Physiological levels of testosterone kill salmonid leukocytes in vitro

Gene Duplication of Androgen Receptor As An Evolutionary Driving Force Underlying the Diversity of Sexual Characteristics in Teleost Fishes

Sexual dimorphism allows species to meet their fitness optima based on the physiological availability of each sex. Although intralocus sexual conflict appears to be a genetic constraint for the evolution of sex-specific traits, sex-linked genes and the regulation of sex steroid hormones contribute to resolving this conflict by allowing sex-specific developments. Androgens and their receptor, androgen receptor (Ar), regulate male-biased phenotypes. In teleost fish, ar ohnologs have emerged as a result of teleost-specific whole genome duplication (TSGD). Recent studies have highlighted the evolutionary differentiation of ar ohnologs responsible for the development of sexual characteristics, which sheds light on the need for comparative studies on androgen regulation among different species. In this review, we discuss the importance of ar signaling as a regulator of male-specific traits in teleost species because teleost species are suitable experimental models for comparative studies owing to their great diversity in male-biased morphological and physiological traits. To date, both in vivo and in vitro studies on teleost ar ohnologs have shown a substantial influence of ars as a regulator of male-specific reproductive traits such as fin elongation, courtship behavior, and nuptial coloration. In addition to these sexual characteristics, ar substantially influences immunity, inducing a sex-biased immune response. This review aims to provide a comprehensive understanding of the current state of teleost ar studies and emphasizes the potential of teleost fishes, given their availability, to find molecular evidence about what gives rise to the spectacular diversity among fish species.

Exploring the effect of dihydrotestosterone on nucleotide-binding and oligomerization domain-like receptor expression in spotted snakehead Channa punctata (Bloch 1793)

Sex steroids are known to modulate immune responses and as a result many of the immune parameters in seasonally breeding organisms show reproductive-phase dependent variation. Androgens, the male sex steroids, are largely reported to be immunosuppressive. Together with other pattern recognition receptors, the nucleotide-binding and oligomerization domain-like receptors (NLRs) serve as intracellular sentinels and are essential to defense mechanisms. Interestingly, to date the transcriptional modulation of NLRs by androgens has not been explored. In the present study, we investigated the reproductive-phase dependent expression of NLRs in the male spotted snakehead Channa punctata. Furthermore, the effect of dihydrotestosterone (DHT) on NLR expression was studied. The expression of NLRs was observed to be most pronounced during the spawning phase of the fish, which is marked by the highest testosterone level. In vivo as well as in vitro studies showed the diverse effect of DHT on NLR expression depending on the duration and mode of treatment, as well as the immune tissue studied.

Crosstalk between reproductive and immune systems: the teleostean perspective

The bidirectional interaction between the hypothalamic-pituitary-gonadal (HPG) axis and the immune system plays a crucial role in the adaptation of an organism to its environment, its survival and the continuance of a species. Nonetheless, very little is known about this interaction among teleost, the largest group of extant vertebrates. Fishes being seasonal breeders, their immune system is exposed to seasonally changing levels of HPG hormones. On the contrary, the presence and infiltration of leukocytes, the expression of pattern recognition receptors as well as cytokines in gonads suggest their key role in teleostean gametogenesis as in the case of mammals. Moreover, the modulation of gametogenesis and steroidogenesis by lipopolysaccharide implicates the pathological significance of inflammation on reproduction. Thus, it is important to engage in the understanding of the interaction between these two important physiological systems, not only from a phylogenetic perspective but also due to the importance of fish as an important economic resource. In view of this, the authors have reviewed the crosstalk between the reproductive and immune systems in teleosts and tried to explore the importance of this interaction in their survival and reproductive fitness.

The humoral immune system of anadromous fish

The immune system of anadromous fish is extremely complex, a direct consequence of their diadromous nature. Hormone levels fluctuate widely throughout their life cycle, as fish move between fresh and salt water. This poses major challenges to the physiology of anadromous fish, including adaptation to very different saline environments, distinct pathogen fingerprints, and different environmental stressors. Elevated cortisol and sex hormone levels inhibit B lymphopoiesis and IgM⁺ antibody responses, while catecholamines, growth hormones and thyroid hormones are generally stimulatory and enhance the humoral immune response. Immunological memory in the form of long-lived plasma cells likely plays important roles in health and survival during the life cycle of anadromous fishes. This review discusses some of the complex immune-endocrine pathways in anadromous fish, focusing on essential roles for B lineage cells in the successful completion of their life cycle. A discussion is included on potential differences in immuno-competence between wild and hatchery-raised fish.

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.

Hormones and fish monosex farming: A spotlight on immunity

Aquaculture is a promising and developing industry worldwide. One of the first step in monosex culturing, particularly in Nile tilapia, is the production of all-male fry; hormones are widely used in this respect. It is known that exogenous treatment with hormones disrupts various systems in the body including the immune and endocrine systems. There has been a growing interest in how hormones shape the biology of the fish. Many researchers all over the world explored how androgen can interact with many of the body systems; however, rarely any of them tried to improve the hormonal method or to find an alternative. The gate is open for research in this field. This review focusses on the potential effects of hormones, particularly androgens on fish immunity, and the up to date solutions (however, they are rare).

