Histopathology of the thymus

Thymic depletion of lymphocytes is associated with the virulence of PRRSV-1 strains

Porcine reproductive and respiratory syndrome virus (PRRSV) exists as two distinct viruses, type 1 (PRRSV-1) and type 2 (PRRSV-2). Atrophy of the thymus in PRRSV-2 infected piglets has been associated with a loss of thymocytes. The present study aimed to evaluate the impact of PRRSV-1 strains of differing virulence on the thymus of infected piglets by analysing the histomorphometry, the presence of apoptotic cells and cells producing cytokines. Thymic samples were taken from animals experimentally infected (with LV, SU1-bel, and 215-06 strains) or mock inoculated animals at 3, 7 and 35days post-infection (dpi) and processed for histopathological and immunohistochemical analyses. PRRSV antigen was detected in the thymus from 3dpi until the end of the study in all virus-infected animals with the highest numbers of infected cells detected in SU1-bel group. The histomorphometry analysis and counts of CD3(+) thymocytes in the thymic cortex displayed significant differences between strains at different time-points (p≤0.011), with SU1-bel group showing the most severe changes at 7dpi. Cell death displayed statistically significant increase in the cortex of all infected animals, with SU1-bel group showing the highest rate at 3 and 7dpi. The number of cells immunostained against IL-1α, TNF-α and IL-10 were predominantly detected in the medulla (p≤0.01). An increase in the number of TNF-α and IL-10 positive cells was observed in LV and SU-1bel groups. Our results demonstrate that different PRRSV-1 strains induced depletion of the thymic cortex due to apoptosis of thymocytes and that the most severe depletion was associated with the highly virulent SU1-bel strain.

Thymic hyperplasia after chemotherapy in adults with mature B cell lymphoma and its influence on thymic output and CD4(+) T cells repopulation

To investigate the thymic regenerative potential in adults accepting chemotherapy for lymphoma. The dynamics of thymic activity in 54 adults from baseline to 12 mo post-chemotherapy was analyzed by assessing thymic structural changes with serial computed tomography (CT) scans, and correlating these with measurements of thymic output by concurrent analysis of single-joint (sj) T-cell receptor excision circles (sjTREC) and CD31⁺ recent thymic emigrants (RTE) in peripheral blood. Furthermore, the consequence of thymic renewal on peripheral CD4⁺ T cell recovery after chemotherapy was evaluated. Time-dependent changes of thymic size and thymic output assessed by both sjTREC levels and CD31⁺ RTE counts in peripheral blood were observed during and after chemotherapy. Enlargement of thymus over baseline following chemotherapy regarded as rebound thymic hyperplasia (TH) was identified in 20 patients aged 18−53 y (median 33 y). By general linear models repeated measure analysis, it was found that, patients with TH (n = 20) had a faster recovery of sjTREC levels and CD31⁺ RTE counts after chemotherapy than patients with comparable age, gender, diagnosis, disease stage, thymic volume and output function at baseline but without TH (n = 18) (p = 0.035, 0.047); besides, patients with TH had a faster repopulation of both naïve CD4⁺ T cell and natural regulatory CD4⁺ T cell subsets than those without TH (p = 0.042, 0.038). These data suggested that adult thymus retains the capacity of regeneration after chemotherapy, especially in young adults. The presence of TH could contribute to the renewal of thymopoiesis and the replenishment of peripheral CD4⁺ T cell pool following chemotherapy in adults.

Spontaneous Pathology and Routine Clinical Pathology Parameters in Aging Beagle Dogs

AstraZeneca ran a bespoke study to generate age-matched clinical pathology and histopathology data from a cohort of Beagle dogs aged between 25 and 37 months to support the use of these older animals in routine preclinical toxicology studies. As the upper age range of Beagle dogs routinely used in toxicology studies does not normally exceed 24 months, there is an absence of appropriate age-matched historical control data. The generation of such data was crucial to understand whether age-related differences in spontaneous findings might confound the interpretation of toxicology study data. While the majority of the histopathology findings in all the older dogs occurred at a similar prevalence as those expected in young adult dogs (<24 months), a number of differences were observed in the thymus (involution), bone marrow (increased adiposity), testes (degenerative changes), and lung (fibrosis, pigment and alveolar hyperplasia) that could be misinterpreted as a test article effect. Minor differences in some clinical pathology values (hemoglobin, alkaline phosphatase, absolute reticulocytes) were of a small magnitude and considered unlikely to affect the interpretation of study data.

