Seasonal distribution and hormonal modulation of reptilian T cells

Haematology, biochemistry and morphological features of peripheral blood cells in captive Boa constrictor

The common boa (Boa constrictor) belongs to the family Boidae and represents one of the most popular traded and kept snake species in captivity. The early diagnosis, prevention and prophylaxis of diseases in this species, and in reptiles in general, still pose major challenges, also due to the lack of reliable reference values. This prompted us to conduct a study on clinically healthy captive B. constrictor to assess their basic health parameters in the blood (haematological and biochemical values, stress markers). Several parameters differed significantly between younger (<3 years) and older (≥3 years) boas; in the latter, the percentages of eosinophils, the haemoglobin and haematocrit levels, as well as the albumin and total protein levels, were higher. In male snakes, cholesterol levels were significantly higher than in females. Light and electron microscopy as well as immunohistochemistry served to identify and determine the morphological features of peripheral blood cells, that is, heterophils, basophils, eosinophils, azurophils, monocytes, lymphocytes, thrombocytes and erythrocytes. Leukocyte subpopulations, that is, T and B cells and monocytes, were also identified based on specific marker expression. The study provides data on haematological, biochemical and stress hormone levels, suitable as reference values, and on the blood cell morphology of B. constrictor which can serve as a guideline for further research on this species.

EPIDEMIOLOGY OF EMYDOIDEA HERPESVIRUS 1 IN FREE-RANGING BLANDING'S TURTLES (EMYDOIDEA BLANDINGII) FROM ILLINOIS

Herpesvirus infections have been associated with high morbidity and mortality in populations of captive emydid chelonians worldwide, but novel herpesviruses have also recently been identified in apparently healthy free-ranging emydid populations. Blanding's turtle (Emydoidea blandingii), an endangered species in Illinois, has experienced range-wide declines because of habitat loss, degradation, and fragmentation. A novel herpesvirus, Emydoidea herpesvirus 1 (EBHV1), was identified in Blanding's turtles in DuPage County, IL, in 2015. Combined oral-cloacal swabs were collected from radio transmitter-fitted and trapped (n = 54) turtles multiple times over the 2016 activity season. In addition, swabs were collected at a single time point from trapped and incidentally captured (n = 84) Blanding's turtles in DuPage (n = 33) and Lake (n = 51) counties over the same field season. Each sample was tested for EBHV1 using quantitative polymerase chain reaction (qPCR). EBHV1 was detected in 15 adult females for an overall prevalence of 10.8% (n = 15/138; 95% confidence interval [CI]: 6.2-17.3%). In radio transmitter-fitted females, there was a significantly higher prevalence of EBHV1 DNA in May (23.8%, n = 10/42) than June (3.6%, n = 1/28), July (0%, n = 0/42), August (0%, n = 0/47), or September (7.7%, n = 3/39) (odds ratio: 12.19; 95% CI: 3.60-41.30). The peak in May corresponds to the onset of nesting and may be associated with increased physiologic demands. Furthermore, all positive turtles were qPCR negative in subsequent months. There were no clinical signs associated with EBHV1 detection. This investigation is the critical first step to characterizing the implications of EBHV1 for Blanding's turtle population health and identifying management changes that may improve sustainability.

Selected emerging infectious diseases of squamata

It is important that reptile clinicians have an appreciation for the epidemiology, clinical signs, pathology, diagnostic options, and prognostic parameters for novel and emerging infectious diseases in squamates. This article provides an update on emerging squamate diseases reported in the primary literature within the past decade. Updates on adenovirus, iridovirus, rhabdovirus, arenavirus, and paramyxovirus epidemiology, divergence, and host fidelity are presented. A new emerging bacterial disease of Uromastyx species, Devriesea agamarum, is reviewed. Chrysosporium ophiodiicola-associated mortality in North American snakes is discussed. Cryptosporidium and pentastomid infections in squamates are highlighted among emerging parasitic infections.

The effects of environment and physiological cyclicity on the immune system of Viperinae

One of the important aspects of species' survival is connected with global climate changes, which also conditions the epidemiology of infectious diseases. Poikilotherms are exposed, as other species, to climatic influence, especially due to their physiological peculiarities such as important stages of their life cycle: hibernation, shedding, and active phase. The immune system serves as an accurate indicator of the health status and stress levels in these species. This study aimed to monitor the changes of innate (leukocyte subpopulations and total immune globulins) and adaptive immunity (in vitro leukocyte blast transformation) of two viper species, V. berus berus and V. ammodytes ammodytes, endemic in Europe and spread in different regions of Romania during their three major life cycles, hibernation, shedding, and active phase. The results indicated that seasonal variance and cycle rather than species and regional distribution influence the functionality of the immune system.