Expression of ayu antimicrobial peptide genes after LPS stimulation

Plecoglossus altivelis (ayu) is one of the most important fish species in the Japanese islands and in internal fish hatcheries. Living in open aquatic environments exposes fish to many pathogens. Therefore, they require rapid and strong immune defenses. We investigated in vivo the direct association between the ayu innate immune response, represented by the relative transcription of genes encoding the cathelicidin and hepcidin antimicrobial peptides, and lipopolysaccharide (LPS), a conventional pathogen-associated molecular patterns (PAMPs) of Gram-negative bacteria. Different concentrations of LPS (1, 10 and 100 µg/fish) were injected intraperitoneally into young (sexually immature) and adult (fully sexually mature) ayu. The relative expression of the antimicrobial peptide genes was measured 6 hr, 24 hr and 1 week after stimulation with LPS. We found a direct association between the expression of the antimicrobial peptide genes investigated and LPS stimulation. This relationship was time-, dose- and age-dependent. Further research is required to determine the cell-specific transcriptional regulation and posttranscriptional regulation of these antimicrobial peptides.

The immunomodulatory role of the hypothalamus-pituitary-gonad axis: Proximate mechanism for reproduction-immune trade offs?

The present review discusses the communication between the hypothalamic-pituitary-gonad (HPG) axis and the immune system of vertebrates, attempting to situate the HPG-immune interaction into the context of life history trade-offs between reproductive and immune functions. More specifically, (i) we review molecular and cellular interactions between hormones of the HPG axis, and, as far as known, the involved mechanisms on immune functions, (ii) we evaluate whether the HPG-immune crosstalk serves as proximate mechanism mediating reproductive-immune trade-offs, and (iii) we ask whether the nature of the HPG-immune interaction is conserved throughout vertebrate evolution, despite the changes in immune functions, reproductive modes, and life histories. In all vertebrate classes studied so far, HPG hormones have immunomodulatory functions, and indications exist that they contribute to reproduction-immunity resource trade-offs, although the very limited information available for most non-mammalian vertebrates makes it difficult to judge how comparable or different the interactions are. There is good evidence that the HPG-immune crosstalk is part of the proximate mechanisms underlying the reproductive-immune trade-offs of vertebrates, but it is only one factor in a complex network of factors and processes. The fact that the HPG-immune interaction is flexible and can adapt to the functional and physiological requirements of specific life histories. Moreover, the assumption of a relatively fixed pattern of HPG influence on immune functions, with, for example, androgens always leading to immunosuppression and estrogens always being immunoprotective, is probably oversimplified, but the HPG-immune interaction can vary depending on the physiological and envoironmental context. Finally, the HPG-immune interaction is not only driven by resource trade-offs, but additional factors such as, for instance, the evolution of viviparity shape this neuroendocrine-immune relationship.

Innate and adaptive immune responses in migrating spring-run adult chinook salmon, Oncorhynchus tshawytscha

Adult Chinook salmon (Oncorhynchus tshawytscha) migrate from salt water to freshwater streams to spawn. Immune responses in migrating adult salmon are thought to diminish in the run up to spawning, though the exact mechanisms for diminished immune responses remain unknown. Here we examine both adaptive and innate immune responses as well as pathogen burdens in migrating adult Chinook salmon in the Upper Willamette River basin. Messenger RNA transcripts encoding antibody heavy chain molecules slightly diminish as a function of time, but are still present even after fish have successfully spawned. In contrast, the innate anti-bacterial effector proteins present in fish plasma rapidly decrease as spawning approaches. Fish also were examined for the presence and severity of eight different pathogens in different organs. While pathogen burden tended to increase during the migration, no specific pathogen signature was associated with diminished immune responses. Transcript levels of the immunosuppressive cytokines IL-10 and TGF beta were measured and did not change during the migration. These results suggest that loss of immune functions in adult migrating salmon are not due to pathogen infection or cytokine-mediated immune suppression, but is rather part of the life history of Chinook salmon likely induced by diminished energy reserves or hormonal changes which accompany spawning.

Effects of (Anti) Androgenic Endocrine Disruptors (DEHP and Butachlor) on Immunoglobulin M (IgM) and Leukocytes Counts of Male Rainbow Trout (Oncorhynchus mykiss)

The effect of two anti-androgenic endocrine disrupting compounds, i.e. the plasticizer di (2-ethylhexyl) phthalate (DEHP) and herbicide butachlor, were evaluated for their effects on immunoglobulin M (IgM) and leukocytes in male rainbow trout. Also, plasma testosterone (T) concentration was measured to confirm their anti-androgenic effects. In the first experiment, trout were treated with 50 mg/kg (body weight) DEHP intraperitoneally, and in the second one, fish were exposed to 0.39 mg/L butachlor for 10 days. The results showed that T concentrations and white blood cells were significantly lower in fish exposed to either DEHP or butachlor compared to control fish (p < 0.05). Fish showed significantly elevated neutrophil levels and decreased lymphocyte levels in the butachlor (p < 0.05); however, no significant difference was observed in lymphocyte and neutrophils values in the DEHP treatment (p > 0.05). In addition, no significant differences were found in IgM, eosinophil and monocyte parameters in either DEHP or butachlor treatments (p > 0.05). These results confirmed that leukocytes counts can be considered as a novel marker of immunotoxicity triggered by (anti) androgenic endocrine disruptors.

