Melanomacrophage aggregations and their age relationships in the yellow mud turtle, Kinosternon flavescens (Kinosternidae)

The melano-macrophage: The black leukocyte of fish immunity

Melanin and the process of melanin synthesis or melanogenesis have central roles in the immune system of insects, and production of melanin-synthesizing enzymes from their haemocytes may be induced following activation through danger signals. Melanin-containing macrophage-like cells have been extensively studied in amphibians and they are also present in reptiles. In fish, melano-macrophages are especially recognized with respect to melano-macrophage centres (MMCs), hypothesized to be analogues of germinal centres in secondary lymphoid organs of mammals and some birds. Melano-macrophages are in addition present in several inflammatory conditions, in particular melanised focal changes, or black spots, in the musculature of farmed Atlantic salmon, Salmo salar. Melanins are complex compounds that may be divided into different forms which all have the ability to absorb and scatter light. Other functions include the quenching of free radicals and a direct effect on the immune system. According to the common view held in the pigment cell community, vertebrate melanin synthesis with melanosome formation may only occur in cells of ectodermal origin. However, abundant information suggests that also myeloid cells of ectothermic vertebrates may be classified as melanocytes. Here, we discuss these opposing views and review relevant literature. Finally, we review the current status on the research concerning melanised focal muscle changes that represent the most severe quality problem in Norwegian salmon production, but also other diseases where melano-macrophages play important roles.

Ultrastructural evidence of four types of lipofuscins in the melanomacrophagic centers in hepatocytes of zebrafish (Denio rerio)

Melanomacrophagic centers (MMCs) were studied in the hepatocytes of zebrafish using transmission electron microscope (TEM). The MMCs with irregular or amoeboid nucleus were located in the hepatocytes adjacent to the bile canaliculi. Several engulfed structures were present in the cytoplasm of MMCs. The most frequent observation was the presence of mitochondria, ranging in size from small to giant, with distorted shape and inconspicuous cristae. Occasionally the fragments of erythrocytes were found. The rough endoplasmic reticulum (rER) showed whirling around the mitochondria and lipid droplets, forming membrane-like structures. The damaged mitochondria were invaded by the lysosomes, and this was covered by a membrane led to the formation of lipofuscin. Four different types of lipofuscins were observed; namely, (1) granular with/without vacuoles of high electron-density, (2) homogenous surrounded by indistinct limiting membrane, (3) lamellated structures similar to inner matrix and cristae of mitochondria, and, (4) compound structure made by the combinations of first 3 types, (granular and homogenous, granular and lamellated, homogenous and lamellated). The present evidence suggests that MMCs in the hepatocytes of zebrafish perform continuous functions of removal of the damaged cellular organelles. The lipofuscin formation work in coordination with the cellular players of immune system and remove pathogens and maintain the internal homeostasis of cells.

Immunoglobulin VDJ repertoires reveal hallmarks of germinal centers in unique cell clusters isolated from zebrafish (Danio rerio) lymphoid tissues

DNA mutagenesis during antibody affinity maturation has potentially oncogenic or autoimmune outcomes if not tightly controlled as it is in mammalian germinal centers. Cold blooded vertebrates lack germinal centers, yet have a functional Ig gene mutator enzyme, Aicda. In fish there are clusters of Aicda⁺ cells encircled by pigmented 'melano-macrophages' and we test the hypothesis that these clusters are functionally analogous to germinal centers. Sequenced IgH VDJ repertoire libraries from individual isolated clusters showed evidence of B-cell clonal expansion and VDJ somatic hypermutation. Construction of Ig clonal lineage trees revealed that unlike surrounding lymphoid tissue, each cluster is dominated by a few B-cell VDJ clonotypes having hundreds of mutated variants. Recruitment of B-cells to the clusters appears to be ongoing, as there are additional Ig clones having smaller lineages. Finally, we show evidence for positive selection for replacement mutations in regions encoding the antigen contact loops, but not in the framework regions, consistent with functional antibody modification. Melano-macrophages appear to trap the Ag used for post-mutation B-cell selection, performing a role analogous to the follicular dendritic cells of mammalian germinal centers. These findings provide insights into the evolution of the affinity maturation process, the improvement of fish vaccines and possibly also the workings of atypical ectopic germinal centers generated in several human diseases.

