Phylogeny of lymphocyte heterogeneity. II. Differential effects of temperature on fish T-like and B-like cells

Temperature effects on teleost immunity in the light of climate change

Temperature is an important environmental modulator of teleost immune activity. Susceptibility of teleosts to temperature variation depends on the species-specific adaptive temperature range, and the activity of the teleost immune system is generally temperature-dependent. Similar to many physiological and metabolic traits of ectotherms, temperature modulates the activity of immune traits. At low temperatures, acquired immunity of many teleost species is down-modulated, and their immuno-competence mainly depends on innate immunity. At intermediate temperatures, both innate and acquired immunity are fully active and provide optimal protection, including long-lasting immunological memory. When temperatures increase and reach the upper permissive range, teleost immunity is compromised. Moreover, temperature shifts may have negative effects on teleost immune functions, in particular if shifts occur rapidly with high amplitudes. On the contrary, short-term temperature increase may help teleost immunity to fight against pathogens transiently. A major challenge to teleosts therefore is to maintain immuno-competence throughout the temperature range they are exposed to. Climate change coincides with rising temperatures, and more frequent and more extreme temperature shifts. Both are likely to influence the immuno-competence of teleosts. Nonetheless, teleosts exist in habitats that differ substantially in temperature, ranging from below zero in the Arctic's to above 40°C in warm springs, illustrating their enormous potential to adapt to different temperature regimes. The present review seeks to discuss how changes in temperature variation, induced by climate change, might influence teleost immunity.

Effects of Sex Steroids on Fish Leukocytes

In vertebrates, in addition to their classically reproductive functions, steroids regulate the immune system. This action is possible mainly due to the presence of steroid receptors in the different immune cell types. Much evidence suggests that the immune system of fish is vulnerable to xenosteroids, which are ubiquitous in the aquatic environment. In vivo and in vitro assays have amply demonstrated that oestrogens interfere with both the innate and the adaptive immune system of fish by regulating the main leukocyte activities and transcriptional genes. They activate nuclear oestrogen receptors and/or G-protein coupled oestrogen receptor. Less understood is the role of androgens in the immune system, mainly due to the complexity of the transcriptional regulation of androgen receptors in fish. The aim of this manuscript is to review our present knowledge concerning the effect of sex steroid hormones and the presence of their receptors on fish leukocytes, taking into consideration that the studies performed vary as regard the fish species, doses, exposure protocols and hormones used. Moreover, we also include evidence of the probable role of progestins in the regulation of the immune system of fish.

Seasonal changes of immunocompetence and parasitism in chub (Leuciscus cephalus), a freshwater cyprinid fish

Seasonal variation of water characteristics, predominantly temperature, is considered to strongly affect fish physiology and immunology. In nature, this variation directly influences the life cycle especially in fish parasites, but the infection of parasites is also altered by the host immune response. This study is aimed to analyze the seasonal changes in selected physiological and immunological parameters, the latter a potential measure of fish immunocompetence. Moreover, the seasonal changes in metazoan parasite infection were investigated, and the potential associations between fish physiology, immunocompetence, and parasitism were estimated. No differences in gender were recognized for immunological parameters. The significant differences in the spleen-somatic index were found among fish samples of different seasons indicating higher investment in spleen size in April (after winterizing) and August (post-breeding with low gonado-somatic index [GSI]). The significant seasonal differences in erythrocyte and leukocyte cell counts, as well as in phagocyte count affecting respiratory burst, were recorded. The general trend of leukocyte composition was similar in all seasons investigated; however, the changes in proportion of different neutrophilic cells were reported. The parasite diversity and the infection parameters in parasite communities were highest in spring and early summer. When comparing parasite abundance in infracommunities among seasons, the statistically highest values were observed in April and June for Monogenea, in April and November for Acanthocephala, and in April for Cestoda. The positive correlations between GSI and the parasite abundance of groups with higher infection parameters were found in males. Moreover, the positive association between Monogenea as the dominant parasite group and respiratory burst was observed. The higher investment in condition and the seasonal variation in GSI were associated with a decrease immune function measured by spleen size or leukocyte cell count especially for males suggesting the seasonal energy allocation between immune function and somatic or reproductive investment.

Improved fish lymphocyte culture for chromosome preparation

Cytogenetic methodology is still underdeveloped in fishes compared with mammals. Culture condition for fish lymphocytes was optimized to improve chromosome preparation using the rainbow trout (Oncorhynchus mykiss) as a model after changing the combination of parameters such as mitogens, incubation periods, media, cell components, and freshness of blood. The optimized culture condition included isolation of lymphocytes from fresh blood by a stirring method, their culture in medium 199 supplemented with 10% FBS, 18 microg/ml of phytohemagglutinin (PHA-W) and 100 microg/ml of lipopolysaccharide (LPS) as mitogens, and harvested at 6 days after culture. This condition provided a notably increased mitotic index (MI) of 4.3-10.0% in rainbow trout lymphocytes. In addition, the condition was highly reproducible as shown by the similar level of MI in cultured lymphocytes from 181 individuals without failure. Applicability of this method in a wide range of fish groups was also proven with Ml of 1.1-13.3% in cultured lymphocytes from other 16 freshwater species of Acipenseridae, Anguillidae, Solmonidae, Cyprinidae, and Centrarchidae, and five marine species of Sparidae, Kyphosidae, Paralichthyidae, and Scorpaenidae. Chromosome preparations of improved quality by the present method were successfully applied for the replication R-banding with incorporation of 5-bromo-2'-deoxyuridine and direct R-banding fluorescence in situ hybridization.

