Thymus involution induced by mouse hepatitis virus A59 in BALB/c mice.

Mouse hepatitis virus A59 (MHV-A59) infection of adult BALB/c mice induced a severe, transient atrophy of the thymus. The effect was maximal at 1 week after infection, and thymuses returned to normal size by 2 weeks after infection. There was no effect of glucocorticoids, since thymus atrophy was also found in adrenalectomized, infected mice. In infected thymus, immature CD4+ CD8+ lymphocytes were selectively depleted, and apoptosis of lymphocytes was increased. The MHV receptor glycoprotein MHVR was detected on thymus epithelial cells but not on T lymphocytes. In a small number of stromal epithelial cells, but in very few lymphocytes, the viral genome was detectable by in situ hybridization. These observations suggested that MHV-A59-induced thymic atrophy results not from a generalized lytic infection of T lymphocytes but rather from apoptosis of immature double-positive T cells that might be caused by infection of a small proportion of thymus epithelial cells or from inappropriate secretion of some factor, such as a cytokine.     

Modulation of endoplasmic reticulum chaperone GRP78 by high glucose in hippocampus of streptozotocin-induced diabetic mice and C6 astrocytic cells

Diabetes mellitus is known to increase the risk of neurodegeneration, and both diseases are reported to be linked to dysfunction of endoplasmic reticulum (ER). Astrocytes are important in the defense mechanism of central nervous system (CNS), with great ability of tolerating accumulation of toxic substances and sensitivity in Ca²⁺ homeostasis which are two key functions of ER. Here, we investigated the modulation of the glucose-regulated protein 78 (GRP78) in streptozotocin (STZ)-induced diabetic mice and C6 cells cultured in high glucose condition. Our results showed that more reactive astrocytes were presented in the hippocampus of STZ-induced diabetic mice. Simultaneously, decrease of GRP78 expression was found in the astrocytes of diabetic mice hippocampus.     

Thymic regeneration: teaching an old immune system new tricks

Recent studies in mice and humans show that the importance of the thymus extends well beyond the initial seeding of the peripheral T-cell pool. Although peripheral homeostasis can maintain T-cell numbers, the thymus is the major, if not the exclusive, source of new T-cell specificities. With age, thymus atrophy dramatically reduces the export of new T cells and predisposes an individual to impaired T-cell function, reduced T-cell immunity, and increased autoimmunity. Thymus atrophy is also the primary obstacle to restoration of the T-cell pool in the aftermath of HIV treatment or lymphoablative therapies. Here, we review thymus T-cell production, with particular attention to the factors that influence thymocyte export, and examine the impact that recent thymic emigrants have on the peripheral pool. In the future, thymic regeneration might become a feasible and potentially powerful approach to rejuvenating a depleted peripheral T-cell pool.     

Enhanced immune reconstitution by sex steroid ablation following allogeneic hemopoietic stem cell transplantation

Delayed immune reconstitution in adult recipients of allogeneic hemopoietic stem cell transplantations (HSCT) is related to age-induced thymic atrophy. Overcoming this paucity of T cell function is a major goal of clinical research but in the context of allogeneic transplants, any strategy must not exacerbate graft-vs-host disease (GVHD) yet ideally retain graft-vs-tumor (GVT) effects. We have shown sex steroid ablation reverses thymic atrophy and enhances T cell recovery in aged animals and in congenic bone marrow (BM) transplant but the latter does not have the complications of allogeneic T cell reactivity. We have examined whether sex steroid ablation promoted hemopoietic and T cell recovery following allogeneic HSCT and whether this benefit was negated by enhanced GVHD. BM and thymic cell numbers were significantly increased at 14 and 28 days after HSCT in castrated mice compared with sham-castrated controls. In the thymus, the numbers of donor-derived thymocytes and dendritic cells were significantly increased after HSCT and castration; donor-derived BM precursors and developing B cells were also significantly increased. Importantly, despite restoring T cell function, sex steroid inhibition did not exacerbate the development of GVHD or ameliorate GVT activity. Finally, IL-7 treatment in combination with castration had an additive effect on thymic cellularity following HSCT. These results indicate that sex steroid ablation can profoundly enhance thymic and hemopoietic recovery following allogeneic HSCT without increasing GVHD and maintaining GVT.     

Estrogen receptor alpha is necessary in thymic development and estradiol-induced thymic alterations.

Estrogens affect the development, maturation, and function of multiple organ systems, including the immune system. One of the main targets of estrogens in the immune system is the thymus, which undergoes atrophy and phenotypic alterations when exposed to elevated levels of estrogen. To determine how estrogens influence the thymus and affect T cell development, estrogen receptor alpha (ERalpha) knockout (ERKO) mice were examined. ERKO mice have significantly smaller thymi than their wild-type (WT) littermates. Construction of ER radiation bone marrow chimeras indicated that the smaller thymi were due to a lack of ERalpha in radiation-resistant tissues rather than hemopoietic elements. ERKO mice were also susceptible to estradiol-induced thymic atrophy, but the extent of their atrophy was less than what was seen in WT mice. The estradiol-treated ERKO mice failed, however, to manifest alterations in their thymic CD4/CD8 phenotypes compared with WT mice. Therefore, ERalpha is essential in nonhemopoietic cells to obtain a full-sized thymus, and ERalpha also mediates some of the response of the thymus to elevated estrogen levels. Finally, these results suggest that in addition to ERalpha, another receptor pathway is involved in estradiol-induced thymic atrophy.     

