Polymorphous granular cells in the lung of the primitive fish, the bichirPolypterus senegalus

Coelomocytes of the Oligochaeta earthworm Lumbricus terrestris (Linnaeus, 1758) as evolutionary key of defense: a morphological study

Metazoans have several mechanisms of internal defense for their survival. The internal defense system evolved alongside the organisms. Annelidae have circulating coelomocytes that perform functions comparable to the phagocytic immune cells of vertebrates. Several studies have shown that these cells are involved in phagocytosis, opsonization, and pathogen recognition processes. Like vertebrate macrophages, these circulating cells that permeate organs from the coelomic cavity capture or encapsulate pathogens, reactive oxygen species (ROS), and nitric oxide (NO). Furthermore, they produce a range of bioactive proteins involved in immune response and perform detoxification functions through their lysosomal system. Coelomocytes can also participate in lithic reactions against target cells and the release of antimicrobial peptides. Our study immunohistochemically identify coelomocytes of Lumbricus terrestris scattered in the epidermal and the connective layer below, both in the longitudinal and in the smooth muscle layer, immunoreactive for TLR2, CD14 and α-Tubulin for the first time. TLR2 and CD14 are not fully colocalized with each other, suggesting that these coelomocytes may belong to two distinct families. The expression of these immune molecules on Annelidae coelomocytes confirms their crucial role in the internal defense system of these Oligochaeta protostomes, suggesting a phylogenetic conservation of these receptors. These data could provide further insights into the understanding of the internal defense system of the Annelida and of the complex mechanisms of the immune system in vertebrates.

Spirulina promotes macrophages aggregation in zebrafish (Danio rerio) liver

The immune system of teleosts offers many ideas to deepen the immune mechanisms and cells in general. The use of zebrafish as an experimental model is increased in recent years, thanks to its genetic and anatomical characteristics. It is known that several natural compounds exert an action on the immune system, boosting it. Spirulina, a non-toxic blue-green alga, has been declared a superfood for its peculiar biological activities. In this study, we test the immunostimulant effect of spirulina on zebrafish liver macrophages by immunohistochemical analysis using optical and confocal microscopy. Our results have shown an increase in the number of macrophages after feeding with spirulina, furthermore, this natural 'superfood' can induce macrophages aggregation. These data not only provide information on the possible effect of this alga as a complementary feed on the immune cells of teleost, but also improve the knowledge of the immune mechanisms of vertebrates.

Gill structure and neurochemical markers in the African bonytongue (Heterotis niloticus): A preliminary study

We have conducted a morphological and immunohistochemical study of the gills of juvenile specimens of the obligate air-breathing fish Heterotis niloticus. The study has been performed under normoxic and hypoxic conditions. The gills showed a reduced respiratory surface area by development of an interlamellar cellular mass (ILCM). The ILCM persisted without changes under both normoxia and hypoxia. Neuroepithelial cells (NECs), the major oxygen and hypoxia sensing cell type, were located in the distal end of the gill filaments and along the ILCM edges. These cells expressed 5HT, the neuronal isoform of the nitric oxide synthase (nNOS) and the vesicular acetylcholine transporter (VAChT). Furthermore, NECs appeared associated with nitrergic nerve fibres. The O2 levels did not modify the location, number or the immunohistochemical characteristics of NECs. Pavement cells covering the ILCM were also positive to nNOS and VAChT. The mechanisms of O₂ sensing in the gills of Heterotis appears to involve several cell populations, the release of multiple neurotransmitters and a diversity of excitatory, inhibitory and modulatory mechanisms.

