Melatonin mediates seasonal changes in immune function

Immunoregulatory properties of melatonin in the humoral immune system: A narrative review

Melatonin is the major product both synthesized and secreted by the pineal gland during the night period and it is the principal chronobiotic hormone that regulates the circadian rhythms and seasonal changes in vertebrate biology. Moreover, melatonin shows both a broad distribution along the phylogenetically distant organisms and a high functional versatility. At the present time, a significant amount of experimental evidence has been reported in scientific literature and has clearly shown a functional relationship between the endocrine, nervous, and immune systems. The biochemistry basis of the functional communication between these systems is the utilization of a common chemicals signals. In this framework, at present melatonin is considered to be a relevant member of the so-called neuro-endocrine-immunological network. Thus, both in vivo and in vitro investigations conducted in both experimental animals and humans, have clearly documented that melatonin has an important immunomodulatory role. However, most of the published results refer to information on T lymphocytes, i.e., cell-mediated immunity. On the contrary, fewer studies have been carried out on B lymphocytes, the cells responsible for the so-called humoral immunity. In this review, we have focused on the biological role of melatonin in the humoral immunity. More precisely, we report the actions of melatonin on B lymphocytes biology and on the production of different types of antibodies.

Melatonin in Health and Disease: A Perspective for Livestock Production

Mounting evidence in the literature indicates an important role of endogenous and exogenous melatonin in driving physiological and molecular adaptations in livestock. Melatonin has been extensively studied in seasonally polyestrous animals whereby supplementation studies have been used to adjust circannual rhythms in herds of animals under abnormal photoperiodic conditions. Livestock undergo multiple metabolic and physiological adaptation processes throughout their production cycle which can result in decreased immune response leading to chronic illness, weight loss, or decreased production efficiency; however, melatonin’s antioxidant capacity and immunostimulatory properties could alleviate these effects. The cardiovascular system responds to melatonin and depending on receptor type and localization, melatonin can vasodilate or vasoconstrict several systemic arteries, thereby controlling whole animal nutrient partitioning via vascular resistance. Increased incidences of non-communicable diseases in populations exposed to circadian disruption have uncovered novel pathways of neurohormones, such as melatonin, influence health, and disease. Perturbations in immune function can negatively impact the growth and development of livestock which has been examined following melatonin supplementation. Specifically, melatonin can influence nutrient uptake, circulating nutrient profiles, and endocrine profiles controlling economically important livestock growth and development. This review focuses on the physiological, cellular, and molecular implications of melatonin on the health and disease of domesticated food animals.

Photoperiodic regulation of the splenocyte immune responses in the fresh water snake, Natrixpiscator

Photoperiod and melatonin are important regulators of immunity. We hypothesized that these two factors play an important role in the regulation of immune responses in the Natrix piscator. Animals were kept in either short or long days and splenocyte immune responses were studied. Respiratory burst activity of splenocytes was assessed through reduction of nitrobluetetrazolium salt while production of nitric oxide was assessed indirectly by nitrite assay. Density gradient centrifugation was used to isolate splenic lymphocytes which were utilized to study proliferation with and without mitogens. Super oxide production by splenocytes was reduced significantly in the cultures obtained from animals kept either in short or long days. Nitrite release was decreased when animals were subjected to long days. The photoperiodic alterations acted differentially on proliferations of the splenic lymphocytes. Spontaneous and mitogen-induced proliferation of splenic lymphocytes were enhanced in cultures obtained from snakes maintained in short days when compared with cultures from snakes obtained either from long day or natural day length conditions. In vitro melatonin significantly enhanced the splenic lymphocyte proliferation of the cultures obtained from animals kept in long days when compared with splenic lymphocyte proliferations of the cultures obtained from long day animals or the animals kept in natural day length conditions. We found evidence which suggest that photoperiod may influence seasonal energy budgets and induce adjustments which optimize energy allocation for costly physiological processes such as immune function. In seasonally breeding animals such as Natrix piscator, the pineal hormone melatonin assists in the suppression of reproduction and elevation of immunity, which are the crucial adaptation for perpetuation of species.

Impact of Up- and Downregulation of Metabolites and Mitochondrial Content on pH and Color of the Longissimus Muscle from Normal-pH and Dark-Cutting Beef

Limited knowledge is currently available on the biochemical basis for the development of dark-cutting beef. The objective of this research was to determine the metabolite profile and mitochondrial content differences between normal-pH and dark-cutting beef. A gas chromatography-mass spectrometer-based nontargeted metabolomic approach indicated downregulation of glycolytic metabolites, including glucose-1- and 6-phosphate and upregulation of tricarboxylic substrates such as malic and fumaric acids occurred in dark-cutting beef when compared to normal-pH beef. Neurotransmitters such as 4-aminobutyric acid and succinate semialdehyde were upregulated in dark-cutting beef than normal-pH beef. Immunohistochemistry indicated a more oxidative fiber type in dark-cutting beef than normal-pH beef. In support, the mitochondrial protein and DNA content were greater in dark-cutting beef. This increased mitochondrial content, in part, could influence oxygen consumption and myoglobin oxygenation/appearance of dark-cutting beef. The current results demonstrate that the more tricarboxylic metabolites and mitochondrial content in dark-cutting beef impact muscle pH and color.

The Impact of Photoperiod on the Leptin Sensitivity and Course of Inflammation in the Anterior Pituitary

Leptin has a modulatory impact on the course of inflammation, affecting the expression of proinflammatory cytokines and their receptors. Pathophysiological leptin resistance identified in humans occurs typically in sheep during the long-day photoperiod. This study aimed to determine the effect of the photoperiod with relation to the leptin-modulating action on the expression of the proinflammatory cytokines and their receptors in the anterior pituitary under physiological or acute inflammation. Two in vivo experiments were conducted on 24 blackface sheep per experiment in different photoperiods. The real-time PCR analysis for the expression of the genes IL1B, IL1R1, IL1R2, IL6, IL6R, IL6ST, TNF, TNFR1, and TNFR2 was performed. Expression of all examined genes, except IL1β and IL1R2, was higher during short days. The leptin injection increased the expression of all examined genes during short days. In short days the synergistic effect of lipopolysaccharide and leptin increased the expression of IL1B, IL1R1, IL1R2, IL6, TNF, and TNFR2, and decreased expression of IL6ST. This mechanism was inhibited during long days for the expression of IL1R1, IL6, IL6ST, and TNFR1. The obtained results suggest the occurrence of leptin resistance during long days and suggest that leptin modulates the course of inflammation in a photoperiod-dependent manner in the anterior pituitary.

