Thymic Abnormalities Research Articles

Myasthenia gravis and the thymus gland. A historical review

The first report of an association between myasthenia gravis (MG) and the thymus gland was in 1901. Although the underlying mechanisms are uncertain, thymic abnormalities are clearly associated with MG. This review article summarises, from a historical point of view, our knowledge of these associations, and the surgical and medical treatment of MG, including symptom management, immunosuppression, intravenous immunoglobulin and plasmapheresis.

Folic acid and methionine in the prevention of teratogen-induced congenital defects in mice

Periconceptional supplementation with multivitamins containing folic acid reduces the risk of congenital malformations. We have previously investigated the effect on the murine development of a multiple retinoic acid competitive antagonist, Bristol-Myers-Squibb 189453, showing that treated fetuses were affected with heart defects, thymus aplasia or hypoplasia, and severe anomalies of the central nervous system. Hereby, we analyzed the effects of nutritive therapy involving folic acid and methionine on teratogen-induced congenital defects in mice. A total of 132 outbred CD1 litters were studied. Pregnant mice were divided into four experimental groups, and an oral supplementation of H(2)O or folic acid, or methionine, or folic acid+methionine was administered from 0.5 days postcoitum until the end of pregnancy. At 7.5 days postcoitum, mice from all these groups were administered Bristol-Myers-Squibb 189453 to induce the teratogenic effect. At the end of pregnancy, fetuses were dissected and tissues were analyzed by histology and flow cytometric assays. Folic acid reduces congenital heart diseases from 81.3% to 64.8%, neural tube defects from 20.3% to 3.7%, and thymus abnormalities from 98.4% to 27.8%, restoring a normal number of differentiated thymus cells. Methionine is less effective in contrasting congenital heart diseases and neural tube defects, and induces thymus cell proliferation but not differentiation. Folic acid+methionine weakly reduce congenital heart diseases and neural tube defects, but consistently reduce the incidence of fetuses affected with thymus pathologies from 98.4% to 67.7%. Our results suggest that folic acid and methionine periconceptional supplementations may influence the incidence of congenital defects and may probably induce negative selection of embryos presenting developmental anomalies.

Abstract 939: Galpha-i Signaling in Neural Crest Cells is Required for Normal Migration of Cardiac Neural Crest Cells, Cardiac Development, and Survival

G protein coupled receptors (GPCRs) have long been known to play crucial roles in transducing environmental signals to the adult cardiovascular system. In recent years, the roles of G protein-mediated signaling pathways in orchestrating the interactions of different tissues during cardiovascular development have become increasingly evident. To analyze the role of G protein signaling pathways in vivo we have generated mice where the function of the heterotrimeric G alpha subunit Gai can be ablated in a cell type specific manner utilizing the Cre-loxP system. We have mated these mice to two different neural crest-specific Cre lines in order to probe the effects of loss of Gai mediated signaling on the ability of neural crest cells (NCC) to contribute to the developing outflow tract and aortic arch arteries. METHODS: We have generated mice that express the Gai-inhibiting pertussis toxin S1 subunit (PTX) from the ROSA26 locus in a Cre recombination dependent manner (ROSA-PTX mice). These were mated to mice expressing either the Wnt1 Cre or P0 Cre transgene. Wnt1Cre is active in both premigratory and migratory NCC, whereas P0Cre is active only in migratory NCC and their derivatives. RESULTS: P0Cre-ROSA-PTX mice were normal at birth and demonstrated no structural heart defects. In contrast, Wnt1Cre-ROSA-PTX mice were present in normal numbers at late gestation but died perinatally due in part to cardiac outflow tract defects. Excision reporter and in situ hybridization studies suggest this is secondary to a delay/blockage of cardiac NCC migration into the developing outflow tract. NCC migration into the pharyngeal arches was unaffected in these mice and no craniofacial, thymic, or aortic arch abnormalities were observed. CONCLUSIONS: These results indicate that Gai-mediated signaling is required in premigratory or early migratory cardiac NCC for normal development of the outflow tract. In contrast, endothelin A receptor knockout mice (currently the only GPCR knock out with a neural crest phenotype) are thought to exhibit defects of postmigratory NCC function. RNA profiling of NCC for GPCRs involved in this Gai-dependent pathway has revealed several potential candidate receptors, including orphan receptors. Further analysis of these receptors is underway.

