Increased liver protein and mRNA expression of natural killer cell-enhancing factor B (NKEF-B) in ayu (Plecoglossus altivelis) after Aeromonas hydrophila infection

Natural killer cell-enhancing factor (NKEF) may mediate cellular responses to proinflammatory molecules. The liver proteins of Aeromonas hydrophila-infected ayu (Plecoglossus altivelis) and healthy control fish were analyzed by 2DE. A protein, which increased significantly in diseased fish, was identified as NKEF-B by MALDI-TOF-MS. A full-length cDNA clone of this protein was subsequently isolated. It contains 1092 bp with an open reading frame of 591 bp, coding for 197 amino acids with MW 21.9 kDa and pI 6.38, values similar to those determined by 2DE. Ayu NKEF-B had highest similarity (93.1% amino acid identity) to those of carp and zebrafish. Phylogenetic analysis showed that ayu NKEF-B falls into the fish NKEF-B cluster and is most closely related to that of carp and zebrafish. It was determined that ayu NKEF-B mRNA expression was significantly increased in many tissues at the early stage of bacterial infection. In conclusion, the increased NKEF-B mRNA and protein expression in ayu were closely associated with A. hydrophila infection.