Innate immunity of fish (overview).

Probiotics and immunity: a fish perspective.

The zebrafish is firmly established as a genetic model for the study of vertebrate blood development. Here we have characterized the blood-forming system of adult zebrafish. Each major blood lineage can be isolated by flow cytometry, and with these lineal profiles, defects in zebrafish blood mutants can be quantified. We developed hematopoietic cell transplantation to study cell autonomy of mutant gene function and to establish a hematopoietic stem cell assay. Hematopoietic cell transplantation can rescue multilineage hematopoiesis in embryonic lethal gata1-/- mutants for over 6 months. Direct visualization of fluorescent donor cells in embryonic recipients allows engraftment and homing events to be imaged in real time. These results provide a cellular context in which to study the genetics of hematopoiesis.

Transplantation and in vivo imaging of multilineage engraftment in zebrafish bloodless mutants

The immune system of fish is very similar to vertebrates, although there are some important dif - ferences. Fish are free-living organisms from the embryonic stage of life in their aquatic environment. They have mechanisms to protect themselves from a wide variety of microorganisms. Consequently, fish rely on their innate immune system for an extended period of time, beginning at the early stages of embryogenesis. The components of the innate immune response are divided into physical, cellular and humoral factors and include humoral and cellular receptor molecules that are soluble in plasma and other body fluids. The lymphoid organs found in fish include the thymus, spleen and kidney. Immunoglobulins are the principal components of the immune response against pathogenic organisms. Immunomodulatory products, including nucleotides, glucans and probiotics, are increasingly used in aquaculture production. The use of these products reduces the need for therapeutic treatments, enhances the effects of vaccines and, in turn, improves the indicators of production. The aim of this review is to provide a review of the immune system in fish, including the ontogeny, mechanisms of unspecific and acquired immunity and the action of some immunomodulators.

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Innate and adaptive immunity in teleost fish: a review.

Teleost fish are the most primitive bony vertebrates that contain immunoglobulins. In contrast to mammals and birds, these species are devoid of immunoglobulin A (IgA) or a functional equivalent. This observation suggests that specialization of immunoglobulin isotypes into mucosal and systemic responses took place during tetrapod evolution. Challenging that paradigm, here we show that IgT, an immunoglobulin isotype of unknown function, acts like a mucosal antibody. We detected responses of rainbow trout IgT to an intestinal parasite only in the gut, whereas IgM responses were confined to the serum. IgT coated most intestinal bacteria. As IgT and IgA are phylogenetically distant immunoglobulins, their specialization into mucosal responses probably occurred independently by a process of convergent evolution.

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IgT, a primitive immunoglobulin class specialized in mucosal immunity

Teleost intestinal immunology.

Soybean meal induces intestinal inflammation in common carp (Cyprinus carpio L.).

Adaptive immune responses at mucosal surfaces of teleost fish

Phylogeny and ontogeny of fish leucocytes.

Electrophoretic analysis did not reveal clear differences between skin mucus and serum immunoglobulin (Ig) of carp. The majority of both Igs were tetrameric (±760 kDa) and composed of 25 kDa light (L) chains and 70 kDa heavy (H) chains, but dimeric and monomeric forms were found as well. Monoclonal antibody (mAb) WCI 12 produced from serum Ig appeared to react with the H chain of both molecules. After immunisation of mice with purified mucus Ig, mAbs could be selected that were reactive with mucus Ig only. Two of these mAbs (WCI M1 and WCI M2) were immunoreactive with the H chain of mucus Ig and not or hardly immunoreactive with the H chain of serum Ig, indicating differences in the composition of the H chains of both molecules. Because WCI M2 appeared to recognize a carbohydrate determinant, differences seem to occur in the protein as well as carbohydrate composition of mucus and serum Ig. Flow cytometric results showed that both mAbs were reactive with the same subpopulation of WCI 12-positive B cells. Immunohistochemical reactions on cryosections also showed a limited reaction by these mAbs compared with WCI 12; only epithelium of skin and bile ducts and capillaries in the liver were strongly positive with these mAbs. The presence of mucus Ig at these locations is discussed. Our results indicate structural and functional differences between mucus and serum Ig, which may explain the mucosal immune responses reported for fish. Such a specific mucosal defense system can be very important for fish, living in a pathogenrich environment.

Jan H.W.M. Rombout

Papers

Teleost intestinal immunology.

Soybean meal induces intestinal inflammation in common carp (Cyprinus carpio L.).

Adaptive immune responses at mucosal surfaces of teleost fish

Phylogeny and ontogeny of fish leucocytes.

Differences in mucus and serum immunoglobulin of carp (Cyprinus carpio L.)