A New Approach to Idiopathic Nephrotic Syndrome

Minimal-change disease (MCD) and primary FSGS are important causes of idiopathic nephrotic syndrome (INS) and, in the case of FSGS, end-stage renal failure. Intriguing features of these diseases include their frequent response to steroids, their association with immune abnormalities, the existence

ΔNp63 regulates thymic development through enhanced expression of FgfR2 and Jag2

p63, a homologue of the tumor suppressor p53, is pivotal for epithelial development, because its loss causes severe epithelial dysgenesis, although no information is so far available on the role of p63 in the thymus. We identified the expression of all p63 isoforms in the developing thymus. The p63(-/-) thymi show severe abnormalities in size and cellularity, even though the organ expresses normal levels of keratins 5 and 8, indicating a p63-independent differentiation of thymic epithelial cells (TEC). TEC were sufficiently developed to allow a significant degree of education to produce CD4/CD8 single- and double-positive T cells. To study the selective contribution of transactivation-active p63 (TAp63) and amino-deleted p63 (DeltaNp63) isoforms to the function of the TEC, we genetically complemented p63(-/-) mice by crossing p63(+/-) mice with transgenic mice expressing either TAp63alpha or DeltaNp63alpha under the control of the keratin 5 promoter. Thymic morphology and cellularity were partially restored by complementation with DeltaNp63, but not TAp63, one downstream effector being fibroblast growth factor receptor 2-IIIb (FgfR2-IIIb). Indeed, FgfR2-IIIb is regulated directly by p63, via its interaction with apobec-1-binding protein-1, and its knockout shows thymic defects similar to those observed in p63(-/-) thymi. In addition, expression of Jag2, a component of the Notch signaling pathway known to be required for thymic development, was enhanced by p63 in vivo genetic complementation. Like Jag2(-/-) thymi, p63(-/-) thymi also show reduced gammadelta cell formation. Therefore, p63, and particularly the DeltaNp63 isoform, is essential for thymic development via enhanced expression of FgfR2 and Jag2. The action of DeltaNp63 is not due to a direct regulation of TEC differentiation, but it is compatible with maintenance of their "stemness," the thymic abnormalities resulting from epithelial failure due to loss of stem cells.

Zusatzdiagnostik bei Myasthenieverdacht - Myasthenia gravis

Die Zusatzdiagnostik bei Verdacht auf Myasthenia gravis ruht auf vier Säulen: Erstens die serologische Diagnostik mit dem Nachweis des pathognomischen Acetylcholinrezeptorantikörper, der aber nicht bei allem Betroffenen positiv ist (bei einem Teil der „seronegativen” sind MuSK-Antikörper nachweisbar). Zweitens zeigt die pharmakologische Testung mit Injektion von Edrophoniumchlorid eine rasche klinische Symptomverbesserung. Drittens zeigt die neurophysiologische Testung der neuromuskulären Transmission mit drei Reizen pro Sekunde Serienstimulation im positiven Fall ein signifikantes Dekrement der Reizantworten. Viertens erfordert die Assoziation der Myasthenie mit Thymomen, bildgebend (CT oder MRT) danach zu suchen.

Myasthénie du sujet âgé : diagnostic, comorbidité et évolution : À propos de 45 cas

Analyze the clinical presentation, laboratory indicators, and outcome of patients with late-onset myasthenia gravis (after 60 years).This retrospective cohort design with prospective follow-up included 45 patients with late-onset myasthenia gravis diagnosed in hospitals in Avignon, Montpellier, and Nimes between 1993 and 2000. Prospective data collection of their subsequent course took place in 2001.Median age at onset was 72 years and median follow-up 35.5 months. Initial symptoms were ocular (38/45, 95%) and bulbar (31/45, 69%). Initial Osserman grades were distributed as follows: 10 grade I, 2 grade IIA, 25 grade IIB, 8 grade III and no grade IV. Anticholinesterase antibodies were positive in 39 patients (91%), response to anticholinesterase positive in 31/33 (94%), and electrophysiological abnormalities observed in 20/33 (61%). Thoracic computed tomography, performed in 42 patients (93%), found thymic abnormalities in 7. At least one comorbid disease was diagnosed in 41/43 patients (93%) and an autoimmune disorder in 18/43 (42%). In all, 42 patients (93%) received anticholinesterase and 36 (80%) immunosuppressive therapy. Sixteen patients (36%) died during follow-up, 8 of causes directly related to the myasthenia gravis. The relative risk of death estimated by odds ratios (OR) was highest for patients with comorbid cancer (OR 8.6 [1.8-40.6]) and those with the highest Osserman scores: grades I-II OR: 0.05 [0.01-0.29] versus grades III-IV OR: 15.5 [2.9-83.0].Late-onset myasthenia gravis is specific in many aspects (presentation, autoimmune and other comorbid conditions, and course) that require attentive care.