Aggravation of hepatic lipidosis in red-footed tortoise Chelonoidis carbonaria with age is associated with alterations in liver mitochondria

The occurrence of hepatic lipidosis is commonly reported in different reptilian species, especially in animals under captivity. Liver accumulation of fat is associated with disorders, better described in mammals as non-alcoholic fatty liver diseases (NAFLD), ranging from simple steatosis, to non-alcoholic steatohepatitis (NASH), and to more severe lesions of cirrhosis and hepatocellular carcinoma. Mitochondria play a central role in NAFLD pathogenesis, therefore in this study we characterized livers of ad libitum fed captive red-footed tortoise Chelonoidis carbonaria through histological and mitochondrial function evaluations of juvenile and adult individuals. Livers from adult tortoises exhibited higher levels of lipids, melanomacrophages centers and melanin than juveniles. The observed high score levels of histopathological alterations in adult tortoises, such as microvesicular steatosis, inflammation and fibrosis, indicated the progression to a NASH condition. Mitochondrial oxygen consumption at different respiratory states and with different substrates was 30 to 58% lower in adult when compared to juvenile tortoises. Despite citrate synthase activity was also lower in adults, cardiolipin content was similar to juveniles, indicating that mitochondrial mass was unaffected by age. Mitochondrial Ca²⁺ retention capacity was reduced by 70% in adult tortoises. Overall, we found that aggravation of NAFLD in ad libitum fed captive tortoises is associated with compromised mitochondrial function, indicating a critical role of the organelle in liver disease progression in reptiles.

Nonylphenol and cyproterone acetate effects in the liver and gonads of Lithobates catesbeianus (Anura) tadpoles and juveniles

Environmental pollution plays an important role in amphibian population decline. Contamination with endocrine disrupting chemicals (EDCs) is particularly worrying due to their capacity to adversely affect organisms at low doses. We hypothesized that exposure to EDCs such as 4-nonylphenol (NP) and cyproterone acetate (CPA) could trigger responses in the liver and gonads, due to toxic and endocrine disrupting effects. Growth rate may also be impaired by contamination. We investigated sublethal effects of a 28-day exposure to three different concentrations of NP and CPA on liver pigmentation, gonadal morphology, body mass, and length of tadpoles and juveniles Lithobates catesbeianus. Liver pigmentation and the gonadal morphologies of treated tadpoles did not differ from control, but growth rate was impaired by both pollutants. Juveniles treated with 10 μg/L NP and 0.025 and 0.25 ng/L CPA displayed increased liver melanin pigmentation, but gonadal morphologies, sex ratios, and body mass were not affected after treatments. The increase in liver pigmentation may be related to defensive, cytoprotective role of melanomacrophages. The decreased growth rate in tadpoles indicates toxic effects of NP and CPA. Thus, contamination with NP and CPA remains a concern and sublethal effects of different dosages of the compounds on native species should be determined.

Increased melanomacrophage centres in the liver of reproductively dysfunctional female greater amberjack Seriola dumerili (Risso, 1810)

The greater amberjack Seriola dumerili is a new aquaculture fish that may display reproductive dysfunctions. During extensive follicular atresia, which is a common reproductive dysfunction in females during vitellogenesis, part of the reabsorbed yolk returns to the liver to be metabolized and recycled. Melanomacrophage centres (MMCs) are aggregates of macrophage-like cells that play a role in the destruction, detoxification and recycling of endogenous and exogenous materials, and have been associated with systemic stress. Wild and captive-reared greater amberjack were sampled in the Mediterranean Sea during two different phases of the reproductive cycle. The liver of reproductively dysfunctional captive-reared females sampled during the spawning season showed a high density of both MMCs and apoptotic cells. A weak liver anti-cytochrome P450 monooxygenase 1A immunoreactivity was observed, suggesting that the examined fish were not exposed to environmental pollutants. We propose that the observed increase in MMCs and apoptosis in captive-reared fish was related to the hepatic overload associated to the metabolism of yolk proteins reabsorbed during extensive follicular atresia. Since follicular atresia is a frequent physiological and pathological event in teleosts, we suggest that the reproductive state should be always assessed when MMCs are used as markers of exposure to stress or pollutants.