The trenbolone acetate affects the immune system in rainbow trout, Oncorhynchus mykiss

In aquatic systems, the presence of endocrine-disrupting chemicals (EDC) can disrupt the reproductive function but also the immune system of wildlife. Some studies have investigated the effects of androgens on the fish immune parameters but the mechanisms by which the xenoandrogens alter the immunity are not well characterized. In order to test the effects of trenbolone acetate (TbA) on fish immune system, we exposed rainbow trout male juveniles during three weeks to TbA levels at 0.1 and 1μg/L. The present results suggest that TbA impacts, in a tissue-dependent manner, the rainbow trout immunity by affecting primarily the humoral immunity. Indeed, TbA inhibited lysozyme activity in plasma and liver and enhanced the alternative complement pathway activity (ACH50) in kidney. In plasma, the modulation of the complement system was time-dependent. The mRNA expression of genes encoding some cytokines such as renal TGF-β1, TNF-α in skin and hepatic IL-1β was also altered in fish exposed to TbA. Regarding the cellular immunity, no effect was observed on the leucocyte population. However, the expression of genes involved in the development and maturation of lymphoid cells (RAG-1 and RAG-2) was decreased in TbA-treated fish. Among those effects, we suggest that the modulation of RAG-1 and mucus apolipoprotein-A1 gene expression as well as plasma and hepatic lysozyme activities are mediated through the action of the androgen receptor. All combined, we conclude that trenbolone affects the rainbow trout immunity.

Detection of immunotoxic effects of estrogenic and androgenic endocrine disrupting compounds using splenic immune cells of the female three-spined stickleback, Gasterosteus aculeatus (L.)

Today, the list of endocrine disrupting compounds (EDCs) in freshwater and marine environments that mimic or block endogenous hormones is expanding at an alarming rate. As immune and reproductive systems may interact in a bidirectional way, some authors proposed the immune capacities as attractive markers to evaluate the hormonal potential of environmental samples. Thus, the present work proposed to gain more knowledge on direct biological effects of natural and EDCs on female fish splenic leucocyte non-specific immune activities by using ex vivo assays. After determining the optimal required conditions to analyze splenic immune responses, seven different EDCs were tested ex vivo at 0.01, 1 and 100nM over 12h on the leucocyte functions of female three-spined stickleback, Gasterosteus aculeatus. In summary, we found that natural hormones acted as immunostimulants, whilst EDCs were immunosuppressive.

Transcriptomics profiling and steroid production in mummichog (Fundulus heteroclitus) testes after treatment with 5α-dihydrotestosterone

5α-Dihydrotestosterone (DHT) is a potent androgen in mammals with multiple roles; however the physiological actions of DHT in male fishes are not well known. To address this knowledge gap, male mummichog (Fundulus heteroclitus) were continuously exposed to 0, 5, and 50 μg/L DHT for 21 days. Following exposure, testes were separated for histology, ex vivo incubation to measure steroidogenic capacity, and gene expression analyses (real-time PCR and microarray). DHT significantly decreased ex vivo 11-ketotestosterone (11KT) production in males exposed to 50 μg/L DHT but not 5 μg/L DHT, and DHT exposure did not affect ex vivo testosterone production. Histological examination revealed that the amount of interlobular and connective tissue present in the testes was increased in the 50 μg/L DHT treatment. Despite reductions in the production of 11KT, DHT did not affect the expression of targeted genes in the steroidogenic pathway such as steroidogenic acute regulatory protein (star), P450 side chain cleavage (cyp11a1) and 11β-hydroxysteroid dehydrogenase (hsd11b3). Microarray analysis in the testes of individuals from control and 50 μg/L DHT revealed that males exposed to 50 μg/L DHT showed regulated transcriptional sub-networks that were related to immunity, regulation of blood flow, lipids and xenobiotic clearance, suggesting that DHT may be involved in the physiological regulation of these processes in the fish testes. A second objective of this study was to determine the feasibility of measuring mRNA levels in tissues used for ex vivo steroid production by comparing RNA integrity and transcript levels in testes of both immediately flash frozen tissue and incubated tissue. There was no significant difference in RNA quality between the two time points, indicating RNA integrity can remain intact for at least 18 h in ex vivo assays, thereby providing a viable option for researchers assessing multi-level biological reproductive endpoints when limited tissue is available. While the gene expression levels of actb, efla, rps12, rps18, star, and hsd11b3 remained unchanged, esr2a (esrba), esr2b (esrbb) and cyp11a1 were significantly lower in incubated tissue compared to flash frozen tissue. Therefore caution must be used as the steady-state levels of select genes may change over time. This study improves our understanding of DHT action in the teleostean testis and generates new hypotheses regarding cell processes that are regulated by this underexplored and potent androgen.