Flow-cytometric analysis of circulating leukocyte populations in turkeys: Establishment of a whole blood analysis approach and investigations on possible influencing factors

The blood cell counting methods used for diagnostic and research purposes in turkeys are, up to date, inferior to the techniques established for mammals and chickens. While microscopic counts are time consuming, previous flow cytometric approaches did not cover all blood cell types of interest due to the lack of turkey-specific markers for the different cell populations. Moreover, it is unknown to what extent the different leukocyte populations are affected by host and environmental factors including age, breed of the bird, and housing environment, respectively. In this study we established a whole blood based flow cytometric analysis method for turkeys. This method was used to determine baseline values depending on the age of the birds as well as under consideration of variations between trials and animal room effects. During three trials whole blood samples of B.U.T. 6 female turkeys were collected to analyze different leukocyte concentrations (cells/μl whole blood). In the first trial one group and in the second and third trial two groups with 22 birds/group were housed. Blood samples were collected at days one, 23, 43, 60, and 88 post hatch and concentrations of monocytes, MHC class II-positive, CD4⁺, and CD8⁺ lymphocytes, as well as thrombocytes and granulocytes were determined by flow cytometric analysis. Concentrations of all identified populations were not only influenced by the bird's age (p < 0.05), they varied also among trials (p < 0.05) and even for some of the populations between animal rooms within the same trial despite comparable housing and management conditions. Therefore, for the establishment of baseline values for leucocyte concentrations in whole blood effects of age and housing have to be considered. In addition, our data emphasize the importance of the establishment of baseline values for different age groups, as age had the strongest effect on the blood cell numbers in this study.

Blue Light Enhances Bacterial Clearance and Reduces Organ Injury During Sepsis

OBJECTIVES

The physiology of nearly all mammalian organisms are entrained by light and exhibit circadian rhythm. The data derived from animal studies show that light influences immunity, and these neurophysiologic pathways are maximally entrained by the blue spectrum. Here, we hypothesize that bright blue light reduces acute kidney injury by comparison with either bright red or standard, white fluorescent light in mice subjected to sepsis. To further translational relevance, we performed a pilot clinical trial of blue light therapy in human subjects with appendicitis.

DESIGN

Laboratory animal research, pilot human feasibility trial.

SETTING

University basic science laboratory and tertiary care hospital.

SUBJECTS

Male C57BL/6J mice, adult (> 17 yr) patients with acute appendicitis.

INTERVENTIONS

Mice underwent cecal ligation and puncture and were randomly assigned to a 24-hour photoperiod of bright blue, bright red, or ambient white fluorescent light. Subjects with appendicitis were randomized to receive postoperatively standard care or standard care plus high-illuminance blue light.

MEASUREMENTS AND MAIN RESULTS

Exposure to bright blue light enhanced bacterial clearance from the peritoneum, reduced bacteremia and systemic inflammation, and attenuated the degree of acute kidney injury. The mechanism involved an elevation in cholinergic tone that augmented tissue expression of the nuclear orphan receptor REV-ERBα and occurred independent of alterations in melatonin or corticosterone concentrations. Clinically, exposure to blue light after appendectomy was feasible and reduced serum interleukin-6 and interleukin-10 concentrations.

CONCLUSIONS

Modifying the spectrum of light may offer therapeutic utility in sepsis.

Blue light reduces organ injury from ischemia and reperfusion

Evidence suggests that light and circadian rhythms profoundly influence the physiologic capacity with which an organism responds to stress. However, the ramifications of light spectrum on the course of critical illness remain to be determined. Here, we show that acute exposure to bright blue spectrum light reduces organ injury by comparison with bright red spectrum or ambient white fluorescent light in two murine models of sterile insult: warm liver ischemia/reperfusion (I/R) and unilateral renal I/R. Exposure to bright blue light before I/R reduced hepatocellular injury and necrosis and reduced acute kidney injury and necrosis. In both models, blue light reduced neutrophil influx, as evidenced by reduced myeloperoxidase (MPO) within each organ, and reduced the release of high-mobility group box 1 (HMGB1), a neutrophil chemotactant and key mediator in the pathogenesis of I/R injury. The protective mechanism appeared to involve an optic pathway and was mediated, in part, by a sympathetic (β3 adrenergic) pathway that functioned independent of significant alterations in melatonin or corticosterone concentrations to regulate neutrophil recruitment. These data suggest that modifying the spectrum of light may offer therapeutic utility in sterile forms of cellular injury.

Influenza Burden and Transmission in the Tropics

Each year, influenza causes substantial mortality and morbidity worldwide. It is important to understand influenza in the tropics because of the significant burden in the region and its relevance to global influenza circulation. In this review, influenza burden, transmission dynamics, and their determinants in the tropics are discussed. Environmental, cultural, and social conditions in the tropics are very diverse and often differ from those of temperate regions. Theories that account for and predict influenza dynamics in temperate regions do not fully explain influenza epidemic patterns observed in the tropics. Routine surveillance and household studies have been useful in understanding influenza dynamics in the tropics, but these studies have been limited to only some regions; there is still a lack of information regarding influenza burden and transmission dynamics in many tropical countries. Further studies in the tropics will provide useful insight on many questions that remain.

Melatonin: a "Higgs boson" in human reproduction

As the Higgs boson could be a key to unlocking mysteries regarding our Universe, melatonin, a somewhat mysterious substance secreted by the pineal gland primarily at night, might be a crucial factor in regulating numerous processes in human reproduction. Melatonin is a powerful antioxidant which has an essential role in controlling several physiological reactions, as well as biological rhythms throughout human reproductive life. Melatonin, which is referred to as a hormone, but also as an autocoid, a chronobiotic, a hypnotic, an immunomodulator and a biological modifier, plays a crucial part in establishing homeostatic, neurohumoral balance and circadian rhythm in the body through synergic actions with other hormones and neuropeptides. This paper aims to analyze the effects of melatonin on the reproductive function, as well as to shed light on immunological and oncostatic properties of one of the most powerful hormones.

Seasonal variability in the incidence of carcinomatous meningitis

OBJECT

The aim of the study was to investigate whether there are seasonal differences in the occurrence of carcinomatous meningitis (CM), with a greater prevalence of the disease in months with higher temperatures.

