Teleost intestinal immunology

Abstract

Teleosts clearly have a more diffuse gut associated lymphoid system, which is morphological and functional clearly different from the mammalian GALT. All immune cells necessary for a local immune response are abundantly present in the gut mucosa of the species studied and local immune responses can be monitored after intestinal immunization. Fish do not produce IgA, but a special mucosal IgM isotype seems to be secreted and may (partly) be the recently described IgZ/IgT. Fish produce a pIgR in their mucosal tissues but it is smaller (2 ILD) than the 4-5 ILD pIgR of higher vertebrates. Whether teleost pIgR is transcytosed and cleaved off in the same way needs further investigation, especially because a secretory component (SC) is only reported in one species. Teleosts also have high numbers of IEL, most of them are CD3-ɛ+/CD8-α+ and have cytotoxic and/or regulatory function. Possibly many of these cells are TCRγδ cells and they may be involved in the oral tolerance induction observed in fish. Innate immune cells can be observed in the teleost gut from first feeding onwards, but B cells appear much later in mucosal compartments compared to systemic sites. Conspicuous is the very early presence of putative T cells or their precursors in the fish gut, which together with the rag-1 expression of intestinal lymphoid cells may be an indication for an extra-thymic development of certain T cells. Teleosts can develop enteritis in their antigen transporting second gut segment and epithelial cells, IEL and eosinophils/basophils seem to play a crucial role in this intestinal inflammation model. Teleost intestine can be exploited for oral vaccination strategies and probiotic immune stimulation. A variety of encapsulation methods, to protect vaccines against degradation in the foregut, are reported with promising results but in most cases they appear not to be cost effective yet. Microbiota in fish are clearly different from terrestrial animals. In the past decade a fast increasing number of papers is dedicated to the oral administration of a variety of probiotics that can have a strong health beneficial effect, but much more attention has to be paid to the immune mechanisms behind these effects. The recent development of gnotobiotic fish models may be very helpful to study the immune effects of microbiota and probiotics in teleosts.

Optimal dietary protein level improved growth, disease resistance, intestinal immune and physical barrier function of young grass carp (Ctenopharyngodon idella)

“…Fish intestines are continuously exposed to foreign substances, such as microbes, pathogens and other toxic substances from food [1]. To prevent foreign substance invasion, fish have developed intestinal immune barriers and physical barriers [2].…”

Intestinal immune function, antioxidant status and tight junction proteins mRNA expression in young grass carp ( Ctenopharyngodon idella ) fed riboflavin deficient diet

“…However, no studies have investigated the effects of riboflavin on antibacterial compounds, meanwhile, the effects of riboflavin on inflammatory cytokines production and the signaling pathways of NF-kB and TOR were also unknown in fish intestine. In fish, the intestinal lymphoid tissue contains lymphoid cells, macrophages, eosinophilic and neutrophilic granulocytes [10]. These cells could secrete antibacterial components in mammals [3].…”

Effect of dietary isoleucine on the immunity, antioxidant status, tight junctions and microflora in the intestine of juvenile Jian carp (Cyprinus carpio var. Jian)

“…The intestine is an important immune organ of fish, which contain many lymphoid cells, macrophages, eosinophilic and neutrophilic granulocytes [4,5]. Nevertheless, the intestine contacts most extensively with the exterior environment and has greatest chance to contact with foreign substances such as microorganisms, viruses and antigens in food [6].…”