand, genes from the naive library coded for viral structural and functional proteins. To our knowledge, this is the first report demonstrating that penaeidin-3 isoforms and crustin are over expressed in haemocytes of WSSV-infected pre-challenged P. vannamei.