Sockeye salmon retain immunoglobulin-secreting plasma cells throughout their spawning journey and post-spawning

Antibody-producing plasma cells are a major source of protective immunity in vertebrates, including salmon. During the spawning phase, salmon undergo drastic, hormonally driven changes in their physiology, including elevated levels of cortisol, which are known to suppress the immune system. As adult fish need to survive their long journey to the spawning grounds, we hypothesized that humoral immunity, in the form of IgM-secreting plasma cells, remains functional until post-spawning. This was investigated by measuring changes in membrane and secreted immunoglobulin heavy chain mu and Pax5 transcripts in spleen and kidney from migrating sockeye salmon, using real-time qPCR. As an additional measurement, the abundance of developing B, mature B, and plasma cells was determined in spawning fish, using flow cytometry. Immune tissue samples were collected from fish from the Kenai River drainage and Main Bay, Prince William Sound. Our results reveal that spawning fish express high levels of secreted heavy chain mu transcripts in their spleen and anterior kidney throughout the spawning journey. Furthermore, we show that IgM-secreting PCs (HCmu++/Pax5-) remain abundant in anterior kidney and spleen of post-spawning sockeye salmon, with a concomitant loss in developing B cells (HCmu-/Pax5+). This suggests that successful spawners retain their PCs throughout the spawning journey and post-spawning.

Specific and non-overlapping functions of testosterone and 11-ketotestosterone in the regulation of professional phagocyte responses in the teleost fish gilthead seabream

Sex hormones, both estrogens and androgens, have a strong impact on immunity in mammals. In fish, the role of androgens in immunity has received little attention and contradictory conclusions have been obtained. However, it is well known that sex steroids are involved in fish growth, osmoregulation and gonad remodelation. In this study, we examine the in vitro effects of testosterone and 11-ketotestosterone, the two main fish androgens, on the professional phagocytes of the teleost fish gilthead seabream (Sparus aurata L.). Although both testosterone and 11-ketotestosterone failed to modulate the respiratory burst of seabream phagocytes, testosterone but not 11-ketotestosterone was able to increase the phagocytic ability of non-activated phagocytes. Curiously, 11-ketotestosterone was more powerful than testosterone at inducing the expression of its own receptor, namely androgen receptor b (ARb), in acidophilic granulocytes (AGs), but none of them affected the basal ARb expression levels in macrophages (MØ). Furthermore, although physiological concentrations of testosterone exerted a pro-inflammatory effect on both AGs and MØs, 11-ketotestosterone showed an anti-inflammatory effect in AGs and a strong pro-inflammatory effect in MØs. Interestingly, both androgens modulated the expression of toll-like receptors in these two immune cell types, suggesting that androgens might regulate the sensitivity of phagocytes to pathogens and damage signals. Testosterone and 11-ketotestosterone have a competitive effect, at least, on the modulation of the expression of some genes. Therefore, our results show for the first time a non-overlapping role for testosterone and 11-ketotestosterone in the regulation of professional phagocyte functions in fish.

The effects of estrogenic and androgenic endocrine disruptors on the immune system of fish: a review

During the last decade, a number of studies have shown that, in addition to their classically described reproductive function, estrogens and androgens also regulate the immune system in teleosts. Today, several molecules are known to interfere with the sex-steroid signaling. These chemicals are often referred to as endocrine disrupting contaminants (EDCs). We review the growing evidence that these compounds interfere with the fish immune system. These studies encompass a broad range of approaches from field studies to those at the molecular level. This integrative overview improves our understanding of the various endocrine-disrupting processes triggered by these chemicals. Furthermore, the research also explains why fish that have been exposed to EDCs are more sensitive to pathogens during gametogenesis. In this review, we first discuss the primary actions of sex-steroid-like endocrine disruptors in fish and the specificity of the fish immune system in comparison to mammals. Then, we review the known interactions between the immune system and EDCs and interpret the primary effects of sex steroids (estrogens and androgens) and their related endocrine disruptors on immune modulation. The recent literature suggests that immune parameters may be used as biomarkers of contamination by EDCs. However, caution should be used in the assessment of such immunotoxicity. In particular, more attention should be paid to the specificity of these biomarkers, the external/internal factors influencing the response, and the transduction pathways induced by these molecules in fish. The use of the well-known mammalian models provides a useful guide for future research in fish.

