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Yersinia ruckeri is a well-established bacterial pathogen for many salmonid species, against which a formalin-killed bacterin vaccine has been effective in reducing disease outbreaks. Previous studies have reported conflicting results about the protective value of the systemic humoral response to Y. ruckeri vaccination. Here we directly demonstrate that plasma contains the long-term protective component elicited by both immersion and intraperitoneal injection vaccination of rainbow trout. A total of 0.5 μL of plasma from vaccinated fish provided almost complete protection against experimental challenge. Conversely, the cells obtained from peripheral blood conferred little or no protection in naive recipients. The protective component of immune sera was IgM based on size exclusion chromatography and recognition by monoclonal antibody Warr 1–14. Immune plasma generated against a Y. ruckeri biotype 1 strain protected equally against challenges with Y. ruckeri biotype 1 and 2 strains. These results illustrate the importance of the humoral IgM response against Y. ruckeri and the use of doubled haploid rainbow trout ( Oncorhynchus mykiss ) and transfer of plasma/serum and cells into F1 outcross progeny as a model system for dissection of the mechanism(s) of vaccine-induced protection.

Natural killer cell enhancement factor (NKEF) belongs to the antioxidant protein family. In the human, NKEF has the ability to enhance natural killer cell cytotoxic activity in vitro. In the present work, the cDNAs of NKEF from three strains of homozygous clones of rainbow trout were cloned from the splenic cDNA library of one of the strains, OSU142, and then by RT-PCR for the Hot Creek (HC) and Arlee (AR) strains. The HC sequence has 99% sequence identity with both OSU142 and AR. OSU142 and AR have only one nucleotide difference in the cDNA sequence. All three sequences have the same deduced NKEF peptide, which contains 199 amino acids. The 6.5 kb genomic DNA of OSU142 containing NKEF was sequenced and contains six exons and five introns. Tissue specific expression of NKEF was studied by RT-PCR in eight different tissues of OSU142 and revealed that all tissues expressed NKEF . A southern blot revealed that the gene for NKEF is present in a single copy. The cDNA and amino acid sequences of trout NKEF have high similarity with human, rat, mouse and carp sequences, therefore, indicating that NKEF is a very conserved gene.

Six lines of homozygous rainbow trout ( Oncorhynchus mykiss ) from different genetic and geographical backgrounds have been produced as aquatic models for biomedical research by the chromosome set manipulation techniques of androgenesis and gynogenesis Messenger RNA from spleens was extracted and the MHC II B cDNA sequences amplified by RT–PCR were cloned into plasmids Sequences of the MHC II β 2 domains were highly conserved between the different plasmids from the same and different lines of trout Most of the variability among sequences was found in the amino terminal half of the β 1 domain which corresponds with the peptide binding region of the MHC II molecule This diversity suggests that the different lines of trout may exhibit differences in immune response Rainbow trout MHC II B sequences were similar to the MHC II B sequences of the Pacific salmon ( O gorbuscha O tshawytscha O nerka O masou O kisutch ) Southern blot analysis performed on the restricted DNA of the OSU and Hot Creek trout and the doubled haploid progeny produced by androgenesis from OSU×Hot Creek hybrids indicates that two distinct genes encode the MHC II B sequences and that these genes are unlinked © 1999 Elsevier Science Ltd All rights reserved