Ultrastructural Evidence of Melanomacrophagic Centers and Lipofuscin in the Liver of Zebrafish (Denio rerio)

Melanomacrophagic centers (MMCs) were studied in the liver of zebrafish using transmission electron microscope (TEM). The MMCs were located in the space of Disse (SD), and their pseudopodia protruded into the lumen of sinusoids. The degree of extension of body structure of MMCs in the SD was determined by the size of the phagocytosed content. An irregular or amoeboid nucleus was present. Vacuoles were occasionally present, both, in endothelium and MMCs. The cytoplasm of MMCs showed several engulfed structures. The most common structure was the presence of mitochondria of small to giant size and distorted shape with inconspicuous cristae. The product of mitochondrial degeneration accompanied by lysosomes contributed to the formation of lipofuscins. Besides, changes were also observed in rough endoplasmic reticulum (rER), the Golgi complex, and lysosomes. Occasionally, small to large fragments of the erythrocytes were found in the cytoplasm of MMCs. The rER encompassed the mitochondria and lipid droplets forming a membrane-like structure. Golgi complex were dilated. Lysosomes fused with such membrane-bound structures contributed to the formation of the lipofuscin. The results provide evidence of the role of liver-resident MMCs of zebrafish in phagocytosis of damaged organelles, clearance of the worn-out erythrocytes, and lipofuscin formation.

Induction of hyperpigmentation and heat shock protein 70 response to the toxicity of methomyl insecticide during the organ development of the Arabian toad, Bufo arabicus (Heyden,1827)

Methomyl (MET) is a carbamate insecticide which is used as a substitute for organophosphorus compounds to protect crops against insects. The present study aims to evaluate the cytoprotection response of pigment cells and heat shock protein 70 (HSP70) after exposure to MET during the tadpole developmental stages of the Arabian toad, Bufo arabicus. Three developmental larval stages of the toad were selected and divided into two groups; Control and MET-exposed (MET-EX) tadpoles (10ppm). MET-EX tadpoles showed an increased number of pigment cells in the liver, kidney, anterior eye chamber, and skin tissues as compared to the control. The glycogen content in the developing liver and muscles (myotomes) of MET-EX tadpoles was decreased as compared to the control. In the MET-EX tadpoles, immunohistochemical staining showed an increase of HSP70 expression in the liver hepatocytes, the nucleated red blood cells (nRBC) in kidney glomeruli, the iridocorneal angle of anterior eye chamber, and the skin as compared to the control. The current study concluded that pigment cells and HSP70 represented a cytoprotecting response against MET insecticide during the organ development of B. arabicas tadpoles. Therefore, MET use should be regularly monitored in the environment to protect animals and human from exposure to this insecticide.

LPS-induced alterations in reproductive organs and liver pigmentation in the toad Rhinella diptycha (Bufonidae)

Anurans can be naturally infected by the bacterium Escherichia coli (Migula, 1895) Castellani and Chalmers, 1919, which contain lipopolysaccharides (LPS) in their external membrane. LPS affects reproductive functions in mammals and extracutaneous pigmentary system of anurans. Besides the functional gonad, bufonid amphibians have an undeveloped female organ (Bidder’s organ), whose function is poorly known. We aimed to investigate the effects of LPS on testis and Bidder’s organ germ cells and on liver pigmentation in the toad Rhinella diptycha (Cope, 1862). Animals were inoculated with 0.1 mL of saline solution (control) or LPS solution (18 mg/kg) and then euthanized after 24 or 48 h. The organs were processed for histology and then evaluated with morphometric analysis. The LPS decreased the area of bundle spermatozoa and increased lumen spermatozoa, while in Bidder’s organ, the number of degenerating oocytes decreased. Liver melanin increased after 24 h and decreased after 48 h. Our results suggest that LPS delays the release of spermatozoa, possibly due to alterations in serum levels of testosterone and (or) gonadotropins, which may also explain fewer degrading cells in Bidder’s organ. Increased melanin in the liver was expected due to the bactericidal role of this pigment. Thus, LPS affected reproductive organs and induced cytoprotective responses in the liver of amphibians.

Liver melanomacrophage centres and CYP1A expression as response biomarkers to environmental pollution in European anchovy (Engraulis encrasicolus) from the western Mediterranean Sea

The goal of the present study was to verify the suitability of using melanomacrophage centres (MMCs) as response biomarkers of marine pollution in European anchovy, which are short-lived, migratory, small pelagic fish. This suitability was verified by analysing the MMC density and cytochrome P450 monooxygenase 1A (CYP1A) expression in livers of anchovies from four areas of southern Italy. Age 2 anchovies sampled from three areas exposed to pollutants of industrial/agricultural origin (Gulf of Gela, Mazara del Vallo and Gulf of Naples) showed liver areas occupied by MMCs and numbers of MMCs that were significantly higher than those in the anchovies from Pozzallo, which is a marine area not subjected to any source of pollution. Anti-CYP1A immunoreactivity was observed in the hepatocytes of all specimens sampled from the Gulf of Gela. These findings suggest the utility of liver MMCs as biomarkers of exposure to pollutants in this small pelagic fish.

