Rainbow trout lymphoid organs: cellular effects of corticosteroids and anti-thymocyte serum

Stress, nutrition and parental care in a teleost fish: exploring mechanisms with supplemental feeding and cortisol manipulation

Parental care is an essential life-history component of reproduction for many animal species, and it entails a suite of behavioural and physiological investments to enhance offspring survival. These investments can incur costs to the parent, reducing their energetic and physiological condition, future reproductive capabilities and survival. In fishes, relatively few studies have focused on how these physiological costs are mediated. Male smallmouth bass provide parental care for developing offspring until the brood reaches independence. During this energetically demanding life stage, males cease active foraging as they vigorously defend their offspring. Experimental manipulation of cortisol levels (via implantation) and food (via supplemental feeding) in parental males was used to investigate the fitness consequences of parental care. Improving the nutritional condition of nest-guarding males increased their reproductive success by reducing premature nest abandonment. However, supplemental feeding and cortisol treatment had no effect on parental care behaviours. Cortisol treatment reduced plasma lymphocyte numbers, but increased neutrophil and monocyte concentrations, indicating a shift in immune function. Supplemental feeding improved the physiological condition of parental fish by reducing the accumulation of oxidative injury. Specifically, supplemental feeding reduced the formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) on DNA nucleotides. Increasing the nutritional condition of parental fish can reduce the physiological cost associated with intensive parental activity and improve overall reproductive success, illustrating the importance of nutritional condition as a key modulator of parental fitness.

Sarcoma in the thymus of juvenile meagre Argyrosomus regius reared in an intensive system

Juvenile meagre Argyrosomus regius (Asso, 1809) maintained in experimental conditions developed lateral and/or bilateral circular-shaped sarcoma within the opercular cavity. The sarcoma was dense, reddish and its growth from the branchial arch exerted pressure on the operculum forcing it to open. Histologically, the neoplasm exhibited marked proliferation of mesenchymal connective tissue composed largely of fusiform cells, which developed in a solid pattern accompanied by abundant mononuclear cell types. Multifocal areas of discrete necrosis were also observed, compatible with a sarcomatous proliferation. The immunological parameters analysed suggested an inflammatory response. No bacteria were isolated from the hematopoietic organs. However, Vibrio species, components of the normal seawater flora, were isolated from the tumour, which may have had a role in eliciting the immune response. No evidence of viral pathogens was found by electron microscopy. In order to look for cytogenetic alterations often linked to sarcomas, the diploid number and karyotype of this species were determined for the first time. An increase in the aneuploidy level was observed in sarcoma cell metaphase stages compared to other tissues. The aetiology of this tumour remains unknown.

Factors influencing in vitro respiratory burst assays with head kidney leucocytes from rainbow trout, Oncorhynchus mykiss (Walbaum)

Abstract Head kidney leucocytes are central elements in a number of in vivo and in vitro assays elucidating innate and adaptive immune mechanisms in teleosts following stimulation with various antigens. These systems are sensitive to several factors affecting the outcome of the assays. The present work describes the importance of temperature, cell concentration, exposure time and immune-modulatory molecules on the respiratory burst activity (RBA) of rainbow trout head kidney leucocytes in vitro. Some variation in RBA was observed among individual fish. However, use of cells pooled from four individuals produced satisfactory results following exposure to phorbol 12-myristate 13-acetate, zymosan and beta-glucan. Temperature was shown to have a significant effect on production of reactive radicals as illustrated by a high activity in cells maintained at 15-20 degrees C and a reduced activity at temperature extremes (1, 4 and 30 degrees C). Highest activity was found at a cell concentration of 1 x 10(7) cells mL(-1). Reactivity showed a clear decline when cells were exposed for more than 4 h. Moreover, incubation of cells with inhibitory substances viz., DiMePE2, cortisol and superoxide dismutase decreased the RBA. It is concluded that several biotic and abiotic factors should be taken into account when conducting RBA assays with head kidney leucocytes for elucidation of rainbow trout immune responses.

Innate immunity as a driving force in renal disease

Mrug et al. propose that innate immunity is a hallmark of progressive polycystic kidney disease (PKD). We propose that innate immunity is a driving force in the progression of many renal diseases. Renal epithelial cells are capable of expressing a large variety of proinflammatory genes resulting in the production of cytokines, chemokines, cell-adhesion molecules, and complement components. We suggest that future therapeutic interventions should be directed toward control of innate immunity in renal disease.