Immunocytochemical detection of Ig-positive cells in blood, lymphoid organs and the gut associated lymphoid tissue of the turbot (Scophthalmus maximus)

The present study was designed to search for the sites of the B-cell lineage in the different lymphoid organs of turbot (Scophthalmus maximus) by immunoperoxidase staining with a rabbit polyclonal antiserum against deglycosylated turbot IgM (TUDG-6). A turbot immunoglobulin (Ig) fraction, isolated by protein A, was checked for purity by gel filtration and SDS-PAGE under reducing conditions. The turbot IgM was deglycosylated and used to raise an antiserum. The antiserum titre was evaluated in ELISA. It was then used to analyse turbot peripheral blood leucocytes for membrane and cytoplasmic Ig and for immunohistochemistry with turbot lymphoid tissues. Very low numbers of Ig+ cells were found in thymus sections. In sections of spleen, Ig+ cells were observed in white pulp, around ellipsoids but were mostly concentrated and associated with melanomacrophage centers (MMCs). The lymphoid Ig+ cells in the kidney tended to be dispersed among haematopoietic and granulopoietic cell populations and were in intimate association with the MMCs and blood vessels. This association between MMCs and Ig+ cells in the spleen and the kidney, is discussed with respect to the role played by these organs in the immune system of fish. Last, the lymphoid population in the gut associated lymphoid tissue (GALT) of turbot was characterised with respect to staining for Ig. Immunoreactive cells were rarely detected in the epithelial layer although many lymphocytes were present, but they were frequently observed in the lamina propria, presumably as part of the GALT and involved in mucosal immune responses.

Regulation of innate immunity in tilapia: activation of nonspecific cytotoxic cells by cytokine-like factors

Exposure of tilapia (Oreochromis niloticus) to water temperatures of 10-15 degrees C for 3-5 min produces physiological stress responses characterized by immediate phenotypic and immunological changes. In the present study, this general stress response was utilized as a model system to study innate immunity mediated by soluble factors and cytotoxic cells. Acute innate cytotoxic responses of nonspecific cytotoxic cells (NCC) in the peripheral blood (PBL), anterior kidney (AK) and spleen (SPL) were measured. Following temperature stress, the levels of NCC activity depended on the presence of soluble factors and on the cell compartments from which the NCC were obtained. NCC from PBL of stressed tilapia had 30x or greater cytotoxic activity compared to nonstressed PBLs from controls. NCC activity from the AK and SPL of stressed tilapia was lower than controls. Flow cytometric analysis of NCC in each tissue showed that increased cytotoxicity was not produced by increased numbers of NCC. To determine the mechanism of amplification of cytotoxicity, NCC from nonstressed tilapia were passively treated with serum from temperature stressed tilapia. Serum containing the "stress activated serum factor" (SASF) passively increased naive NCC cytotoxicity (from PBL) 3-4 fold. The cytotoxic cell response was inhibited by addition of anti-NCC monoclonal antibody 5C6. These data indicated that NCC are (at least one of) the target cells for SASF. SASF required only 15 min pre-incubation with naive NCC to activate cytotoxicity. Activation was nonreversible and concentration dependent. Pretreatment of NCC with SASF reduced the assay time required to amplify target cell cytotoxicity from 12-24 h to 6 h. SASF amplification of NCC cytotoxicity was not restricted by different histological types of target cells. Determination of select physical/chemical properties of SASF revealed: complete heat inactivation of cytotoxicity amplification following 55 degrees C and 65 degrees C pretreatment; SASF was thermostable at room temperature to 45 degrees C for 15 min; and freeze-thaw treatment reduced but did not completely remove amplification activity. The molecular weight range of SASF activity was identified in a 50-100 kDa fraction obtained by differential dialysis. SASF appears to be a protein sensitive to trypsin digestion.

Mitogenic effect of naturally occurring elevated plasma prolactin on ring dove lymphocytes

3H-thymidine incorporation into isolated ring dove lymphocytes in vitro was used as a measure of lymphocyte proliferation. Lymphocytes taken from doves with increased plasma concentrations of prolactin demonstrated significantly increased 3H-thymidine incorporation. In vitro incubation with mitogens significantly increased incorporation of 3H-thymidine into lymphocytes from non-breeding doves. However, similar treatment of lymphocytes taken from doves which had elevated levels of plasma prolactin failed to induce any further increase in the stimulation index. Antigen caused a significant increase in 3H-thymidine incorporation in non-breeding doves. Antigen administration also led to the production of specific antibodies. The titre of specific anti-human red blood cell (HRBC) agglutinins was greatest in those birds which also had elevated levels of plasma prolactin, reaching significance in the group of incubating doves with naturally occurring increased concentrations of plasma prolactin. The results presented here may be relevant to our understanding of the role of hormones such as prolactin on lymphocyte activation.

