Immune Defences of Teleost Fish - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 40

regulation/suppression but at the same time maintain the capability to respond positively in
response to pathogenic challenge.
2.9 CONCLUSION
Teleost fish have a well-developed, fast, potent innate immune response which results in an
efficient first-line defence against pathogens which are encountered in the aquatic environ-
ment. This constitutive immunity responds to a broad spectrum of pathogens and their PAMPs
in a variety of ways which involve innate cytokines, reactive oxygen and nitrogen interme-
diates, complement factors, lysozyme and proteolytic anti-bacterial factors, shared with the
immune systems of higher animals. The mechanisms involving cells and molecules of innate
responses are relatively well characterized; the adaptive response, on the other hand, is less
well understood. This paucity of mechanistic information regarding adaptive responses is as
a result of the lower dominance of adaptive responses in poikilothermic fish and the scarcity
of reagents, such as specific antibodies to immune molecules that facilitate characterization of
adaptive mechanisms. The characterizations of gene homologues of human immune molecules
such as cytokines, T cell markers and transcription factors have been important observations
which, by inference from the human immune system, suggest teleost adaptive responses to
be similar to those in humans. Teleost fish adaptive responses include CMI driven by Th 1 ,
Th 17 and Tc, whereas Th 2 cells drive humoral responses, and these are all likely to be con-
trolled by the suppressive activities of T reg . The involvement of these components of both the
innate and the adaptive immune responses in the mucosal tissues of teleost fish suggest that
the mucosa are integral to immune activation versus regulation decisions made by the teleost
immune system as a consequence of exposure to harmful non-self pathogens, non-harmful
non-self commensals, or self. The comprehensive investigation of teleost immune responses
elicited to pathogenic challenge will facilitate the manipulation of fish immunity to the advan-
tage of the host. Finally, these responses characterized will introduce new and improved future
prophylactic and therapeutic interventions through the use of probiotics, nutrient supplemen-
tation and vaccination protocols, resulting in improved aquaculture and fish productivity for
years to come!
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