Humoral and Cellular Effects of Stress-An Extensive Model System

Abstract

The influence of stress on the immune system of the common carp (Cyprinus carpio) was studied by measuring leukocytes levels using flow cytometry and mRNA immune components by real time qPCR. Acute and chronic oxidative stresses were generated by different regimes of exposure of carp to environmental air. In acute stress, induced by single air exposure, the pro-inflammatory cytokines (IL1β, IL6 and TNFα) and the down-regulatory ones (IL10 and TGFβ) showed significant simultaneous elevations (515, 147, 373, 300 and 198% respectively). Following chronic stress (multiple air exposures) however, a drastic decline of 80%, in macrophages/monocytes, B-cells likes and plasma-cells like, occurred in peripheral blood. No statistical changes in IL6 and TNFα, as well as in IgM and C3s mRNA levels could be shown during this experiment. CD4 mRNA decreased up to 6% in the 2nd week of chronic stress and elevated only to 55% at the 3rd week Vs a temporal decline of up to 22% in CD8a mRNA at the 2nd week. The regulatory cytokines (IL10, FoxP3 and TGFβ) as well as the pro-inflammatory ones (IL1β and IL17) decreased significantly up to 0.06, 0.2, 5, 6 and 4% respectively, at the second week before being restored to normal at the 3rd week. Moreover, a persistent decrease, up to null levels, in the cytokines IFNγ2b, IL12b and IL8 was also revealed. These downregulations were suggested as a result of the impaired Th1 and/or cytotoxic cell function and, to a certain degree, the leukocytes mobilization. The above findings show that in contrast to the detrimental effects of chronic stress, in which cells and functions of acquired immunity were partially or completely impaired, the acute stress was found rather beneficial and in line with the known ephemeral "fight and flight" response.

Influence of chronic stress on the mechanism of the cytotoxic system in common carp (Cyprinuscarpio)

“…Therefore, following up changes in cytokines and leucocytes levels in peripheral blood during stress treatments was preferred over sampling their levels in the spleen, kidney, head kidney and liver. Monitoring the blood enables changes in each carp to be ascertained without killing the specimen [ 100 ]. A systematic study revealed which function of the carp immune system was most affected by hypoxic stress and how the duration of stress influences the expression of these functions.…”

“…Acute stress enhances the fast pathway that activates the sympathetic nervous system to release catecholamines, such as adrenaline and noradrenaline, from chromaffin cells in the head kidney, and the released catecholamines bind to their receptors in leucocytes [ 101 , 102 ]. As a result, the proinflammatory function (IL‐1b, IL‐6 and tumour necrotic factor α (TNFa)) is upregulated and, at the same time, the activity of regulatory function (TGFb and IL‐10) is upregulated, probably in order to return proinflammatory activity to homeostasis [ 100 , 103 ]. Chronic stress activates the hypothalamus‐pituitary‐interrenal cell axis and, as a result, interrenal cells in the head kidney mainly release cortisol [ 65 ].…”

“…The results of monitoring the influence of chronic hypoxic stress on immune activity in the common carp peripheral blood leucocytes are shown in Table 1 , and these results reveal a downregulation of regulatory (IL‐10, TGFb, forkhead box P3 (FoxP3)), proinflammatory (IL‐1β, IL‐6), and inflammatory (IL‐17) functions until the second week of chronic stress. However, in the third week, their change in levels overcame and returned to homeostasis [ 100 ]. TNFa levels did not change during hypoxic stress treatments (Table 1 ), but TNFa behaved slightly differently in chronic cortisol implants in rainbow trout ( Oncorhynchus mykiss ) for five days [ 104 ].…”

“…The chronic cortisol treatment showed results similar to those in acute hypoxic stress (Table 1 ). In contrast, the main impaired functions, even after 22 days of chronic stress [ 100 , 105 ], were as follows: (1) cytotoxic mediators, such as interferon (IFN)‐γ2b, Fas ligand (FasL), NK lysin and granzyme; (2) IL‐12 and Tbet, which are responsible for Th1 cell proliferation and maturation, which mediates host defence against intracellular pathogens [ 106 , 107 , 108 ]; and (3) IL‐8, which attracts leucocytes to the infection site [ 109 ]. IL‐8, which was downregulated during the 22‐day chronic stress period, can explain the macrophage/neutrophil/leucocyte mobilization decline in different body compartments, as shown by Wojtaszek and colleagues [ 110 ].…”

“…The chronic cortisol treatment showed results similar to those in acute hypoxic stress (Table 1). In contrast, the main impaired functions, even after 22 days of chronic stress [100,105], were as follows:…”