Effects and mechanisms of environmental temperature on carp (Cyprinus carpio) anti-DNP antibody response and non-specific cytotoxic cell activity: a kinetic study

The effect of environmental temperatures on immune competence was investigated in carp which were subjected to changes in water temperature. The activity of non-specific cytotoxic cells (NCC) against P815 target cells, and the anti-DNP antibody response were evaluated until day 56 after transfer. Low environmental temperature (12 +/- 0.5 degrees C) enhanced NCC activity and decreased antibody production. In contrast a high environmental temperature (28 +/- 0.5 degrees C) was without effect on these parameters when compared to the standard temperature (20 +/- 0.5 degrees C). The results showed a maximum effect of low environmental temperature on day 28 and an adaptation in these immune responses 56 days following transfer. Collectively, the results indicated that non-specific immunity tends to offset specific immune suppression at low environmental temperatures. To determine the mechanism(s) by which environmental temperature affects cellular immune function, membrane fluidity measurements and sialic acid titration, as well as stress assessment by plasma cortisol measurement, were determined on day 28. Taken together, the results revealed a direct effect of temperature on cellular immune function which is modulated by membrane fluidity and sugar concentration and not by stress induction.

Influence of the temperature upon the proliferative response of lymphocytes of tench (Tinca tinca) during winter and summer

The influence of incubation temperature upon proliferation of Tinca tinca lymphocytes induced by phytohemagglutinin (PHA) and E. coli lipopolisaccharide (LPS) mitogens was studied during the summer and the winter. The cultures were performed in vitro at 22 degrees C in both summer and winter, and at 12 and 30 degrees C in winter and summer respectively. The proliferative response at 22 degrees C was higher than that at 12 degrees C during the winter, and a small increase was observed at 30 degrees C respective to 22 degrees C in summer. These results indicate that in vitro lymphocyte proliferation requires temperatures higher than those in the fish environment.

Seasonal variations in the immune system of the cyprinid Tinca tinca. Phagocytic function

Seasonal variations in the in vitro phagocytic process of blood granulocytes from the tench Tinca tinca were examined. Different stages of the phagocytic process: mobility rate, attachment, ingestion and killing of Candida albicans were evaluated. Tench were kept in natural ponds in ambient water temperature, and the in vitro assays were performed at both 22 degrees C and the relative ambient temperature. Results between the seasonal samples were then compared. In vitro induced mobility, attachment, ingestion and killing of C. albicans showed strong seasonal variations, furthermore, the phagocytic process at 22 degrees C varied significantly according to season. Phagocytic activity from samples taken during the spring demonstrated the highest activity at 22 degrees C, whilst greatest activity at seasonal temperature, in terms of mobility rate, phagocytic index and microbicide capacity, occurred during the winter. These results are consistent with the hypothesis that phagocytosis in fish is resistant to low temperatures.

Effect of high summer temperatures upon granulocyte phagocytic function of the tench (Tinca tinca, L.)

Phagocytic activity and NBT reduction by blood granulocytes was evaluated in tench during the summer, when water temperature was high (30 degrees C). In vitro assays were performed at two temperatures, 30 degrees C, the temperature of the natural habitat in summer, and 22 degrees C, a commonly used temperature within the optimum range of warm-water fish. The results indicate that blood granulocytes from tench possess a lower capacity to ingest inert particles at 30 degrees C than at 22 degrees C, particularly during long periods of incubation (60 min). The lower capacity for ingesting inert particles at 30 degrees C is due to a decreased effectiveness of phagocytosis at this temperature, but not to a lower number of granulocytes with phagocytic capacity. The decline in inert particle ingestion capacity does not correspond to a lower production of superoxide anion at 30 degrees C, which is similar at both temperatures during phagocytosis, thus indicating a similar capacity for destruction of the antigen at 30 and 22 degrees C.

Effects of temperature on carp leukocyte mitogen-induced proliferation and nonspecific cytotoxic activity

The effect of environmental temperature on immune competence was investigated in carp subjected to abrupt changes in water temperature. The activity of nonspecific cytotoxic cells (NCC) against P815 target cells and the lymphoproliferation induced by PHA and ConA were evaluated. Low in vivo temperature (12 +/- 0.5 degrees C) enhances NCC activity and decreases the mitogen effect of PHA, respectively; by contrast high in vivo temperature (28 +/- 0.5 degrees C) is without effect on these parameters as compared to the standard temperature (20 +/- 0.5 degrees C). The stress induced by environmental temperature variation was evaluated by plasmatic cortisol measurement. Results indicate a significant increase (p < 0.05) of cortisol levels 2 hours after transfer at low but not at high temperature as compared to the standard thermic control (60.96 +/- 17.08 vs. 16.74 +/- 4.32 ng/mL, respectively). Because only approximately 20 minutes are required before carp body and environmental temperatures are identical, the same experiments were reproduced in vitro. Results show trends similar to those found in vivo. Taken together, these data reveal a direct effect of temperature on immune cellular functions and indicate that nonspecific immunity tends to offset specific immune suppression at low environmental temperature.