Interaction between endocrine and immune systems in fish

Diseases in fish are serious problems for the development of aquaculture. The outbreak of fish disease is largely dependent on environmental and endogenous factors resulting in opportunistic infection. Recent studies, particularly on stress response, have revealed that bidirectional communication between the endocrine and immune systems via hormones and cytokines exists at the level of teleost fish. Recently information on such messengers and receptors has accumulated in fish research particularly at the molecular level. Furthermore, it has become apparent in fish that cells of the immune system produce or express hormones and their receptors and vice versa to exchange information between the two systems. This review summarizes and updates the knowledge on endocrine-immune interactions in fish with special emphasis on the roles of such mediators or receptors for their interactions.

In vitro and in vivo effects of rabbit anti-thymocyte serum on circulating leucocytes and production of complement fixing antibodies in thymectomized Oncorhynchus mykiss (Walbaum) infected with Cryptobia salmositica Katz 1951

Rabbit anti-thymocyte serum (RATS) against thymocytes of rainbow trout was toxic to leucocytes from intact and thymectomized rainbow trout at 10 °C under in vitro conditions. The total number of leucocytes decreased significantly in 24 h after RATS was injected intraperitoneally into intact rainbow trout, but the number returned to pre-injection level within 1 week. RATS destroyed a lower percentage of leucocytes in thymectomized fish than in intact fish under both in vitro and in vivo conditions and the recovery in the number of leucocytes was slower in thymectomized fish. The parasitaemia, packed cell volume and production of complement fixing antibody in thymectomized and intact fish (injected with RATS before Cryptobia salmositica infection) were not significantly different from control fish (not injected with RATS), and they both acquired protective immunity against cryptobiosis on recovery. This indicates that RATS is not cytotoxic to B-like cells in the lymphoid tissue which produce complement fixing antibody against C. salmositica and that the protective antigen in C. salmositica seems to be thymus-independent.

Association between immunisation, reduced weight gain and plasma cortisol concentrations in juvenile Baltic salmon (Salmo salar)

The changes in plasma cortisol levels, immune response parameters and growth of juvenile Atlantic salmon (Salmo salar) were monitored during a 50 days period following a DNP-HSA (di-nitrophenyl human serum albumin) immunisation program. Antibody titers rose significantly after a single immunisation. An increased plasma cortisol concentration was observed in association with injection of both antigen and saline. A single injection had a significant negative effect on growth of fish and fish subjected to 2 injections with a 25 days interval had an even larger growth reduction. The plasma cortisol concentration and the specific antibody response were compared at an individual level but no correlation was found. Total serum protein increased during the experimental period independently of immunisation. In contrast the total serum immunoglobulin 50 days after the first immunisation was clearly connected to antigen exposure. The observations are discussed in relation to immunophysiological changes during immunisation and stress induction.

Fish as biomarkers in immunotoxicology

This paper presents an overview on the state of the art in the development and application of biomarkers for immunotoxicology in fish. There are several reasons for developing this field: many fish diseases are related to environmental quality, various environmental pollutants have immunotoxic potential and many fish diseases have an immunological component. As in immunotoxicology in general, this aspect, in fish, has received ample attention in the recent past. Much benefit has been obtained from progress in related fields of science, such as fish immunology and rodent immunotoxicology. Meanwhile there is a broad spectrum of potential biomarkers for immunotoxicology in fish, from which macrophage parameters seem to be most widely used. The application of others, such as lymphoid cell parameters is still limited, probably due to practical problems such as lack of experience with conduct, validation and interpretation. Specific problems include the paucity of background data in the case of epidemiological field studies and the important role of other (non-chemical) stress factors in the immune response, and hence the lack of specificity of potential biomarkers.

Seasonal variations in the immune system of lower vertebrates

Seasonal variation, affecting the structure and function of the ectotherm immune system, is an excellent 'natural' model of the influence of neuroendocrine rhythms on immunity. In this review, Agustín Zapata, Alberto Varas and Marta Torroba examine the correlations between seasonal changes and circulating steroid levels, and investigate the possibility of a neuroendocrine-immune network in lower vertebrates.

