Identification of CD3+ T lymphocytes in the green turtle Chelonia mydas

Immunity in Sea Turtles: Review of a Host-Pathogen Arms Race Millions of Years in the Running

The immune system of sea turtles is not completely understood. Sea turtles (as reptiles) bridge a unique evolutionary gap, being ectothermic vertebrates like fish and amphibians and amniotes like birds and mammals. Turtles are ectotherms; thus, their immune system is influenced by environmental conditions like temperature and season. We aim to review the turtle immune system and note what studies have investigated sea turtles and the effect of the environment on the immune response. Turtles rely heavily on the nonspecific innate response rather than the specific adaptive response. Turtles' innate immune effectors include antimicrobial peptides, complement, and nonspecific leukocytes. The antiviral defense is understudied in terms of the diversity of pathogen receptors and interferon function. Turtles also mount adaptive responses to pathogens. Lymphoid structures responsible for lymphocyte activation and maturation are either missing in reptiles or function is affected by season. Turtles are a marker of health for their marine environment, and their immune system is commonly dysregulated because of disease or contaminants. Fibropapillomatosis (FP) is a tumorous disease that afflicts sea turtles and is thought to be caused by a virus and an environmental factor. We aim, by exploring the current understanding of the immune system in turtles, to aid the investigation of environmental factors that contribute to the pathogenesis of this disease and provide options for immunotherapy.

The peripheral blood mononuclear cells preparation and the hematology of Varanus salvator

The objectives of this study were to evaluate the proper anticoagulants coated in blood-collecting tube for the peripheral blood mononuclear cells (PBMCs) isolation and to evaluate the proper culture temperature for the Varanus salvator's PBMCs, in addition, the hematological characteristics also reported. The heparin treated blood (n = 10) and EDTA treated blood (n = 10) from Varanus salvator were obtained for PBMCs evaluation. The PBMCs obtained from the heparin treated blood was significantly higher than that of EDTA treated blood during the culture period (P < 0.05) indicated heparin would be more appropriated anticoagulant for blood collection. The PBMCs cultured under 37°C and 27°C were not significantly difference on first three days but 37°C showed significantly higher effect in the following days (P < 0.05) indicated both temperatures can be used which 37°C should be an optimal for PBMCs preparation. The peripheral blood cells of Varanus salvator (n = 49) were analyzed for hematological profiles and characteristics which the number of erythrocytes 1.19 ± 0.04 x 1012/L (1.17-1.35 x 1012/L) and WBC 2.41 ± 0.13 x 109/L (2.29-2.81 x 109/L) with absolute differential count of heterophils 0.92 ± 0.02 x 109/L (0.87-0.95 x 109/L), lymphocytes 1.17 ± 0.01 x 109/L (1.15-1.23 x 109/L), azurophils 0.40 ± 0.01 x 109/L (0.37-0.42 x 109/L), basophils 0.000 ± 0.001 x 109/L (0.004-0.011 x 109/L) and monocytes 0.027 ± 0.002 x 109/L (0.028-0.039 x 109/L). These results would play an important role on the cell immunological studies of the Varanus salvator in the future.

Molecular characterization of a marine turtle tumor epizootic, profiling external, internal and postsurgical regrowth tumors

Sea turtle populations are under threat from an epizootic tumor disease (animal epidemic) known as fibropapillomatosis. Fibropapillomatosis continues to spread geographically, with prevalence of the disease also growing at many longer-affected sites globally. However, we do not yet understand the precise environmental, mutational and viral events driving fibropapillomatosis tumor formation and progression.Here we perform transcriptomic and immunohistochemical profiling of five fibropapillomatosis tumor types: external new, established and postsurgical regrowth tumors, and internal lung and kidney tumors. We reveal that internal tumors are molecularly distinct from the more common external tumors. However, they have a small number of conserved potentially therapeutically targetable molecular vulnerabilities in common, such as the MAPK, Wnt, TGFβ and TNF oncogenic signaling pathways. These conserved oncogenic drivers recapitulate remarkably well the core pan-cancer drivers responsible for human cancers. Fibropapillomatosis has been considered benign, but metastatic-related transcriptional signatures are strongly activated in kidney and established external tumors. Tumors in turtles with poor outcomes (died/euthanized) have genes associated with apoptosis and immune function suppressed, with these genes providing putative predictive biomarkers.Together, these results offer an improved understanding of fibropapillomatosis tumorigenesis and provide insights into the origins, inter-tumor relationships, and therapeutic treatment for this wildlife epizootic.

