Cortisol response and immune-related effects of ...

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Title Cortisol response and immune-related effects of Atlantic salmon (Salmo salar Linnaeus) subjected to short- and long-term stress
Author(s) Mark D. Fast, Sho Hosoya, Stewart C. Johnson, Luis O.B. Afonso
Journal Fish and Shellfish Immunology
Date 2008
Volume 24
Issue 2
Start page 194
End page 204
Abstract It is generally considered that stress causes decreased immune function in fish. In this study we examined in Atlantic salmon (Salmo salar Linnaeus) the effects of both short- (a single 15s out of water) and long-term (4weeks of daily handling 15s out of water) stress on plasma cortisol (free and total) and glucose levels, expression of interleukin-1β (IL-1β) and survival of head kidney (HK) macrophages under culture with Aeromonas salmonicida. In the short-term study, samples were collected prior to the application of the stressor, and at 1, 3, 6, 12 and 24h post stress. Free and total plasma cortisol levels and the percentage of free cortisol increased significantly in the stressed group at 1 and 3h post stress. Plasma glucose levels were significantly higher than those of control fish at 1, 3 and 6h post stress. Constitutive expression of IL-1β in macrophages isolated from head kidneys in stressed fish was significantly higher at 1 and 3h post stress. However, lipopolysaccharide (LPS) stimulated expression of IL-1β in HK macrophages, exhibited significantly higher fold increases in unstressed fish compared to stressed fish. In the long-term study, with the exception of an increase in plasma glucose levels at 1week, there were no significant differences in stress parameters between groups. There was a significantly higher constitutive IL-1β expression in macrophages isolated from stressed fish over the first 2weeks. At weeks 1, 2 and 3 the magnitude of IL-1β response of isolated HK macrophages to LPS stimulation was reduced in >90% of the stressed fish. At 4weeks there was no significant difference in inducible IL-1β expression between the groups. Macrophages isolated from stressed fish also showed significantly decreased survival when exposed to A. salmonicida. This study shows a clear pattern from repeated handling stress, whereby effects on immune cells begin with increased constitutive expression of IL-1β, followed by decreased stimulation of leucocytes by extracellular antigen, and finally decreased leukocyte survival when exposed to A. salmonicida. The implications of these changes in the immune system will be discussed with respect to the use of classical indicators of stress to predict possible effects on the immune system of fish.
DOI 10.1016/j.fsi.2007.10.009

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