Adenomatous Polyposis Coli (APC) Is Required for Normal Development of Skin and Thymus

The tumor suppressor gene Apc (adenomatous polyposis coli) is a member of the Wnt signaling pathway that is involved in development and tumorigenesis. Heterozygous knockout mice for Apc have a tumor predisposition phenotype and homozygosity leads to embryonic lethality. To understand the role of Apc in development we generated a floxed allele. These mice were mated with a strain carrying Cre recombinase under the control of the human Keratin 14 (K14) promoter, which is active in basal cells of epidermis and other stratified epithelia. Mice homozygous for the floxed allele that also carry the K14-cre transgene were viable but had stunted growth and died before weaning. Histological and immunochemical examinations revealed that K14-cre–mediated Apc loss resulted in aberrant growth in many ectodermally derived squamous epithelia, including hair follicles, teeth, and oral and corneal epithelia. In addition, squamous metaplasia was observed in various epithelial-derived tissues, including the thymus. The aberrant growth of hair follicles and other appendages as well as the thymic abnormalities in K14-cre; ApcCKO/CKO mice suggest the Apc gene is crucial in embryonic cells to specify epithelial cell fates in organs that require epithelial–mesenchymal interactions for their development.

Non-small-cell lung cancer associated with non-thymomatous myasthenia gravis

A non-small-cell lung cancer without distant metastases was incidentally found in a 77-year-old man who had suffered from myasthenia gravis (MG) without thymoma. The patient's condition was stabilized by oral pyridostigmine bromide which he had taken during the past 6 years. He simultaneously underwent thymectomy and left lower lobectomy with regional lymph node dissection. Although postoperative myasthenic crisis occurred, mechanical ventilation and intravenous steroid pulse relieved the patient and the symptoms improved thereafter. Cases of operable lung cancer with non-thymomatous MG have rarely been reported and the appropriate therapeutic strategy for such cases remains to be debated. Their causal association remains to be identified, whereas some studies have implied that immune disorder due to the abnormal thymus might possibly enhance the oncogenesis of extrathymic malignancies. Myasthenic crisis should also be taken into account in postoperative management of MG patients who simultaneously undergo thymectomy and lobectomy for synchronous lung cancer.

Thymus Acetylcholinesterase Activity is Reduced in Mice With Congenital Muscular Dystrophy

Lama2dy mice constitute an animal model for congenital muscular dystrophy (CMD) by merosin (laminin alpha2-chain) deficiency. This pathology affects the properties of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) of mouse skeletal muscle and nerves (Moral-Naranjo et al., 1999, 2002). AChE and BChE are involved through catalytic and noncatalytic actions in multiple processes, such as hydrolysis of acetylcholine (ACh), morphogenesis, hematopoiesis, and tumorigenesis (Soreq and Seidman, 2001). AChE and BChE molecules can be globular (G1, G2, and G4) or asymmetric forms (A4, A8, and A12) (Massoulié, 2002), and G molecules can show amphiphilic (detergent-interacting, GA) or hydrophilic (GH) behavior. AChE catalytic subunits are encoded by three mRNAs (T, H, or R) generated by alternative splicing. The presence of AChE in lymphoid tissues (Rossi et al., 1991; Nieto-Cerón et al., 2004), the role of immune responses in muscular dystrophy (Spencer and Tidball, 2001), the abnormalities of Lama2dy thymus (Magner et al., 2000), and the role of ACh in thymocyte function (Kawashima and Fujii, 2000) prompted us to investigate thymus AChE and the possible effect of merosin deficiency on it.