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

To understand the role of the immune system with respect to disease in reptiles, there is the need to develop tools to assess the host's immune response. An important tool is the development of molecular markers to identify immune cells, and these are limited for reptiles. We developed a technique for the cryopreservation of peripheral blood mononuclear cells and showed that a commercially available anti-CD3 epsilon chain antibody detects a subpopulation of CD3 positive peripheral blood lymphocytes in the marine turtle Chelonia mydas. In the thymus and in skin inoculated with phytohemagglutinin, the same antibody showed the classical staining pattern observed in mammals and birds. For Western blot, the anti-CD3 antibodies identified a 17.6k Da band in membrane proteins of peripheral blood mononuclear cell compatible in weight to previously described CD3 molecules. This is the first demonstration of CD3+ cells in reptiles using specific antibodies.

Combining immunological and molecular data to assess phylogenetic relations of some Greek Podarcis species

Most recent molecular studies revealed the phylogeny of Greek Podarcis species, which for years remained elusive, due to discordant data produced from various chromosomal, complement fixation and protein studies. In this report, we analyzed cellular immune responses of spleen-derived lymphocytes from six allopatric Podarcis species encountered in Greece, by assessing two-way mixed lymphocyte reaction (MLR)-induced proliferation. On the basis of stimulation indices (S.I.) as determined from cultures set up from xenogeneic splenocytes coincubated in pairs, we generated a phylogenetic tree, fully consistent with the phylogenetic relationships of Podarcis as determined by parallel analyses based on partial mitochondrial (mt) DNA sequences. Although the exact mechanisms triggering lymphocyte responses in lizard two-way xenogeneic MLR are not fully understood, our results show the potential use of cell-mediated immune responses as an additional approach to mtDNA analysis, for species delimitation within specific lizard taxa.

Mechanism of androgen-induced thymic atrophy in the wall lizard, Hemidactylus flaviviridis: an in vitro study

The present in vitro study demonstrates the effect of androgen on thymocyte apoptosis leading to thymic atrophy in the wall lizard, Hemidactylus flaviviridis. Thymocytes collected from castrated lizards were incubated with varying concentrations of dihydrotestosterone (DHT) to observe its effect on proliferation and apoptosis. DHT treatment reduced the tritiated thymidine incorporation in thymocytes, suggesting that androgen directly inhibits thymocyte proliferation. It also caused apoptosis of thymocytes effectively at 10(-7)M. However, the increased apoptotic action of DHT was indirectly mediated through thymic epithelial cell-rich stromal cell components (TEC). This observation was reaffirmed by in vitro incubation of thymocytes with DHT-pretreated TEC-conditioned medium. However, the DHT-induced TEC-secreted apoptotic factors could induce thymocyte DNA fragmentation only when DHT was added to the conditioned medium. It implies that DHT priming of thymocytes is required for the apoptotic effect of DHT-induced TEC-secreted factor. DHT-induced thymocyte apoptosis was found to be caspase-dependent since it activated the initiator (caspase-9) and effector caspases (caspases-3 and -7) as well as cleaved the enzyme substrate poly(ADP-ribose) polymerase (PARP). Further, the apoptotic effect of DHT was routed through its classical receptors, as non-steroidal antiandrogen flutamide blocked the DHT-induced thymocyte apoptosis. The inhibition of apoptosis by transcription/translation inhibitors further substantiates the genomic pathway of DHT action. It can be concluded that DHT, in addition to inhibiting thymocyte proliferation directly, accelerates caspase-dependent apoptotic process in thymocytes indirectly through TEC via a genomic pathway. Nevertheless, the priming of thymocytes with DHT is required for the apoptotic effect of TEC-secreted factor.

Reptile virology

Reptiles are hosts to diverse viral infections. This article reviews the viruses that are known to infect reptiles and discusses associated pathology, available diagnostic methods, and management techniques for the reptile clinician.