Social modulation of testosterone levels in male black howlers (Alouatta pigra)

The influence of social factors on the modulation of male testosterone levels has been demonstrated among several vertebrate species. In addition to sexual activity, parental care and reproductive competition affect testosterone secretion. We examined variations in testosterone levels among male black howlers (Alouatta pigra) in various social contexts. Fecal samples were collected from nine males living in five different groups in the Mexican state of Campeche. The potential for intragroup and extragroup competition varied among the groups. The number of resident males living in the groups was the only variable that significantly explained variations in testosterone levels. Males living in unimale groups had higher testosterone levels; the highest testosterone levels were recorded for males that had experienced a shift from multimale to unimale group compositions. In this species, the probability of being challenged by extragroup males and evicted from the group during immigration events increases when males live in unimale groups. Therefore, our results suggest that male black howlers respond to competition for group membership by increasing their testosterone levels. In this context, testosterone secretion represents an anticipatory response to reproductive conflicts. Therefore, although males living in unimale groups have exclusive access to females, they face higher physiological costs associated with sustaining high testosterone levels for extended time periods.

Interactions between immunocompetence, somatic condition and parasitism in the chub Leuciscus cephalus in early spring

Relationships between immunocompetence, somatic condition, parasitism and water temperature in a wild population of chub Leuciscus cephalus were investigated. The effects of a rapid temperature increase in early spring were studied for both sexes as water temperature affects immunocompetence. Investment in gonads and activity of mucus lysozyme were negatively correlated; lysozyme activity decreased as temperature increased. No correlations were found between lysozyme activity and parasitism or intensity of infection by monogeneans, the most abundant metazoan parasite group in L. cephalus. There was a positive correlation, however, between respiratory burst intensity and parasitism. Indices of investment in gonads and spleen were correlated, showing that energetic reserves allowed either investment in gonads and spleen, or that spleen investment, even if often used in other studies in immunoecology, was not always a significant indicator of immunocompetence during this period. This last proposition is supported by the lack of correlation between spleen investment and other factors linked to immunocompetence.

Curcumin analogue inhibits lipid peroxidation in a freshwater teleost, Anabas testudineus (Bloch)--an in vitro and in vivo study

The effect of a synthetic curcumin analogue (salicylcurcumin) on fish lipid peroxidation was investigated in both in vitro and in vivo conditions using a teleost model Anabas testudineus (Bloch). Curcumin analogue inhibited the formation of lipid peroxidation products and thiobarbituric acid reactive substances (TBARS) content at the three concentrations (10(-2) M, 10(-3) M and 10(-4) M) in vitro. TBARS content was reduced by 80% in the liver and 68% in brain by the higher concentration of salicylcurcumin. For in vivo study, salicylcurcumin (0.5%) was supplemented along with the basal feed for a period of 60 days. It produced a 60% reduction in liver TBARS content. The antioxidant enzyme superoxide dismutase (SOD) was stimulated, whereas catalase (CAT) and glutathione peroxidase (GPx) were inhibited. Glutathione (GSH) was reduced and glutathione reductase (GR) unchanged. Even though there was an increase in SOD activity, the CAT and GPx did not increase accordingly, maybe due to the direct scavenging of H(2)O(2) by salicylcurcumin. The protein content also increased in the curcumin-fed animals, indicating a positive growth-promoting effect. Therefore, it would be beneficial to supplement salicylcurcumin along with the aquaculture feed in order to help the fish to cope with adverse conditions in the environment. This would increase the survival rate, disease resistance and ultimately the growth rate.

Seasonal and gender variation of peroxisome proliferator activated receptors expression in brown trout liver

PPAR isotypes have been previously identified in the teleost brown trout (Salmo trutta f. fario) and their organ distribution pattern established. Being that the liver is a vital metabolic organ presenting expression of all isotypes and also knowing that estrogens/estrogen receptors seem to interact with PPARs, we hypothesized that the latter may very well change seasonally. So, we studied the expression of these receptors in the liver, along the annual reproductive cycle and in both genders. According to real-time RT-PCR, PPARalpha mRNA expression in females was significantly higher in May and lower in September than in other seasons. No significant variation was observed along the year in males. A significant difference between genders occurred in May, when PPARalpha expression was higher for females. PPARbeta expression showed little variation along the reproductive cycle in females, but in males it was significantly higher in December than in the other seasons. No significant differences existed between genders. PPARgamma was more expressed in February than in September and December, for females. As to males, it was more expressed in February than in all other seasons. No significant differences were observed between genders. The study proved our hypothesis that PPARs gene expression varies along the year. Moreover, PPARalpha expression in females followed the same annual variation pattern as peroxisome volumes and enzyme activities, and an inverse pattern relatively to the salmonid type annual plasma estradiol levels. The data agrees with the idea that PPARalpha is under estradiol modulation and that cross-talk between this receptor and the estrogen receptor possibly exists.

Effects of reproductive activity and sex hormones on apoptosis in the epigonal organ of the skate (Leucoraja erinacea)

In elasmobranchs, a unique association exists between an immune tissue, the epigonal organ, and the gonads. The intimate morphological relationship between these tissues suggests functional interactions. In this study, we used apoptosis to assess differences between epigonal tissues of reproductively active (RA) and non-reproductively active (NRA) skates (Leucoraja erinacea). Plasma steroid levels were significantly higher in RA than in NRA animals, and TUNEL analysis showed that epigonal tissue of RA skates had greater DNA fragmentation than NRA skates. Addition of steroids to epigonal leukocytes in vitro demonstrated that progesterone, testosterone, and dexamethasone, but not estrogen, induced apoptosis of epigonal leukocytes as evidenced by DNA laddering and caspase-3 antibody labeling. This study supports recent evidence that cellular homeostasis of epigonal lymphomyeloid tissue may be influenced by gonadal activity and reproductive steroids in a representative of the most basal gnathastome group.