Identification and characterization of Xenopus laevis homologs of mammalian TRAF6 and its binding protein TIFA

Tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) transduces signals from members of the TNFR superfamily and the Toll/IL-1R family, leading to activation of transcription factors such as NFκB and AP-1. Genetic disruption of the TRAF6 gene in mice results in various developmental abnormalities during embryogenesis, including osteopetrosis, failure of neural tube closure, defective formation of skin appendices, absence of lymph nodes, and absence of mature thymic epithelial cells. To clarify the effect of TRAF6 in development, we previously identified a TRAF-interacting protein with a forkhead-associated domain (TIFA), which binds and activates TRAF6 upon extracellular stimulation. To understand the physiological roles of TRAF6 and TIFA in early development, we studied these genes in Xenopus laevis. Here, we describe identification of X. laevis homologs of mammalian TRAF6 (XTRAF6) and TIFA (XTIFA). As was the case for the mammalian homologs, overexpression of XTRAF6 or XTIFA activated NFκB, whereas XTIFA carrying a mutation that abolishes XTRAF6 binding failed to activate NFκB, suggesting that XTIFA activates NFκB by binding to XTRAF6. XTIFA and XTRAF6 mRNAs were expressed at similar levels in zygotes from the neurula stage and then increased. Whole-mount in situ hybridization revealed that XTRAF6 mRNA was expressed in the head region and neural tube during the neurula stage, and the expression expanded to the pharyngeal apparatus during the tailbud stage. This localization is consistent with the defective neural tube closure and abnormal thymus organogenesis observed in TRAF6-deficient mice. Our results suggest possible cooperation between XTRAF6 and XTIFA during embryogenesis.

Increased Toll-Like Receptor 4 Expression in Thymus of Myasthenic Patients with Thymitis and Thymic Involution

Thymic abnormalities are present in approximately 80% of myasthenia gravis (MG) patients, and the thymus seems to be the main site of autosensitization to the acetylcholine receptor. In view of findings that the innate immune system can generate an autoimmune response, we studied the expression of Toll-like receptors (TLRs) 2 to 5, key components of innate immunity signaling pathways, in 37 thymuses from patients with autoimmune MG. TLR4 mRNA levels were significantly greater in thymitis (hyperplasia with diffuse B-cell infiltration) and involuted thymus than in germinal center hyperplasia and thymoma. By immunohistochemistry and confocal microscopy, cells positive for TLR4 protein were rarely detected in thymoma. However, in thymitis TLR4 protein was mostly found on epitheliomorphic (cytokeratin-positive) cells located in close association with clusters of acetylcholine receptor-positive myoid cells in thymic medulla and also at the borders between cortical and medullary areas. B cells were never TLR4-positive. TLR4 protein was also present in remnant tissue of involuted thymus. This is the first finding of a possible link between innate immunity and MG. We speculate that in a subgroup of MG patients, an exogenous or endogenous danger signal may activate the innate immune system and give rise to TLR4-mediated mechanisms contributing to autoimmunity.

Immunology of Down syndrome: A review

Subjects with Down syndrome (DS) have a high mortality due to infections and a high risk of developing malignancies. These observations, together with the demonstration of a frequent occurrence of HBsAg carrier state and of autoantibodies, have prompted investigations of the immune function in DS. Thymic morphological and functional abnormalities have been demonstrated. Peripheral blood mononuclear cells of DS subjects have been shown to include a high number of T lymphocytes with low avidity for sheep erythrocytes and a very high percentage of cells with an NK phenotype. However, NK activity is low in DS. Production of some important cytokines, such as IL-2, is depressed, thus contributing to T-cell derangement. Abnormalities of the B-cell compartment were also demonstrated, with a tendency towards high IgG and low IgM serum levels. Controversial results have been obtained with regard to antigen-specific antibody response. Also phagocytes of DS subjects display some characteristic functional impairments, with low chemotactic ability and reduced production of oxygen radicals. Despite the clearly established and rather detailed evidence of immune derangements, therapeutic trials have been anecdotal and resulted in marginal effects. HBV vaccination is highly advisable in DS because of the high risk of becoming chronic HBV carriers once infected.