METHODS

The authors searched the records of all patients with a diagnosis of CM from 1998 until 2013 at the University Hospital of Patras, Greece. The date of hospitalization was extracted for each patient. The cases were divided into 2 categories depending on the time of CM diagnosis. Based on the official data regarding the annual temperature distribution in this region, the authors divided the patients into 2 groups. The first group consisted of cases diagnosed with CM from October 15 to April 15 (cold climate and shorter daytime duration), whereas the second group comprised patients diagnosed between April 15 and October 15 (warm climate and longer daytime duration).

RESULTS

Overall, 44 confirmed cases of CM were found. The most common type of malignancy associated with the development of CM was breast cancer (27 patients), while the second most common tumor was lung carcinoma (11 patients). The median interval between the time of initial cancer diagnosis and CM was 4.5 years. Thirty-one patients were diagnosed with CM during the period between April 15 and October 15, while the remaining 13 patients developed CM between October 15 and April 15, a significant difference (p = 0.01).

CONCLUSIONS

Significantly more patients developed CM during the warm season of the year. To the authors' knowledge, this is the first study to provide evidence for the potential seasonal variability in CM incidence. However, these results should be validated prospectively in larger cohorts.

Relationship between cortisol and acute phase protein concentrations in female rabbits

Rabbit meat production in Europe is usually based on a semi-intensive system, in which lactation and gestation overlap. The demands of lactation and pregnancy are likely to be relatively stressful for female rabbits and may compromise the immune system and reproductive performance. The present study was designed to characterise circulating levels of cortisol, haptoglobin (Hp), C-reactive protein (CRP), and serum amyloid A (SAA) in non-lactating and lactating female rabbits at first and second mating, and to determine whether any relationship exists between these biomarkers and litter size. Serum cortisol concentrations were at their greatest (mean ± SEM = 39.5 ± 3.9 nmol/L) in animals at the end of lactation. However, after weaning, cortisol concentrations were not significantly different compared to nulliparous females (19.9 ± 3.6 vs. 16.3 ± 2.2 nmol/L, respectively). The highest concentrations of circulating Hp (0.14 ± 0.01 g/L) were seen in early lactating primiparous females, and lower in nulliparous females and in rabbits after weaning. In contrast, nulliparous female rabbits showed the highest plasma CRP values (13.1 ± 1.1 mg/L). No significant differences were found for SAA. Nulliparous females had smaller litter sizes than early lactating and non-lactating primiparous female rabbits. CRP and SAA showed a positive correlation (r = +0.24, P = 0.011) and were negatively related to litter size (r = -0.23, P = 0.017 and P = 0.032, respectively). Cortisol and Hp were not related to CRP, SAA, nor to litter size. These results suggest a closer association between the mechanisms that regulate release of CRP and SAA, compared to those that regulate Hp production. Thus, lactation is associated with changes in several stress biomarkers. CRP and SAA might be more useful for evaluating animal welfare and for predicting subsequent reproductive performance of female rabbits.

The role of melatonin in the cells of the innate immunity: a review

Melatonin is the major secretory product synthesized and secreted by the pineal gland and shows both a wide distribution within phylogenetically distant organisms from bacteria to humans and a great functional versatility. In recent years, a considerable amount of experimental evidence has accumulated showing a relationship between the nervous, endocrine, and immune systems. The molecular basis of the communication between these systems is the use of a common chemical language. In this framework, currently melatonin is considered one of the members of the neuroendocrine-immunological network. A number of in vivo and in vitro studies have documented that melatonin plays a fundamental role in neuroimmunomodulation. Based on the information published, it is clear that the majority of the present data in the literature relate to lymphocytes; thus, they have been rather thoroughly investigated, and several reviews have been published related to the mechanisms of action and the effects of melatonin on lymphocytes. However, few studies concerning the effects of melatonin on cells belonging to the innate immunity have been reported. Innate immunity provides the early line of defense against microbes and consists of both cellular and biochemical mechanisms. In this review, we have focused on the role of melatonin in the innate immunity. More specifically, we summarize the effects and action mechanisms of melatonin in the different cells that belong to or participate in the innate immunity, such as monocytes-macrophages, dendritic cells, neutrophils, eosinophils, basophils, mast cells, and natural killer cells.

Seasonal variation in months of birth and symptom flares in Korean patients with inflammatory bowel disease

Background/Aims

Seasonal variation may influence the development and exacerbation of inflammatory bowel disease (IBD). However, most epidemiologic studies on this topic have been conducted in Western countries. The purpose of this study was to determine whether birth dates and symptom flares follow a seasonal pattern in Korean patients with IBD.

Methods

Patients with a diagnosis of IBD established between January 2003 and December 2010 were investigated at six university hospitals in Korea. The expected births and flares, with a uniform distribution during the year and considering differences in the number of days in the months of 1 year, were calculated.

Results

A total of 411 patients with ulcerative colitis (UC) and 316 patients with Crohn disease (CD) were included in the study. Birth during the winter period, and especially in January and February, was associated with an increased risk of IBD, especially in UC patients. The symptom flares of CD patients occurred most frequently in the spring, with a nadir in the autumn. However, no disease flare seasonality was noted for UC patients.

Conclusions

Our data suggest that seasonally varying environmental factors during pregnancy and the postpartum period are associated with a susceptibility to IBD later in life and that exacerbations of CD are influenced by seasonal factors.

The concept of the immune-pineal axis tested in patients undergoing an abdominal hysterectomy

OBJECTIVE

Activation of the immune-pineal axis induces a transient reduction in nocturnal melatonin in the plasma during the proinflammatory phase of an innate immune response to allow the proper migration of leukocytes to the lesion site. This transient reduction should be regulated by inflammatory mediators, which are responsible for the fine-tuning of the process. In the present study, we measured the pre- and postoperative serum concentrations of melatonin, tumor necrosis factor (TNF) and cortisol in women who underwent an elective hysterectomy and correlated the variation in melatonin with postoperative pain.

METHODS

We evaluated 12 women who had an abdominal hysterectomy. Blood was collected at 10.00 and 22.00 h 1 week and 1 day before the surgery, on the 1st and 2nd days after the surgery and at 22.00 h on the day of the surgery.

RESULTS

On the night after the surgery, there was no melatonin detected at 22.00 h. High TNF levels were accompanied by a lower nocturnal melatonin output, higher postoperative pain according to a visual analog scale and the request of higher doses of analgesics. In addition, low cortisol levels were accompanied by a lower nocturnal melatonin output.

