Quantification of acetylcholinesterase-positive structures in human thymus during development and aging

Bidirectional crosstalk between the peripheral nervous system and lymphoid tissues/organs

The central nervous system (CNS) influences the immune system generally by regulating the systemic concentration of humoral substances (e.g., cortisol and epinephrine), whereas the peripheral nervous system (PNS) communicates specifically with the immune system according to local interactions/connections. An imbalance between the components of the PNS might contribute to pathogenesis and the further development of certain diseases. In this review, we have explored the "thread" (hardwiring) of the connections between the immune system (e.g., primary/secondary/tertiary lymphoid tissues/organs) and PNS (e.g., sensory, sympathetic, parasympathetic, and enteric nervous systems (ENS)) in health and disease in vitro and in vivo. Neuroimmune cell units provide an anatomical and physiological basis for bidirectional crosstalk between the PNS and the immune system in peripheral tissues, including lymphoid tissues and organs. These neuroimmune interactions/modulation studies might greatly contribute to a better understanding of the mechanisms through which the PNS possibly affects cellular and humoral-mediated immune responses or vice versa in health and diseases. Physical, chemical, pharmacological, and other manipulations of these neuroimmune interactions should bring about the development of practical therapeutic applications for certain neurological, neuroimmunological, infectious, inflammatory, and immunological disorders/diseases.

Neuro-immune modulation of the thymus microenvironment (review)

The thymus is the primary site for T-cell lympho-poiesis. Its function includes the maturation and selection of antigen specific T cells and selective release of these cells to the periphery. These highly complex processes require precise parenchymal organization and compartmentation where a plethora of signalling pathways occur, performing strict control on the maturation and selection processes of T lymphocytes. In this review, the main morphological characteristics of the thymus microenvironment, with particular emphasis on nerve fibers and neuropeptides were assessed, as both are responsible for neuro-immune‑modulation functions. Among several neurotransmitters that affect thymus function, we highlight the dopaminergic system as only recently has its importance on thymus function and lymphocyte physiology come to light.

Intrinsic innervation and dopaminergic markers after experimental denervation in rat thymus

The aim of this study was to examine rat thymus innervation using denervation techniques and to explore the related microanatomical localization of dopamine, D1, D2 receptors and dopamine membrane transporter (DAT).

In the thymus subcapsular region, the parenchymal cholinergic fibers belong exclusively to phrenic nerve branching. No somatic phrenic nerve branching was detected in any other analysed thymus lobule regions.

In rats subjected to sympathetic or parasympathetic ablation, it was observed that catecholaminergic and cholinergic nerve fibers respectively contributed to forming plexuses along vessel walls.

In the subcapsular and septal region, no parenchymal nerve branching, belonging to sympathetic or parasympathetic nervous system was noted. Instead, in the deep cortical region, cortico-medullary junction (CM-j) and medulla, catecholaminergic and cholinergic nerve fibers were detected along the vessels and parenchyma.

Dopamine and dopamine receptors were widely diffused in the lobular cortico-medullary junction region and in the medulla, where the final steps of thymocyte maturation and their trafficking take place.

No variation in dopamine and DAT immune reaction was observed following total or partial parasympathectomy or phrenic nerve cutting. After chemical or surgical sympathectomy however, neither dopamine nor DAT immune reaction was noted again. Instead, D1 and D2 dopamine receptor expression was not affected by thymus denervation.

In rats subjected to specific denervation, it was observed the direct intraparenchymal branching of the phrenic nerve and sympathetic and parasympathetic fibers into thymus parenchyma along vessels. These findings on the dopaminergic system highlight the importance of neurotransmitter receptor expression in the homeostasis of neuroimmune modulation.

Butyrylcholinesterase activity and molecular components in thymus of healthy and merosin-deficient Lama2dy mice

The laminin-alpha2 chain, referred to as merosin, forms part of the laminin-2 heterotrimer (alpha2beta1gamma1), which is principally expressed in the basement membrane of muscle. Nearly half of patients suffering from congenital muscular dystrophy (CMD) have abnormalities in the laminin-alpha2 chain (LAMA2) gene, and the merosin-deficient Lama2dy mouse shows CMD. The expression of merosin in thymus, the abnormalities in the gland of Lama2dy mice, and the presence of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in thymus prompted us to study the possible effects of the deficiency of merosin on thymus BuChE. We found that, while AChE activity decreased by approximately 50% in merosin-deficient thymus, the deficiency had little effect on BuChE activity. About 65% of thymus BuChE activity was extracted with a saline buffer and 30% with 1% Triton X-100. Sedimentation analyses and phenyl-agarose chromatography showed that thymus contained amphiphilic BuChE monomers (G(1)(A),44%) and dimers (G(2)(A),33%), and hydrophilic tetramers (G(4)(H),23%). Binding assays with various plant lectins revealed differences between the oligoglycans linked to BuChE tetramers and lighter components. The deficiency of merosin had no effect on the biosynthesis of thymus BuChE as judged by the lack of major changes between control and Lama2dy mice thymuses in the distribution of BuChE molecules and the level of lectin binding. The detoxifying action of BuChE, its role as a backup to AChE, and the relevance of the cholinergic dialogue between T cells and stromal cells for T lymphocyte proliferation, maturation and survival support a physiological function for BuChE in thymus.