Lambert–Eaton myasthenic syndrome associated with thymitis

Lambert–Eaton myasthenic syndrome (LEMS) is an autoimmune disorder characterized by a presynaptic defect of neuromuscular transmission and associated with circulating voltage-gated calcium channel antibodies. Although myasthenia gravis (MG) is often associated with thymic abnormalities, including thymitis and thymomas, these pathologic changes have not previously been associated with LEMS. A previously fit 46-year-old man presented in February 2002 with a 6-month history of general lethargy and decreased exercise tolerance. He described the sensation of “wading through water” and had difficulty climbing stairs and rising from a chair. He had no diplopia or ptosis and no abnormalities of speech or swallowing. Symptoms of autonomic dysfunction were not present. He had no relevant medical or family history and took no medication. He was a nonsmoker. Examination revealed normal optic fundi and cranial nerves. There was no muscle wasting, but he had weakness of both triceps. Otherwise, muscle power was full with no facilitation or fatigability. He …

Responses in vitro of peripheral blood lymphocytes from patients with myasthenia gravis to stimulation with human acetylcholine receptor α-chain peptides: Analysis in relation to age, thymic abnormality, and ethnicity

Peripheral blood lymphocytes (PBLs) were isolated from 24 patients with myasthenia gravis of three ethnic groups (Caucasian, African American, and Hispanic) and ten healthy individuals. We determined the in vitro proliferative responses of the PBL samples to each of 18 overlapping synthetic peptides corresponding to the entire main extracellular domain (residues 1–210) of the α-subunit of human acetylcholine receptor. The profiles of the T-cell responses (expressed in stimulation index [SI]) to the peptides varied among the 24 patient samples. There was a significant difference in the overall patient responses relative to controls toward 17 of 18 peptides. T cells from the patients gave responses greater than control mean SI + 4 standard deviation ( Z SI > 4) to 2∼9 peptides/sample. Six peptides, α23–38, α34–49, α78–93, α122–138, α146–162, and α182–198, were recognized with Z > 4 level by 42% to 58% of the patients’ PBLs. The grouped patient responses, divided according to age, thymic diagnosis, or ethnicity, were compared with controls and with each other. Significant differences were observed between early- and late-onset cases in recognition of residues α34–49 ( p = 0.015) and α78–93 ( p = 0.053), and in recognition of residues α12–27, α56–71, α134–150, and α146–162 (0.0072 < p < 0.064) when two ethnic groups were compared with each other.

Comparative study of pre-operative thymic imaging and pathology in patients with myasthenia gravis

The objective of our study is to compare the diagnostic significance of mediastinal CT and 201Tl-single-photon emission computed tomography (SPECT) with thymic histology in patients with myasthenia gravis (MG). The subjects were 30 patients with MG who were scheduled to receive thymectomy. They did not receive immunosuppressive therapy. The mediastinal CT and 201Tl-SPECT were performed before the thymectomy. As a consequence, 9 patients had thymoma, 11 had lymphoid follicular hyperplasia (LFH), and 10 had normal thymus on histologic examination after thymectomy. Retrospectively, CT diagnosed the histology of all 9 patients with thymoma, and 5 of 11 with LFH. 201Tl-SPECT could detect abnormal accumulations in only 6 of 9 cases of thymoma, and 6 of 11 cases of LFH. 201Tl-SPECT could not distinguish thymoma from LFH. We conclude that a CT study is recommended as an essential study for the detection of thymic abnormalities in pre-operative patients with MG.

The role of Brg1, a catalytic subunit of mammalian chromatin-remodeling complexes, in T cell development.

Mammalian SWI–SNF-related complexes use brahma-related gene 1 (Brg1) as a catalytic subunit to remodel nucleosomes and regulate transcription. Recent biochemical data has linked Brg1 function to genes important for T lymphocyte differentiation. To investigate the role of SWI–SNF-related complexes in this lineage, we ablated Brg1 function in T lymphocytes. T cell–specific Brg1-deficient mice showed profound thymic abnormalities, CD4 derepression at the double negative (DN; CD4− CD8−) stage, and a developmental block at the DN to double positive (CD4+ CD8+) transition. 5′-bromo-2′-deoxyuridine incorporation and annexin V staining establish a role for Brg1 complexes in the regulation of thymocyte cell proliferation and survival. This Brg1-dependent cell survival is specific for developing thymocytes as indicated by the presence of Brg1-deficient mature T lymphocytes that have escaped the developmental block in the thymus. However, reductions in peripheral T cell populations lead to immunodeficiency and compromised health of mutant mice. These results highlight the importance of chromatin-remodeling complexes at different stages in the development of a mammalian cell lineage.