Immunocytochemical analysis of mitogen responses of carp (Cyprinus carpio L.) peripheral blood leucocytes

Phytohaemagglutinin (PHA) and lipopolysaccharide (LPS) responses of surface immunoglobulin-positive (sIg+) and surface immunoglobulin-negative (sIg-) carp peripheral blood leucocytes (PBL) were studied. sIg+ cell-enriched and depleted carp PBL populations (sIg+ and sIg- cell fractions, respectively) were obtained by magnetic cell sorting (MACS) and mitogenic stimulation in vitro was measured by 3H-thymidine incorporation. The mitogen responses of sIg+ and sIg- cells in non-separated carp PBL cultures were analysed by simultaneous detection of incorporated 5-bromo-2'-deoxyuridine (BrdU) and sIg with the fluorescence microscope and flow cytometer. Flow cytometric determination of the percentage of sIg+ cells in combination with absolute cell counting, revealed an increase of sIg+ cells but not of sIg- cells after LPS stimulation while the number of sIg- cells and not of sIg+ cells was enhanced after PHA stimulation. LPS stimulation showed an increased 3H-thymidine incorporation in the sIg- cell fraction compared with non-separated cells and BrdU incorporation was observed in sIg- cells from LPS-stimulated cultures by fluorescence microscopy. However, flow cytometric analysis showed that mainly dull sIg+ cells and not sIg- cells are stimulated by LPS. These dull sIg+ cells were not sorted from sIg- cells with MACS and could apparently not be distinguished from sIg- cells by light microscopy. PHA stimulates sIg- cells and not sIg+ cells as was estimated by all techniques used.

Effect of temperature on macrophage activation and the production of macrophage activating factor by rainbow trout (Oncorhynchus mykiss) leucocytes

Production of macrophage activating factor (MAF) by rainbow trout leucocytes has been shown to be temperature dependent in vivo and in vitro. Cells from fish held at 14 degrees C and stimulated to produce MAF immediately after isolation were capable of secreting MAF down to 6 degrees C (the lowest temperature tested). However, after 48 h at 6 degrees C, these leucocytes show impaired MAF secretion. Acclimation of fish to low temperatures (7 degrees C) did not recover the inhibitory effects of low in vitro temperatures on MAF production, but if these leucocytes were preincubated at 10 or 18 degrees C for 48 h, MAF was produced from these cells. Interestingly, macrophages isolated from fish kept at 7 or 14 degrees C and cultured at low temperatures (6 degrees C) were responsive to MAF-containing supernatants, and showed a higher relative increase in respiratory burst activity compared with their counterparts cultured at 10 and 18 degrees C. Such observations clearly demonstrate that a major impairment of bactericidal activity at low temperatures resides within the specific immune compartment of fish. The implications for fish health are discussed.

Mitogenesis of rainbow trout peripheral blood lymphocytes requires homologous plasma for optimal responsiveness

An improved method for obtaining optimal mitogenic responses in peripheral blood lymphocytes has been devised by utilizing autologous or homologous rainbow trout plasma. The use of 10% plasma in culture results in up to a 60-fold increase in the proliferative potential of the peripheral blood lymphocyte response to lipopolysaccharide when compared to the more routinely used fetal bovine serum. Furthermore, it has been observed that lymphocytes which were unresponsive to in vitro mitogenic challenge when cultured in fetal bovine serum, responded well when cultured in the presence of trout plasma. Also in contrast to previous mitogen studies where maximal stimulation was reported to occur on Day 4-5 of culture, the stimulatory effects of lipopolysaccharide were greatest on Day 10 when plasma was employed. Together these data suggest that former conditions of lymphocyte cell culture, employing only fetal bovine serum, not only fail to provide the optimal conditions for cell growth, but in many cases the essential conditions. However, these requirements are met by supplementation with trout plasma, which seems to contain heat-stable factors responsible for the enhanced mitogenic responsiveness.

Effect of temperature on the immune system of channel catfish (Ictalurus punctatus)--I. Leucocyte distribution and phagocyte function in the anterior kidney at 10 degrees C

1. Temperatures of 18 degrees C for acclimation or assay had minimal or no effect on channel catfish phagocyte function. Significant suppression was observed at 10 degrees C acclimation and assay temperature. 2. According to the results of a multiple acclimation/assay temperature combination study, the primary impact of temperature on phagocyte function was due to the assay temperature. 3. The only functional change caused by acclimation temperature was the possible adaptation of the respiratory burst. However, 10 degrees C acclimation did cause a decline in the number of lymphocytes in the anterior kidney but not the number of neutrophils. In a temperature-kinetic study, the suppressive effect of 10 degrees C assay temperature was confirmed. 4. Results of our study indicated that phagocytosis in channel catfish is temperature-mediated. However, phagocytes appeared to be more resistant to low temperature than lymphocytes, which implies the importance of phagocytosis in the defense mechanisms of channel catfish at low temperatures.

Effect of temperature on the immune system of channel catfish (Ictalurus punctatus)--II. Adaptation of anterior kidney phagocytes to 10 degrees C

1. Anterior kidney phagocytes from channel catfish (Ictalurus punctatus) exposed to 10 and 24 degrees C from 1 day to 5 weeks were assayed for phagocytic ability and respiratory burst activity to Aeromonas hydrophila and Edwardsiella ictaluri. 2. The results of this study indicated that phagocytosis in channel catfish remained partially functional at low temperature without adaptation, although partial suppression was observed. 3. Adaptation to low temperature did lead to an improvement in the respiratory burst which would imply improved bacterial killing ability. 4. Our study suggests that phagocytosis may play a significant role in preventing disease at low environmental temperature.