Increased Expression of Connective Tissue Growth Factor (CTGF) in Multiple Organs After Exposure of Non-Human Primates (NHP) to Lethal Doses of Radiation

Exposure to sufficiently high doses of ionizing radiation is known to cause fibrosis in many different organs and tissues. Connective tissue growth factor (CTGF/CCN2), a member of the CCN family of matricellular proteins, plays an important role in the development of fibrosis in multiple organs. The aim of the present study was to quantify the gene and protein expression of CTGF in a variety of organs from non-human primates (NHP) that were previously exposed to potentially lethal doses of radiation. Tissues from non-irradiated NHP and NHP exposed to whole thoracic lung irradiation (WTLI) or partial-body irradiation with 5% bone marrow sparing (PBI/BM5) were examined by real-time quantitative reverse transcription PCR, western blot, and immunohistochemistry. Expression of CTGF was elevated in the lung tissues of NHP exposed to WTLI relative to the lung tissues of the non-irradiated NHP. Increased expression of CTGF was also observed in multiple organs from NHP exposed to PBI/BM5 compared to non-irradiated NHP; these included the lung, kidney, spleen, thymus, and liver. These irradiated organs also exhibited histological evidence of increased collagen deposition compared to the control tissues. There was significant correlation of CTGF expression with collagen deposition in the lung and spleen of NHP exposed to PBI/BM5. Significant correlations were observed between spleen and multiple organs on CTGF expression and collagen deposition, respectively, suggesting possible crosstalk between spleen and other organs. These data suggest that CTGF levels are increased in multiple organs after radiation exposure and that inflammatory cell infiltration may contribute to the elevated levels of CTGF in multiple organs.

Histologic Features of Postnatal Development of Immune System Organs in the Sprague-Dawley Rat

The immune system of the rat undergoes substantial functional and morphological development during the postnatal period. Some aspects of this development are genetically predetermined, while other aspects depend on environmental influences. Detailed information on postnatal development is important in the interpretation of histopathologic findings in juvenile toxicology and pubertal assay studies, as well as other studies conducted in juvenile rats. Studies were conducted to provide detailed characterization of histologic features of the major functional compartments of immune system organs in male and female Sprague-Dawley rats at weekly intervals from the day of birth through postnatal day (PND) 42. Maturation of the individual immune system organs occurred across a range of ages, with histologic maturation of T-cell-related compartments typically occurring prior to maturation of B-cell-related compartments. The sequence of histologic maturation was bone marrow and thymus on PND 14, mesenteric lymph node on PND 21, Peyer's patches and bronchus-associated lymphoid tissue on PND 28, mandibular lymph node, nasopharynx-associated lymphoid tissue, and diffuse mucosal mononuclear cell population of small intestine on PND 35, and spleen on PND 42. An estimation of functional maturation can be made based on the morphological indications of maturity of each compartment of immune system organs, but histologic indications of maturity do not confirm functional immunocompetence.

Differences in post-mortem findings after stillbirth in women with and without diabetes

AIMS

The reason for the fivefold increased risk of stillbirth in women with diabetes is not known. Further understanding of the underlying mechanisms may facilitate identification of pregnancies at increased risk. We have compared post-mortem reports in matched pairs of stillbirths in women with and without diabetes.

METHODS

Post-mortem reports were provided by the Centre for Maternal and Child Enquiries. Stillbirths as a result of lethal congenital and genetic abnormalities were excluded. Whole body, placenta and organ weights and histo-pathological findings in cases and controls were compared and also related to published reference values.

RESULTS

We analysed post-mortem reports on 23 matched pairs of stillbirths from 2009 to 2010. Mean placental weight in women with diabetes was 75 g less than in control subjects (95% CI -143 to -7 g; P = 0.032). In maternal diabetes, the thymus was often small and showed a 'starry sky' pattern on histology in 11 of 20 cases compared with four of 22 controls (P = 0.03). This histological finding was associated with a particularly low mean placental weight z-score -2.1 (1.1) standard deviations below a reference population corrected for gestational age.