Melanomacrophage Centers As a Histological Indicator of Immune Function in Fish and Other Poikilotherms

Melanomacrophage centers (MMCs) are aggregates of highly pigmented phagocytes found primarily in the head kidney and spleen, and occasionally the liver of many vertebrates. Preliminary histological analyses suggested that MMCs are structurally similar to the mammalian germinal center (GC), leading to the hypothesis that the MMC plays a role in the humoral adaptive immune response. For this reason, MMCs are frequently described in the literature as “primitive GCs” or the “evolutionary precursors” to the mammalian GC. However, we argue that this designation may be premature, having been pieced together from mainly descriptive studies in numerous distinct species. This review provides a comprehensive overview of the MMC literature, including a phylogenetic analysis of MMC distribution across vertebrate species. Here, we discuss the current understanding of the MMCs function in immunity and lingering questions. We suggest additional experiments needed to confirm that MMCs serve a GC-like role in fish immunity. Finally, we address the utility of the MMC as a broadly applicable histological indicator of the fish (as well as amphibian and reptilian) immune response in both laboratory and wild populations of both model and non-model vertebrates. We highlight the factors (sex, pollution exposure, stress, stocking density, etc.) that should be considered when using MMCs to study immunity in non-model vertebrates in wild populations.

Flutamide effects on morphology of reproductive organs and liver of Neotropical Anura, Rhinella schneideri

Water contamination is one of the factors influencing the decline of amphibians. Flutamide is an antiandrogenic medicine that occurs as water contaminant. This compound especially affects the reproductive organs, but it can also show hepatotoxic effects. The Bufonidae family has a peculiar organ named Bidder's organ, considered by some authors as a rudimentary ovary, but capable to respond to some external stimuli. This study investigated flutamide effects on testes and Bidder's organ germ cells, liver pigmentation, and sexual hormones levels in Rhinella schneideri males. We randomly divided 15 males in three groups (N=5): two groups were injected with flutamide, at 1 and 5mg/kg, while the control group received only mineral oil, for 7days. After euthanasia, blood samples were collected and the organs were sent to histological routine. In the testes, both treatments caused an increase in spermatogonia and spermatocytes, and a decrease in spermatozoa and locular area. In the Bidder's organ, the final diplotene oocytes increased, but the initial diplotene, degrading and atresic oocytes reduced in both treatments. The lipofuscin in the Bidder's organ was not affected. In the liver, melanin and lipofuscin increased only for the 1mg/kg flutamide treatment. The 5mg/kg treatment did not affect the liver. Serum testosterone and estradiol levels did not vary compared with the control group. This compound has antiandrogenic activity, which can affect the spermatogenetic process. The decrease in degrading and atresic Bidderian oocytes indicated that flutamide could stimulate the organ, retarding the degradation processes. The increase in liver melanin, which has protective role, and lipofuscin, a sign of degradation, indicates that flutamide cause hepatotoxic effects. So we conclude that flutamide negatively affects the testes, especially by reducing the sperm area, and the liver, inducing cell degradation and producing protective responses. Furthermore, the compound encourages lower degradation rates of the Bidder's organ germ cells.

Liver melanomacrophage centres as indicators of Atlantic bluefin tuna, Thunnus thynnus L. well-being

Melanomacrophage centres (MMCs), located in different organs of non-mammalian vertebrates, play a role in the destruction, detoxification or recycling of endogenous and exogenous materials. Cytochrome P450 monoxygenase 1A (CYP1A) is involved in xenobiotics biotransformation, and its liver expression is considered as a biomarker for detecting exposure to environmental pollutants. Atlantic bluefin tuna (ABFT), Thunnus thynnus L., liver samples were collected from: wild animals caught in the eastern Atlantic; juveniles reared in the central Adriatic; juveniles reared in the northern Adriatic; adults reared in the western Mediterranean. The samples were processed for basic histology, histochemistry and for CYP1A immunodetection. An unexpected high density of MMCs, containing ferric iron and lipofuscin-ceroids, was detected in the juveniles sampled in the northern Adriatic Sea. These individuals showed also a strong anti-CYP1A immunopositivity in hepatocytes and in the epithelium of bile ducts. This study supports the utility of MMCs as biomarkers of fish 'health status' and gives concern for a potential contaminant accumulation in ABFT.