CONCLUSION

Our results confirm that the same antagonistic pattern between TNF and glucocorticoids observed in cultured pineal glands also occurs in humans. This integrative pattern suggests that the cross talk between the immune and endocrine system orchestrates longitudinal changes in pineal activity, reinforcing the hypothesis of an immune-pineal axis.

Light interference as a possible stressor altering HSP70 and its gene expression levels in brain and hepatic tissues of golden spiny mice

Light at night and light interference (LI) disrupt the natural light:dark cycle, causing alterations at physiological and molecular levels, partly by suppressing melatonin (MLT) secretion at night. Heat shock proteins (HSPs) can be activated in response to environmental changes. We assessed changes in gene expression and protein level of HSP70 in brain and hepatic tissues of golden spiny mice (Acomys russatus) acclimated to LI for two (SLI), seven (MLI) and 21 nights (LLI). The effect of MLT treatment on LI-mice was also assessed. HSP70 levels increased in brain and hepatic tissues after SLI, whereas after MLI and LLI, HSP70 decreased to control levels. Changes in HSP70 levels as a response to MLT occurred after SLI only in hepatic tissue. However, hsp70 expression following SLI increased in brain tissue, but not in hepatic tissue. MLT treatment and SLI caused a decrease in hsp70 levels in brain tissue and an increase in hsp70 in hepatic tissue. SLI acclimation elicited a stress response in A. russatus, as expressed by increased HSP70 levels and gene expression. Longer acclimation decreases protein and gene expression to their control levels. We conclude that for brain and hepatic tissues of A. russatus, LI is a short-term stressor. Our results also revealed that A. russatus can acclimate to LI, possibly because of its circadian system plasticity, which allows it to behave both as a nocturnal and as a diurnal rodent. To the best of our knowledge, this is the first study showing the effect of LI as a stressor at the cellular level, by activating HSP70.

The effect of season on inflammatory response in captive baboons

INTRODUCTION

Highly seasonal animals demonstrate predictable changes in immune function that coincide with changes in photoperiod. Little is known about the effect of season on immune response in baboons. The objective of this study was to determine the effect of season on inflammatory response in baboons.

MATERIALS AND METHODS

Peripheral blood mononuclear cell cytokine response following immune stimulation and serum markers of inflammation were assessed during each season in two groups of young male baboons: one housed under natural light and one in a controlled environment of 12 hours light:12 hours dark.

RESULTS

A seasonal immune rhythm was evident in both groups, with a greater TNF-α and IL-6 response to stimulation and serum CRP concentration in June and September compared with December.

CONCLUSIONS

Season is an important experimental confounder, and therefore, time of year should be controlled when designing studies and analyzing data from immune studies in baboons.

Light and the outcome of the critically ill: an observational cohort study

Introduction

Light before and during acute illness has been associated with both benefit and harm in animal models and small human studies. Our objective was to determine the associations of light duration (photoperiod) and intensity (insolation) before and during critical illness with hospital mortality in ICU patients. Based on the 'winter immunoenhancement' theory, we tested the hypothesis that a shorter photoperiod before critical illness is associated with improved survival.

Methods

We analyzed data from 11,439 patients admitted to 8 ICUs at the University of Pittsburgh Medical Center between June 30, 1999 and July 31, 2004. Daily photoperiod and insolation prior to and after ICU admission were estimated for each patient by using data provided by the United States Naval Observatory and National Aeronautics and Space Administration and direct measurement of light gradient from outside to bedside for each ICU room. Our primary outcome was hospital mortality. The association between light and risk of death was analyzed using multivariate analyses, adjusting for potential confounders, including severity of illness, case mix, and ICU type.

Results

The cohort had an average APACHE III of 52.9 and a hospital mortality of 10.7%. In total, 128 ICU beds were analyzed; 108 (84%) had windows. Pre-illness photoperiod ranged from 259 to 421 hours in the prior month. A shorter photoperiod was associated with a reduced risk of death: for each 1-hour decrease, the adjusted OR was 0.997 (0.994 to 0.999, p = 0.03). In the ICU, there was near complete (99.6%) degradation of natural light from outside to the ICU bed. Thus, light exposure once in the ICU approached zero; the 24-hour insolation was 0.005 ± 0.003 kWh/m² with little diurnal variation. There was no association between ICU photoperiod or insolation and mortality.

Conclusions

Consistent with the winter immunoenhancement theory, a shorter photoperiod in the month before critical illness is associated with a reduced risk of death. Once in the ICU, patients are exposed to near negligible natural light despite the presence of windows. Further studies are warranted to determine the underlying mechanisms and whether manipulating light exposure, before or during ICU admission, can enhance survival.

Seasonal changes in activities of human neutrophils in vitro

Objective and design

We present a retrospective analysis of previously collected blood samples to determine whether the immune response of neutrophils depends on the season i.e., short versus long days, in which blood samples were collected.

Methods

The bactericidal activity and adhesive capacity of neutrophils, the production of reactive oxygen species (ROS), and CD11b/CD18 molecule expression level were investigated. The investigated neutrophils were divided into two groups based on the time of blood collection: the winter season with short days and the summer season with long days.

Results

We found seasonal variation in measurements of all the analyzed functional responses of neutrophils to stimuli. The strongest adhesion, as well as maximum values of ROS production, was presented by neutrophils isolated from the summer group. The highest bactericidal activity of neutrophils was also observed in blood donors from summer group.

Conclusions

The magnitude of the immune functional activity of neutrophils varies with the season of the year and is decreased in winter.

Environmental agents and autoimmune diseases

Autoimmune diseases, which comprise over 80 clinically distinct conditions, are characterized by the presence of autoantibodies or autoreactive T cells directed against self structures (autoantigens). While these often incurable disorders appear to be rapidly increasing in recognition throughout the world, their rarity, heterogeneity and complex etiologies have limited our understanding of their pathogeneses. The precise mechanisms for the development of autoimmune diseases are not known, however, evidence from many complementary lines of investigation suggests that autoimmune diseases result from the interactions of both environmental and genetic risk factors. While considerable progress has been made in understanding multiple genetic risk factors for many autoimmune diseases, relatively little information is now available regarding the role of the environment in the development of these illnesses. This chapter examines the limited but growing evidence for the role of the environment in the development and progression of autoimmune diseases, the specific exposures that have been suspected of being involved, the possible mechanisms by which these agents may induce and sustain autoimmune processes and the approaches needed to better understand these issues in the future. Identifying the necessary and sufficient genetic and environmental risk factors for disease holds the promise of allowing for the prevention of some illnesses through avoidance of environmental risk factors by genetically susceptible individuals or via gene or other therapies to correct the effects of deleterious genetic risk factors in the case of unavoidable environmental agents.