Confocal Characterization of Intestinal Dendritic Cells from Myxines to Teleosts

Dendritic cells (DCs) are antigen-presenting cells (APCs) that regulate the beginning of adaptive immune responses. The mechanisms of tolerance to antigens moving through the digestive tract are known to be regulated by intestinal DCs. Agnatha and Gnathostoma are descendants of a common ancestor. The Ostracoderms gave rise to Cyclostomes, whereas the Placoderms gave rise to Chondrichthyes. Sarcopterygii and Actinopterygii are two evolutionary lines of bony fishes. Brachiopterygii and Neopterygii descend from the Actinopterygii. From Neopterygii, Holostei and Teleostei evolved. Using immunohistochemistry with TLR-2, Langerin/CD207, and MHC II, this study aimed to characterize intestinal DCs, from myxines to teleosts. The findings reveal that DCs are positive for the antibodies tested, highlighting the presence of DCs and DC-like cells phylogenetically from myxines, for the first time, to teleosts. These findings may aid in improving the level of knowledge about the immune system's evolution and these sentinel cells, which are crucial to the body's defense.

Histological and Chemical Analysis of Heavy Metals in Kidney and Gills of Boops boops: Melanomacrophages Centers and Rodlet Cells as Environmental Biomarkers

Industrialization has resulted in a massive increase in garbage output, which is frequently discharged or stored in waterways like rivers and seas. Due to their toxicity, durability, bioaccumulation, and biomagnification, heavy metals (such as mercury, cadmium, and lead) have been identified as strong biological poisons. Their presence in the aquatic environment has the potential to affect water quality parameters and aquatic life in general. Teleosts’ histopathology provides a sensitive indicator of pollutant-induced stress, because their organs have a central role in the transformation of different active chemical compounds in the aquatic environment. In particular, the gills, kidneys, and liver are placed at the center of toxicological studies. The purpose of this study is to examine the morphological changes caused by heavy metals in the kidney and gills of Boops boops, with a focus on melanomacrophages centers (MMCs) and rodlet cells (RCs) as environmental biomarkers, using histological and histochemical stainings (hematoxylin/eosin, Van Gieson trichrome, Periodic Acid Schiff reaction, and Alcian Blue/PAS 2.5), and immunoperoxidase methods. Our findings show an increase of MMCs and RCs linked to higher exposure to heavy metals, confirming the role of these aggregates and cells as reliable biomarkers of potential aquatic environmental changes reflected in fish fauna. The cytological study of RCs and MMCs could be important in gaining a better understanding of the complicated immune systems of teleosts.

Localization of vasoactive intestinal peptide and toll-like receptor 2 immunoreactive cells in endostyle of urochordate Styela plicata (Lesueur, 1823)

The endostyle is the first component of the ascidian digestive tract, it is shaped like a through and is located in the pharynx's ventral wall. This organ is divided longitudinally into nine zones that are parallel to each other. Each zone's cells are physically and functionally distinct. Support elements are found in zones 1, 3, and 5, while mucoproteins secreting elements related to the filtering function are found in zones 2, 4, and 6. Zones 7, 8, and 9, which are located in the lateral dorsal section of the endostyle, include cells with high iodine and peroxidase concentrations. Immunohistochemical technique using the following antibodies, Toll‐like receptor 2 (TLR‐2) and vasoactive intestinal peptide (VIP), and lectin histochemistry (WGA—wheat‐germagglutinin), were used in this investigation to define immune cells in the endostyle of Styela plicata (Lesueur, 1823). Our results demonstrate the presence of immune cells in the endostyle of S. plicata, highlighting that innate immune mechanisms are highly conserved in the phylogeny of the chordates.

Rodlet cells in kidney of goldfish (Carassius auratus, Linnaeus 1758): A light and confocal microscopy study

Rodlet cells (RCs) have always been an enigma for scientists. RCs have been given a variety of activities over the years, including ion transport, osmoregulation, and sensory function. These cells, presumably as members of the granulocyte line, are present only in teleosts and play a role in the innate immune response. RCs are migratory cells found in a variety of organs, including skin, vascular, digestive, uropoietic, reproductive, and respiratory systems, and present distinct physical properties that make them easily recognizable in tissues and organs. The development of RCs can be divided into four stages: granular, transitional, mature, and ruptured, having different morphological characteristics. Our study aims to characterize the different stages of these cells by histomorphological and histochemical techniques. Furthermore, we characterized these cells at all stages with peroxidase and fluorescence immunohistochemical techniques using different antibodies: S100, tubulin, α-SMA, piscidin, and for the first time TLR-2. From our results, the immunoreactivity of these cells to the antibodies performed may confirm that RCs play a role in fish defense mechanisms, helping to expand the state of the art on immunology and immune cells of teleosts.