CONCLUSIONS

In over half of the stillbirths occurring in women with diabetes, there was a 'starry sky' appearance in the fetal thymus on histology, this being associated with a small placenta. These findings are consistent with a critical subacute metabolic disturbance being a prominent cause of the increased risk of stillbirth in pregnancies complicated by maternal diabetes.

Drug-induced reactivation of apoptosis abrogates HIV-1 infection

HIV-1 blocks apoptosis, programmed cell death, an innate defense of cells against viral invasion. However, apoptosis can be selectively reactivated in HIV-infected cells by chemical agents that interfere with HIV-1 gene expression. We studied two globally used medicines, the topical antifungal ciclopirox and the iron chelator deferiprone, for their effect on apoptosis in HIV-infected H9 cells and in peripheral blood mononuclear cells infected with clinical HIV-1 isolates. Both medicines activated apoptosis preferentially in HIV-infected cells, suggesting that the drugs mediate escape from the viral suppression of defensive apoptosis. In infected H9 cells, ciclopirox and deferiprone enhanced mitochondrial membrane depolarization, initiating the intrinsic pathway of apoptosis to execution, as evidenced by caspase-3 activation, poly(ADP-ribose) polymerase proteolysis, DNA degradation, and apoptotic cell morphology. In isolate-infected peripheral blood mononuclear cells, ciclopirox collapsed HIV-1 production to the limit of viral protein and RNA detection. Despite prolonged monotherapy, ciclopirox did not elicit breakthrough. No viral re-emergence was observed even 12 weeks after drug cessation, suggesting elimination of the proviral reservoir. Tests in mice predictive for cytotoxicity to human epithelia did not detect tissue damage or activation of apoptosis at a ciclopirox concentration that exceeded by orders of magnitude the concentration causing death of infected cells. We infer that ciclopirox and deferiprone act via therapeutic reclamation of apoptotic proficiency (TRAP) in HIV-infected cells and trigger their preferential elimination. Perturbations in viral protein expression suggest that the antiretroviral activity of both drugs stems from their ability to inhibit hydroxylation of cellular proteins essential for apoptosis and for viral infection, exemplified by eIF5A. Our findings identify ciclopirox and deferiprone as prototypes of selectively cytocidal antivirals that eliminate viral infection by destroying infected cells. A drug-based drug discovery program, based on these compounds, is warranted to determine the potential of such agents in clinical trials of HIV-infected patients.

The compensatory expression of reproductive hormone receptors in the thymus of the male rat following active immunization against GnRH

To determine whether hormone-receptor signaling pathways in the thymus are altered by active immunization against gonadotrophin-releasing hormone I (GnRH), 3-week-old Sprague-Dawley male rats received GnRH-tandem-OVA peptides (200 μg/ml), and the effects were compared to a control group. Serum testosterone, LH and FSH concentrations were markedly reduced, with severe testicular atrophy, compared to controls, demonstrating effective blockade of the pituitary-gonadal axis. The reduction in LH and FSH concentrations in the thymus of immunized animals was lower than that observed in the serum, where a significant difference (P<0.001) in concentration was observed between both groups. Concentrations of GnRH were increased in the thymus of immunized rats. In thymic tissue, GnRHR, FSHR and LHR demonstrated stronger immunostaining, and AR weaker staining, in the immunized group compared to controls. Reproductive hormone receptor mRNA expression was consistent with protein variations in the immunized thymus. Compared to controls, GnRHR gene levels were significantly increased (P<0.05), however, AR mRNA expression were greatly decreased with immune week-age (P<0.05). Both FSHR and LHR mRNA expression levels were significantly higher in the treated group than in controls in the first three samples (P<0.05). When GnRHR was blocked by an antagonist in thymocytes, all reproductive hormone receptor gene expressions were significantly increased (P<0.001). In summary, these findings suggest that active immunization against GnRH can up-regulate GnRH receptor and gonadotropin receptor signaling, by stimulating thymic autocrine and paracrine function, whereas the androgen receptor is down-regulated due to a lack of testosterone secretion in the thymus.