Stress responses and disease resistance in salmonid fish: Effects of chronic elevation of plasma cortisol

Basal levels of plasma cortisol in unstressed salmonid fish are normally in the range 0-5 ng ml(-1). An acute stress such as handling or 1 h confinement caused a temporary elevation of the plasma cortisol levels of both brown trout,Salmo trutta L., and rainbow trout,Salmo gairdneri Richardson, in the range 40-200 ng ml(-1) with a return to basal levels within 24-48 h. The extent of the cortisol elevation in response to an acute stress was dependent upon both the species and strain of trout. Chronic stresses, such as prolonged confinement or crowding, resulted in an elevation of plasma cortisol levels to approximately 10 ng ml(-1). Under these circumstances, blood cortisol levels remained elevated for periods of up to 4 weeks before acclimation finally occurred.It is shown, by means of intraperitoneal implantation of cortisol, that chronic elevation of plasma cortisol levels in the brown trout results in a dose-dependent increase in mortality due to common bacterial and fungal diseases. This effect is apparent at plasma cortisol levels as low as 10 ng ml(-1), levels below those often reported as being representative of 'unstressed' fish. These findings are discussed in relation to the known immunosuppressive effects of corticosteroids in teleost fish.

Alterations in the peripheral lymphoid organs and differential leukocyte counts in Saprolegnia-infected brown trout, Salmo trutta fario

The number of circulating leukocytes and the structure of splenic and renal lymphoid tissue were comparatively analysed in healthy and Saprolegnia-infected wild brown trout, Salmo trutta fario. Sick trout showed lymphopenia, mainly due to decreased numbers of circulating small lymphocytes, and heterophilia. The splenic and renal lymphoid tissue of infected trout exhibited similar changes, consisting of cellular depletion, lymphoid cell degeneration, and vascular alterations with blood vessel enlargement and hypertrophy of sinusoidal endothelial cells. Furthermore, the endothelial cells in the spleen and kidney of the infected trout contained cytoplasmic vesicles filled with material of possible fungal origin. The absence of a reticular sheath was also evident in the splenic ellipsoids. These results suggest some immunodepression in Saprolegnia-infected trout which might favour the course of the disease.

The effects of gamma irradiation on the lymphoid organs of rainbow trout and subsequent susceptibility to fish pathogens

Fish were irradiated with 60Co gamma rays at doses ranging from 10 to 50 Gy. Lethal doses were determined in fishes of different ages. For a given dose, fry and fingerlings were more susceptible than subadults. Whatever the irradiation dose was, the fish displayed a sharp decrease in blood leucocyte count. At the lowest doses, this acute leucopaenia was reversible. The cellular damage in the lymphoid organs was particularly obvious in the thymus. The depletion of lymphoid cells from immunocompetent organs decreased (viral hemorrhagic septicaemia, VHS) or increased (Y. ruckeri, A salmonicida) the susceptibility of trout to pathogens. The suppressive effect of radiation was age dependent. Irradiation appeared to be a reliable technique to detect asymptomatic carrier fish.

Cortisol-induced lymphocytopenia in brown trout, Salmo trutta L

The administration of cortisol in the food of brown trout produced peak plasma cortisol titres of about 140 ng ml-1 at 12 hr and markedly reduced the number of circulating lymphocytes, which reached their lowest count at 36 hr. Cortisol did not affect the erythrocyte, thrombocyte, or neutrophil count. Sexual maturation of the male fish was associated with an increase in erythrocytes and a decrease in lymphocytes in the blood. These findings are discussed in relation to the increased susceptibility of the brown trout to a variety of infections during sexual maturation and under conditions of stress.

The thymus of the rainbow trout (Salmo gairdneri). Light and electron microscopic study

The rainbow trout thymus is a paired organ, organized in 3 adjacent zones. The gland lying on a thick connective tissue layer, is covered by a thin epithelial capsule. Cellular components of thymus are essentially the thymocytes and the epithelial cells. Thymocytes occur mainly in the inner and outer zones but neither cortex nor medulla are clearly delimited. Septa represent a typical epithelial structure associated with thymocytes and blood vessels. Thymus is well vascularized and electron microscopy demonstrates a characteristic relationship between vascular system and lymphoid tissue.