Relationship between Immune Cells, Depression, Stress, and Psoriasis: Could the Use of Natural Products Be Helpful?

Psoriasis is one of the most widespread chronic inflammatory skin diseases, affecting about 2%-3% of the worldwide adult population. The pathogenesis of this disease is quite complex, but an interaction between genetic and environmental factors has been recognized with an essential modulation of inflammatory and immune responses in affected patients. Psoriatic plaques generally represent the clinical psoriatic feature resulting from an abnormal proliferation and differentiation of keratinocytes, which cause dermal hyperplasia, skin infiltration of immune cells, and increased capillarity. Some scientific pieces of evidence have reported that psychological stress may play a key role in psoriasis, and the disease itself may cause stress conditions in patients, thus reproducing a vicious cycle. The present review aims at examining immune cell involvement in psoriasis and the relationship of depression and stress in its pathogenesis and development. In addition, this review contains a focus on the possible use of natural products, thus pointing out their mechanism of action in order to counteract clinical and psychological symptoms.

Resveratrol and Immune Cells: A Link to Improve Human Health

The use of polyphenols as adjuvants in lowering risk factors for various debilitating diseases has been investigated in recent years due to their possible antioxidant action. Polyphenols represent a fascinating and relatively new subject of research in nutraceuticals and nutrition, with interest rapidly expanding since they can help maintain health by controlling metabolism, weight, chronic diseases, and cell proliferation. Resveratrol is a phenolic compound found mostly in the pulp, peels, seeds, and stems of red grapes. It has a wide variety of biological actions that can be used to prevent the beginning of various diseases or manage their symptoms. Resveratrol can influence multiple inflammatory and non-inflammatory responses, protecting organs and tissues, thanks to its interaction with immune cells and its activity on SIRT1. This compound has anti-inflammatory, antioxidant, anti-apoptotic, neuroprotective, cardioprotective, anticancer, and antiviral properties, making it a potential adjunct to traditional pharmaceutical therapy in public health. This review aims to provide a comprehensive analysis of resveratrol in terms of active biological effects and mechanism of action in modifying the immune cellular response to promote human psychophysical health.

Role of nutraceuticals on neurodegenerative diseases: neuroprotective and immunomodulant activity

Neurodegeneration is a degenerative process characterized by the progressive loss of the structure and function of neurons that involves several immune cells. It is the primary cause of dementia and other several syndromes, known as neurodegenerative diseases. These disorders are age-related and it is estimated that by 2040 there will be approximately 81.1 million people suffering from these diseases. In addition to the traditional pharmacological therapy, in recent years nutraceuticals, naturally based compounds with a broad spectrum of biological effects: anti-aging, antioxidants, hypoglycaemic, hypocholesterolemic, anticancer, anxiolytic, antidepressant, etc., assumed an important role in counteracting these pathologies. In particular, several compounds such as astaxanthin, baicalein, glycyrrhizin, St. John's wort, and Ginkgo biloba L. extracts show particular neuroprotective and immunomodulatory abilities, involving several immune cells and some neurotransmitters that play a critical role in neurodegeneration, making them particularly useful in improving the symptoms and progression of neurodegenerative diseases.

Neuroepithelial cells (NECs) and mucous cells express a variety of neurotransmitters and neurotransmitter receptors in the gill and respiratory air-sac of the catfish Heteropneustes fossilis (Siluriformes, Heteropneustidae): a possible role in local immune defence

