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The warm temperature acclimation related 65 kDa protein-2 (Wap65-2), a teleost plasma glycoprotein, plays an important role in immune regulation against bacterial infection. Here, for the first time we determined the full length cDNA sequence of the Japanese sea bass Wap65-2 gene (1 601 bp in length excluding the 3'-polyA tail). The sequence contains an open reading frame that encodes a protein of 436 amino acids with a molecular weight of 4.87×10(4). The predicted protein had a signal peptide in the N-terminal domain containing 19 residues. Sequence comparison and phylogenetic tree analysis showed that the Japanese sea bass Wap65-2 has a relatively high similarity to the Dicentrarchus labrax Wap65-2. In the healthy Japanese sea bass, Wap65-2 mRNA was expressed mainly in the liver and weakly in the heart and muscle. qRT-PCR results revealed that liver Wap65-2 transcripts were significantly increased after a Vibrio harveyi infection, and peaked 24 hour post injection (6.89 fold increase). The Japanese sea bass Wap65-2 protein was expressed in Escherichia coli and subsequently used for antiserum preparation. Western blot analysis showed that Wap65-2 was significantly increased in V. harveyi infected Japanese sea bass and reached a maximum of 5.33-fold increase at 36 h. In conclusion, the alteration of Japanese sea bass Wap65-2 expression was tightly associated with the progression of the V. harveyi bacterial infection.