Post-mortem investigations on a leatherback turtle Dermochelys coriacea stranded along the Northern Adriatic coastline

Leatherback sea turtles Dermochelys coriacea are regularly reported in the Mediterranean Sea but rarely reach the northern Adriatic Sea. In the summer of 2009, a well-preserved carcass of an adult female of this species was found dead along the coast of Lido di Venezia. A complete necropsy was carried out, along with evaluation of levels of tissue trace elements. The the post-mortem revealed acute severe bacterial gastroenteritis caused by Photobacterium damselae ssp. piscicida, an opportunistic agent that infected an apparently debilitated animal weakened by ingested plastic debris. High levels of heavy metals (Hg, Pb, Cd and As) found in the liver and kidneys might have contributed to the animal's demise. These findings support previous indications that marine debris is one of the major threats to marine animals, particularly for critically endangered species such as the leatherback turtle.

Postmortem diagnostic investigation of disease in free-ranging marine turtle populations: a review of common pathologic findings and protocols

Over the past few decades, there have been increasing numbers of reports of diseases in marine turtles. Furthermore, in recent years, there have been documented instances of apparently new diseases emerging in these species of which the etiology and/or pathogenesis remain unknown. These instances i) raise concern for the survival of marine turtles, and ii) question the health and stability of the benthic marine environments in which turtles live. Knowledge of common disease processes and pathologic changes in lesions, along with a standardized approach to postmortem and sample collection are required to document and understand the host-agent-environment interactions in marine turtle health. This review combines, for the first time, a standardized approach to the postmortem of marine turtles for veterinary clinicians, with a concurrent descriptive review of the gross and microscopic pathologic changes in lesions commonly seen.

Melanocytes in the Testes ofEupemphix nattereri (Anura, Leiuperidae): Histological, Stereological, and Ultrastructural Aspects

Ectothermic vertebrates have a well-developed system of melanin-containing cells, which localize in several organs and tissues and compose an extracutaneous pigmentary system. This research aimed at characterizing histological and ultrastructural patterns of pigmented cells in the testes of the anura Eupemphix nattereri (Steindachner, 1963), including the stereological and quantitative evaluation of this cell type in the gonads. Ten adult males were collected in Nova Itapirema, São Paulo, Brazil, and submitted to morphological studies with light and transmission electron microscopy. The testis presents a great number of large cells with many brown granules and long cytoplasmic processes. The pigmented cells found in the testis are structurally similar to melanocytes, characterized by large amounts of melanosomes. The cells may be in intimate contact with the same cell type, with myoid cells surrounded by a large amount of collagen fibers, Leydig cells, and next to fibroblasts. The distribution and amount of extracutaneous melanocytes is variable when other organs and membranes are analyzed, allowing the establishment of species-specific patterns for the extracutaneous pigmentary system.

Thyroid and hypoxic stress in the newt Triturus carnifex

When specimens of the newt Triturus carnifex, under anaesthesia by submersion in a 0.2% chlorbutol solution for 25 min, are isolated in a respiratory chamber at 18 degrees C containing water with only 1.3 ppm of oxygen, they consume the oxygen completely in about 3 hr, but they can stay alive for many more hours and wake up with no apparent exterior consequences. Hypoxia induces rapid onset of hepatic steatosis and melanosis, as well as a controlled haemolytic process involving a pool of red blood cells of the same order of size as that held as a reserve in the spleen by animals in an aerial habitat. At the origin of the phenomena is an intense response by the hypophysis, histologically detectable 1 hr from the onset of treatment and confirmed 2 hr later by a highly significant increase in the plasma thyroidstimulating hormone (TSH) concentration compared with the controls (41.5 +/- 13.7 microU/L vs. 15.5 +/- 6.2; P < 0.005). The thyroid follicles react by reabsorbing their colloid, but instead of an increase in the plasma free T3 and T4 concentrations, fT3 falls significantly (1.5 +/- 0.3 pg/mL vs., the 2.4 +/- 0.7; P < 0.05), whereas fT4 remains stationary (4.0 +/- 0.5 pg/mL vs. 4.6 +/- 0.8; N.S.). After 6 hr, the plasmatic TSH concentration is still higher than in the controls (27.0 +/- 3.0 microU/L vs. 15.5 +/- 6.2; P < 0.05), whereas fT3 and fT4 remain stable (1.5 +/- 0.3 and 4.4 +/- 0.5 pg/mL, respectively). If T3 or T4 labelled with 125I is administered prior to hypoxia, after 6 hr of treatment the radioactivity is found to be limited exclusively to the liver and kidney; the thyroid, gall bladder and gut result negative, and this does not agree with hypotheses of hormone inactivation by deiodination, sulphation or glucuronidation. This apparently peculiar endocrine path has not been observed in previous studies on hypoxia in vertebrates, because the experiments were always designed to analyse plasma hormone levels after at least 24 hr of hypoxia or during chronic treatments, losing the most interesting phases of the endocrine response. The possibility that the hypoxic newt possesses alternative or complementary metabolic pathways to anaerobic glycolysis to sustain steatogenesis and melanogenesis and maintain the same cardiac activity as the controls is briefly discussed.