Histologic and ultrastructural studies of dermal sarcoma of walleye (Pisces: Stizostedion vitreum)

Sixty-seven adult walleye fish were examined by light and transmission electron microscopy. The fish were affected by a mesenchymal tumor previously termed Walleye Dermal Sarcoma that commonly affects up to 27% of the population seasonally. Biopsies from 24 fish were collected, and complete postmortem examinations were performed on 43 fish. Grossly, the tumors had the appearance of randomly distributed, often clustered, spherical nodules, 2-5 mm in diameter with a smooth and often ulcerated surface. The tumors arose from the superficial surface of scales and consisted of fibroblast-like cells separated by a moderate amount of collagen (43/67) or osteoid material (24/67). Lymphocytic infiltration (28/67) associated with vacuolar degeneration of tumor cells (28/67) and centrally located coagulation necrosis (30/67) were observed. Although tumor cells were often highly anaplastic, no local invasions or metastases were present. In contrast with previous descriptions of this tumor, no viral particles could be observed electron microscopically. The variably anaplastic appearance of the tumor, its biological behavior, and its restriction to dermis are features in common with canine cutaneous histiocytoma and equine sarcoid. The multicentric origin, the restriction to the dermis, and the absence of invasion or metastases of Walleye Dermal Sarcoma differ from retrovirus-induced avian and murine sarcomas that arise locally, that invade, and that often metastasize.

Temperature-mediated processes in immunity: differential effects of low temperature on mouse T helper cell responses

A low culture temperature of 27 degrees C inhibited mouse primary in vitro anti-hapten plaque-forming cell responses to a thymus-dependent (TD) antigen (Ag) (trinitrophenyl-keyhole limpet hemocyanin, TNP-KLH). In contrast, the magnitudes of secondary responses to TNP-KLH or primary responses to a thymus-independent (TI) Ag (TNP-lipopolysaccharide (LPS)) were unaffected. The low-temperature-sensitive step in the primary TD response occurred relatively early and preceded interleukin 2 (IL-2) secretion. Furthermore, the low-temperature-induced suppression could be obviated (rescued) by recombinant IL-2 or IL-4, but not by IL-1. Thus, the low temperature appeared to inhibit the function of virgin Th cells by preferentially affecting T cell-derived interleukin synthesis/secretion and not other cellular activities. These results also imply fundamental differences between the activation requirements of memory and virgin Th cells.

Recent applications of fish cell culture to biomedical research

Tissues of the fishes are as amenable to the techniques of modern cell culture as mammalian tissues and organs, and yet this vast resource, comprising thousands of vertebrate species, remains largely unexplored. The model systems that have been developed demonstrate the utility of fish cells as sources of special adaptations and exaggerated physiological systems. In this review, we briefly describe several of the successful models along with recent developments in fish cell culture with the hope of stimulating increased interest in the lower vertebrates as useful complements to mammalian cell culture in biomedical research. The topics covered include epithelial ion transport, endocrinological studies, the cellular stress (heat shock) response, thermotolerance, cancer biology, and environmental toxicology.

Temperature mediated processes in teleost immunity: differential abilities of channel catfish T and B lymphocytes to cap membrane antigen

1. The effect of both in vivo acclimation temperature and in vitro assay temperatures on channel catfish T and B lymphocyte membrane antigen (mAg) capping were investigated to determine if capping might be the temperature sensitive step involved in the low temperature immunosuppression of channel catfish T cell responses. 2. Flow cytometry was used to monitor the kinetics of capping induced by a mouse monoclonal antibody (mAb 11G3) specific for a common antigenic determinant present on channel catfish T and B cells. Results indicated that the kinetics of mAg capping were dependent on in vitro assay and in vivo acclimation temperatures and the length of time of in vivo acclimation. 3. T cells from fish appropriately acclimated to 27 degrees C cap mAg more efficiently at low assay temperatures than do B cells. 4. Activation energies were 32 and 47 kcal/mol for B and T cells, respectively, from fish acclimated to 17 degrees C for 3 weeks, but were significantly lower (14 and 22 kcal/mol, respectively) after acclimation for 5 weeks. 5. In summary, it appears that after appropriate in vivo acclimation, channel catfish T cells are better able to cap mAg at low assay temperatures than are B cells. These results suggest that mAg capping is not the low temperature sensitive step involved in T cell immunosuppression in channel catfish.

In vitro mitogenesis of peripheral blood lymphocytes from rainbow trout (Salmo gairdneri)

1. In vitro mitogenesis of rainbow trout peripheral blood lymphocytes (RBT PBL) was investigated to assess the applicability of this procedure in assessment of fish health. The assay variables of media, mitogen type and concentration, serum supplementation, lymphocyte isolation procedure, and duration of incubation were assessed. 2. Concanavalin A (Con A) stimulated greater proliferation of RBT PBL than did lipopolysaccharide (LPS), phytohemagglutinin (PHA), or pokeweed mitogen (PWM). 3. RBT PBL, cultured with 10 micrograms Con A/ml and incubated for four or five days, exhibited greater proliferation than with other treatment combinations. 4. The degree of Con A-induced PBL proliferation varied significantly (P less than 0.05) among fish. The mean was positively correlated with the relative standard deviation and thus exhibited significant heteroscedasticity. 5. Human serum, as an alternative to FBS supplementation of the culture medium, did not enhance RBT PBL proliferation or reduce variation in mean proliferation. 6. Power analysis with variance estimates from this study reveal that sample size requirements of further studies under the given conditions could severely limit the applicability of this procedure for RBT health assessment. Further work in this area should center around standardization of culture conditions pertaining to the source of protein supplementation.