Chronic social stress during adolescence: interplay of paroxetine treatment and ageing

Exposure to chronic stress during developmental periods is a risk factor for a number of psychiatric disorders. While the direct effects of stress exposure have been studied extensively, little is known about the long-lasting effects and the interaction with ageing. The same holds true for the treatment with selective serotonin reuptake inhibitors (SSRIs), which have been shown to prevent or reverse some stress-induced effects. Here, we studied the direct and long-lasting impact of chronic social stress during adolescence and the impact of chronic treatment with the SSRI paroxetine in adulthood and aged animals. Therefore, male CD1 mice at the age of 28 days were subjected to 7 weeks of chronic social stress. Treatment with paroxetine was performed per os with a dosage of 20 mg/g BW. We were able to reverse most of the effects of chronic social stress in adult mice (4 months old) and to some extend in aged animals (15 months old) with the SSRI treatment. Especially the regulation of the HPA axis seems to be affected in aged mice with a shift to the use of vasopressin. Our results demonstrate that chronic stress exposure and antidepressant treatment at the end of the developmental period can have a significant and long-lasting impact, highly relevant for healthy ageing.

Preclinical toxicity evaluation of erythrocyte-encapsulated thymidine phosphorylase in BALB/c mice and beagle dogs: an enzyme-replacement therapy for mitochondrial neurogastrointestinal encephalomyopathy

Erythrocyte-encapsulated thymidine phosphorylase (EE-TP) is currently under development as an enzyme replacement therapy for mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), an autosomal recessive disorder caused by a deficiency of thymidine phosphorylase. The rationale for the development of EE-TP is based on the pathologically elevated metabolites (thymidine and deoxyuridine) being able to freely diffuse across the erythrocyte membrane where the encapsulated enzyme catalyses their metabolism to the normal products. The systemic toxic potential of EE-TP was assessed when administered intermittently by iv bolus injection to BALB/c mice and Beagle dogs for 4 weeks. The studies consisted of one control group receiving sham-loaded erythrocytes twice weekly and two treated groups, one dosed once every 2 weeks and the other dosed twice per week. The administration of EE-TP to BALB/c mice resulted in thrombi/emboli in the lungs and spleen enlargement. These findings were also seen in the control group, and there was no relationship to the number of doses administered. In the dog, transient clinical signs were associated with EE-TP administration, suggestive of an immune-based reaction. Specific antithymidine phosphorylase antibodies were detected in two dogs and in a greater proportion of mice treated once every 2 weeks. Nonspecific antibodies were detected in all EE-TP-treated animals. In conclusion, these studies do not reveal serious toxicities that would preclude a clinical trial of EE-TP in patients with MNGIE, but caution should be taken for infusion-related reactions that may be related to the production of nonspecific antibodies or a cell-based immune response.

End-point effector stress mediators in neuroimmune interactions: their role in immune system homeostasis and autoimmune pathology

Much evidence has identified a direct anatomical and functional link between the brain and the immune system, with glucocorticoids (GCs), catecholamines (CAs), and neuropeptide Y (NPY) as its end-point mediators. This suggests the important role of these mediators in immune system homeostasis and the pathogenesis of inflammatory autoimmune diseases. However, although it is clear that these mediators can modulate lymphocyte maturation and the activity of distinct immune cell types, their putative role in the pathogenesis of autoimmune disease is not yet completely understood. We have contributed to this field by discovering the influence of CAs and GCs on fine-tuning thymocyte negative selection and, in particular, by pointing to the putative CA-mediated mechanisms underlying this influence. Furthermore, we have shown that CAs are implicated in the regulation of regulatory T-cell development in the thymus. Moreover, our investigations related to macrophage biology emphasize the complex interaction between GCs, CAs and NPY in the modulation of macrophage functions and their putative significance for the pathogenesis of autoimmune inflammatory diseases.