DiGeorge's syndrome: a gene at last

DiGeorge's syndrome, velocardiofacial syndrome, and conotruncal anomaly face syndrome have been associated with a heterozygous chromosomal deletion of 22q11.2 (del22q11), and they are usually referred to as the 22q11 deletion syndromes (22q11DS).1,2 Patients present with pharyngeal, neurobehavioural, and other clinical findings. The pharyngeal phenotype refers to abnormalities attributable to developmental defects of the embryonic pharyngeal apparatus (heart outflow tract, craniofacial, velopharyngeal, ear, thymic, and parathyroid abnormalities).

Retinoic acid as a neurobehavioral teratogen

Animal research on retinoic acids (RA) has helped to establish a principle of neurobehavioral teratology: embryonic exposure to a CNS teratogen produces a continuum of outcomes, ranging from death, to malformation, to subtle functional alterations. Demonstrating this principle in human studies was problematic prior to the introduction in 1982 of 13‐cis RA (Accutane, Hoffman‐LaRoche) for the treatment of severe cystic acne. 13 cis RA is a potent human teratogen that causes a 40% rate of spontaneous abortion, and, among liveborn infants, a 35% rate of major malformation (Lammer et al, 1985; 2001). The characteristic pattern includes hindbrain, craniofacial, cardiac, and thymic abnormalities. Longitudinal follow‐up of this original cohort and the matched controls has focused on neuropsychological characteristics at 5 and 10 years of age, and the relationships between malformation and cognitive status. Of 35 children exposed to RA between postconception days 14 and 60 and tested at age 5, 46% scored in the below average range of general mental ability, as compared to 10% of the controls. Boys were more frequently affected than girls with respect to major malformations and reduced intelligence. Presence of a major malformation was associated with reduced intellectual performance, however, 6 of 16 children scoring in the below average range had no detectable malformations. Thus, as in the animal studies, features at birth, such as major malformations, do not fully characterize the adverse consequences of embryonic RA exposure. Likewise, the effects cannot be fully characterized by examining only reduced intelligence. As compared to control children, RA exposed children with average mental ability were three times more likely to have a specific, non‐verbal learning disability and boys were again over‐represented.

The phytoestrogen genistein induces thymic and immune changes: a human health concern?

Use of soy-based infant formulas and soy/isoflavone supplements has aroused concern because of potential estrogenic effects of the soy isoflavones genistein and daidzein. Here we show that s.c. genistein injections in ovariectomized adult mice produced dose-responsive decreases in thymic weight of up to 80%. Genistein's thymic effects occurred through both estrogen receptor (ER) and non-ER-mediated mechanisms, as the genistein effects on thymus were only partially blocked by the ER antagonist ICI 182,780. Genistein decreased thymocyte numbers up to 86% and doubled apoptosis, indicating that the mechanism of the genistein effect on loss of thymocytes is caused in part by increased apoptosis. Genistein injection caused decreases in relative percentages of thymic CD4(+)CD8(-) and double-positive CD4(+)CD8(+) thymocytes, providing evidence that genistein may affect early thymocyte maturation and the maturation of the CD4(+)CD8(-) helper T cell lineage. Decreases in the relative percentages of CD4(+)CD8(-) thymocytes were accompanied by decreases in relative percentages of splenic CD4(+)CD8(-) cells and a systemic lymphocytopenia. In addition, genistein produced suppression of humoral immunity. Genistein injected at 8 mg/kg per day produced serum genistein levels comparable to those reported in soy-fed human infants, and this dose caused significant thymic and immune changes in mice. Critically, dietary genistein at concentrations that produced serum genistein levels substantially less than those in soy-fed infants produced marked thymic atrophy. These results raise the possibility that serum genistein concentrations found in soy-fed infants may be capable of producing thymic and immune abnormalities, as suggested by previous reports of immune impairments in soy-fed human infants.