Pigmentação testicular em Physalaemus nattereri (Steindachner) (Amphibia, Anura) com observações anatômicas sobre o sistema pigmentar extracutâneo

O presente estudo foi realizado com o intuito de relatar a ocorrência e morfologia de células pigmentares viscerais constituintes do "sistema pigmentar extracutâneo" em Physalaemus nattereri (Steindachner, 1863) (Leptodactylidae). Foram utilizados dez exemplares machos para a análise macroscópica e obtenção de fragmentos testiculares incluídos em resina e corados com H/E. Os anuros, dentre outros animais exotérmicos, possuem células especiais, os melanócitos, que se caracteriza por intensa pigmentação e sintetiza melanina, além de melanomacrófagos, que se caracteriza por atividade fagocítica e muitas vezes apresentam intensa pigmentação. A nomenclatura destas células não é consensual e, por isso, várias denominações são apresentadas, principalmente nos seguintes órgãos: fígado (como sinônimo de células de Kupffer), rins, baço e menos freqüentemente em outras localizações, com os termos - células pigmentares, células pigmentares extracutâneas, macrófagos pigmentados, melanomacrófagos, melanófagos, melanóforos e melanócitos. Para os anuros os estudos são recentes e relatam células pigmentares em poucas espécies. Em Physalaemus nattereri e alguns anuros, os pigmentos melânicos são encontrados, além da cútis, em outros órgãos constituindo um sistema pigmentar extracutâneo, com diferentes ocorrências, tipos e quantidade em distintas espécies. Associados ao aparelho reprodutor de P. nattereri, os melanócitos foram observados nas gônadas, na albugínea e no interstício, especialmente associado com vasos sangüíneos. A notória presença de numerosas células com pigmento distribuídas no testículo confere uma coloração que varia do preto mesclado com branco ao preto intenso. Trata-se de uma rara peculiaridade e não há informações sobre seu significado funcional ou valor biológico.

Function of the hepatic melanogenesis in the newt, Triturus carnifex

Like the majority of lower vertebrates, the newt Triturus carnifex holds varying quantities of melanin and hemosiderin in the Kupffer cells of the liver. Following hypoxic treatment, the amount of these two pigments can increase to such an extent that they can occupy nearly a quarter of the surface of histological sections. A group of six specimens, anesthetised with chlorbutol, were subjected to hypoxic treatment by keeping them in a respiratory chamber containing degassed water under vacuum, with only 1.1 ppm of residual oxygen, until they had consumed the oxygen completely (4 hours, at a temperature of 18 degrees C). Using hematological and histochemical techniques and computerised image analysis, it has been shown that hypoxic animals not only increase the extent of the melanic areas of the liver from about 5-7% to almost 24% compared to control groups kept under two different respiratory conditions (6 anesthetised specimens exposed to the air and 6 submerged in normoxic water), they also went through a remarkable hemolytic process to justify a parallel increase in hemosiderin deposits. Melanin was extracted from the liver by keeping fragments of the organ for one hour at 37 degrees C in an oxidising solution (20 mL of benzyl alcohol, 10 mL of acetone, 5 mL of 10% hydrogen peroxide, and 4 drops of concentrated ammonia solution), then quickly rinsing them in 50% acetone and subsequently letting them stand for 6 hours in 10 mL of distilled water alkalised to pH 12 with a drop of ammonia solution. The extract was then left to sediment at pH 2.5 and the black precipitate washed and dried under vacuum. Elemental and spectrophotometric analyses revealed a significant presence of purines in the melanic pigment. This phenomenon can be explained by the animals' need under hypoxic crisis to rapidly neutralise purines resulting from lysis of the nucleated red blood cells by introducing them into an inert molecular complex. A partial model of structure is proposed here. Synthesis of the mixed polymer is possible through the well-known capacity of ferrous iron to activate tyrosinase (the enzyme responsible for melanogenesis) even in the absence of DOPA.