Immune system and immune responses in fish and their role in comparative immunity study: a model for higher organisms

The basal position of fish in vertebrate phylogeny makes them very attractive for genomic and functional comparative immunity studies. Adaptive immunity arose early in vertebrate evolution, 450 million years ago between the divergence of cyclostomes and cartilaginous fish. The fundamental immune molecules, which include Ag-recognizing lymphocytes, immunoglobulins (Abs and Ig-family TCR), MHC products, and recombination-activating (RAG) 1 and 2 genes and the recombination mechanisms (cause of diversity in TCRs and Igs) are similar in fish and mammals. These molecules and their immune response mechanisms unravelled the primordial vertebrate immune system repertoire and adaptive radiations. Moreover, screening of animal models like zebrafish has a great importance to discover genes involved in T cell development, thymic organogenesis, and in immunity to infections. The zebrafish model may also be useful for cancer research due to its various features like rapid development, tractable genetics, ease in in vivo imaging and chemical screening.

Differentiation of rodent immune and hematopoietic system reactive lesions from neoplasias

The immune and hematopoietic systems play an important role in the normal homeostasis of blood and blood cells and for immune responses to endogenous and exogenous processes and insults. In order to interpret histopathologic changes in the immune and hematopoietic systems, it is important to understand the normal anatomy and histology of the thymus, spleen, lymph nodes, bone marrow, and other tissues. The thymus, spleen, and lymph nodes can be categorized by anatomical compartments, each of which contributes to specific immune functions. Lesions may be diagnosed by interpretive or descriptive (semiquantitative) methods. The interpretation of these tissues by lesion in anatomical compartments should allow for better understanding of these reactions and more definitive pathologic findings. Proliferative lesions may be difficult to differentiate from lymphomas and leukemias. The use of immunohistochemistry, compartmental pathology, and methods for the evaluation of clonality will make interpretation easier.

Internet and Print Resources to Facilitate Pathology Analysis When Phenotyping Genetically Engineered Rodents

Genetically engineered mice and rats are increasingly used as models for exploring disease progression and mechanisms. The full spectrum of anatomic, biochemical, and functional changes that develop in novel, genetically engineered mouse and rat lines must be cataloged before predictions regarding the significance of the mutation may be extrapolated to diseases in other vertebrate species, including humans. A growing list of reference materials, including books, journal articles, and websites, has been produced in the last 2 decades to assist researchers in phenotyping newly engineered rodent lines. This compilation provides an extensive register of materials related to the pathology component of rodent phenotypic analysis. In this article, the authors annotate the resources they use most often, to allow for quick determination of their relevance to research projects.

Adrenocortical hypertrophy: establishing cause and toxicological significance

The primary cause of adrenocortical hypertrophy is increased adrenocorticotrophic hormone (ACTH) stimulation. In toxicology studies, such a condition can arise as a result of the stress response, but it may also occur due to deficient glucocorticoid feedback regulation of ACTH due to toxicity to the adrenal cortex. This latter condition is defined as adrenocortical insufficiency and represents a serious adverse toxic effect on the function of the adrenal cortex. Adrenocortical hypertrophy may occur in the absence of other adrenocortical lesions such that a toxicopathological mechanism is not obvious, for example by pharmacological inhibition of steroidogenesis at the biochemical level. This review discusses the different aetiological factors and mechanisms producing adrenocortical hypertrophy. The need for further evidence in ascribing findings to stress is discussed, as is a protocol for establishing differential diagnoses between stress-induced and toxicity-induced adrenocortical hypertrophy, which is useful in cases where there are no other histopathological lesions in the adrenal cortex. It is concluded that all cases of adrenocortical hypertrophy require further investigation or evidence to ascribe such findings to either stress or adrenocortical inhibition/insufficiency, and that all cases of adrenocortical insufficiency (whether due to a histopathological lesion or reversible pharmacological enzyme inhibition) represent a serious adverse effect that must be properly considered in toxicological risk assessment.

Fourteen-week toxicity study of green tea extract in rats and mice

The toxicity of green tea extract (GTE) was evaluated in 14-week gavage studies in male and female F344/NTac rats and B6C3F1 mice at doses up to 1,000 mg/kg. In the rats, no treatment-related mortality was noted. In the mice, treatment-related mortality occurred in male and female mice in the 1,000 mg/kg dose groups. The cause of early deaths was likely related to liver necrosis. Treatment-related histopathological changes were seen in both species in the liver, nose, mesenteric lymph nodes, and thymus. In addition, in mice, changes were seen in the Peyer's patches, spleen, and mandibular lymph nodes. The no adverse effect level (NOAEL) for the liver in both species was 500 mg/kg. In the nose of rats, the NOAEL in males was 62.5 mg/kg, and in females no NOAEL was found. No NOAEL was found in the nose of female or male mice. The changes in the liver and nose were considered primary toxic effects of GTE, while the changes in other organs were considered to be secondary effects. The nose and liver are organs with high metabolic enzyme activity. The increased susceptibility of the nose and liver suggests a role for GTE metabolites in toxicity induction.