Long-term melatonin administration attenuates low-LET gamma-radiation-induced lymphatic tissue injury during the reproductively active and inactive phases of Indian palm squirrels (Funambulus pennanti)

A comparative analysis of low linear energy transfer (LET) gamma-radiation-induced damage in the lymphatic tissue of a tropical seasonal breeder, Indian palm squirrel (Funambulus pennanti), during its reproductively active phase (RAP) and inactive phase (RIP) was performed with simultaneous investigation of the effects of long-term melatonin pre-treatment (100 microg/100 g body weight). A total of 120 squirrels (60 during RAP and 60 during RIP) were divided into 12 groups and sacrificed at 4, 24, 48, 72 and 168 h following 5 Gy gamma-radiation exposure; control groups were excluded from exposure. Total leukocyte count and absolute lymphocyte count (ALC) and melatonin only of peripheral blood, stimulation index, thiobarbituric-acid-reactive substances (TBARS) level, superoxide dismutase (SOD) activity, and the apoptotic index of spleen as analysed by terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick-end labelling (TUNEL) noted at observed time-points were significantly reduced in melatonin pre-treated groups during RAP and RIP. Long-term melatonin pre-treatment mitigated radiation-induced alterations more prominently during RIP, as assessed by ALC, TBARS, SOD, TUNEL and caspase-3 activity, at some time-points. Our results demonstrate an inhibitory role of melatonin on caspase-3 activity in splenocytes during RAP and RIP following gamma-radiation-induced caspase-mediated apoptosis. Hence, we propose that melatonin might preserve the viability of immune cells of a seasonal breeder against background radiation, which is constantly present in the environment.

Association of disease-predisposition polymorphisms of the melatonin receptors and sunshine duration in the global human populations

Melatonin is predominantly involved in signaling circadian and seasonal rhythms, and its synthesis is regulated by the environmental light/dark cycle. The selection pressure by geographically different environmental light/dark cycles, which is predominantly determined by sunshine duration, on the global distribution of genetic polymorphisms in the melatonin pathway is not well understood. Recent genetic association studies identified various disease-predisposition polymorphisms in this pathway. We investigated the correlations between the prevalence of these clinically important single nucleotide polymorphisms (SNPs) and sunshine duration among worldwide human populations from twelve regions in the CEPH-HGDP database rs4753426, a recently reported predisposition SNP for type 2 diabetes in the promoter of the MT(2) melatonin receptor gene (MTNR1B), which was not included in the CEPH-HGDP genotyping array, was additionally genotyped. This SNP showed a marginally significant correlation in 760 CEPH-HGDP DNA samples (r = -0.5346, P = 0.0733), and it showed the most prominent association among the candidate melatonin pathway SNPs examined. To control for population structure, which may lead to a false positive correlation, we genotyped this SNP in a replication set of 1792 subjects from China. The correlation was confirmed among Chinese populations (r = -0.8694, P = 0.0002), and was also statistically significant after correction of other climatic and geographical covariants in multiple regression analysis (beta = -0.907, P = 1.94 x 10(-5)). Taken together, it suggests that the human melatonin signaling pathway, particularly MT(2) melatonin receptor may have undergone a selective pressure in response to global variation in sunshine duration.

The changing biological roles of melatonin during evolution: from an antioxidant to signals of darkness, sexual selection and fitness

Melatonin is a molecule present in a multitude of taxa and may be ubiquitous in organisms. It has been found in bacteria, unicellular eukaryotes, macroalgae, fungi, plants and animals. A primary biological function of melatonin in primitive unicellular organisms is in antioxidant defence to protect against toxic free radical damage. During evolution, melatonin has been adopted by multicellular organisms to perform many other biological functions. These functions likely include the chemical expression of darkness in vertebrates, environmental tolerance in fungi and plants, sexual signaling in birds and fish, seasonal reproductive regulation in photoperiodic mammals, and immunomodulation and anti-inflammatory activity in all vertebrates tested. Moreover, its waning production during aging may indicate senescence in terms of a bio-clock in many organisms. Conversely, high melatonin levels can serve as a signal of vitality and health. The multiple biological functions of melatonin can partially be attributed to its unconventional metabolism which is comprised of multi-enzymatic, pseudo-enzymatic and non-enzymatic pathways. As a result, several bioactive metabolites of melatonin are formed during its metabolism and some of the presumed biological functions of melatonin reported to date may, in fact, be mediated by these metabolites. The changing biological roles of melatonin seem to have evolved from its primary function as an antioxidant.

Predictors of death after severe Streptococcus pyogenes infection

An evaluation of the relative importance of host and pathogen factors on the survival rate of patients with invasive Streptococcus pyogenes infection found a number of clinical and demographic factors to be associated with risk for death. Some evidence suggested a seasonal pattern to patient survival rate.

Comparative effect of melatonin and vitamin E on phenylhydrazine-induced toxicity in the spleen of Funambulus pennanti

Phenylhydrazine (PHZ) oxidation resulting in free iron release followed by free radical generation has increased frequency of cancer. This study aims towards the dose-dependent response of PHZ and the role of melatonin in comparison with vitamin E following PHZ-induced toxicity within the lymphoid tissue (spleen) of Indian tropical seasonal breeder, Funambulus pennanti, during reproductively active phase. An increase in the damages in terms of lipid peroxidation (LPO), apoptosis percentage, and splenomegaly was observed following different doses of PHZ treatment, i.e., 0.025, 0.5, and 1 mg/100 g body weight (b.wt.), where dose of 1 mg/100 g b.wt. showed more significant damages. Both melatonin (0.5 mg/100 g b.wt.) and vitamin E (1 mg/100 g b.wt.) administration ameliorated oxidative damages of 1 mg/100 g b.wt. PHZ-treated group. Melatonin altered PHZ-induced responses significantly to a greater degree than vitamin E as evidenced by LPO status, SOD activity, and ABTS radical cation scavenging activity of antioxidants. Thus, melatonin might be able to restrict carcinogenic property of PHZ-induced oxidative stress by protecting macromolecules of the cell from harmful effects of PHZ and instead preserving cell viability.