Cellular requirements for mixed leucocyte reactivity in the cyclostome, Eptatretus stoutii

Unfractionated peripheral blood leucocytes from allogeneic hagfish proliferated vigorously in one-way mixed leucocyte reaction (MLR) at 20-22 degrees. Maximum responsiveness was observed after 5 days of co-culture of responder and irradiated stimulator cells. Separation of leucocytes on the basis of laser scatter parameters yielded a small leucocyte population which responded but did not stimulate in MLR and a large leucocyte population capable of stimulating but not responding. Adherent cell depletion of the total leucocyte population did not affect the ability to respond in MLR but did ablate the stimulatory capacity of hagfish leucocytes. Together with previous phenotypic studies, these results confirm the presence of lymphocyte and macrophage/accessory cell populations in hagfish peripheral leucocytes.

Temperature-mediated processes in teleost immunity: the effects of temperature on membrane immunoglobulin capping on channel catfish B lymphocytes

1. In order to better understand ligand-induced redistribution of membrane receptors and lymphocyte activation in ectothermic vertebrates, flow cytometry was used to monitor the effects of both in vivo acclimation temperature and in vitro assay temperatures on the kinetics of monoclonal antibody-induced membrane immunoglobulin (mIg) capping on channel catfish lymphocytes. 2. It was observed that the kinetics of mIg capping were dependent on in vitro assay temperatures, in vivo acclimation temperatures, and the length of time of in vivo acclimation. In the latter situation in vivo acclimation of fish to 27, 22 and 17 degrees C was considered complete after 3 weeks, while acclimation to 12 degrees C required a minimum of 5 weeks. 3. The energies of activation required for mIg capping ranged from 33 to 24 kcal/mol; lower energies of activation were observed with lower temperature acclimation. 4. It was also noted that the lower energies of activation were associated with concomitant decreases in cellular phospholipid saturated/unsaturated fatty acid ratios. 5. It appears that channel catfish B cell mIg capping, presumably a requisite for immune function, can be significantly affected by environmental temperatures; most likely such effects are attributable to changes in plasma membrane viscosities.

Paradoxical effects of cadmium exposure on antibacterial antibody responses in two fish species: inhibition in cunners (Tautogolabrus adspersus) and enhancement in striped bass (Morone saxatilis)

Previous work in a marine fish, the cunner (Tautogolabrus adspersus), showed that endocytosis of bacteria by cells in the liver and spleen was affected by 96-h exposure of the fish to cadmium at a concentration of 12 micrograms/ml; however, antibody response to sheep erythrocytes was not affected. Since the latter finding was questionable because of short immunization times, and data from more than a single fish species were desirable, both the cunner and an anadromous fish, the striped bass (Morone saxatilis), were examined for antibody responses against the bacterium Bacillus cereus in Freund's complete adjuvant during a 6- to 8-wk time period. Exposure to 12 micrograms/ml cadmium caused significant inhibition of serum antibody titers (P less than 0.007) in cunners. Paradoxically, antibody response in striped bass exposed to 10 micrograms/ml cadmium was enhanced sixfold. This enhancement was weaker but still evident when the antigen was injected 48 d after cadmium exposure. Peritoneal exudate cells from cadmium-exposed striped bass also showed more active migration through microporous filters than cells from non-exposed fish. Since the 96-h cadmium LC50 was 26 micrograms/ml for cunners and 20 micrograms/ml for striped bass, the differences in antibody response could not be explained on the basis of differences in cadmium toxicity. Although geometric mean liver cadmium levels after exposure at 15 degrees C were higher in cunners (163.8 +/- 1.2 micrograms/gm) than in striped bass (64.4 +/- 1.2 micrograms/g), cunners exposed to cadmium at 2 degrees C had lower cadmium levels (46.4 +/- 1.2 micrograms/g) which were still effective in inhibiting antibody production at 8 degrees C. On the other hand, striped bass not exposed to cadmium showed a strong, exponential rise in serum antibody when the temperature at immunization, 14 degrees C, was reduced to 9 degrees C; whereas cunners held in the same tanks exhibited a weaker, biphasic serum antibody response. Regardless of the cause (innate differences in cellular response, or better stress adaptability in an anadromous fish), the data show that chemical-stress effects on the immune system of one fish species cannot be extrapolated to another species.

The effects of in vivo acclimation temperature on the fatty acid composition of channel catfish (Ictalurus punctatus) peripheral blood cells

Channel catfish were acclimated in vivo to 12, 17, 22 or 27 degrees C and their peripheral blood erythrocytes, thrombocytes, T lymphocytes and B lymphocytes assayed for cellular fatty acid composition. Excepting cells from 12 degrees C acclimated fish, all cells responded to acclimation to lower temperatures by exhibiting increased levels of phospholipid unsaturated fatty acids. Although temperature independent differences were observed between erythrocytes, thrombocytes and lymphocytes, no differences between T lymphocytes and B lymphocytes were seen.