CHARACTERIZATION OF TESTUDINE MELANOMACROPHAGE LINEAR, MEMBRANE EXTENSION PROCESSES—CABLEPODIA—BY PHASE AND ATOMIC FORCE MICROSCOPY

Melanomacrophages (MMs) are a component of an internal, pigmented cell system in liver and splenic tissues of some fishes, anurans, and reptiles. The cells have been found in centers or aggregates in sinusoids and are associated with cells capable of producing a peptide cytokine and immunoglobulins. A unique cell extension process has been observed in turtle MMs placed into cell culture, and this process has been studied by light and atomic force microscopy. These structures, referred to as cablepodia, are uniquely straight, narrow, and unbranching and appear to originate from growth cones opposite lamellipodia. Cablepodia were found to connect with other turtle MMs and fibroblasts forming cell networks. Dividing fibroblasts to which a cablepodium attached ceased cell division. The observations collectively suggest that a principal reason for aggregations of MMs in internal organs of lower vertebrates is their ability to form interconnected networks of cell processes for trapping and processing of particulate matter, cells, and infectious organisms and, possibly, for the communication of cell signals and transfer of intracellular materials.

Biogenesis of melanosomes in Kupffer cells of Proteus anguinus (Urodela, Amphibia)

The ultrastructural characteristics of melanosomes and premelanosomes observed during the biogenesis of melanosomes in liver pigment cells of the neotenic cave salamander Proteus anguinus (Proteidae) are described. It is well known that amphibian liver pigment cells, also known as Kupffer cells (KC), contain melanosomes and are able to synthesize melanin. Liver pigment cells of P. anguinus contain numerous siderosomes and melanosomes. The melanosomes are grouped together within single-membrane-bounded bodies, named as 'clusters of melanosomes' or 'melanosomogenesis centers'. Inside such clusters, different structures are present: (1) filament-like structures, characteristic of the initial stage of melanosome biogenesis, (2) medium electron-dense melanosomes in different stages of melanization, (3) melanosomes with an electron-dense cortical area and a less electron-dense medullar area, and (4) uniformly highly electron-dense mature melanosomes or melanin granules. Histochemical and cytochemical dihydroxyphenylalanine (DOPA) oxidase reactions in pigment cells were positive. Our results confirm the ability of amphibian KC to synthesize melanin and contribute to this little known subject.

Mechanisms of changes to the liver pigmentary component during the annual cycle (activity and hibernation) of Rana esculenta L

The present study was performed to elucidate the mechanisms responsible for the changes of melanin content/ distribution we had previously discovered in the liver parenchyma of Rana esculenta during natural hibernation. Melanomacrophagic component response was analysed using morphocytochemical methods. The results demonstrated that during the prehibernation period (October-November) the melanomacrophages reach the highest proliferative activity (BrdU, PCNA labelling) which is accompanied by an evident melanosynthesis (dopa-oxidase activity). In contrast, after hibernation, the decrease of liver pigmentation was the consequence of a partial cell loss by apoptotic mechanisms (TUNEL labelling, pyknosis-karyorhexis) accompanied by a decrease of melanosome content by autophagy and low melanosynthetic activity. On the basis of these findings, there is evidence that liver melanomacrophages represent a metabolically (melanin synthesis/degradation) and cytokinetically (proliferation/ death) active cell population during the annual cycle of the frog. The results are also discussed in relation to the functional synergism between hepatocytes and pigment cells in the adaptation to environmental changes.

The antimicrobial properties of melanocytes, melanosomes and melanin and the evolution of black skin

A biological issue that has not been satisfactorily resolved is the role of melanin in skin and other animal tissues. A hypothesis is outlined here to account for the evolution of black skin and the ubiquity of melanin in vertebrate tissues. Evidence is presented that melanization of skin and other tissues forms an important component of the innate immune defense system. A major function of melanocytes, melanosomes and melanin in skin is to inhibit the proliferation of bacterial, fungal and other parasitic infections of the dermis and epidermis. This function can potentially explain (a) the latitudinal gradient in melanization of human skin; (b) the fact that melanocyte and melanization patterns among different parts of the vertebrate body do not reflect exposure to radiation; (c) provide a theoretical framework for recent empirical findings concerning the antimicrobial activity of melanocytes and melanosomes and their regulation by known mediators of inflammatory responses.