HTLV-1 propels thymic human T cell development in "human immune system" Rag2⁻/⁻ gamma c⁻/⁻ mice

Alteration of early haematopoietic development is thought to be responsible for the onset of immature leukemias and lymphomas. We have previously demonstrated that Tax(HTLV-1) interferes with ?-selection, an important checkpoint of early thymopoiesis, indicating that human T-cell leukemia virus type 1 (HTLV-1) infection has the potential to perturb thymic human αβ T-cell development. To verify that inference and to clarify the impact of HTLV-1 infection on human T-cell development, we investigated the in vivo effects of HTLV-1 infection in a "Human Immune System" (HIS) Rag2?/?γ(c)?/? mouse model. These mice were infected with HTLV-1, at a time when the three main subpopulations of human thymocytes have been detected. In all but two inoculated mice, the HTLV-1 provirus was found integrated in thymocytes; the proviral load increased with the length of the infection period. In the HTLV-1-infected mice we observed alterations in human T-cell development, the extent of which correlated with the proviral load. Thus, in the thymus of HTLV-1-infected HIS Rag2?/?γc?/? mice, mature single-positive (SP) CD4? and CD8? cells were most numerous, at the expense of immature and double-positive (DP) thymocytes. These SP cells also accumulated in the spleen. Human lymphocytes from thymus and spleen were activated, as shown by the expression of CD25: this activation was correlated with the presence of tax mRNA and with increased expression of NF-kB dependent genes such as bfl-1, an anti-apoptotic gene, in thymocytes. Finally, hepato-splenomegaly, lymphadenopathy and lymphoma/thymoma, in which Tax was detected, were observed in HTLV-1-infected mice, several months after HTLV-1 infection. These results demonstrate the potential of the HIS Rag2?/?γ(c)?/? animal model to elucidate the initial steps of the leukemogenic process induced by HTLV-1.     

Cellular and molecular interactions of thymus with endocrine organs and nervous system.

T-cell ontogenesis has been disclosed to depend on the interactions of thymus with endocrine glands and nervous system as follows: i/ Thymic deprivation not only impaired the immunological development but also brought about the dysgenesis of pituitary anterior lobe. Conversely, hypophysectomy resulted in thymus atrophy with the disturbed immune responses. ii/ Binding of pituitary acidophilic cell hormones to their receptors on thymus epithelial cells (TECs) augmented the release of thymic hormonal peptides (THPs) in vitro. iii/ Elevation of blood glucocorticoid level after stress caused atrophy of thymus cortex through double positive thymocyte apoptosis. Morpho-molecular alterations of cytoplasm preceded nuclear damage in the apoptotic thymocytes. iv/ Administration of thymosin to the streptozotocin-induced diabetic mice repressed mononuclear cell infiltration to the pancreatic islets. v/ Autonomic nerve fibers innervate thymic parenchyma. Binding of acetylcholines (Achs) to Ach receptors on TECs enhanced protein synthetic activity which seemed to connect with THP production. vi/ Thymectomy not only depressed the immune responses but also accelerated the reduction of leaming and memory ability with aging. The operation appears to disturb the brain adrenoceptor functions and to suppress the regulatory roles of hypothalamus to other nervous tissues. vii/ Several kinds of THPs, separated from the culture supernatant of TEC line by high performance liquid chromatography, showed a favorable effect on the thymocytes at different stage of differentiation and maturation. viii/ Thymosin, thymulin and THPs were capable of proliferating and differentiating thymocytes in vitro. However, the administration of each thymic product to the thymus-deprived animals could not restore from their "wasting disease". Since TECs are composed of a heterogeneous population, it would be one of essential ways for isolating "true thymus hormone" (TTH) to use the material which consists of functionally homogeneous subset of TECs. ix/ An additional grafting of pituitary gland to the thymus-grafted nude mice improved the disturbed T-cell ontogeny. Accordingly, the administration of "TTH" and pituitary acidophilic cell hormones might be more hopeful procedure for rescuing the thymus-deprived animals from "wasting disease".     

