Immunosuppression in Atlantic salmon by an extracellular protein of Aeromonas salmonicida

Noor, Iffat (1996) Immunosuppression in Atlantic salmon by an extracellular protein of Aeromonas salmonicida. PhD thesis, University of Glasgow.

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Abstract

The extracellular products of Aeromonas salmonicida inhibited the antibody response of Atlantic salmon to a second antigen, namely phage MS2. During the characterisation of the humoral immunosuppressive factor (HIF) evidence suggested that the suppressor was the 64-kD serine protease of A. salmonicida. Before any further work could be undertaken it was imperative to establish that the immunosuppressive action of the protease was not merely due to proteolytic degradation of the antibody molecule. This was shown not to be the case by both in vivo and in vitro experiments. Further, it was also illustrated that MS2 phage used as the second antigen was also not degraded by the protease and that the antibody response elicited in fish was specific for the phage. The effect of the protease on the proliferation of leucocytes from peripheral blood and anterior kidney was investigated and it was shown that the protease caused a dose related inhibition of the cell stimulation in response to the B cell mitogen, LPS. This effect was enhanced when the cells were preincubated with the protease before activation with LPS suggesting that the protease may be interfering with the lymphocyte commitment to blastogenesis. The involvement of prostaglandins was implicated by in vivo experiments which showed that indomethacin, an inhibitor of prostaglandin synthesis, blocked the immunosuppressive activity of the protease when administered to fish. Subsequently, PGE2 concentration in serum samples of fish injected with indomethacin with or without protease was measured and it was clear that the protease caused an enhancement of PGE2 concentration. This result was also duplicated in in vitro experiments using leucocytes from both peripheral blood and anterior kidney which demonstrated increased levels of PGE2 in response to the protease. Furthermore, the protease stimulated an increase in the concentration of intracellular cyclic AMP of salmon leucocytes. It remains to be determined whether there is a relationship between increased levels of PGE2 and cyclic AMP stimulated by the protease. These observations indicate that the inhibitory effect of the serine protease of A. salmonicida on the humoral response of Atlantic salmon occurs via a prostaglandin-dependent pathway probably involving cyclic AMP as a secondary messenger. Although it is tentatively concluded that the suppressive factor is the 64-kDa serine protease, conclusive proof is still required. Many roles have been attributed to this protease in the pathogenesis of A. salmonicida during furunculosis in Atlantic salmon. However, its involvement in immunosuppression has not been reported before.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: T H Birdbeck
Keywords: Immunology, Aquatic sciences
Date of Award: 1996
Depositing User: Enlighten Team
Unique ID: glathesis:1996-71842
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 17 May 2019 09:31
Last Modified: 17 May 2019 09:31
URI: http://theses.gla.ac.uk/id/eprint/71842

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