Glucocorticoid-induced thymocyte apoptosis in wall lizard Hemidactylus flaviviridis

The aim of the present study is to demonstrate the phenomenon and mechanism of GC-induced cell death of thymocytes in wall lizard Hemidactylus flaviviridis. Lizard thymocytes were treated in vitro with different concentration of corticosterone (CS) for varying durations and the genomic DNA was analyzed both by agarose gel electrophoresis and flow cytometry. Corticosterone induced DNA fragmentation in a dose-dependent manner, as the DNA laddering was more prominent at 10(-14) M than at lower concentrations. However, CS could activate the programmed cell death of thymocytes only when incubated for 48 h and not at 3, 6, 12, or 24 h. Similar results were obtained following the flow cytometric analysis. The highest apoptotic cell death was noted at 10(-14) M concentration. CS-induced programmed cell death was decreased dramatically when the thymocytes were preincubated with RU 486 (10(-9) ng /ml) for 24 h, suggesting the classical receptor-mediated genomic pathway of glucocorticoid action in inducing apoptosis of thymocytes in wall lizard H. flaviviridis.

Effects of 17alpha-ethinylestradiol on immune parameters in the lizard Sceloporus occidentalis

We examined the effect of 17alpha-ethinylestradiol on immunity of the Western fence lizard, Sceloporus occidentalis. Injection of 17alpha-ethinylestradiol resulted in dose-dependent suppression of peripheral blood leukocyte levels as determined by cell counts, whereas total spleen cell levels were decreased only at higher doses of 17alpha-ethinylestradiol. In contrast, spleen cell proliferation was enhanced by 17alpha-ethinylestradiol as measured by reduction of MTT to formazan following a two-way mixed lymphocyte reaction. Antibody responses were unaffected. Effects on peripheral blood leukocyte levels and spleen cell proliferation similar to those observed in response to injection of 17alpha-ethinylestradiol were observed following injection of a single dose of hydrocortisone. However, injection of lizards with 17alpha-ethinylestradiol did not result in a significant increase in serum cortisol. Results of this study suggest that exposure of Western fence lizards to 17alpha-ethinylestradiol leads to decreased numbers of circulating leukocytes and total spleen cell numbers and the enhancement of spleen cell proliferation in a two-way mixed lymphocyte reaction. These effects probably involve mechanisms other than or in addition to the induction of cortisol release.

The effect of the seasonal cycle on the splenic leukocyte functions in the turtle Mauremys caspica

The reptile immune system is strikingly affected by seasonal variations, which induce changes in the structure of the lymphoid organs and in the function of the leukocytes. The aim of this work is to study several functions of splenic leukocytes from the turtle Mauremys caspica along its seasonal cycle. The functions assayed were adherence to substrate, mobility directed to a chemoattractant gradient (chemotaxis), lymphoproliferative response to mitogens, antibody-dependent cellular cytotoxicity, and natural killer-like cell-mediated cytotoxicity. Splenic leukocytes showed a positive response in all the assays, and this response was similar to that of mammals. In regard to the effect of the seasonal cycle, we have observed in winter a low adherence to substratum and high chemotaxis and cytotoxic activity, whereas in spring, only lymphoproliferation induced by mitogens showed high values except with lipopolysaccharide, which did not induce any seasonal variation in proliferation percentages. In summer, a high chemotaxis and cytotoxicity were observed, while in autumn, adherence to substratum was increased, but chemotaxis, cytotoxicity, and proliferation were clearly diminished. Our results demonstrate that splenic leukocyte functions are affected by the seasonal cycle, which induces a different pattern of response depending on the function studied.

Life history of a malaria parasite (Plasmodium mexicanum) in its host, the western fence lizard (Sceloporus occidentalis): host testosterone as a source of seasonal and among-host variation?

The course of infection of a malaria parasite (Plasmodium mexicanum) is highly variable in its host, the fence lizard (Sceloporus occidentalis). However, a seasonal trend is superimposed on this variation such that gametocyte production is intensified during mid- to late summer. Host testosterone levels follow a similar seasonal fluctuation and are variable among individual lizards. We sought to determine if testosterone levels affect seasonal and among-host variation in 11 P. mexicanum life history traits: rate of increase in level of infection (3 measures), peak parasitemia (3 measures), duration of increase (3 measures), time to detectable infection, and timing of production of gametocytes. We followed the course of infection in 125 male S. occidentalis, each randomly assigned to 1 of 4 treatment groups: castrated, castrated and implanted with exogenous testosterone, sham implanted, and unmanipulated controls. Median values for the 11 life history traits did not differ among treatment groups, and variances were homogeneous among the treatment groups for 10/11 traits. However, elevated testosterone significantly reduced the variation in timing of the onset of gametocyte production. Therefore, testosterone does not appear to be a primary regulator of P. mexicanum life history, yet testosterone may have some effect on when gametocytes first become detectable.