Thymic lymphocytes bear a surface antigen which cross-reacts with acetylcholine receptor

Modeling the intrathymic pathogenesis of myasthenia gravis

Myasthenia gravis is (MG) a prototypic autoimmune disease; the immune effector mechanisms and autoantigenic target have been delineated. However, the events that lead to the abrogation of self-tolerance to neuromuscular acetylcholine receptors (nAChRs) remain a mystery. The thymus gland has long been considered to hold the key to solving this mystery, although the nature of its involvement remains to be elucidated. The nAChR was one of the first self-proteins associated with a defined autoimmune disease that was found to be expressed on thymic stromal populations. The studies described herein represent our efforts to determine how this "promiscuous" autoantigen expression may be involved in the immunopathogenesis of MG. We review our work, characterizing the expression of the nAChR alpha subunit in the thymus, and advance a hypothesis and experimental model, which explore how intrathymic expression of this autoantigen may contribute to the immunopathogenesis of this autoimmune disease.

Acetylcholine receptor antibody: clinical and experimental aspects

Anti-acetylcholine (ACh) receptor antibody is the specific antibody in myasthenia gravis (MG). Groups of patients distinguished by thymic pathology and age of onset have shown differences in sex and HLA antigen incidence and in anti-ACh receptor antibody levels. Group differences in the characteristics of this antibody, including the percentage of kappa and gamma light chains, IgG subclass and reactivity with other ACh receptor preparations, were detected only in patients with ocular MG. This group alone showed a possible association with Gm allotype in Caucasians; the anti-ACh receptor antibody had a greater proportion of kappa light chain and better reactivity with human ocular ACh receptor than did generalized MG. The results indicate heterogeneity of this disease. Thymic cells from myasthenic patients with thymic hyperplasia spontaneously synthesize anti-ACh receptor antibody in culture and, after irradiation to abrogate antibody production and any suppressor effects, can selectively enhance the synthesis of anti-ACh receptor antibody by autologous blood lymphocytes in co-culture. The cell types that underlie these responses have been investigated by deleting cell subsets by complement-mediated lysis using monoclonal antibodies. Neither cortical (NA1/34+) thymocytes nor mature T cells (MBG6+) are essential for antibody production in vitro by thymic cells. The enhancement of antibody production by irradiated thymic cells may depend on antigen-presenting cells not expressing the HLA-DR surface marker, or possibly antigen-specific helper T cells, or both.

Relationship between diseases accompanied by tissue destruction and granulocytes with surface adrenergic receptors

It is well-known that physiological phenomena and certain diseases, including neonatal granulocytosis, age-associated granulocytosis, periodontitis, pancreatitis, Crohn's disease, ulcerative colitis, hemorrhoids, endometriosis, and NSADs-enteritis, are accompanied by tissue destruction and granulocytosis. We investigated what is a key factor connecting tissue destruction and granulocytosis, attention being focused on adrenergic receptors on granulocytes and stress-induced sympathetic nerve stimulation. If we introduce the concept that "granulocytosis and subsequent tissue destruction are induced by sympathetic nerve stimulation," the mechanisms underlying many physiological phenomena and the etiology of several uncurable diseases in humans can be clearly understood.

A New Model Linking Intrathymic Acetylcholine Receptor Expression and the Pathogenesis of Myasthenia Gravis

The thymus is thought to play an important role in the pathogenesis of myasthenia gravis (MG), an autoimmune disease characterized by skeletal muscle weakness. However, its role remains a mystery. The studies described represent our efforts to determine how intrathymic expression of the neuromuscular type of acetylcholine receptors (nAChRs) is involved in the immunopathogenesis of MG. We review our work characterizing the expression of the alpha subunit of nAChR (nAChRalpha) in the thymus and advance a new hypothesis that examines the intrathymic expression of this autoantigen in disease pathogenesis.

Acetylcholine receptor alpha subunit mRNA expression in human thymus: augmented expression in myasthenia gravis and upregulation by interferon-gamma

Previous studies by us and others have demonstrated the expression of acetylcholine receptors on epithelial cells in the thymus of myasthenia gravis (MG) and control subjects. In the present experiments, we used a reverse transcription-polymerase chain reaction (RT-PCR) to analyze the profile of the two major isoforms of the alpha chain of these receptors (AChRalpha), P3A- and P3A+, in thymus tissue obtained from MG and control subjects and a human thymic epithelial cell line (TEC9). In addition, using a semiquantitative RT-PCR, we compared the amounts of P3A- and P3A+ mRNA expressed in thymic tissue obtained from these two sources and determined if their expression in TEC9 is modulated by cytokines. We found that mRNAs encoding P3A- and P3A+ are expressed at approximately a 5:1 ratio in both MG and control thymus tissue. This contrasts with skeletal muscle where mRNAs encoding these isoforms are expressed equally. A pattern of preferential P3A- vs P3A+ mRNA expression was also observed in TEC9. We observed 2.8-fold greater expression of both isoforms in MG than in control thymus. Expression of both isoforms in TEC9 was enhanced significantly by treatment with interferon-gamma whereas IL-1alpha, IL-4, and IL-6 had no effect. Thus, there is differential regulation of AChRalpha variants in thymus and TEC relative to muscle and interferon-gamma represents a novel regulator of AChRalpha mRNA expression. MG thymus is distinguished by increased expression of both isoforms of this autoantigen, a finding that may reflect enhancement of transcription by local microenvironmental factors.