An Experimental Test of the Immunocompetence Handicap Hypothesis in a Teleost Fish: 11‐Ketotestosterone Suppresses Innate Immunity in Three‐Spined Sticklebacks

The immunocompetence handicap hypothesis (ICHH) provides a functional explanation for how sexual ornaments can provide honest signals of male quality. A key aspect of this hypothesis is that testosterone (T) has a bimodal effect: a higher T level enhances the expression of ornaments (increasing mating success and, ultimately, fitness); however, at the same time, it suppresses immune function. Tests of the latter assumption, which have focused mainly on aspects of adaptive immunity in birds, led to equivocal results. We performed a hormone-implant experiment in male three-spined sticklebacks (Gasterosteus aculeatus) to test the key assumptions of the ICHH in a fish, where the dominant circulating androgen is 11-ketotestosterone (11kT) rather than T. Males were implanted with 11-ketoandrostenedione, which is a natural precursor of 11kT. Each individual's circulating 11kT level, ornamentation, and immunocompetence were measured 2 weeks later. In addition, we quantified oxidative tissue damage because the ICHH has been hypothesized to work via oxidative stress. We found that the males' 11kT levels correlated positively with ornamentation but negatively with immunocompetence, in particular, measures of innate immunity. Moreover, there was a trend for fish with high 11kT levels to suffer more from oxidative stress. Thus, our data provide support for the ICHH.

Effect of sex-steroid hormones, testosterone and estradiol, on humoral immune parameters of gilthead seabream

The role of sex-steroid hormones, testosterone (T) and 17beta-estradiol (E2), on the humoral immune parameters of the teleost gilthead seabream Sparus aurata was studied attempting to deepen on the knowledge of the immune-reproductive system interactions. Fish were injected intraperitoneally with coconut oil containing different dosages of T (0, 2, or 5 microg g(-1) body weight [bw]) or E2 (0, 1, or 2 microg g(-1) bw) and sampled 1, 3, and 7 days later. Hormonal levels and immune parameters (complement, peroxidase and antiprotease activities and IgM levels) were determined in plasma. Plasma hormone levels peaked at 1 day post-injection decreasing thereafter. Treatment with T significantly increased both complement and peroxidase activities after 3 days of injection but antiprotease activity and IgM levels remained unchanged. Treatment with E2 enhanced complement activity 1 day post-injection while decreased it after 3 and 7 days. However, peroxidase activity increased at 3 and 7 days post-injection while total IgM levels decreased. Implications of T and E2 in the immune-reproductive system interactions were discussed.

Alternative male reproductive tactics and the immunocompetence handicap in the Azorean rock-pool blenny, Parablennius parvicornis

In the Azorean rock-pool blenny (Parablennius parvicornis) reproductively active males display alternative morphotypes, which differ in the expression of secondary sexual characters (SSC). Males expressing SSC, the M+ morphotype, have high androgen levels and compete for crevices that will be visited by females to spawn. M+ males holding nests court females and care for the eggs. Males with low expression of SSC, the M- morphotype, have low levels of androgens and reproduce by stealing fertilizations from the M+ males. Based on the hypothesis that androgens are immunosuppressive, we expected these morphotypes to differ in immunocompetence. To test this hypothesis, we conducted a field study in which we collected repeated blood samples to monitor leukocyte populations (blood smears), and to measure the primary antibody response of males that were experimentally challenged with a foreign non-pathogenic antigen (sheep red blood cells). Circulating levels of 11-ketotestosterone and testosterone were higher in M+ males than in M- males. Neither granulocyte nor thrombocyte counts did covariate with androgens or male tactic. In contrast, lymphocyte counts and humoral antibody response were negatively correlated with body size, and as expected, both were lower in M+ than in M- males. Interestingly, in M+ males androgen levels decreased after immunization, and this was less in nest-holder males than in M+ males that were floating around in the pools. Within each morphotype we found no relationship between androgens and immunocompetence. The latter result is not supportive for androgen regulated immunosuppression in M+ males. A possible alternative is enhancement of immunity in M- males. These males had relatively high levels of injuries in comparison with M+ males. High immunity might be a consequence of high infection rate because of such injuries.