Heteropneustes fossilis is an air-breathing teleost inhabiting environments with very poor O₂ conditions, and so it has evolved to cope with hypoxia. In the gills and respiratory air-sac, the sites for O₂ sensing and the response to hypoxia rely on the expression of acetylcholine (Ach) acting via its nicotinic receptor (nAChR). This study examined the expression patterns of neuronal markers and some compounds in the NECs of the gills and respiratory air sac having an immunomodulatory function in mammalian lungs. Mucous cells, epithelial cells and neuroepithelial cells (NECs) were immunopositive to a variety of both neuronal markers (VAChT, nAChR, GABA-B-R1 receptor, GAD679) and the antimicrobial peptide piscidin, an evolutionary conserved humoral component of the mucosal immune system in fish. We speculate that Ach release via nAChR from mucous cells may be modulated by GABA production in the NECs and it is required for the induction of mucus production in both normoxic and hypoxic conditions. The presence of piscidin in mucous cells may act in synergy with the autocrine/paracrine signals of Ach and GABA binding to GABA B R1B receptor that may play a local immunomodulatory function in the mucous epithelia of the gills and the respiratory air sac. The potential role of the NECs in the immunobiological behaviour of the gill/air-sac is at moment a matter of speculation. The extent to which the NECs as such may participate is elusive at this stage and waits investigation.

Expression of acetylcholine, its contribution to regulation of immune function and O2 sensing and phylogenetic interpretations of the African butterfly fish Pantodon buchholzi (Osteoglossiformes, Pantodontidae)

Acetylcholine (Ach) is the main neurotransmitter in the neuronal cholinergic system and also works as a signaling molecule in non-neuronal cells and tissues. The diversity of signaling pathways mediated by Ach provides a basis for understanding the biology of the cholinergic epithelial cells and immune cells in the gill of the species studied. NECs in the gill were not found surprisingly, but specialized cells showing the morphological, histochemical and ultrastructural characteristics of eosinophils were located in the gill filaments and respiratory lamellae. Much remains unknown about the interaction between the nerves and eosinophils that modulate both the release of acetylcholine and its nicotinic and muscarinic receptors including the role of acetylcholine in the mechanisms of O₂ chemosensing. In this study we report for the first time the expression of Ach in the pavement cells of the gill lamellae in fish, the mast cells associated with eosinophils and nerve interaction for both immune cell types, in the gill of the extant butterfly fish Pantodon buchholzi. Multiple roles have been hypothesized for Ach and alpha nAChR in the gills. Among these there are the possible involvement of the pavement cells of the gill lamellae as O₂ chemosensitive cells, the interaction of Ach positive mast cells with eosinophils and interaction of eosinophils with nerve terminals. This could be related to the use of the vesicular acetylcholine transporter (VAChT) and the alpha 2 subunit of the acetylcholine nicotinic receptor (alpha 2 nAChR). These data demonstrate the presence of Ach multiple sites of neuronal and non-neuronal release and reception within the gill and its ancestral signaling that arose during the evolutionary history of this conservative fish species.

Expression of Acetylcholine- and G protein coupled Muscarinic receptor in the Neuroepithelial cells (NECs) of the obligated air-breathing fish, Arapaima gigas (Arapaimatidae: Teleostei)

The air-breathing specialization has evolved idependently in vertebrates, as many different organs can perfom gas exchange. The largest obligate air-breathing fish from South America Arapaima gigas breathe air using its gas bladder, and its dependence on air breathing increases during its growth. During its development, gill morphology shows a dramatic change, remodeling with a gradual reduction of gill lamellae during the transition from water breathing to air breathing . It has been suggested that in this species the gills remain the main site of O₂ and CO₂ sensing. Consistent with this, we demonstrate for the first time the occurrence of the neuroepithelial cells (NECs) in the glottis, and in the gill filament epithelia and their distal halves. These cells contain a broader spectrum of neurotransmitters (5-HT, acetylcholine, nNOS), G-protein subunits and the muscarininic receptors that are coupled to G proteins (G-protein coupled receptors). We report also for the first time the presence of G alpha proteins coupled with muscarinic receptors on the NECs, that are thought as receptors that initiate the cardiorespiratory reflexes in aquatic vertebrates. Based on the specific orientation in the epithelia and their closest vicinity to efferent vasculatures, the gill and glottal NECs of A. gigas could be regarded as potential O₂ and CO₂ sensing receptors. However, future studies are needed to ascertain the neurophysiological characterization of these cells.

