Innate immunity of fish (overview).

The innate immune system of fish is considered to be the first line of defence against a broad spectrum of pathogens and is more important for fish as compared with mammals. Lysozyme level or activity is an important index of innate immunity of fish and is ubiquitous in its distribution among living organisms. It is well documented that fish lysozyme possess lytic activity against both Gram-positive bacteria and Gram-negative bacteria. It is also known to be opsonic in nature and activates the complement system and phagocytes. It is present in mucus, lymphoid tissue, plasma and other body fluids of freshwater and marine fish. It is also expressed in a wide variety of tissues. Lysozyme activity has been shown to vary depending on the sex, age and size, season, water temperature, pH, toxicants, infections and degree of stressors. Here, we review our current understanding of different types of lysozyme and their expression and its role in fish innate immune system.

Lysozyme: an important defence molecule of fish innate immune system

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.

/pdf/innate-and-adaptive-immunity-in-teleost-fish-a-review-4hejusxbjz.pdf

Innate and adaptive immunity in teleost fish: a review.

Introduction Basic biology of mucus Production and composition The state of mucus on fish surfaces Biophysical properties of fish mucus Experimental approaches Osmotic, ionic and acid-base regulation, gas exchange and excretion Unstirred layers Water Ions Respiratory gases, acid-base balance and ammonia excretion Defence Locomotion Filter feeding, adhesion and abhesion Conclusions References page 401 402

Functions for fish mucus

Although fish immunology has progressed in the last few years, the contribution of the normal endogenous microbiota to the overall health status has been so far underestimated. In this context, the establishment of a normal or protective microbiota constitutes a key component to maintain good health, through competitive exclusion mechanisms, and has implications for the development and maturation of the immune system. The normal microbiota influences the innate immune system, which is of vital importance for the disease resistance of fish and is divided into physical barriers, humoral and cellular components. Innate humoral parameters include antimicrobial peptides, lysozyme, complement components, transferrin, pentraxins, lectins, antiproteases and natural antibodies, whereas nonspecific cytotoxic cells and phagocytes (monocytes/macrophages and neutrophils) constitute innate cellular immune effectors. Cytokines are an integral component of the adaptive and innate immune response, particularly IL-1β, interferon, tumor necrosis factor-α, transforming growth factor-β and several chemokines regulate innate immunity. This review covers the innate immune mechanisms of protection against pathogens, in relation with the installation and composition of the normal endogenous microbiota in fish and its role on health. Knowledge of such interaction may offer novel and useful means designing adequate therapeutic strategies for disease prevention and treatment.

A review on the interactions between gut microbiota and innate immunity of fish.

Noncellular nonspecific defence mechanisms of fish

The concentration of protein in the sera of rainbow trout, Salmo gairdneri, brown trout S. trutta and Atlantic salmon S. salar has been measured by six standard techniques viz refractometry, copper sulphate specific gravity, automated and manual biuret, optical density and Lowry et al. phenol reagent and the results compared. Good correlation was obtained in most cases and interconversion formulae are given between each method in the three salmonid species. The concentrations obtained with the refractometer and optical density methods were approximately one and a half times those obtained with the others.

A comparison of five of the methods commonly used to measure protein concentrations in fish sera

Immunoglobulin production in the primary and secondary immune response of brown trout to keyhole limpet haemocyanin has been investigated including the effect of dose size, route and number of injections, and the use of adjuvant. Antibody activity was found in the first fraction from Sephadex G200 and in the second from Sepharose 6B. Trout immunoglobulin had β2—Γ1 electrophoretic mobility, and Sapp of 16·7 and an approximate molecular weight of 670 000 daltons. It was sensitive to dithiothreitol and stable at 56°C for 30 min. Immunoglobulin concentrations were measured by single radial immunodiffusion with a specific rabbit antiserum. Sera from non-injected trout had a mean immunoglobulin level of 7·3 ± 0·3 mg ml−1 which accounted for 10% of the total serum protein. Phosphate buffered saline-injected controls contained 6·7 ± 0·2. In fish given a single injection the mean concentration ranged from 7·5 to 12·9 and in those given more than one injection from 12·6 to 16·8. The use of adjuvant resulted in higher immunoglobulin concentrations. Neither dose nor route had any significant effect on the primary response. However, in the secondary response the intramuscular route resulted in significantly increased immunoglobulin production.

The immunoglobulin of the brown trout, Salmo trutta and its concentration in the serum of antigen-stimulated and non-stimulated fish

Brown trout produced high molecular weight, thermostable, dithiothreitol sensitive, non-precipitating, complement-fixing antibodies and agglutinins to lipopolysaccharides after intramuscular injection with adjuvant. Antibodies were first detected on Day 14 and reached maximum titres after 56 to 63 days when a single injection was given. When either a second or a third injection was administered maximum titres occurred 34 to 40 days after the injection. After each injection the titres increased significantly, and the protein concentration of the sera was significantly decreased. In cellulose acetate electrophoresis experiments those bands which migrated in the β- to γ-globulin regions were increased.



Antibody-secreting and antigen-binding cells were detected on Days 8 and 4 respectively and maxima were reached between Day 16 and Day 18. The number of cells per 106 lymphoid cells was higher in the spleen than in the kidney.

The immune response of the brown trout Salmo trutta to lipopolysaccharide

Brown trout were subjected to the hyperosmotic infiltration method of bacterial immunization. The route of entry of E. coli into fish was observed by the immunoperoxidase technique on instantly frozen tissue to be through the gills. The passage of bacteria directly into the lateral line system of the fish was not observed.

Hyperosmotic infiltration: immunological demonstration of infiltrating bacteria in brown trout, Salmo trutta L.

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