Systemic and mucosal antibody response in tilapia, Oreochromis niloticus (L.), following immunization with Flavobacterium columnare.

Specific antibody responses to Flavobacterium columnare (isolate ATCC 23463T) were characterized in plasma and mucus of tilapia following intraperitoneal (i.p.) injection or immersion immunization with formalin-killed sonicated or whole cell preparations. Fish (30 per treatment) received a primary immunization and were booster immunized 4 weeks later. An enzyme-linked immunosorbent assay was developed for detection and quantification of specific anti-F. columnare antibody, and it was found that formalin-killed sonicated cells in Freund's complete adjuvant (FCA) injected i.p. stimulated a significant systemic antibody response within 2 weeks (mean titre 11,200) which increased to 30,600 following secondary immunization. At 10 weeks post-immunization, the mean titre remained significantly elevated above the controls. Antibodies were also observed in cutaneous mucus of fish immunized i.p. with formalin-killed sonicated cells in FCA at 6 and 8 weeks post-immunization (mean titres 67 and 33, respectively). Although some individual fish responded, mean plasma and cutaneous mucus antibody titres were not significantly greater than controls in any of the other treatment groups. The results of this study demonstrate that tilapia can mount a significant humoral response in plasma and cutaneous mucus to F. columnare, but i.p. immunization with FCA is required to elicit this response.

Coding sequences of the MHC II beta chain of homozygous rainbow trout (Oncorhynchus mykiss).

Six lines of homozygous rainbow trout (Oncorhynchus mikiss) 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 beta2 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 beta1 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. miasou, 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 x Hot Creek hybrids indicates that two distinct genes encode the MHC II B sequences and that these genes are unlinked.

Arlee line of rainbow trout (Oncorhynchus mykiss) exhibits a low level of nonspecific cytotoxic cell activity.

Nonspecific cytotoxic cell (NCC) activity was assessed in the peripheral blood of four isogenic lines of rainbow trout (Oncorhynchus mykiss) which were derived by the chromosome set manipulation technique of androgenesis. In these fish, whose isogenicity was previously confirmed by multilocus DNA fingerprint analysis, NCC activity was studied by the release of 51Cr from YAC-1 targets. Two groups of trout (the homozygous Arlee 12 line and the heterozygous hybrid of the Arlee 63 and Arlee 12 lines) had significantly lower levels of NCC activity in peripheral blood than either outbred rainbow trout or other lines with Hot Creek or hybrid Arlee x Hot Creek ancestry. The low NCC activity in the Arlee line appears to be inherited as a recessive trait. Peripheral blood cells of the trout mediated lectin dependent cellular cytotoxicity (LDCC) with the addition of phytohemagglutinin to co-cultures of effector cells and YAC-1 cells. The low NCC activity in the peripheral blood of these fish is not due to a condition analogous to the NCC-deficient Chediak-Higashi syndrome of man or the beige mutation of mice.