Nonsystemic locally invasive thymic T-cell lymphoma in a fifteen-week-old male CD-1 mouse

A male CD-1 mouse from a segment I reproduction toxicity study died at the age of fifteen weeks. At necropsy, the thymus was abnormally enlarged and virtually obliterated the thoracic cavity. Histopathological examination of thymus revealed abundant cell population consisting of mature lymphocytes and few lymphoblasts arranged in cords and sheets. Neoplastic cells completely obliterated the thymic architecture, and loss of corticomedullary junction was evident. Microscopically, neoplastic cells were round with moderate cytoplasm. Nuclei were spherical and hyperchromatic with centrally placed nucleoli. Mitotic figures and tingible body macrophages imparting "starry sky appearance" were seen. Multifocal necrotic areas were also observed. Proliferating neoplastic cells invaded the thymic capsule, surrounding adipose tissue and neighboring organs such as lungs, heart and fat pad of aorta, esophagus, trachea, and thoracic vertebrae. No evidence of systemic metastasis was observed in other organs. Immunostained neoplastic cells were positive for CD3 antigen. Gross, histopathology, and immunohistochemistry results were suggestive of thymic T-cell lymphoma.

Importance of starting age for myelotoxicity study in dietary restricted rats

The aim of this study was to prove our hypothesis that adult rats with lowering of body weight gain, rats at 12 weeks of age as an example, are suitable for evaluation of myelotoxicity. Age-related differences between young rats (6-week-old study) and adult rats (12-week-old study) were analyzed in hematological examination values. The data of the young rats were reprinted from our previous report (Miyata et al., 2009) since our hypothesis was verified by comparison with that previous report. Several experimental groups were defined for the 12-week-old study as well as for the 6-week-old study; these included 5-fluorouracil (5-FU) treated groups receiving 12, 15 and 18 mg/kg/day (FU12, FU15 and FU18), pair-feeding groups (R12, R15 and R18 receiving the same amount of food as in the FU12, FU15 and FU18 groups, respectively) and a nontreated control group. Numerous hematologic and bone marrow parameters in the 5-FU treated groups were comparable to those in the corresponding pair-feeding groups in both age studies. Generally, the influences of undernutrition were more apparent in the young rats than in the adult rats. Histopathological examinations showed a decrease in hematopoiesis in the bone marrow in the 5-FU treated and pair-feeding groups. No apparent differences were observed in the decreased hematopoiesis between the 5-FU treated and pair-feeding groups in the 6-week-old study, but a difference between these groups was noted in the 12-week-old study; decreased hematopoiesis was more frequently noted in the 5-FU treated groups. These facts suggest that adult rats are more suitable than young rats for evaluation of 5-FU-induced myelotoxicity.

Magnetic resonance imaging of radiation-induced thymic atrophy as a model for pathologic changes in acute feline immunodeficiency virus infection

The development of a protocol to reproducibly induce thymic atrophy, as occurs in feline immunodeficiency virus (FIV) infection and other immunosuppressive diseases, and to consistently estimate thymic volume, provides a valuable tool in the search of innovative and novel therapeutic strategies. Magnetic resonance imaging (MRI) using the short tau inversion recovery (STIR) technique, with fat suppression properties, was determined to provide an optimized means of locating, defining, and quantitatively estimating thymus volume in young cats. Thymic atrophy was induced in four, 8-10-week-old kittens with a single, directed 500 cGy dose of 6 MV X-rays from a clinical linear accelerator, and sequential MR images of the cranial mediastinum were collected at 2, 7, 14, and 21 days post irradiation (PI). Irradiation induced a severe reduction in thymic volume, which was decreased, on average, to 47% that of normal, by 7 days PI. Histopathology confirmed marked, diffuse thymic atrophy, characterized by reduced thymic volume, decreased overall cellularity, increased apoptosis, histiocytosis, and reduced distinction of the corticomedullary junction, comparable to that seen in acute FIV infection. Beginning on day 7 PI, thymic volumes rebounded slightly and continued to increase over the following 14 days, regaining 3-35% of original volume. These findings demonstrate the feasibility and advantages of using this non-invasive, in vivo imaging technique to measure and evaluate changes in thymic volume in physiologic and experimental situations. All experimental protocols in this study were approved by the Institutional Animal Care and Use Committee (IACUC) at Auburn University.