Regulation of immunocompetence by different androgen metabolites in a blenny with alternative reproductive tactics

In Parablennius parvicornis, small reproductive males with relatively low expression of secondary sexual characters (M- morphotype) parasite on the parental investment of the larger nest-holder males which have fully developed secondary sexual characters (M+ morphotype). In comparison with M+ males, M- males have relatively low levels of androgens while having high blood cell percentages of lymphocytes and antigen responsiveness. Here we test the hypothesis that androgens are a causal factor for these differences in immunocompetence between morphotypes. After drawing an initial blood sample, males received a silastic implant containing either oil only (C), or oil with testosterone (T) or 11-ketotestosterone (KT). Males were re-caught 2 weeks later for drawing of the final blood sample. KT but not T induced the development of secondary sexual characters in M- males. M- males treated with KT showed lower swimming activity than the males treated with T or C implants, suggesting that KT also mediates behavioral changes in M- males. As expected, blood cell percentages of lymphocytes, but not of granulocytes, were higher in M- males than in M+ males. Overall, lymphocyte percentages increased in the C group which might have been a response to the surgery/treatment. In concordance with the hypothesis, lymphocyte percentages were suppressed in males treated with T in comparison with controls. However, no significant change was found in KT-treated males. This suggests that androgens modulate central, morphological and immunological traits by partly independent androgen mechanisms in P. parvicornis.

Androgen control of immunocompetence in the male house finch, Carpodacus mexicanus Müller

The immunocompetence handicap (ICH) hypothesis predicts that elevated levels of the gonadal androgen testosterone (T) entail obligatory costs, such as immunosuppression, but evidence supporting this immunosuppressive influence is equivocal. To investigate this question, adult males house finches, Carpodacus mexicanus, were exposed to short days and chronically treated with T-filled (T males; N=10) or empty (C males; N=10) Silastic capsules. Testosterone administration increased plasma T levels and the size of the cloacal protuberance, an androgen-dependent secondary sexual characteristic. To study humoral immunity, finches received injections of sheep red blood cells (SRBC) and we measured circulating concentrations of antibodies to these cells with a hemagglutination test. All males produced antibodies following four SRBC injections at weekly intervals. Antibody titers in T and C males did not differ 5 days after the fourth injection, but were 59% lower in T than C males 2 weeks later. To study cell-mediated immunity, we measured the local inflammatory response to an injection of phytohemaglutinin (PHA). This response in T and C males was similar 1 day after PHA injection, but was 58% less in T than C males 2 days following the injection. Thus, T and C males mounted similar humoral and cell-mediated immune responses, but T treatment compromised maintenance of these responses. The results, demonstrating immunosuppressive effects of elevated T, are consistent with the ICH hypothesis.

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.

Rapid action of cortisol and testosterone on lipogenic enzymes in a fresh water fish Oreochromis mossambicus: short-term in vivo and in vitro study

Rapid action of steroid hormones on lipid metabolism is not reported so far in any vertebrate. The present study was intended to evaluate the quick actions of cortisol and testosterone on enzymes, namely malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PDH), and isocitrate dehydrogenase (ICDH) in Oreochromis mossambicus. Cortisol and testosterone produced rapid and opposite effects on the lipogenic enzymes studied. Cortisol significantly decreased the activities of ME, G6PDH, as early as 5 min and ICDH as early as 10 min in vitro (10(-6) M), and 30 min in vivo (0.1 microg/g body wt.) whereas the same doses of testosterone significantly stimulated the activity of all enzymes as early as 5 min in vitro and 30 min in vivo. Actinomycin D treatment did not interfere with the inhibiting effect of cortisol on enzyme activities when measured at 10 min in the in vitro system. The transcriptional inhibitor appeared to partially block the effect of cortisol in vivo. The stimulatory effect of testosterone was insensitive to the action of actinomycin D both in vivo and in vitro. These effects appear to be brought about independently of new protein synthesis because the rapid responses occurred within a latent period of 5-30 min and were insensitive to the action of actinomycin D, suggesting a non-genomic action.

Rapid action of testosterone and diethylstilbestrol on enzymes of osmoregulation in a freshwater fish Oreochromis mossambicus

The rapid action of sex steroids on enzymes of osmoregulation has not been studied in teleosts. In vivo administration of 0.1 microg/g body wt. of testosterone and diethylstilbestrol (DES) significantly enhanced branchial Na+-K+ ATPase, Ca2+ ATPase, and Na+, K+, and Ca2+ ions as early as 30 minutes in a freshwater teleost Oreochromis mossambicus. Treatment with 10(-6) M testosterone significantly stimulated Na+-K+ ATPase as early as 5 minutes in vitro. The same dose of DES also stimulated Na+-K+ ATPase activity within 10 minutes of incubation in a gill culture study. Administration of the transcriptional inhibitor, actinomycin D (0.1 microg/g body wt. in vivo and 10(-6) M in vitro), prior to hormone treatment, did not prevent the steroid-induced ATPase activity both in vivo and in vitro. It seems that stimulation of Ca2+ ion may be responsible for the hormonal effects to increase enzyme activity. A possible nongenomic mode of action for testosterone and DES is suggested in Oreochromis.