Architectural changes in the thymus of aging mice

Age-associated thymic involution is one of the most dramatic and ubiquitous changes in the immune system, although the precise mechanisms involved still remain obscured. Several hypotheses have been proposed incorporating extrinsic and intrinsic factors, however, changes in the thymic microenvironment itself is one of the least investigated. We therefore decided to undertake a detailed histological examination of the aging thymus in order to elucidate possible mechanisms of thymic atrophy. This investigation provides insight into the changes within the murine thymus with age, demonstrating a new approach to quantify protein expressional differences while preserving the thymic architecture. There is a decline in expression of thymic epithelial cell-specific makers and an increase in fibroblast content in the aging mouse thymus. This is concurrent with a disorganization of the thymic compartments, a morphological transformation within the epithelial cells and alterations of their archetypal staining patterns. Furthermore, this is linked to a rise in apoptotic cells and the novel finding of increased senescence in the thymus of older mice that appears to be colocalized in the epithelial compartment. These changes within the thymic epithelial cells may be in part accountable for thymic atrophy and responsible for the decline in T-cell output.     

Effects of Pentoxifylline on Liver and Thymus of Plasmodium berghei ANKA Infected Swiss Albino Mice

Infection of Swiss albino mice with Plasmodium berghei ANKA (PbA), a lethal strain, led to injury of the liver, thymic atrophy and high host mortality. Action of pentoxifylline (PTX), an inhibitor of TNF-α (tumor necrosis factor alpha), was investigated on hepatic necrosis, thymic atrophy, increased percentage of Sub G0/G1 hepatic and thymic populations, parasitemia and survivability of the infected mice host. Our data suggest the importance of PTX in mice survival and curing of liver cirrhosis, without affecting the parasitemic condition of the infected mice. Histomorphological changes were well evident from the appearance of hypertrophied hepatic cells with abundance of pigments. In the thymus no cortico-medullary demarcation was observed with presence of hypertrophied thymocytes. Hyperplasia of hepatic cells in the Sub-G0/G1 stage as revealed by flow cytometric analyses, was suppressed by PTX which is an indication of apoptotic effect of PTX in mice. Mice treated with PTX showed a significant decrease of necrotic areas in liver and thymus, suggesting that PTX treatment controls TNF-α effect, and thus PTX may be used as an adjuvant in the treatment of malaria.     

Temporal activation of Nrf2 in the penumbra and Nrf2 activator-mediated neuroprotection in ischemia–reperfusion injury

Oxidative stress plays a critical role in mediating tissue injury and neuron death during ischemia–reperfusion injury (IRI). The Keap1–Nrf2 defense pathway serves as a master regulator of endogenous antioxidant defense, and Nrf2 has been attracting attention as a target for the treatment of IRI. In this study, we evaluated Nrf2 expression in IRI using OKD (Keap1-dependent oxidative stress detector) mice and investigated the neuroprotective ability of an Nrf2 activator. We demonstrated temporal changes in Nrf2 expression in the same mice with luciferase assays and an Nrf2 activity time course using Western blotting. We also visualized Nrf2 expression in the ischemic penumbra and investigated Nrf2 expression in mice and humans using immunohistochemistry. Endogenous Nrf2 upregulation was not detected early in IRI, but expression peaked 24 h after ischemia. Nrf2 expression was mainly detected in the penumbra, and it was found in neurons and astrocytes in both mice and humans. Intravenous administration of the Nrf2 activator bardoxolone methyl (BARD) resulted in earlier upregulation of Nrf2 and heme oxygenase-1. Furthermore, BARD decreased infarction volume and improved neurological symptoms after IRI. These findings indicate that earlier Nrf2 activation protects neurons, possibly via effects on astrocytes.     

Borna disease virus accelerates inflammation and disease associated with transgenic expression of interleukin-12 in the central nervous system

Targeted expression of biologically active interleukin-12 (IL-12) in astrocytes of the central nervous system (CNS) results in spontaneous neuroimmunological disease of aged mice. Borna disease virus (BDV) can readily multiply in the mouse CNS but does not trigger disease in most strains. Here we show that a large percentage of IL-12 transgenic mice developed severe ataxia within 5 to 10 weeks after infection with BDV. By contrast, no disease developed in mock-infected IL-12 transgenic and wild-type mice until 4 months of age. Neurological symptoms were rare in infected wild-type animals, and if they occurred, these were milder and appeared later. Histological analyses showed that the cerebellum of infected IL-12 transgenic mice, which is the brain region with strongest transgene expression, contained large numbers of CD4(+) and CD8(+) T cells as well as lower numbers of B cells, whereas other parts of the CNS showed only mild infiltration by lymphocytes. The cerebellum of diseased mice further showed severe astrogliosis, calcifications and signs of neurodegeneration. BDV antigen and nucleic acids were present in lower amounts in the inflamed cerebellum of infected transgenic mice than in the noninflamed cerebellum of infected wild-type littermates, suggesting that IL-12 or IL-12-induced cytokines exhibited antiviral activity. We propose that BDV infection accelerates the frequency by which immune cells such as lymphocytes and NK cells enter the CNS and then respond to IL-12 present in the local milieu causing disease. Our results illustrate that infection of the CNS with a virus that is benign in certain hosts can be harmful in such normally disease-resistant hosts if the tissue is unfavorably preconditioned by proinflammatory cytokines.