Microsystem for in vitro primary and secondary immunization of channel catfish (Ictalurus punctatus) leukocytes with hapten-carrier conjugates

Methods are described for the in vitro generation and detection of antibody-secreting cells (PFC) from channel catfish. Hapten-specific PFC can readily be enumerated by an indirect plaque assay employing rabbit antiserum to catfish Ig and guinea pig complement. A modified Mishell-Dutton-type culture system was developed for effectively generating significant in vitro anti-hapten PFC responses with catfish leukocytes at 27 degrees C. The classical hapten-carrier effect and primary responses to both TI and TD antigens were demonstrable with catfish cells. Variables found to be important with catfish cells included the serum supplement, cell densities and, to a lesser extent, antigen form. Optimistically these methods will prove useful in attempts to delineate the functional roles of different lymphocyte subpopulations in 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 effect of environmental temperature on the immune response of a marine teleost (Paralichthys dentatus)

The kinetics of the primary immune response to horse erythrocytes were studied in summer flounder ( Paralichthys dentatus). This species produced antibody over a wide temperature range. The fish were divided into five groups and the experiments carried out at environmental temperatures of 27, 22, 17, 12, and 7.5 degrees C. At the lower environmental temperatures, a corresponding delay in the appearance of circulation antibody occurred, although the magnitude and duration of the response was not appreciably affected. After immunizing at 12 degrees C, lowering the environmental temperature gradually to 8 degrees C, did not appear to inhibit an ongoing primary responses. Typical secondary responses were seen in fishes kept at warmer temperatures, but when the temperature was lowered to 8 degrees C, no anamnestic response was seen. Individual variation was most noticeable at middle temperature ranges.

Immunoglobulin-bearing blood leucocytes in the Pacific hagfish

The occurrence of immunoglobulin (Ig) bearing leucocytes in the blood of the Pacific hagfish, Eptatretus stoutii , was examined using a murine monoclonal antibody (45.3) and a rabbit antiserum specific for hagfish serum Ig. Binding of antibody 45.3 to hagfish leucocytes assessed by radioimmunoassay was inhibited by preincubation of antibody with purified serum Ig thus verifying the presence of cell surface Ig cross reactive with serum Ig. The monoclonal antibody identified approximately 65% of blood leucocytes as Ig+ve while the rabbit antiserum indicated 81% Ig+ve cells. Both antibody preparations failed to react specifically with cells from mouse, horned shark, tunicate or sea star; this indicates the distinctive nature of hagfish Ig. The high percentage of blood cells bearing surface Ig in the hagfish raises the possibility that lymphocyte divergence to separate B and T pathways may not have occurred in this most primitive vertebrate. Alternatively, an Ig-like specificity characteristic of both "T" and "B" lymphocytes may have been detected. In any event, a subset of Ig negative leucocytes is evident in hagfish.

Temperature-mediated processes in teleost immunity: differential effects of in vitro and in vivo temperatures on mitogenic responses of channel catfish lymphocytes

The in vitro mitogenic responses of channel catfish peripheral blood leucocytes to ConA and LPS were differentially affected by both in vitro and in vivo temperatures. The magnitude of the response to LPS was relatively independent of both in vitro culture temperature and in vivo acclimation temperature. The magnitude of the response to ConA was suppressed at lower in vitro temperatures although this suppression could be reduced by lower in vivo acclimation temperatures. In vitro temperature-shift experiments indicated that channel catfish PBL could respond to ConA at a lower in vitro temperature if first stimulated with ConA at a higher in vitro temperature. The converse, however was not true in that channel catfish PBL did not respond at a higher in vitro temperature after an initial stimulation with ConA at a lower in vitro temperature. This latter failure to respond could not be attributed to the induction of a suppressor cell (or factor) by exposure to ConA at a lower temperature. These studies, when coupled with other available data on channel catfish PBL subpopulations, are interpreted as supporting the hypothesis that low temperature immunosuppression in fish may result from preferential inhibitory effects on T cells rather than B cells.

Evidence for the existence of an IL-2-like lymphocyte growth promoting factor in a bony fish, Cyprinus carpio

Activity promoting the growth of carp T-like cells has been found in supernatants of mitogen (PHA)- and alloantigen (MLR)-stimulated carp leukocyte cultures. Activity level in culture supernatants was elevated by phorbol myristate acetate. Proliferation of carp T-like lymphoblasts was also promoted in the presence of Il-2-containing supernatants of mammalian origin. The significance of these findings is discussed.

A comparison of temperature-mediated immunomodulation between two species of flounder

The kinetics of the temperature-mediated immunomodulation of the humoral antibody response to an erythrocyte antigen was remarkably different in two species of a marine teleost, the winter flounder (Pseudopleuronectes americanus) and the summer flounder (Paralichthys dentatus). These two species were caught in the same area, maintained under the same conditions and injected with the same antigen (horse red blood cells). Experiments were performed at 8, 12 and 17 degrees C during the same time of the year. Summer flounder showed only a delay in the appearance of circulating antibody at lower temperatures while winter flounder showed both a delay and a marked suppression at lower temperatures. Antibody titers remained high for over three months in summer flounder while in winter flounder antibody levels began decreasing after one month.

Induction of nonspecific immunosuppression in a primitive teleost, rainbow trout (Salmo gairdneri)

Induction of immunological non-reactivity to goldfish red blood cells (GFRBC), sheep red blood cells (SRBC) and to formalin-killed Aeromonas salmonicida cells was obtained in yearling rainbow trout raised under laboratory aquarium conditions (at 10 degrees C). Haemolysin and agglutinin titres were measured 1 to 4 weeks after immunization. While trout immunized with low and high doses of antigen by intramuscular (im) and intraperitoneal (ip) injections produced high antibody titres, administration of high doses of antigen by intravascular (iv) injection induced a state of tolerance which was antigen nonspecific. This lack of response persisted for at least 3 weeks. The phagocytic activity of peritoneal exudate cells from immunosuppressed fish was reduced. The numbers of plaque-forming cells amongst peripheral lymphocytes collected from trout receiving a high dose of GFRBC iv was markedly low when compared with those from trout receiving a similar dose ip. These findings are of interest since they demonstrate that the induction of antigen-nonspecific tolerance by iv administration of high doses of antigen in rainbow trout may be due to the generation of nonspecific suppressor cells.

