Non-specific cytotoxic cell receptor (NCCRP)-1 type gene in tilapia (Oreochromis niloticus): its cloning and analysis Yasuko Ishimoto a , Ram Savan b , Makoto Endo c , Masahiro Sakai a * a Faculty of Agriculture, Miyazaki University, Gakuen kibanadai nishi 1-1, Miyazaki 889-2192, Japan b United Graduate School of Agricultural Sciences, Kagoshima University, Korimoto, 1-21-24, Kagoshima 890-0065, Japan c Laboratory of Fish Health Management, Graduate School of Fisheries Sciences, Tokyo University of Fisheries, Konan 4-5-7, Minato Ku, Tokyo 108-8477, Japan Received 23 December 2002; received in revised form 31 March 2003; accepted 1 May 2003 Abstract Non specific cytotoxic cells are natural killer cell equivalent in teleosts. These cells are known to mediate innate immune responses in fishes. In this study, from tilapia, a non-specific cytotoxic cell receptor protein (NCCRP) like cDNA composed of 960 bps with a 12 bps 5# UTR, 702 bps open reading frame and 246 bps 3# UTR has been cloned. The predicted gene product is 233 amino acid with a molecular weight of 26.6 kDa and pI of 6.07. The gene has a typical F-box associated domain, which harbors the antigen binding region, implicated in formation of conjugates with target cells necessary for killing. By semi-quantitative RT–PCR studies, the expression level of NCCRP-1 was highest in liver followed by head kidney, spleen and intestine. Low expression levels were recorded in brain, gill and heart. Lowest expression of transcripts was in the skin. As evidenced by in situ hybridisation the NCCRP-1 transcripts were expressed on lymphocyte like cells as well as neutrophils.  2003 Elsevier Ltd. All rights reserved. Keywords: Innate immunity; Tilapia; cDNA library; CpG oligonucleotide; In situ hybridisation; RT–PCR 1. Introduction Natural killer (NK) like lymphoid cells have been demonstrated in several lower vertebrate groups including birds, reptiles, amphibians and teleost fish. NCC are NK cell equivalents in catfish (Ictalurus punctatus), tilapia and other teleosts. These cells are known to be the most important cytotoxic effectors of innate immune responses in fishes. NCC along with other non specific effector provide innate resistance during acute stress response induced by opportunistic pathogens, protozoan parasites and also participate in tumor cell recognition [1]. NCC like activity has been shown in other fish species like rainbow trout (Onchorhynchus mykiss) [2], carp (Cyprinus carpio L.) [3,4], damselfish (Stegastes partitus) [5] and tilapia [6]. * Corresponding author. Tel.: +81-985-58-7219; fax: +81-985-58-7219 E-mail address: m.sakai@cc.miyazaki-u.ac.jp (M. Sakai). Fish & Shellfish Immunology 16 (2004) 163–172 Fish & Shellfish Immunology www.elsevier.com/locate/fsi 1050-4648/04/$ - see front matter  2003 Elsevier Ltd. All rights reserved. doi:10.1016/S1050-4648(03)00059-7