Leukocyte and Platelet Characteristics of the Giant Panda (Ailuropoda melanoleuca): Morphological, Cytochemical, and Ultrastructural Features

The giant panda (Ailuropoda melanoleuca) is a vulnerable species and a charismatic member of zoological collections worldwide. Despite its importance as a representative species for global wildlife conservation efforts, no studies to date have described normal cell morphology or cytoplasmic constituents by traditional techniques such as cytochemical staining and evaluation of ultrastructural features. The objective of this study was to accurately identify and characterize the leukocytes and platelets of clinically healthy giant pandas using routine Wright-Giemsa stain, eight cytochemical stains, immunocytochemistry (CD3), and transmission electron microscopy (TEM) to further the collective understanding of normal cellular morphological features, cytochemical reactivity, and cytoplasmic contents found in health. Voluntary venipuncture was performed on four healthy individual animals (two adults and two juveniles), as part of routine preventive health evaluation. Blood was collected for routine and cytochemical stains, and into 2.5% glutaraldehyde for TEM. On Wright-Giemsa-stained blood films, leukocytes were differentiated into granulocytes (neutrophils, eosinophils, basophils) and mononuclear cells (lymphocytes, monocytes). Cytochemical staining revealed similar leukocyte and platelet staining patterns to those reported in other mammals, with some notable differences. By TEM, leukocytes with nuclear and cytoplasmic features of mononuclear cells were readily differentiated from granulocytes, and platelets had similar ultrastructural features to those reported in other mammals. Neutrophils were the predominant cell type followed by lymphocytes, while basophils were rare. Rare large or reactive lymphocytes, rare reactive monocytes, and rare large platelets were noted in apparently healthy giant pandas of this study. A unique mononuclear cell, with a moderately indented nucleus and shared cytochemical and ultrastructural characteristics of lymphocytes and monocytes, was discovered in this species. The combined cytochemical, immunocytochemical (CD3), and ultrastructural features of these unique cells more closely resemble those of monocytes, but the definitive cell lineage remains unknown at this time. This study provides novel information on giant panda leukocyte morphology and cellular constituents in health, shows the importance of manual blood film review, has important implications for hemogram interpretation in future clinical cases and research, and provides a baseline for future characterization and understanding of hemogram changes in response to disease.

Immune response declines with age in a wild lizard

The immune system allows animals to survive the constant attacks of pathogens. Although it is essential for survival and fitness, the performance of the immune system can decline with age (a process known as immunosenescence), which may be responsible for the increased mortality of older individuals. Only a few studies have investigated the effect of age on the immune system in reptiles, and no evidence of immunosenescence has yet been reported in lizards. In a wild population of Dickerson’s collared lizards (Crotaphytus dickersonae), we evaluated the effect of age (estimated by skeletochronology) on the male’s immune response to a novel antigen (phytohaemagglutinin). We found a strong negative relationship between immune response and age, the first evidence of immunosenescence in a lizard. Our results show that immunosenescence can occur even in relatively short-lived reptiles and underline the importance of age on performance in fitness-related traits.

Unraveling avian and reptilian hematology: An optical and electron microscopic study of the buffy coat

BACKGROUND

Blood centrifugation and buffy coats are at the cornerstone of hematology. In mammals, the buffy coat has a layered disposition (from bottom to top) with neutrophils on top of erythrocytes, followed by monocytes/lymphocytes, and platelets. In nonmammals, this distribution is unknown. Recently, the cell tube block (CTB) technique was developed to study the buffy coat, but it was never applied to nonmammal buffy coats.

OBJECTIVES

This study aimed to evaluate using the CTB technique to study reptilian and avian buffy coats and to propose its use for clinical applications.

METHODS

Blood from five birds and eight reptiles of different species was obtained to make CTBs that were processed for optical/electron microscopy. H&E, Sirius red, and immunohistochemistry staining against CD3 (to label T lymphocytes) were applied to the CTBs.