Lungs and gas bladders: Morphological insights

This paper summarizes the main morphological tracts exhibited by lungs and gas bladders in fishes. The origin and organ location, the presence of a glottal region, the inner architecture, the characteristics of the exchange barrier and the presence of pulmonary arteries have been reviewed in the two types of air-breathing organs. With the exception of the dorsal (bladders) or ventral (lungs) origin from the posterior pharynx, none of the morphological traits analyzed can be considered specific for either lungs or gas bladders. This is exemplified by analysis of the morphology of the lung of the Dipnoii and Polypteriformes and of the bladder of the Lepisosteiformes. All of them are obligate air-breathers and show a lung-like (pulmonoid) air-breathing organ. However, while the lungfish lung and the bladder of the Lepisosteiformes occupy a dorsal position and are highly trabeculated, the polypterid lung occupies a ventral position and shows a smooth inner surface. Structural and ultrastructural differences are also highlighted. Noticeably, a large part of the inner surface area of the lung of the Australian lungfish is covered by a ciliated epithelium. A restricted respiratory surface area may help to explain the incapability of this species to aestivate. The respiratory bladder of basal teleosts displays a more complex morphology than that observed in more primitive species. The bladder of basal teleosts may appear divided into respiratory and non-respiratory portions, exhibit intricate shapes, invade adjacent structures and gain additional functions. The increase in morphological and functional complexity appears to prelude the loss of the respiratory functions.

Air- breathing in fish: Air- breathing organs and control of respiration: Nerves and neurotransmitters in the air-breathing organs and the skin

In fishes, exploitation of aerial gas exchange has evolved independently many times, involving a variety of air-breathing organs. Indeed, air-breathing occurs in at least 49 known families of fish (Graham, 1997). Many amphibious vertebrates, at some stage of their development are actually trimodal breathers that use various combinations of respiratory surfaces to breath both water (skin and/or gill) and air (skin and/or lung). The present review examines the evolutionary implications of air-breathing organs in fishes and the morphology of the peripheral receptors and the neurotransmitter content of the cells involved in the control of air-breathing. Control of breathing, whether gill ventilation or air-breathing, is influenced by feedback from peripheral and/or central nervous system receptors that respond to changes in PO2, PCO2 and/or pH. Although the specific chemoreceptors mediating the respiratory reflexes have not been conclusively identified, studies in water-breathing teleosts have implicated the neuroepithelial cells (NECs) existing in gill tissues as the O2 sensitive chemoreceptors that initiate the cardiorespiratory reflexes in aquatic vertebrates. Some of the air-breathing fishes, such as Protopterus, Polypterus and Amia have been shown to have NECs in the gills and/or lungs, although the role of these receptors and their innervation in the control of breathing is not known. NECs have been also reported in the specialized respiratory epithelia of accessory respiratory organs (ARO's) of some catfish species and in the gill and skin of the mudskipper Periophthalmodon schlosseri. Unlike teleosts matching an O2-oriented ventilation to ambient O2 levels, lungfishes have central and peripheral H+/CO2 receptors that control the acid-base status of the blood.

Immunohistochemical characterization of epidermal dendritic-like cells in giant mudskipper, Periophthalmodon schlosseri

Giant Mudskipper, Periophthalmodon schlosseri (Pallas, 1770), is euryhaline, amphibious, and air-breathing fish. These fishes live in close association to mangrove forests and often spend over 90% of time out of water, in adjacent mudflats. They have developed morphological and physiological adaptations to satisfy their unique lifestyles. The skin is the primary interface between the body and the environment, and has a central role in host defence. The initiation of immune responses to antigens in the vertebrate skin has often been attributed to epidermal Langerhans'cells (LC) that are dendritic cells (DC), antigen-presenting cells (APC) which reside in the epidermis. Dendritic cells have been characterized morphologically and functionally in the teleost fish tissues such as rainbow trout, salmonids, medaka, African catfish and zebrafish. However, there is no evidence of the presence of DCs and their role in mudskippers immunity. The aim of this preliminary study was to characterize, through use of specific antibodies: Toll-like receptor 2, S100, serotonin (5-HT), and Vesicular acetylcholine transporter VAChT, a specific DC-like subpopulation in Pn. schlosseri's epidermis.