The thymic theme of acetylcholinesterase splice variants in myasthenia gravis

Cholinergic signaling and acetylcholinesterase (AChE) influence immune response and inflammation. Autoimmune myasthenia gravis (MG) is mediated by antibodies to the acetylcholine receptor and current therapy is based on anti-AChE drugs. MG is associated with thymic hyperplasia, showing signs of inflammation. The objectives of this study were to analyze the involvement of AChE variants in thymic hyperplasia. We found lower hydrolytic activities in the MG thymus compared with adult controls, accompanied by translocation of AChE-R from the cytoplasm to the membrane and increased expression of the signaling protein kinase PKC-betaII. To explore possible causal association of AChE-R changes with thymic composition and function, we used an AChE-R transgenic model and showed smaller thymic medulla compared with strain-matched controls, indicating that AChE-R overexpression interferes with thymic differentiation mechanisms. Interestingly, AChE-R transgenic mice showed increased numbers of CD4(+)CD8(+) cells that were considerably more resistant in vitro to apoptosis than normal thymocytes, suggesting possibly altered positive selection. We further analyzed microarray data of MG thymic hyperplasia compared with healthy controls and found continuous and discrete changes in AChE-annotated GO categories. Together, these findings show that modified AChE gene expression and properties are causally involved in thymic function and development.

Muscular dystrophy by merosin deficiency decreases acetylcholinesterase activity in thymus of Lama2dy mice

Half of congenital muscular dystrophy cases arise from laminin alpha2 (merosin) deficiency, and merosin-deficient mice (Lama2dy) exhibit a dystrophic phenotype. The abnormal development of thymus in Lama2dy mice, the occurrence of acetylcholinesterase (AChE) in the gland and the impaired distribution of AChE molecules in skeletal muscle of the mouse mutant prompted us to compare the levels of AChE mRNAs and enzyme species in thymus of control and Lama2dy mice. AChE activity in normal thymus (mean +/- SD 1.42 +/- 0.28 micromol acetylthiocholine/h/mg protein, U/mg) was decreased by approximately 50% in dystrophic thymus (0.77 +/- 0.23 U/mg) (p = 0.007), whereas butyrylcholinesterase activity was little affected. RT-PCR assays revealed variable levels of R, H and T AChE mRNAs in thymus, bone marrow and spinal cord. Control thymus contained amphiphilic AChE dimers (G2A, 64%) and monomers (G1A, 19%), as well as hydrophilic tetramers (G4H, 9%) and monomers (G1H, 8%). The dimers consisted of glycosylphosphatidylinositol-anchored H subunits. Western blot assays with anti-AChE antibodies suggested the occurrence of inactive AChE in mouse thymus. Despite the decrease in AChE activity in Lama2dy thymus, no differences between thymuses from control and dystrophic mice were observed in the distribution of AChE forms, phosphatidylinositol-specific phospholipase C sensitivity, binding to lectins and size of AChE subunits.

Age-dependent changes in the nervous and endocrine control of the thymus

The immune system, especially the thymus, undergoes age-related modifications leading to structural and functional changes in the lymphoid organs and immunocompetent cells. Nevertheless, the consequences of thymic involution in the peripheral pool of T-cells are still a matter of controversy. The control of the thymic function is very complex and involves intrathymic signals, the autonomic nervous system, and the endocrine system. Both thymocytes and thymic stromal cells express receptors for a wide range of hormones, as well as for neurotransmitters and neuropeptides, thus affecting thymocytes maturation. This review summarizes the age-dependent variations in the extrathymic components of the thymic microenvironment, i.e., vegetative nerves and hormones, and the possible effects of those changes in the immune function.

Effect of interferon on human thymus microenvironment

Interferon, a thymic immunostimulator, was used with the aim of assessing the importance of adrenergic nerve fibers (ANF) and/or AChE-positive nerve fibers (AChENF) in the regulation of some immunological functions in humans. Thymic normal control fragments and/or thymic fragments of immunostimulated patients were removed during surgical biopsies. Thymic slices were stained with eosin-orange (for the recognition of microanatomical details of the microenvironment) and with Bodian's method for staining of nerve fibers. Histofluorescence microscopy was employed for staining ANF. AChENFs were detected by means of the direct-coloring thiocholine method. All images were submitted to quantitative morphometrical analysis and statistical comparisons of data. Moreover, the amount of proteins and noradrenaline was measured on thymic homogenates of the same patients. Treatment with interferon induces substantial changes in the thymic microenvironment, on ANF, on AChENFs and on the total amount of proteins and noradrenaline in thymic tissue homogenates. In conclusion immunostimulation with interferon induces substantial changes in the whole thymus and in its microenvironment, involving both sympathetic and parasympathetic nerve fibers.

Acetylcholinesterase activity in rat thymus after immunostimulation with interleukin beta

The occurrence and distribution of Acetylcholinesterase (AChE) activity were examined in the thymus of normal and immuno-stimulated adult and aged rats using biochemical and enzymehistochemical methods. Specific AChE reactivity was found primarily in the arteries and, to a lesser extent, in the veins. Only a small amount of activity could be observed in association with the subcapsular and medullary part of the parenchyma and nerve fibers. Our findings indicate that AChE activity in the rat thymus increases after treatment with interleukin beta. In fact treatment with interleukin beta induces an increase of protein content, of the amounts of AChE biochemically assayed and at the levels of AChE histoenzymatically stained. Furthermore, staining of the different structures of the thymus in treated or untreated rats shows that the significant modifications concern the parenchyma, the structures resembling nerve fibers and the whole thymus, while only small changes are observed in AChE activity located in the walls of arteries, veins and lymphatic vessels.