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The continued existence of the aquaculture industry depends on its
profitability. Stress is considered a primary factor contributing to impaired
health in cultured fish. Studying the influence of stress on the immune system
can suggest tools to handle sensitivity to the morbidity and mortality of fish
in fish ponds. This article supplies guidelines on how to isolate the factors
down regulating the immune system following stress. Analyzing the varied
components of the immune system highlighted the influence of chronic stress on
the down regulation of cytotoxic components.
INTRODUCTION
Aquaculture conditions are often exposed to
various stressors, such as the invasion of predatory birds, seasonal
fluctuations in temperature, and variable environmental pollutants that
increase fish sensitivity and expose them to various pathogens, resulting in
high morbidity and mortality that influence the feasibility of the fishery
industry. Stress influences humoral and cellular immune systems that are
regulated by the nervous and endocrine systems via cytokines, hormones,
neurotransmitters and receptors, which are in constant communication. Stress
was widely studied in mammals and less in fish, but several studies on fish
support the stress mechanism as reported in mammals [1].
Stressors might have profound positive or
negative effects on the immune system, depending on the duration, intensity,
and type of stressor. The aim of this study was to distinguish and isolate the
main causes of the developing imbalance of the immune system that lead to the
increase of morbidity [2].
RESEARCH METHODOLOGY
The authors assumed that in order to increase
the profitability of the aquaculture industry, we have to improve the welfare
and reduce the morbidity of the fish. Stress seems to be the main cause of the
increased sensitivity to diseases and mortality in fish, therefore, it was
important to:
1)
Determine the type of stress down regulating the immune system function.
2)
Classify the immune components to cells and constituents of main
functions in the immune system.
3)
Examine and analyse the functions that are mostly
influenced by stress.
4)
Focus the study on the most influenced functions [2].
In accordance with these principals, immune
cells were grouped into small and large lymphocytes, polymorphonuclear cells,
and monocytes/macrophages. Their levels were measured by flow cytometry during
stress treatments.
Similarly, the immune components were
classified to:
1)
CD4 and CD8α cells, which represent the majority of cells involved in
immune processes.
2)
Significant agents of the innate immunity (IgM and the complement C3).
3)
Pro-inflammatory cytokines IL1β, IL6 and TNFα.
4)
Inflammatory cytokines related to Th1 cells (IFNγ2b and IL12β) and Th17
cells (IL17).
5)
Regulatory cell cytokines, such as IL10, TGFβ and FoxP3.
6)
Chemoattractant CXCL8, which acts similarly to the mammalian IL8 in
mobilizing macrophages/neutrophils/leukocytes to the target area.
Their mRNA levels were measured by real-time
qPCR [2].
THEORETICAL VALUE OF THE
ARTICLE
The above-mentioned
guidelines enabled us to differentiate between the different types of stress,
and focus on the detrimental effects of chronic stress on the immune system.
Moreover, these guidelines enabled us to determine the severity of the
influence of chronic stress on immune components and differentiate between: (1)
unchanged influence on components' mRNA levels, such as on the innate system
(IgM, C3s) and pro-inflammatory cytokines (IL6, TNFα); (2) fluctuating
influence, in which chronic stress temporarily changed mRNA levels of immune
components, such as regulatory cytokines (IL10, TGFβ, FoxP3), pro-inflammatory
cytokines (IL1β, IL17), and CD8 cells; and (3) prominent effects on the decline
to null levels, e.g of IFNγ and IL12β. The severe decline of IFNγ and IL12β
focused the study on their decrease. The authors did not impose the
responsibility for that decline of IFNγ and IL12β only on Th1 cells because in
carp, there are additional cells that prominently produce IFNγ, such as γ/δT,
NK and MR1 cells. Therefore, the following study also emphasized the sharp
decline of additional cytotoxic metabolites such as FasL, granzyme, NK lysin and
Tbet mRNA versus minor changes in cell levels [3]. These findings focus on the
detrimental influence of chronic stress on the metabolism of cytotoxic
cytokines, which leads to unresponsiveness to pathogens and unwanted cells.
CONCLUSION
This article
highlights the need to isolate the main type of stress sharply down regulating
the immune system as well as to determine the most affected factor in the
immune system. The above findings enable us to improve the well-being and
growth of fish in the ponds.
1. Tort
L (2011) Stress and immune modulation in fish. Dev Comp Immunol 35: 1366-1375.
2. Shimon-Hophy
M, Avtalion RR (2017) Humoral and cellular effects of stress - An extensive
model system. Am J Immunol 13: 131-143.
3. Shimon-Hophy
M, Avtalion RR (2018) Chronic stress down regulate IFNγ in cytotoxic cells of
the common carp (Cyprinus carpio).
Arch Immunol Allerg 1: 54-66.