IDENTIFICATION OF NATURAL KILLER ENHANCING FACTOR-B COUNTERPART FROM Anguilla japonica: INVESTIGATION OF IMMUNE RESPONSES UPON BACTERIAL AND IMMUNOSTIMULANT CHALLENGE  

Japanese eel (Anguilla japonica) is a one of popular aquaculture species in Asia pacific region. Due to the high market value, recent supply shortage and its unique taste, the Japanese eels have become most important fish species in aquaculture industry. However, because of pathogenic infection, Japanese eels are easily susceptible for several diseases, causing mass mortalities. Therefore understand about Japanese eel's immune components and their defense mechanism is important for disease prevention. In this study we identified and molecular characterized Natural killer enhancing factor B homolog from Japanese eel, designated as AjNKEF-B at transcriptional level.  Natural killer enhancing factors (NKEF) are thioredoxin dependent peroxidase, which play critical role in antioxidative defense via peroxidase activity, apoptosis, cell proliferation and enhancing ability of cytotoxicity of the natural killer cells.Japanese eel transcriptomic library was constructed and full length coding sequence of AjNKEF-B was identified. The deduced protein of AjNKEF-B showed typical domain architecture of NKEF-B including redoxin domain profile. All the domains and active sites of AjNKEF-B were highly conserved with its counterparts from teleost, amphibians and mammals. According to the phylogenetic study, AjNKEF-B was clustered in AjNKEF-B fish clade, suggesting that AjNKEF-B is a homolog of NKEF-B family. The AjNKEF-B mRNA was ubiquitously expressed in all the tissues we tested, while greatest expression level was detected in liver. In order to identify putative immune relevancy of AjNKEF-B, Four groups of Japanese eels were intraperitoneally injected with   Edwardsiella tarda (E.tarda),  Polyinosinic:polycytidylic (Poly I:C) and  lipopolysaccharide (LPS). Thereafter expression levels of AjNKEF-B were detected in liver by qPCR. The AjNKEF-B mRNA was significantly upregulated upon post E.tarda, LPS and Poly I:C injection compared to the un-injected control (Fig.1.). Unlike post mitogen injection (LPS and Poly I:C), the E.tarda caused later phase induction of AjNKEF-B mRNA (Fig.1.). Collectively these observation suggest that AjNKEF-B might be involved in post innate immune responses upon pathogenic infection. However, further studies are required for determine the exact mechanism of AjNKEF-B expression upon pathogenic stress.