Effect of exogenous melatonin on X-ray induced cellular toxicity in lymphatic tissue of Indian tropical male squirrel, Funambulus pennanti

PURPOSE

The radioprotective ability of melatonin was investigated in the Indian tropical rodent, Funambulus pennanti during its reproductively inactive phase (RIP) when peripheral melatonin is high and the animal is under the influence of environmental stresses.

MATERIALS AND METHODS

Fifty male squirrels were divided into two sets of 25 each; with set 1 receiving 0.9% saline and set 2 receiving 25 mug melatonin/100 g body weight/day for four weeks during evening hours. Five saline-treated and five-melatonin treated squirrels were sacrificed at times of 4, 24, 48 and 72 hours following 2.06 Gy X-ray radiation. Remaining squirrels that were not exposed to X-ray were used as control and melatonin treated, respectively. Total leukocyte count (TLC) and lymphocyte count (LC) in peripheral blood and lipid peroxidation (LPO) status, superoxide dismutase (SOD) activity, total antioxidant status (TAS), apoptotic percentage on the basis of morphological changes and DNA fragmentation and caspase-3 activity were measured in the spleens of squirrels.

RESULTS

Peripheral blood and spleens with higher intrinsic levels of environmental and X-radiation induced free radical generation had inhibited TLC, LC, SOD activity and TAS and increased LPO and apoptosis. Melatonin pre-treatment significantly reduced and altered the changes brought on by X-radiation.

CONCLUSION

Exogenous melatonin with its anti-apoptotic and antioxidant properties additively increased the immunity of the squirrels, by protecting their hematopoietic system and lymphoid organs against X-ray radiation induced cellular toxicity.

Studies of chinese original quiet sitting by using functional magnetic resonance imaging

Since different meditations may activate different regions in brain, we can use functional magnetic resonance imaging (fMRI) to investigate it. Chinese original quiet sitting is mainly one kind of traditional Chinese meditation. It contains two different parts: a short period of keeping phrase and intake spiritual energy, and a long period of relaxation with no further action. In this paper, both those two stages were studied by fMRI. We performed two different paradigms and found the accurate positions in the brain. The pineal gland and the hypothalamus showed positive activation during the first and second stages of this meditation. The BOLD (Blood Oxygenation Level Dependent) signal changes had also been found.

The immune-pineal axis: a shuttle between endocrine and paracrine melatonin sources

The time course of the innate immunological response involves a pro-inflammatory phase followed by an anti-inflammatory phase. Pro-inflammatory responses serve as a defense against several stressor conditions, and sequential processes that shut down these responses are necessary to avoid exacerbation or the development of chronic diseases. In the present review, we put together recent data that show that the pineal gland is a player in bidirectional control of the inflammatory response. Healthy organisms stay in standby mode, ready to react. The nocturnal melatonin surge impairs the rolling and adherence of leukocytes to endothelial layers, limiting cell migration, and stimulates nocturnal production of IL-2 by T helper lymphocytes, exerting an immunostimulatory effect. Otherwise, the release of TNF-alpha from activated macrophages suppresses the nocturnal melatonin surge, allowing a full cell migration and inhibiting IL-2 production. In sequence, activated mononuclear and polymorphonuclear cells produce melatonin in a paracrine manner at the site of injury, which scavenges free radicals and collaborates to resolve the inflammatory response. The sequential diminution of TNF-alpha production is followed by the recovery of the nocturnal melatonin surge and IL-2 production. In summary, the immune-pineal axis, implicated in the sequential involvement of the melatonin produced by the pineal gland and immune-competent cells, is an integral participant of the innate immune response.

Melatonin and human rhythms

Melatonin signals time of day and time of year in mammals by virtue of its pattern of secretion, which defines 'biological night.' It is supremely important for research on the physiology and pathology of the human biological clock. Light suppresses melatonin secretion at night using pathways involved in circadian photoreception. The melatonin rhythm (as evidenced by its profile in plasma, saliva, or its major metabolite, 6-sulphatoxymelatonin [aMT6s] in urine) is the best peripheral index of the timing of the human circadian pacemaker. Light suppression and phase-shifting of the melatonin 24 h profile enables the characterization of human circadian photoreception, and circulating concentrations of the hormone are used to investigate the general properties of the human circadian system in health and disease. Suppression of melatonin by light at night has been invoked as a possible influence on major disease risk as there is increasing evidence for its oncostatic effects. Exogenous melatonin acts as a 'chronobiotic.' Acutely, it increases sleep propensity during 'biological day.' These properties have led to successful treatments for serveal circadian rhythm disorders. Endogenous melatonin acts to reinforce the functioning of the human circadian system, probably in many ways. The future holds much promise for melatonin as a research tool and as a therapy for various conditions.

Functional MT1 and MT2 melatonin receptors in mammals

Melatonin, dubbed the hormone of darkness, is known to regulate a wide variety of physiological processes in mammals. This review describes well-defined functional responses mediated through activation of high-affinity MT1 and MT2 G protein-coupled receptors viewed as potential targets for drug discovery. MT1 melatonin receptors modulate neuronal firing, arterial vasocon-striction, cell proliferation in cancer cells, and reproductive and metabolic functions. Activation of MT2 melatonin receptors phase shift circadian rhythms of neuronal firing in the suprachiasmatic nucleus, inhibit dopamine release in retina, induce vasodilation and inhibition of leukocyte rolling in arterial beds, and enhance immune responses. The melatonin-mediated responses elicited by activation of MT1 and MT2 native melatonin receptors are dependent on circadian time, duration and mode of exposure to endogenous or exogenous melatonin, and functional receptor sensitivity. Together, these studies underscore the importance of carefully linking each melatonin receptor type to specific functional responses in target tissues to facilitate the design and development of novel therapeutic agent.

Melatonin, immune function and aging

Aging is associated with a decline in immune function (immunosenescence), a situation known to correlate with increased incidence of cancer, infectious and degenerative diseases. Innate, cellular and humoral immunity all exhibit increased deterioration with age. A decrease in functional competence of individual natural killer (NK) cells is found with advancing age. Macrophages and granulocytes show functional decline in aging as evidenced by their diminished phagocytic activity and impairment of superoxide generation. There is also marked shift in cytokine profile as age advances, e.g., CD3+ and CD4+ cells decline in number whereas CD8+ cells increase in elderly individuals. A decline in organ specific antibodies occurs causing reduced humoral responsiveness. Circulating melatonin decreases with age and in recent years much interest has been focused on its immunomodulatory effect. Melatonin stimulates the production of progenitor cells for granulocytes-macrophages. It also stimulates the production of NK cells and CD4+ cells and inhibits CD8+ cells. The production and release of various cytokines from NK cells and T-helper lymphocytes also are enhanced by melatonin. Melatonin presumably regulates immune function by acting on the immune-opioid network, by affecting G protein-cAMP signal pathway and by regulating intracellular glutathione levels. Melatonin has the potential therapeutic value to enhance immune function in aged individuals and in patients in an immunocompromised state.