Effects of 2,4,6-trinitrotoluene in a holistic environmental exposure regime on a terrestrial salamander, Ambystoma tigrinum

2,4,6-Trinitrotoluene (TNT) is a defense-related environmental contaminant present at high concentrations in soil at some military installations. Tiger salamanders (Ambystoma tigrinum, family Ambystomatidae) were exposed to TNT in a soil matrix and fed earthworms that had also been exposed to TNT via contaminated soil. Such exposure was previously shown to result in significant accumulation of both TNT and TNT metabolites by salamanders. Following 14 days of combined oral and dermal exposures, salamanders were evaluated for signs of toxicity. Control and TNT-exposed salamanders gained weight (p < 0.025). In addition, organ to body weight ratios (kidney, liver, and spleen) were not affected by treatment. The function of splenic phagocytic cells was evaluated because these cells are sensitive to certain environmental chemical exposures. Neither the chemiluminescence response (H2O2 production) nor the phagocytic capacity of such cells were different between controls and treatment groups. In like manner, no changes were seen in the peripheral hematologic parameters investigated. Histopathologic evaluations were inconclusive, yet the liver revealed the presence of heavily pigmented iron-rich phagocytes (melanomacrophages). This investigation presents a realistic approach and preliminary data for investigating the effects of xenobiotic exposure in a soil matrix on a terrestrial vertebrate.

Reptilian melanomacrophages function under conditions of hypothermia: observations on phagocytic behavior

Melanomacrophages (MMs) were removed from livers of turtles of three North American families and cultured. J774 mammalian macrophages were similarly cultured and the MMs were exposed to E. coli(fluor) at approximately 2, 7, 27, and 37 degrees C. At least one third of the MMs continued to function at the low temperatures where less than 2% of the mammalian cells incorporated bacteria deeply into the cytoplasm. In most instances, when the bacteria were not internalized deeply into the cytoplasm, they became stationary just inside, or within, the cell membrane. The MMs were significantly less efficient than the mammalian cells at 37 degrees C and significantly more efficient at 2 and 7 degrees C. In general, it appears that MMs are never as efficient as mammalian macrophages under the most ideal temperatures for the cell but they are capable of functioning at reasonable levels at temperature extremes. The observations are suggestive of a genetic mechanism functioning in the MMs that is rarely expressed in J774 cells under conditions of hypothermia. MMs in vitro and probably in vivo consume bacteria, fungi, attach to helminth eggs, and consume old erythrocytes.

Increase in liver pigmentation during natural hibernation in some amphibians

The amount/distribution of liver melanin in 3 amphibian species (Rana esculenta, Triturus a. apuanus, Triturus carnifex) was studied during 2 periods of the annual cycle (summer activity-winter hibernation) by light and electron microscopy, image analysis and microspectrofluorometry. The increase in liver pigmentation (melanin content) during winter appeared to be correlated with morphological and functional modifications in the hepatocytes, which at this period were characterised by a decrease in metabolic activity. These findings were interpreted according to the functional role (e.g. phagocytosis, cytotoxic substance inactivation) played by the pigment cell component in the general physiology of the heterothermic vertebrate liver and, in particular, in relation to a compensatory engagement of these cells against hepatocellular hypoactivity during the winter period.

In vitro culture of melanomacrophages from the spleen and liver of turtles: comments on melanomacrophage morphology

Melanomacrophages were extracted and cultured from the spleen and liver of three turtle species representing three divergent families, the Chelydridae, Emydidae, and Trionychidae. Homogeneous cultures were obtained by repeatedly forcing minced, frequently washed tissue through a sterile screen and separating the resulting cells by centrifugation. The cells were surprisingly resistant to lysis and were maintained in culture for over 12 weeks where culture characteristics, appearance, and longevity from these two organs were similar. They attached to the T flask substrate as individual cells and aggregates and spread out 14 days after being placed in media. Ridges and ruffles at the distal ends of pseudopodia and the cell surface along with a zone of clearing attest to the cells' phagocytic nature. A few melanomacrophages from both organs underwent mitosis 14 days after treatment with granulocyte macrophage colony-stimulating factor but it is possible that other factors contributed to stimulation of cell division.