Plasma osteopontin modulates chronic restraint stress-induced thymus atrophy by regulating stress hormones: inhibition by an anti-osteopontin monoclonal antibody

Osteopontin (OPN) is a cytokine implicated in mediating responses to certain stressors, including mechanical, oxidative, and cellular stress. However, the involvement of OPN in responding to other physical and psychological stress is largely unexplored. Our previous research revealed that OPN is critical for hind limb-unloading induced lymphoid organ atrophy through modulation of corticosteroid production. In this study, we demonstrate that OPN(-/-) mice are resistant to chronic restraint stress (CRS)-induced lymphoid (largely thymus) organ atrophy; additionally, the stress-induced up-regulation of corticosterone production is significantly reduced in OPN(-/-) mice. Underlying this observation is the fact that normal adrenocorticotropic hormone levels are substantially reduced in the OPN(-/-) mice. Our data demonstrate both that injection of OPN into OPN-deficient mice enhances the CRS-induced lymphoid organ atrophy and that injection of a specific anti-OPN mAb (2C5) into wild-type mice ameliorates the CRS-induced organ atrophy; changes in corticosterone levels were also partially reversed. These studies reveal that circulating OPN plays a significant role in the regulation of the hypothalamus-pituitary-adrenal axis hormones and that it augments CRS-induced organ atrophy.

Thymic cystic degeneration, pseudoepitheliomatous hyperplasia, and hemorrhage in a dog with brodifacoum toxicosis

Thymic cysts with pseudoepitheliomatous hyperplasia are described in a 7-month-old female American Eskimo Dog that died of complications from brodifacoum poisoning. Grossly, there was hemothorax with marked cranial mediastinal hemorrhage. Histologically, thymic lobules were expanded and distorted by irregular cysts, lined by single to multiple layers of plump to slightly attenuated polygonal squamous epithelial cells supported by a basement membrane (pseudoepitheliomatous hyperplasia). The thymus had a paucity of lymphocytes and lacked corticomedullary differentiation. Extensive hemorrhage within the cysts and thymic parenchyma extended into the adjacent adipose tissue. To the authors' knowledge, this is the first report of cystic thymic degeneration with pseudoepitheliomatous hyperplasia in a nonhuman species.

What’s So Special about the Developing Immune System?

The evolution of the subdiscipline of developmental immunotoxicology (DIT) as it exists today has been shaped by significant regulatory pressures as well as key scientific advances. This review considers the role played by legislation to protect children’s health, and on the emergence of immunotoxcity and developmental immunotoxicity guidelines, as well as providing some context to the need for special attention on DIT by considering the evidence that the developing immune system may have unique susceptibilities when compared to the adult immune system. Understanding the full extent of this potential has been complicated by a paucity of data detailing the development of the immune system during critical life stages as well as by the complexities of comparisons across species. Notably, there are differences between humans and nonhuman species used in toxicity testing that include specific differences relative to the timing of the development of the immune system as well as more general anatomic differences, and these differences must be factored into the interpretation of DIT studies. Likewise, understanding how the timing of the immune development impacts on various immune parameters is critical to the design of DIT studies, parameters most extensively characterized to date in young adult animals. Other factors important to DIT, which are considered in this review, are the recognition that effects other than suppression (e.g., allergy and autoimmunity) are important; the need to improve our understanding of how to assess the potential for DIT in humans; and the role that pathology has played in DIT studies in test animals. The latter point receives special emphasis in this review because pathology evaluations have been a major component of standard nonclinical toxicology studies, and could serve an important role in studies to evaluate DIT. This possibility is very consistent with recommendations to incorporate a DIT evaluation into standard developmental and reproductive toxicology (DART) protocols. The overall objective of this review is to provide a ‘snapshot’ of the current state-of-the-science of DIT. Despite significant progress, DIT is still evolving and it is our hope that this review will advance the science.