Residential environmental exposures and other characteristics associated with detectable PAH-DNA adducts in peripheral mononuclear cells in a population-based sample of adult females

The detection of polycyclic aromatic hydrocarbon (PAH)-DNA adducts in human lymphocytes may be useful as a surrogate end point for individual cancer risk prediction. In this study, we examined the relationship between environmental sources of residential PAH, as well as other potential factors that may confound their association with cancer risk, and the detection of PAH-DNA adducts in a large population-based sample of adult women. Adult female residents of Long Island, New York, aged at least 20 years were identified from the general population between August 1996 and July 1997. Among 1556 women who completed a structured questionnaire, 941 donated sufficient blood (25+ ml) to allow use of a competitive ELISA for measurement of PAH-DNA adducts in peripheral blood mononuclear cells. Ambient PAH exposure at the current residence was estimated using geographic modeling (n=796). Environmental home samples of dust (n=356) and soil (n=360) were collected on a random subset of long-term residents (15+ years). Multivariable regression was conducted to obtain the best-fitting predictive models. Three separate models were constructed based on data from : (A) the questionnaire, including a dietary history; (B) environmental home samples; and (C) geographic modeling. Women who donated blood in summer and fall had increased odds of detectable PAH-DNA adducts (OR=2.65, 95% confidence interval (CI)=1.69, 4.17; OR=1.59, 95% CI=1.08, 2.32, respectively), as did current and past smokers (OR=1.50, 95% CI=1.00, 2.24; OR=1.46, 95% CI=1.05, 2.02, respectively). There were inconsistent associations between detectable PAH-DNA adducts and other known sources of residential PAH, such as grilled and smoked foods, or a summary measure of total dietary benzo-[a]-pyrene (BaP) intake during the year prior to the interview. Detectable PAH-DNA adducts were inversely associated with increased BaP levels in dust in the home, but positively associated with BaP levels in soil outside of the home, although CIs were wide. Ambient BaP estimates from the geographic model were not associated with detectable PAH-DNA adducts. These data suggest that PAH-DNA adducts detected in a population-based sample of adult women with ambient exposure levels reflect some key residential PAH exposure sources assessed in this study, such as cigarette smoking.

Latitude affects photoperiod-induced changes in immune response in meadow voles (Microtus pennsylvanicus)

Animals use day length (photoperiod) to time seasonal adaptations to annual changes in their environment. Reproductive adjustments in deer mice (Peromyscus maniculatus (Wagner, 1845)) from high latitudes are more extensive in response to short days than in deer mice from low latitudes. These adjustments may permit individuals to survive the severe seasonal changes (e.g., temperature and food abundance) in high-latitude environments. Immune function is also affected by photoperiod. Short days were predicted to result in elevated immune and reproductive responses in meadow voles (Microtus pennsylvanicus (Ord, 1815)) from the Northwest Territories (NWT), Canada (~62°N), compared with voles from Ohio (OH), USA (~39°N). Male voles from both latitudes were maintained in long or short days for 10 weeks prior to a delayed-type hypersensitivity (DTH) immune challenge. Both populations displayed similar testicular regression and reduction of testosterone concentrations in short days. DTH immune responses, however, diverged between the two populations. DTH immune responses were enhanced in long-day NWT voles and short-day OH voles, but decreased in short-day NWT voles and long-day OH voles. Total and free corticosterone concentrations did not explain the latitudinal differences in immune responses. These results suggest that photoperiod affects reproductive and immune systems differently and that immune responses may reflect other environmental factors.

Seasonality of pineal gland activity and immune functions in chickens

The immunomodulatory action of melatonin in different animal species is already well known, although the mechanism(s) by which the indoleamine influences the immune system have yet to be fully elucidated. Previously, we have shown both anti-inflammatory and opioid-mediated influence of exogenous melatonin on thioglycollate-induced peritonitis in young chickens. In the present study, the kinetics of peritonitis and splenocyte proliferation were compared in chickens reared in both seasons under the same L:D 12:12 conditions. These two aspects of the immune response were correlated with the diurnal rhythm of pineal gland function, measured by the activity of N-acetyltransferase (NAT), a key enzyme in melatonin biosynthesis. The results revealed seasonal changes in the circadian rhythm of pineal NAT activity occurring in parallel to the natural local geophysical seasons. These changes appeared to influence the development of peritonitis and splenocyte responsiveness to mitogenic stimulation in vitro. Moreover, the existence of bidirectional communication between the pineal gland and the activated immune system was supported by the decreased activity of pineal NAT in chickens with peritonitis compared with control birds.

Update on the biology of seasonal affective disorder

The etiology and pathophysiology of seasonal affective disorder (SAD) has been linked to the seasons and to light since its first conceptualization. Aspects of SAD that make it particularly amenable to biological investigation include the predictable recurrent episodes, the rapid response to a nonpharmacologic treatment, the specific neurovegetative features, and the availability of rich animal models of seasonality. This paper reviews new findings for the major biological hypotheses for SAD, focusing on circadian rhythms, neurotransmitters, and molecular genetics. Integrative issues and future directions for the study of SAD, including the heuristic value of a dual-vulnerability hypothesis that conceptualizes seasonality as a dimensional construct and the importance of studying endophenotypes, will be discussed.

Circadian melatonin and cortisol levels in rheumatoid arthritis patients in winter time: a north and south Europe comparison

BACKGROUND

Altered functioning of the hypothalamic-pituitary-adrenal axis and altered melatonin production might modulate the circadian symptoms in patients with rheumatoid arthritis.

OBJECTIVE

To investigate the influence of different winter photoperiods on the circadian rhythms of serum melatonin, cortisol, tumour necrosis factor alpha (TNFalpha), and interleukin 6 (IL6) in patients with rheumatoid arthritis from a north Europe country (Estonia) and a south Europe country (Italy).

