Innovative vaccination protocol against vibriosis in Dicentrarchus labrax (L.) juveniles: improvement of immune parameters and protection to challenge.

The effect of vaccination on immune parameters of European sea bass, Dicentrarchus labrax, is not fully established, as well as surveyed throughout rearing till the commercial size. Furthermore, available information on the possible role of booster treatments is scarce. Sea bass juveniles were vaccinated against Listonella anguillarum using a commercial bivalent formulation administered by immersion (priming: 95 dph; booster: 165 dph) or by immersion (priming: 95 dph; booster: 165 dph) and subsequent i.p. injection (booster: 233 dph). Serum specific IgM and numbers of IgM(+) cells in head kidney and spleen evidenced B-cell responses mainly after the immersion booster, accompanied by increased TcR-ß transcripts and leucocyte respiratory burst. Immune enhancement was confirmed by the protection towards i.p. challenges with a virulent strain. RPS accounted for >70% in fish immersion-boosted and near 100% in fish further boosted i.p. Differently from usual farm practices, this innovative vaccination protocol proved to be highly effective. Booster treatments are therefore strongly recommended.

A monoclonal antibody for the CD45 receptor in the teleost fish Dicentrarchus labrax.

The CD45 tyrosine phosphatase plays an important role in regulating T lymphocyte activation in vertebrate species. In this study we describe some molecular and functional features of the CD45 receptor molecule from the European sea bass Dicentrarchus labrax. Following immunization with fixed sea bass thymocytes, we obtained a murine monoclonal antibody (mAb) able to stain fish leucocytes both alive, by immunofluorescence of thymus and mucosal tissues, and fixed, by in situ immunohistochemistry of tissue sections. The selected IgG(2) mAb (DLT22) was able to recognise by western blots polypeptides mainly at 180 kDa and 130 kDa in thymus, spleen, intestine and gill leucocyte. Accordingly, a 130 kDa polypeptide immunoprecipitated with DLT22 from thymocytes and analysed by nano-RP-HPLC-ESI-MS/MS, gave peptide sequences homologous to Fugu CD45, that were employed for the homology cloning of a partial sea bass CD45 cDNA sequence. This cDNA sequence was employed to measure by quantitative PCR the transcription of the CD45 gene both in unstimulated and in in vitro stimulated leucocytes, showing that the gene transcription was specifically modulated by LPS, ConA, PHA, IL-1, and poly I:C. When splenocytes were stimulated in vitro with ConA and PHA, a cell proliferation paralleled by an increase of DLT22-positive leucocytes was also observed. These data indicate that the DLT22 mAb recognizes a putative CD45 molecule in sea bass, documenting the presence of CD45-like developing lymphocytes in thymus and CD45-associated functional stages of lymphocytes in this species, thus dating back to teleost fish the functional activities of these cell populations in vertebrates.

Monospecies and multispecies probiotic formulations produce different systemic and local immunostimulatory effects in the gilthead seabream (Sparus aurata L.).

The effects of the oral administration of heat-inactivated Lactobacillus delbrüeckii ssp. lactis and Bacillus subtilis, individually or combined, on gilthead seabream immune responses were investigated both systemically and locally in the gut. In a first experiment, seabream (65 g) were fed for 3 weeks different diets supplemented with 1 x 10(7)CFU g(-1)Lactobacillus, 1 x 10(7)CFU g(-1)Bacillus, or 0.5 x 10(7)CFU g(-1)Lactobacillus plus 0.5 x 10(7)CFU g(-1)Bacillus. Controls were fed non-supplemented diet. Six fish per group were sampled at the end of the trial and some humoral and cellular systemic innate immune parameters were evaluated. Feeding the mixture of the two killed bacteria species significantly increased natural complement, serum peroxidase and phagocytic activities compared with controls. In a second experiment, juvenile seabream (13 g) were fed for 3 weeks the same experimental diets and total serum IgM and numbers of gut IgM(+) cells and acidophilic granulocytes were evaluated. All these parameters were significantly higher in the multispecies probiotic group compared to monospecies and control fed groups. The advantages provided by administration of killed probiotic bacteria as well as multispecies versus monospecies formulations are discussed in light of the results obtained and for their possible application in aquacultural practices.