Immunomodulatory effects of dietary potassium perfluorooctane sulfonate (PFOS) exposure in adult Sprague-Dawley rats

Perfluorooctanesulfonate (PFOS) is a stable and environmentally persistent metabolic or degradation product of perfluorooctanyl compounds that were manufactured for a variety of industrial and consumer applications. PFOS itself was sold for use as a surfactant. The structurally related contaminants perfluorooctanoic acid (PFOA), perfluorodecanoic acid (PFDA), and N-ethyl perfluorooctane sulfonamide (N-EtPFOSA) were shown to suppress immune responses in laboratory rodents. Relatively low doses of PFOS were found to be immunosuppressive in mice. To assess effects of PFOS on the rat immune system at doses known to alter hepatic function, changes in the morphology and function of immune tissues and cells were measured in adult rats exposed to PFOS in their diet for 28 d at levels ranging from 2 to 100 mg PFOS/kg diet (corresponding to approximately 0.14 to 7.58 mg/kg body weight [bw]/d) and compared to those receiving control diet. Body weight reductions were significant in male and female rats exposed to 50 and 100 mg PFOS/kg diet. Liver/body weight was significantly increased in females exposed to 2 mg PFOS/kg diet and in males exposed to 20 mg PFOS/kg diet. Female rats exposed to 100 mg PFOS/kg diet exhibited a significant increase in spleen weight relative to body weight; these changes lacked a histologic correlate and were not observed in males. While thymus weights relative to body weights were not affected, numbers of apoptotic lymphocytes rose in thymus with increasing dietary PFOS. There was a significant dose-related increase in total peripheral blood lymphocyte numbers in female but not male rats. In both genders the percentages of cells within lymphocyte subclasses were altered. There was a significant trend toward increasing T and T-helper (Th) cells and decreasing B cells with higher PFOS dose. Serum total immunoglobulin (Ig) G1 levels were significantly reduced in males exposed to 2 and 20 mg PFOS/kg diet. The ability of male and female rats to mount delayed-type hypersensitivity (DTH) responses to the T-cell-dependent antigen keyhole limpet hemocyanin (KLH) was not altered by PFOS. There was a significant trend toward elevated KLH-specific IgG in serum from male rats exposed to increasing levels of PFOS in diet. Splenic T- and B-cell proliferation in response to ex vivo mitogen exposure was unaffected by exposure to dietary PFOS. In conclusion, changes in immune parameters in rat did not manifest as functional alterations in response to immune challenge with KLH and may be secondary to hepatic-mediated effects of PFOS in this model.

A 90-day subchronic toxicity study of nivalenol, a trichothecene mycotoxin, in F344 rats

A subchronic toxicity study of nivalenol (NIV), a trichothecene mycotoxin, was conducted in male and female F344 rats fed diet containing 0, 6.25, 25 or 100 ppm concentration for 90 days. Decrease of body weight and loose stools were observed at 100 ppm in both sexes from the start of the experiment, and body weight reduction was also observed at 25 ppm in males from week 6. At necropsy, many organs demonstrated reduced absolute weights at 100 ppm in both sexes, mostly due to the reduction in the body growth, with reduction of relative thymus weight also being evident in females. Hematologically, decrease of the white blood cell count was found at 100 ppm in males and from 6.25 ppm in females. In addition, decreased platelet counts in both sexes, red blood cell counts in males, and the hemoglobin concentration in females were detected at 100 ppm. Histopathologically, treatment-related changes were predominantly observed in the hematopoietic and immune organs and the anterior pituitary in both sexes and female reproductive organs at 100 ppm, such as thymic atrophy, hypocellularity in the bone marrow, diffuse hypertrophy of basophilic cells with increase of castration cells in the anterior pituitary, and increase of ovarian atretic follicles. Based on the hematological data, the no-observed-adverse-effect level of NIV was determined to be less than 6.25 ppm (0.4 mg/kg body weight/day for both males and females).