Rapid action of glucocorticoids on branchial ATPase activity in Oreochromis mossambicus: an in vivo and in vitro study

The rapid action of cortisol and corticosterone on branchial Na(+)-K(+) ATPase, Ca(2+) ATPase activity and Na(+), K(+) and Ca(2+) ion contents was studied both in vivo and in vitro employing transcription inhibitor actinomycin D in Oreochromis mossambicus. Cortisol and corticosterone administration had significantly increased the activity of branchial Na(+)-K(+) ATPase and Ca(2+) ATPase in vivo after 30 min of injection, and the trend continued for 60 and 120 min for cortisol. The ionic contents were also significantly increased after 30 min in vivo. Na(+)-K(+) ATPase activity was significantly increased 5 min after hormone application in the in vitro system. Actinomycin D did not inhibit the effect of glucocorticoids on ATPase activity both in vivo and in vitro. It is concluded from the present study that cortisol and corticosterone produced a rapid stimulatory effect on branchial ATPase activity and ions in O. mossambicus both in vivo and in vitro. This effect could be due to a non-genomic action of these hormones since the enzyme activity was insensitive to actinomycin D.

Effects of estradiol, progesterone and testosterone on the function of carp, Cyprinus carpio, phagocytes in vitro

The modulation of phagocytic cells by beta-estradiol, 11-ketotestosterone and progesterone was analyzed in common carp Cyprinus carpio. Carp kidney leukocytes were cultured in RPMI 1640 medium containing 0.1, 1, 10, 100 or 1000 nM concentration of each hormone. The production of superoxide anion, nitric oxide (NO) and phagocytosis were measured in vitro. Similar concentrations of cortisol were used as control. Phagocytic activities of carp macrophages was suppressed by treatment with beta-estradiol, progesterone and 11-ketotestosterone. The production of NO in carp macrophages was suppressed by progesterone and 11-ketotestosterone. However, carp macrophages incubated with beta-estradiol, progesterone and 11-ketotestosterone did not show any difference in the production of superoxide anion in comparison with control macrophages in the absence of hormones. Carp macrophages treated with cortisol suppressed phagocytosis and the production of nitric oxide and superoxide anion.

Differential in vitro suppressive effects of steroids on leukocyte phagocytosis in two teleosts, tilapia and common carp

The objectives of this study were to investigate the potential roles of cortisol and gonadal steroids in the phagocytic activity of peripheral blood leukocytes in two teleosts, tilapia (Oreochromis niloticus x O. aureus) and common carp (Cyprinus carpio). An in vitro microtiter plate assay, measuring incorporation of FITC-latex beads into peripheral blood leukocytes, was developed for the first time in teleosts. Peripheral blood leukocytes were cultured in AL medium with tested compounds in a microfluor black plate at 25 degrees C. FITC-latex beads were further incubated for phagocytosis and engulfed fluorescent intensity in phagocytes was detected fluorometrically. Cortisol suppressed leukocyte phagocytosis in a dose (10(-14) to 10(-4) M)- and time (0.5 to 8 h)-dependent manner in tilapia. The glucocorticoid agonist dexamethasone had a suppressive effect similar to that of cortisol, while cortisone and the mineralocorticoid aldosterone had only a weak effect in tilapia. High doses of estradiol and ethynylestradiol, but not of estrone, suppressed phagocytosis in tilapia. No suppressive effect on phagocytosis was observed with various concentrations of progesterone, testosterone, and 11-ketotestosterone. Triiodothyronine was also inactive on phagocytosis. A combination of estradiol and cortisol potentiatingly suppressed phagocytosis. Actinomycin D and cycloheximide blocked the suppressive effects of cortisol and estradiol. Cortisol had weaker suppressive effects on the phagocytosis of leukocytes in common carp than tilapia. Other steroids had no suppressive action on phagocytosis in common carp. It is concluded that the suppressive effects of cortisol and estradiol on phagocytosis in tilapia are mediated by specific glucocorticoid receptors and estrogen receptors, respectively. Cortisol would play a main and important role on the down-regulation of phagocytic activity. Sexual steroids, such as estradiol, also could interact with cortisol to further suppress immunity in tilapia. Differential responsiveness of the immune system to suppressive effects of steroids, among teleosts species, has been demonstrated.

Modulation of the fish immune system by hormones

Immune-neuroendocrine interactions in fish, as in mammals, have become a focus of considerable interest, with the modulation of immune responses by hormones receiving particular attention. Cortisol, growth hormone (GH), prolactin (PRL), reproductive hormones, melanin-concentrating hormone (MCH) and proopiomelanocortin (POMC)-derived peptides have all been shown to influence immune functions in a number of fish species. This review summarises the known effects of these hormones on the fish immune system, as well as the often complex interactions between different hormones. The possible implications for fish health, with respect to aquaculture and the changes in immunocompetence that take place during different stages in the fish life cycle are also discussed.

The role of androgens in female vertebrates

The role of androgens in vertebrate females has been overlooked until recently. We examine the functional significance of androgens in females by reviewing studies that document relatively high levels of circulating plasma androgens, androgen receptors, or androgen-metabolizing enzymes in females. Among the mechanisms of androgenic action identified are enhanced neuron survival, stimulation of muscle satellite cell proliferation, alteration of ion current kinetics, and release of somatostatin. These mechanisms are not sex specific and thus we hypothesize that androgens play a significant role in normal female development. We encourage study in this nontraditional research area.