Effect of temperature and lymphokines on mixed lymphocyte and mitogen responses of chicken lymphoid cells in vitro

The effect of temperature on T cell mitogen and mixed lymphocyte responses (MLR) of chicken lymphoid cells in vitro was examined. Responses at 40 degrees C were much higher than at 37 degrees C. This difference did not appear to be due only to faster kinetics of the responses at 40 degrees C. At the lower temperature the MLR could be enhanced by polyethylene glycol (PEG) for spleen cells and by Con A induced lymphokines for peripheral blood cells (PBL). The positive effect of PEG on the chicken spleen cell MLR appeared to be determined at the stimulator cell level. Responses to mitogens at 37 degrees C of both spleen cells and PBL were enhanced by lymphokines.

The mixed leukocyte reaction (MLR) in carp: bidirectional and undirectional MLR responses

Two-way and one-way mixed leukocyte reaction (MLR) was demonstrated in peripheral blood leukocytes (PBL) of carp. Primary two-way MLR in randomly selected donor pairs were highly variable. Weak primary responses could be strongly augmented by mutual in vivo priming of the reacting donors. One-way MLR was performed using irradiated (16,000 R) allogeneic PBL as stimulators. Reciprocal responses of randomly paired donors were usually unequal, suggesting the usefulness of this method for genetic analysis of MLR-recognized histocompatibility antigens in carp. Kinetics of the primary and secondary two-way MLR were studied, as well as the kinetics of primary one-way MLR against pooled allogenic stimulator cells.

Heterogeneity of mitogen-responsive lymphocytes in carp (Cyprinus carpio)

Peripheral blood leukocytes (PBL) of carp respond in vitro to a variety of phytomitogens, shown to be T-cell specific or B-cell specific in mammalian systems. Some basic differences have been observed in the proliferative response of carp PBL to PHA (phytohemagglutinin), ConA ( concanvalin A) and LPS (lipopolysaccharide): (1) The response to PHA and ConA was found to be highly dependent upon the continuous presence of mitogen in the medium, in contrast to LPS, where after the initial stimulation, cells could continue to proliferate for several days without mitogen. (2) Lymphoblasts grown in long term culture with either PHA or Con A could be transferred into medium containing the other mitogen without impairing cell proliferation, but cell growth was reduced to background level following transfer into LPS-containing medium. LPS grown cells continue to proliferate independently of the mitogen content of the medium. (3) Co-stimulation with LPS+PHA or LPS+ConA results in a synergistic response, while co-stimulation with PHA+ConA results in inhibition of DNA synthesis. (4) Several morphological differences have been observed between cells proliferating in the presence of PHA and those proliferating in the presence of LPS. It is suggested that while the PHA and ConA responsive cells may belong to the same lymphocyte subpopulation, they are distinct from the LPS-responsive subpopulation.

Lymphocyte heterogeneity in the trout, Salmo gairdneri, defined with monoclonal antibodies to IgM

A monoclonal antibody to trout serum IgM was tested by immunofluorescence analysis with lymphocytes from thymus, spleen and head kidney. By visual examination, the antibody reacted with only a subpopulation of lymphocytes. The mean values +/- SE for positive cells were 5.2 +/- 2.3% in the thymus, 30.3 +/- 7.9% in the spleen and 12.4 +/- 3.0% in the head kidney. Flow cytofluorometric analysis revealed evidence of heterogeneity by size among the membrane IgM-positive cells of the head kidney and spleen. Depletion of head kidney cells positive for surface IgM by an immune affinity adherence technique of panning, using monoclonal anti-IgM, significantly reduced the mitogenic response to lipopolysaccharide but not to concanavalin A. It is suggested that this information supports the existence of distinct subpopulations of fish lymphocytes that may be homologous in certain respects to mammalian T and B type cells.

Mitogenic responses of frog lymphocytes to crude and purified preparations of bacterial lipopolysaccharide (LPS)

We have compared in vitro mitogenic responses of frog (Xenopus laevis and Rana pipiens) lymphocytes to various preparations of lipopolysaccharide (LPS). Commercial LPS prepared from E. coli (phenol extraction) and from S. abortus-equi (phenol and TCA extraction procedures) was mitogenic for frog lymphocytes. After reextraction of these LPS preparations with phenol-water, the remaining LPS was either considerably less mitogenic or not mitogenic. Purified E. coli 055:B5 LPS, prepared by phenol water extraction, enzyme treatment and column chromatography, was not mitogenic. Frog cells proliferated poorly or not at all with all concentrations of reextracted or purified LPS tested (0.5-400 micrograms/ml) and at all culture periods examined (days 1-7). All LPS preparations used were mitogenic for CAF1 mouse lymphocytes, whereas reextracted and purified LPS preparations were not mitogenic for lymphocytes from C3H/HeJ cells. Xenopus were also not susceptible to toxicity induced by parenterally administered LPS in concentrations which killed CAF1 mice.