Expression of thyroid-related genes in human thymus

There are several thyroid antigens including human sodium iodide symporter (hNIS), thyrotropin receptor (TSH-R), thyroid peroxidase (TPO), and thyroglobulin (Tg) that have been considered to be thyroid-specific proteins involved in the pathogenesis of autoimmune thyroid diseases. We examined the expression of these thyroid-tolerance related genes in normal human thymus, the lymphoid organ responsible for the induction of central T-cell self. Reverse transcription-polymerase chain reaction (RT-PCR) amplifications were performed with 4 pairs of oligonucleotide primers specific for the hNIS, TSH-R, TPO, and Tg genes, respectively. Gene-specific transcripts were confirmed by Southern hybridization using digoxigenin-labeled internal oligonucleotide probes. To monitor cDNA integrity and quantity, all samples were coamplified with a pair of intron-spanning human beta-actin-specific oligonucleotide primers. Furthermore, using a highly sensitive immunostaining technique and antibodies specific for these 4 antigens, we examined whether NIS-, TSH-R-, TPO-, and Tg-specific immunoreactivity can be detected and localized in normal human thymus. RT-PCR and Southern hybridization revealed expression of each of these 4 thyroid-related genes in normal human thymus. In addition, immunohistochemical analysis of frozen tissue sections derived from normal human thymus showed marked immunoreactivity for NIS, TSH-R, and Tg as well as weaker staining for TPO. Control reactions using isotype matched nonimmune immunoglobulins were consistently negative. Taken together, our results suggest that NIS-, TSH-R-, TPO-, and Tg-RNA are present and actively processed to immunoreactive NIS-, TSH-R-, TPO-, and Tg-like protein in human thymus. These data support the concept that pre-T lymphocytes may be educated to recognize thyroid-related epitopes expressed in thymus, and, thus, to generate self-tolerance against these thyroid-related antigens.

Identification of nicotinic acetylcholine receptors on lymphocytes in the periphery as well as thymus in mice

The existence of nicotinic acetylcholine receptors (nAChR) on lymphocytes remains controversial. We attempted to show the existence of nAChR on murine lymphocytes. The intraperitoneal injection of nicotine induced the lymphocytosis in the spleen on day 3. Although freshly isolated lymphocytes bound small quantities of fluorescein isothiocyanate (FITC)-conjugated alpha-bungarotoxin (alpha BuTx), they began to bind alpha BuTx after incubation in medium. In contrast to granulocytes, various lymphocyte subsets obtained from various lymphoid organs were found to bind alpha BuTx. Affinity purification of alpha BuTx-binding protein revealed that lymphocytes expressed the same nAChR molecules as those of muscle. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis showed that lymphocytes expressed the alpha-subunit mRNA of nAChR. These results suggest that lymphocytes carry nAChR on the surface and are stimulated directly via their nAChR by parasympathetic nerve stimuli.

Thymic hyperplasia in patients with Graves' disease. Identification of thyrotropin receptors in human thymus

Thymic size and density were studied in 23 untreated patients with Graves' disease and 38 control subjects using computed tomography. Both thymic size and density were higher in untreated patients with Graves' disease than in control subjects in the age-matched group. After treatment with antithyroid drugs, both thymic size and density were significantly reduced, with a concomitant decrease in thyrotropin receptor antibodies. PCR of human thymic cDNA using primers for human thyrotropin receptor amplified a fragment in a size expected for the receptor, and its nucleotide sequence was identical to human thyrotropin receptor cDNA in the thyroid. Northern blot analysis of human thymic poly(A)+ RNA demonstrated the presence of the full length form of thyrotropin receptor mRNA. Western blot analysis of human thymic membrane using anti-thyrotropin receptor peptide antibodies demonstrated a band of 100 kD that was also observed in the thyroid membrane. Immunohistochemistry of thymic tissue using mouse antihuman thyrotropin receptor monoclonal antibodies demonstrated the immunostaining of epithelial cells. These results indicate that thymic hyperplasia is apparently associated with Graves' disease and suggest that thymic thyrotropin receptor may act as an autoantigen that may be involved in the pathophysiology of development of Graves' disease.