RESULTS

In birds, the buffy coat had a layered appearance with the granulocyte layer containing granulocytes (heterophils and eosinophils) and nucleated erythrocytes followed by a mononuclear cell layer containing lymphocytes, monocytes, and thrombocytes. In some animals, a nucleated erythrocyte layer was observed admixed with the granulocyte/mononuclear cell layer. A small clot within the buffy coat was seen in seven reptiles, and less definition of layers occurred in reptiles, with only one or two layers. Lymphocytes appeared toward the top of the buffy coat.

CONCLUSIONS

From a comparative hematology perspective, the buffy coat of mammals differs from that of birds and more from that of reptiles. The CTB technique can be used to study these differences in avian and reptilian hematology, especially to study atypical circulating cells, hemoparasites, or blood cell proportions in health and disease.

Functional characterization of neotropical snakes peripheral blood leukocytes subsets: Linking flow cytometry cell features, microscopy images and serum corticosterone levels

Reptiles are the unique ectothermic amniotes, providing the key link between ectothermic anamniotes fish and amphibians, and endothermic birds and mammals; becoming an important group to study with the aim of providing significant knowledge into the evolutionary history of vertebrate immunity. Classification systems for reptiles' leukocytes have been described by their appearance rather than function, being still inconsistent. With the advent of modern techniques and the establishment of analytical protocols for snakes' blood by flow cytometry, we bring a qualitative and quantitative assessment of innate activities presented by snakes' peripheral blood leukocytes, thereby linking flow cytometric features with fluorescent and light microscopy images. Moreover, since corticosterone is an important immunomodulator in reptiles, hormone levels of all blood samples were measured. We provide novel and additional information which should contribute to better understanding of the development of the immune system of reptiles and vertebrates.

Flow cytometric characterization of peripheral blood leukocyte populations of 3 neotropical snake species: Boa constrictor, Bothrops jararaca, and Crotalus durissus

BACKGROUND

The reptilian immune system is represented by innate, humoral, and cell-mediated mechanisms, involving different types of blood leukocytes. The development of optimized methods for the advanced study of origin and function of reptilian blood leukocytes is needed.

OBJECTIVES

The purpose of the study was to optimize leukocyte density gradient isolation protocols from snake peripheral blood samples, and characterize recovered cells by flow cytometry based on size and internal complexity for a qualitative and semi-quantitative assessment of leukocyte populations in one boa (Boa constrictor), and 2 viper species (Bothrops jararaca, Crotalus durissus).

METHODS

Blood samples from 30 snakes (10 from each species, 5 males and 5 females) were collected in tubes with sodium heparin. Fresh blood was centrifuged with either ficoll-paque PLUS or percoll density gradients for leukocyte isolation. Flow cytometric leukocyte gates were defined based on size (forward scatter [FSC]) and internal complexity (side scatter [SSC]). Relative leukocyte differential counts after sorting the cells in these gates in one snake for each species were compared to conventional light microscopic differential counts on unsorted isolated leukocytes.

RESULTS

There was no statistical difference in the relative leukocyte populations, including heterophils, azurophils, and small and large lymphocytes between samples isolated by ficoll or percoll. Four leukocyte gates were identified based on their location in FSC/SSC cytograms. The relative leukocyte differential counts after sorting in single animals showed some agreement with the light microscopy differential count on unsorted cells.

CONCLUSIONS

Based on FSC and SSC, 4 distinct leukocyte populations were found in ficoll or percoll density gradient isolated leukocytes from peripheral blood from boa and viper species. Further optimization of the technique should allow the performance of functional assays.

Evaluation of immune functions in captive immature loggerhead sea turtles (Caretta caretta)

Sea turtles face numerous environmental challenges, such as exposure to chemical pollution and biotoxins, which may contribute to immune system impairment, resulting in increased disease susceptibility. Therefore, a more thorough assessment of the host's immune response and its susceptibility is needed for these threatened and endangered animals. In this study, the innate and acquired immune functions of sixty-five clinically healthy, immature, captive loggerhead sea turtles (Caretta caretta) were assayed using non-lethal blood sample collection. Functional immune assays were developed and/or optimized for this species, including mitogen-induced lymphocyte proliferation, natural killer (NK) cell activity, phagocytosis, and respiratory burst. Peripheral blood mononuclear cells (PBMC) and phagocytes were isolated by density gradient centrifugation on Ficoll-Paque and discontinuous Percoll gradients, respectively. The T lymphocyte mitogens ConA significantly induced lymphocyte proliferation at 1 and 2 μg/mL while PHA significantly induced lymphocyte proliferation at 5 and 10 μg/mL. The B lymphocyte mitogen LPS significantly induced proliferation at 1 μg/mL. Monocytes demonstrated higher phagocytic activity than eosinophils. In addition, monocytes exhibited respiratory burst. Natural killer cell activity was higher against YAC-1 than K-562 target cells. These optimized assays may help to evaluate the integrity of loggerhead sea turtle's immune system upon exposure to environmental contaminants, as well as part of a comprehensive health assessment and monitoring program.