METHODS

The patients from Estonia (n = 19) and Italy (n = 7) had similar disease severity and duration and were compared with healthy age and sex matched controls in the two countries. Blood samples were collected during the period January to February at 8 pm, 10 pm, midnight, 2 am, 4 am, 6 am, 8 am, and 3 pm. Melatonin was measured by radioimmunoassay using (125)I-melatonin. Serum cortisol, TNFalpha, and IL6 cytokines were assayed by standard methods.

RESULTS

Higher circadian melatonin concentrations from 10 pm and an earlier peak were observed in Estonian patients than in their age and sex matched controls (p<0.01). Starting from midnight, melatonin concentrations were significantly higher in the Estonian patients than in the Italian patients. No significant differences were observed for serum cortisol. Serum TNFalpha was higher (p<0.05) in Estonian patients than in their controls and was correlated with the melatonin levels.

CONCLUSIONS

In a north European country (Estonia), the circadian rhythm of serum concentrations of melatonin and TNFalpha in patients with rheumatoid arthritis were significantly higher than in matched controls or in rheumatoid patients from a south Europe country (Italy).

Human lymphocyte-synthesized melatonin is involved in the regulation of the interleukin-2/interleukin-2 receptor system

Since melatonin was first isolated in 1958 up to the last few years, this substance was considered a hormone exclusive to the pineal gland. Although melatonin has lately been identified in a large number of extrapineal sites, its potential biological actions have not yet been studied. This paper shows that human lymphocyte-synthesized melatonin plays a crucial role modulating IL-2/IL-2 receptor system because when blocking melatonin biosynthesis by the tryptophan hydroxylase inhibitor, parachlorophenylalanine, both IL-2 and IL-2 receptor levels fell, restoring them by adding exogenous melatonin. Moreover, we demonstrated that this endogenous melatonin interfered with the exogenous melatonin effect on IL-2 production. Melatonin exerted these effects by a receptor-mediated action mechanism because both IL-2 and IL-2 receptor expressions significantly decreased when lymphocytes were incubated in the presence of the specific membrane and/or nuclear melatonin receptor antagonists, luzindole, and/or CGP 55644, respectively. Finally, we made the real significance of the membrane melatonin receptors in this process clear, so prostaglandin E(2)-induced inhibition on IL-2 production increased when we blocked the membrane receptors using luzindole. In conclusion, these data show that endogenous melatonin is an essential part for an accurate response of human lymphocytes through the modulation of IL-2/IL-2 receptor system.

Evidence of melatonin synthesis by human lymphocytes and its physiological significance: possible role as intracrine, autocrine, and/or paracrine substance

It has been historically assumed that the pineal gland is the major source of melatonin (N-acetyl-5-methoxytryptamine) in vertebrates. Melatonin plays a central role in fine-tuning circadian rhythms in vertebrate physiology. In addition, melatonin shows a remarkable functional versatility exhibiting antioxidant, oncostatic, antiaging, and immunomodulatory properties. Melatonin has been identified in a wide range of organisms from bacteria to human beings. Its biosynthesis from tryptophan involves four well-defined intracellular steps catalyzed by tryptophan hydroxylase, aromatic amino acid decarboxylase, serotonin-N-acetyltransferase, and hydroxyindole-O-methyltransferase. Here, for the first time, we document that both resting and phytohemagglutinin-stimulated human lymphocytes synthesize and release large amounts of melatonin, with the melatonin concentration in the medium increasing up to five times the nocturnal physiological levels in human serum. Moreover, we show that the necessary machinery to synthesize melatonin is present in human lymphocytes. Furthermore, melatonin released to the culture medium is synthesized in the cells, because blocking the enzymes required for its biosynthesis or inhibiting protein synthesis in general produced a significant reduction in melatonin release. Moreover, this inhibition caused a decrease in IL-2 production, which was restored by adding exogenous melatonin. These findings indicate that in addition to pineal gland, human lymphoid cells are an important physiological source of melatonin and that this melatonin could be involved in the regulation of the human immune system, possibly by acting as an intracrine, autocrine, and/or paracrine substance.

Does neuroimmune dysfunction mediate seasonal mood changes in winter depression?

BACKGROUND

Animal studies have demonstrated seasonal changes in immune function mediated by nocturnal melatonin duration as a biological signal for photoperiod. Recent research has highlighted the potential role of neuroimmune dysfunction in depressive disorders. The etiology of winter depression (seasonal affective disorder, or SAD) is not known, but a number of studies have provided support for both photoperiod and neurotransmitter hypotheses.

HYPOTHESIS

A new hypothesis is presented that links the SAD data on melatonin, photoperiod, and neurotransmitters by proposing that seasonal increases in proinflammatory cytokines are critical in the pathophysiology of winter SAD.

TESTING THE HYPOTHESIS

In SAD patients, but not healthy subjects: proinflammatory cytokines will be increased and the Th1/Th2 balance will be shifted to the left in winter compared to summer; neuroimmune function will be correlated with nocturnal melatonin duration in SAD patients; and light treatment will correct neuroimmune dysfunction.

IMPLICATIONS OF THE HYPOTHESIS

Diagnostic tests for SAD may be developed using cytokine assays; neuroimmune dysfunction may be predictors of response to treatments; new treatments for SAD (immune or anti-inflammatory treatment) may be developed.

Melatonin counteracts the inhibitory effect of PGE2 on IL-2 production in human lymphocytes via its mt1 membrane receptor

It is well known that melatonin plays a fundamental role in human neuro-immunomodulation. Thus, melatonin regulates the production of a large number of cytokines, including interleukin-2 (IL-2) in the human system. Both membrane and nuclear receptors for melatonin are present in lymphoid cells. However, most of these effects have been shown to be mediated by the putative nuclear receptor for the neurohormone. In this paper, we show that prostaglandin E2 (PGE2), a potent inflammatory mediator, inhibits IL-2 production in human lymphocytes by a cyclic AMP (cAMP)-dependent mechanism. In this model, melatonin counteracts the effects of PGE2 on IL-2 and cAMP production. We propose that the effect of melatonin is mediated by a membrane receptor, since similar results were obtained when cells were cultured in the presence of S 20098, a specific melatonin membrane receptor agonist. No effect was observed by using CGP 52608, a nuclear receptor agonist. Moreover, when cells were stimulated with phorbol myristate acetate (PMA), which has been shown to inhibit mt1 melatonin membrane receptor expression, the neurohormone failed to counteract the effect of PGE2. Therefore, we postulate, for the first time, a physiological role of the mt1 melatonin membrane receptor in the human immune system.

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.