Identification and distribution of neuronal nitric oxide synthase and neurochemical markers in the neuroepithelial cells of the gill and the skin in the giant mudskipper, Periophthalmodon schlosseri

Mudskippers are amphibious fishes living in mudflats and mangroves. These fishes hold air in their large buccopharyngeal-opercular cavities where respiratory gas exchange takes place via the gills and higher vascularized epithelium lining the cavities and also the skin epidermis. Although aerial ventilation response to changes in ambient gas concentration has been studied in mudskippers, the localization and distribution of respiratory chemoreceptors, their neurochemical coding and function as well as physiological evidence for the gill or skin as site for O₂ and CO₂ sensing are currently not known. In the present study we assessed the distribution of serotonin, acetylcholine, catecholamines and nitric oxide in the neuroepithelial cells (NECs) of the mudskipper gill and skin epithelium using immunohistochemistry and confocal microscopy. Colocalization studies showed that 5-HT is coexpressed with nNOS, Na⁺/K⁺-ATPase, TH and VAChT; nNOS is coexpressed with Na⁺/K⁺-ATPase and TH in the skin. In the gill 5-HT is coexpressed with nNOS and VAhHT and nNOS is coexpressed with Na⁺/K⁺-ATPase and TH. Acetylcholine is also expressed in chain and proximal neurons projecting to the efferent filament artery and branchial smooth muscle. The serotonergic cells c labeled with VAChT, nNOS and TH, thus indicating the presence of NEC populations and the possibility that these neurotransmitters (other than serotonin) may act as primary transmitters in the hypoxic reflex in fish gills. Immunolabeling with TH antibodies revealed that NECs in the gill and the skin are innervated by catecholaminergic nerves, thus suggesting that these cells are involved in a central control of branchial functions through their relationships with the sympathetic branchial nervous system. The Na⁺/K⁺-ATPase in mitochondria-rich cells (MRCs), which are most concentrated in the gill lamellar epithelium, is colabeled with nNOS and associated with TH nerve terminals. TH-immunopositive fine varicosities were also associated with the numerous capillaries in the skin surface and the layers of the swollen cells. Based on the often hypercapnic and hypoxic habitat of the mudskippers, these fishes may represent an attractive model for pursuing studies on O₂ and CO₂ sensing due to the air-breathing that increases the importance of acid/base regulation and the O₂-related drive including the function of gasotransmitters such as nitric oxide that has an inhibitory (regulatory) function in ionoregulation.

Morphological and functional aspects of the epidermis of the sea lamprey Petromyzon marinus throughout development

The development of the epidermis of sea lamprey Petromyzon marinus along the whole life cycle was studied using conventional staining techniques and lectin histochemistry. The epidermis undergoes variations in morphology and thickness throughout development. The simple cuboidal epithelium found in the epidermis of prolarvae becomes stratified cubic in the adult by increasing the number of cell layers. The cuticle thickness undergoes a steady increase during the larval period. There are changes in the glycoconjugate composition of the three main cell types of the P. marinus epidermis, mucous, granular and skein cells, which are more pronounced after metamorphosis. The Alcian blue-periodic acid Schiff (AB-PAS) histochemical method shows the presence of both acidic and neutral glycoconjugates in the mucous cells, indicating their secretory function. Moreover, lectin analysis reveals a mucous secretion containing glycoconjugates such as sulphated glycosaminoglycans (N-acetylglucosamine and N-acetylgalactosamine) and N-glycoproteins rich in mannose. Although granular cells are AB-PAS negative, they exhibit a similar glycoconjugate composition to the mucous cells. Moreover, granular cells show sialic acid positivity in larvae but this monosaccharide residue is not detected after metamorphosis. The skein cells, a unique cell of lampreys, are negative to AB-PAS staining but they mostly contain l-fucose and sialic acid residues, which also disappear after metamorphosis. The function of the granular and skein cells is still unknown but the role of their glycoconjugate composition is discussed. In addition, a different cellular origin is suggested for these two types of cells.