Abstract
The gastrointestinal immune system plays an important role in immune homeostasis regulation. It regulates the symbiotic host-microbiome interactions by training and developing the host’s innate and adaptive immunity. This interaction plays a vital role in host defence mechanisms and at the same time, balancing the endogenous perturbations of the host immune homeostasis. The fish gastrointestinal immune system is armed with intricate diffused gut-associated lymphoid tissues (GALTs) that establish tolerance toward the enormous commensal gut microbiome while preserving immune responses against the intrusion of enteric pathogens. A comprehensive understanding of the intestinal immune system is a prerequisite for developing an oral vaccine and immunostimulants in aquaculture, particularly in cultured fish species. In this review, we outline the remarkable features of gut immunity and the essential components of gut-associated lymphoid tissue. The mechanistic principles underlying the antigen absorption and uptake through the intestinal epithelial, and the subsequent immune activation through a series of molecular events are reviewed. The emphasis is on the significance of gut immunity in oral administration of immunoprophylactics, and the different potential adjuvants that circumvent intestinal immune tolerance. Comprehension of the intestinal immune system is pivotal for developing effective fish vaccines that can be delivered orally, which is less labour-intensive and could improve fish health and facilitate disease management in the aquaculture industry.
Highlights
Diseases have always been the “Achilles’ heel” of intensive farming, and that analogy is especially accurate for aquaculture
Mucosal antigen uptake has been described in the posterior gut of European sea bass (Dicentrarchus labrax) [82], the second segment of the carp gut [12], the second segment of the salmonid midgut [83], the trout stomach and hindgut [84], the ballan wrasse (Labrus bergylta) posterior gut [85], and the Atlantic cod (Gadus morhua) rectum [86]
Oral immune tolerance is a state of immunological unresponsiveness toward particular mucosal antigens, which may be due to the prevention of aberrant or excessive immune reactions to food-derived antigens or intestinal commensal microbiota, or ascribable to prior exposure to the same antigens [87]
Summary
Diseases have always been the “Achilles’ heel” of intensive farming, and that analogy is especially accurate for aquaculture. Owing to high practicability and stress-free administration, oral supplements and vaccines that can ameliorate fish health has been gaining traction and popularity in research, and understanding of gut immune system paves the way to the development of the oral application. Researchers and farmers of fed-aquaculture (i.e., fish that rely on nutrient input from formulated diets) are allowed to manipulate the health of the finfish through the diets by either incorporating feed additives, drugs, or even vaccines [5]. The uniqueness of how each of these orally administered interventions could ameliorate the physiological responses of the host, or how their mechanisms can inhibit pathogen proliferation, deserves to be appraised in a holistic view with the fish intestinal immune system, which prevents disease outbreaks and economic losses. A compilation of recent studies on intestinal immunology of farmed finfish will be interpreted and discussed, as well as the advent of orally delivered vaccines, and plant-based immunostimulants on fish intestinal health
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
