Recombinant VP28 Produced by Cell-Free Technique Confers Protection in Kuruma Shrimp (Marsupenaeus japonicus) Against White Spot Syndrome Virus

Shrimp is one of the most important species in aquaculture. During the last two decades, shrimp culture has been threatened worldwide by viral diseases. A highly pathogenic white spot syndrome virus (WSSV) is responsible for huge economic losses in the shrimp culture industry, and no effective treatment is currently available for it (Rajesh Kumar et al., 2008). Cumulative mortalities in infected population may reach 100% within 2-10 days of onset of clinical signs (Lightner, 1996). WSSV infects penaeid shrimps, such as Chinese shrimp (Fenneropenaeus chinensis), kuruma shrimp (Marsupenaeus japonicus), black tiger shrimp (Penaeus monodon) and other crustaceans, including crayfishes, crabs and lobsters (Otta et al., 1999; Supamattaya et al., 1998). Due to the extreme virulence and wide host range including almost all crustaceans (Sahul Hameed et al., 2003), it is difficult to contain the spread of this virus. Invertebrates lack true adaptive immune system and depend on various innate immune responses (Kimbrell and Beutler, 2001). Innate immune responses are considered to be less sophisticated than adaptive immunity, however, they may rapidly and efficiently recognize and destroy non-self materials including pathogens (Lee and Söderhäll, 2002). Innate immune responses consist of cellular and humoral components. Hemocytes are responsible for most of the cellular responses, such as encapsulation, phagocytosis, melanization, cytotoxicity, cell-to-cell communication, clotting, and the pro-phenoloxidase activating system. Humoral response factors originate from granulocytes and include lectins, defensive enzymes, reactive oxygen intermediates, and the synthesis of a wide array of antimicrobial peptides (Destoumieux et al., 2000; Kimbrell and Beutler, 2001; Lee and Söderhäll, 2002; Söderhäll, 1999). Treatment with microbial products like β-glucan or Vibrio harveyi vaccine stimulates the immune response in shrimp (Alabi et al., 1999; Song and Hsieh, 1994). Moreover, vaccination using inactivated Vibrio spp. was shown to be effective against vibriosis in P. monodon and M. japonicus (Itami et al., 1989; Teunissen et al., 1998). Activation of innate immune responses primarily occurs with recognition of distinct pathogen-associated molecular patterns (PAMPs) by toll-like receptors (TLRs) (Medzhitov and Janeway, 1997). Additionally, TLRs are also activated by recognition of ‘‘self-antigens” such as heat shock proteins and uric acid that are normally present in cells (Akira et al., 2001; Akira, 2003; Shi et al., 2003). TLRs engage a variety of intracellular T. Kono 1 , J. Fall 2 , H. Korenaga 3 , R. Sudhakaran 4 , G. Biswas 5 , T. Mekata 6 , T. Itami 1 , M. Sakai 1, * 1 University of Miyazaki, Faculty of Agriculture, Department of Biochemistry and Applied Biosciences, 1-1 Gakuenkibanadai-nishi, Miyazaki Japan. 2 Institute of Fisheries and Aquaculture, University Cheikh, Austra Diop, UCAD II, Dakar BP5005, Senegal. 3 Drug Discovery Platforms Cooperation Division, RIKEN Center for Sustainable Resource Science, Saitama 351-0198, Japan. 4 School of Bio-Sciences and Technology, VIT University, Vellore 600 014, Tamil Nadu, India. 5 Interdisciplinary Graduate School of Agriculture and Engineering, University of Miyazaki, 1-1 Gakuenkibanadai-nishi, Miyazaki 889-2192, Japan. 6 National Research Institute of Aquaculture, Tsuiura, Kamiura, Saiki City, Oita 879-2602, Japan.