Melanin-based colouration as a potential indicator of male quality in the lizard Zootoca vivipara (Squamata: Lacertidae)

In many animals, aspects of colouration are hypothesized to convey information on the body condition or quality of individuals. This idea has been tested primarily for the carotenoid-based component of body colouration. The significance of other pigments in this context has received far less attention. In the common lizard, Zootoca vivipara, the degree of black patterning on the ventrum and throats is sexually dimorphic and varies considerably among individuals. In this study, we examine whether this melanin-based component of body colouration may reflect individual differences in quality (SVL, condition, immune response). We find that males (but not females) with a higher degree of ventral patterning mount a stronger phytohemagglutinin-induced immune response. The amount of black patterning does not correlate with body size, body condition, aspects of dorsal colouration or parasite load. We conclude that in male Zootoca vivipara, melanin-based ventral colouration may signal an aspect of immune capacity to sexual rivals or potential partners.

Litter quality and inflammatory response are dependent on mating strategy in a reptile

Maintenance of health and the production of offspring are competing processes that can result in trade-offs. As vertebrates invest substantial resources in their immune system, it is crucial to understand the interactions between immunity and reproductive strategies. In the lizard Zootoca vivipara, females have condition- and context-dependent mating strategies. We predicted that, if the risk of infection is higher for polyandrous females, then polyandrous females should invest more in immune system while monandrous females should invest more in reproduction. In order to test our prediction, we captured 62 gravid females of known age in a natural population; we kept them until parturition to access to their offspring. Then, using microsatellite marker-based paternity analyses within litters, we determine the mating strategy of females (monandrous or polyandrous). Females were also challenged with PHA to estimate their inflammatory response. Our results show that polyandrous females have a higher PHA response than the monandrous females, and that monandrous females produce more males and more juveniles of better body condition than polyandrous females. The relationship between mating behaviour and immune function may have consequences for females and may shape the evolution of mating systems.

Variation in the seasonal patterns of innate and adaptive immunity in the red-eared slider (Trachemys scripta)

The primary function of the immune system is to protect the organism from invading pathogens. In vertebrates, this has resulted in a multifaceted system comprised of both innate and adaptive components. The immune system of all jawed vertebrates is complex, but unlike the endothermic vertebrates, relatively little is known about the functioning of the ectothermic vertebrate immune system, especially the reptilian system. Because turtles are long-lived ectotherms, factors such as temperature and age may affect their immune response, but comprehensive studies are lacking. We investigated variation in immune responses of adult male and female red-eared sliders (Trachemys scripta) across the entire active season. We characterized seasonal variation in innate, cell-mediated and humoral components via bactericidal capacity of plasma, delayed-type hypersensitivity and total immunoglobulin levels, respectively. Results indicate that all immune measures varied significantly across the active season, but each measure had a different pattern of variation. Interestingly, temperature alone does not explain the observed seasonal variation. Immune measures did not vary between males and females, but immunoglobulin levels did vary with age. This study demonstrates the highly dynamic nature of the reptilian immune system, and provides information on how biotic and abiotic factors influence the immune system of a long-lived ectotherm.

Understanding the vertebrate immune system: insights from the reptilian perspective

Reptiles are ectothermic amniotes, providing the key link between ectothermic anamniotic fishes and amphibians, and endothermic amniotic birds and mammals. A greater understanding of reptilian immunity will provide important insights into the evolutionary history of vertebrate immunity as well as the growing field of eco-immunology. Like mammals, reptile immunity is complex and involves innate, cell-mediated and humoral compartments but, overall, there is considerably less known about immune function in reptiles. We review the current literature on each branch of the reptilian immune system, placing this information in context to other vertebrates. Further, we identify key areas that are prime for research as well as areas that are lagging because of lack of reagents in non-model systems.