Priming the immune system of Litopenaeus vannamei with bacterial heat shock protein 70 homologue DnaK against Vibrio campbellii and white spot syndrome virus (WSSV) infection

Disease outbreaks are considered to be the main constraint to aquaculture development. The disadvantages of widespread use of antibiotics have been realized in whole animal production industry including aquaculture. Thus there is increasing demand for developing alternative disease control strategies. The heat shock protein 70 (HSP70) were discovered as a potential candidate for the development of a new disease control approach. This thesis evaluates a novel anti-­‐infective strategy to control vibriosis and WSSV in aquaculture. More specifically, investigations were performed to elucidate the role of recombinant heat shock protein 70 (Hsp 70), derived from a prokaryotic source, in generating an immune response and to instigate protection against pathogenic Vibrio campbellii and White Spot Syndrome virus (WSSV). Firstly, the role of bacterial HSP70 (DnaK) as an efficient immuno-­stimulant in L. vannamei was verified by including a chemically synthetic, microbial contaminants free DnaK fragment peptide (DnaK442-­‐491) as control. Secondly, in order to evaluate the acute immune stimulatory effect of DnaK in L. vannamei, regulation of four important immune-­‐related gene groups (prophenoloxidase, transglutaminase, penadins, endogenous HSP70) were monitored 12h after DnaK intramuscular injection. Significantly responding genes were selected as immune markers for subsequent study. Subsequently, the priming effect of bacterial HSP70 DnaK against V. campbellii and WSSV infection was evaluated. Thesis demonstrated that pre-­‐treatment of L. vannamei with the DnaK, followed by a non-­lethal V. campbellii challenge affected the transcription of 3 immune marker genes, TGase-­‐1, proPO-­‐2 and lvHSP70. Similarly, we tested the hypothesis that DnaK can prime the immune system of L.vannamei to cope with a viral infection (WSSV). Transcriptions of two immune related genes, TGase-­‐1 and proPO-­‐2, were quantified within 12 hpp. Strong synergistic effects induced by both DnaK and WSSV on TGase-­‐1 and proPO-­‐2 were exhibited. In conclusion, the results presented in this thesis indicate a possible role for DnaK as an immune priming agent in L. vannamei against V. campbellii and WSSV infections.

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