T-helper epitopes on human nicotinic acetylcholine receptor in myasthenia gravis

The synthesis of AChR antibodies requires intervention of AChR-specific Th cells. Because of the paucity of anti-AChR Th cells in the blood of myasthenia gravis (MG) patients, direct studies of these autoimmune cells in the blood are seldom possible. Propagation in vitro of anti-AChR T cells from MG patients by cycles of stimulation with AChR antigens selectively enriches and expands the autoimmune T-cell clones, allowing investigation of their function and epitope specificity. Torpedo electroplax AChR was initially used for propagation of anti-AChR T-cell lines. Those studies demonstrated the feasibility of in vitro propagation of AChR-specific T cells. These are bona fide CD4+ Th cells, which stimulate production in vitro of anti-AChR antibodies by B cells of myasthenic patients and recognize equally well denatured and native AChR, suggesting the usefulness of synthetic human AChR sequences as antigens for propagation of the autoimmune Th cells. We used pools of overlapping synthetic peptides, corresponding to the complete sequences of the human AChR alpha-, beta-, gamma-, and delta-subunits, to propagate AChR-specific Th cells from the blood of MG patients. The AChR sequence regions forming epitopes recognized by the autoimmune T cells were determined by challenging the lines with individual synthetic peptides, 20 residues long, screening the AChR subunit sequences. Although each line had an individual pattern of epitope recognition--as expected from their different HLA-DR haplotype--some peptides were recognized by most of all the CD4+ T-cell lines, irrespective of their DR haplotype. The existence of immunodominant regions of the AChR sequence was verified by investigating the response of unselected CD4+ cells from the blood of a relatively large number of MG patients to the individual peptides screening the human alpha-, gamma-, and delta-subunit sequences. Those studies confirmed that each patient has an individual pattern of peptide recognition. The studies also identified a large number of T epitopes of the human AChR and verified the existence of sequence regions immunodominant for T-helper sensitization, because a limited number of sequence regions, including all those immunodominant for the T-helper lines, were recognized by most patients. Anti-AChR CD4+ T lines could be propagated from some healthy controls only for a brief period of time. They recognized AChR sequences poorly, suggesting a low affinity of their T-cell receptors for the corresponding AChR epitopes.(ABSTRACT TRUNCATED AT 400 WORDS)

Choline acetyltransferase activity in murine thymus

Murine thymus has been demonstrated to contain both cholinergic receptors and acetylcholinesterase activity. In the present study we have investigated the presence of the enzyme choline acetyltransferase in this organ, which is responsible for the synthesis of acetylcholine. Results reported here demonstrate that (1) an appreciable amount of the enzyme is already present in the thymus on the day of birth; (2) its expression is developmentally regulated; and (3) thymic atrophy, induced in young (2-week-old) and adult (6-week-old) mice by i.p. injection of hydrocortisone for 2 days, is accompanied by significant reduction of choline acetyltransferase activity only in young mice. Altogether these results demonstrate the presence in the murine thymus of functionally relevant markers of the cholinergic system that might interface the interactions between the nervous and immune systems.

Antibodies to thymic epithelial cells in myasthenia gravis

The presence of anti-thymus antibodies was investigated in the serum of 36 patients with myasthenia gravis (MG). Using an immunofluorescence technique on frozen thymic sections, we found 45% of patients sera reacting with normal or MG thymuses. Staining was confined to subcapsular and medullary keratin-positive epithelial cells. Thirty-five out of 36 sera from healthy controls and all 15 sera from patients presenting another autoimmune disorder were negative. Antibodies to thymic epithelial cells were almost exclusively detected in patients presenting thymic hyperplasia and did not disappear after thymectomy. They were not clearly associated with antiacetylcholine receptor antibody titer, nor with disease severity. Their strong association to thymic abnormalities highlights the role of the thymus in pathogenesis of MG. The reasons for the appearance of these antibodies, the structure they recognize on thymic epithelial cells and their possible etiological role are discussed.

Expression of mRNAs in human thymus coding for the alpha 3 subunit of a neuronal acetylcholine receptor

We report the isolation of clones from a human thymus cDNA library that code for the alpha 3 subunit of a neuronal acetylcholine receptor (AcChR). The clones hybridize to one major 3.0-kb mRNA thymic species and four minor ones of approximately 2.3, 4.0, 5.0, and 6.5 kb, but they do not hybridize to human muscle mRNA. These clones may be of value in defining the cholinergic thymic makeup and the putative role that a thymic AcChR may have in the triggering and/or maintenance of an anti-AcChR response in the autoimmune condition myasthenia gravis.

Physiological basis for neuroimmunomodulation

A large number of clinical and experimental observations indicate that immune responses may be modulated by the central nervous system (CNS). The immune system (IS) and CNS are known to communicate via the endocrine and the autonomic nervous systems. In this overview, we will focus on the immunomodulating role of neurotransmitters and neuropeptides. Immune cells appear to express membrane antigens similar to those of neural cells. Similarities re-enforce analogies between CNS and IS cells. The concept that the CNS modulates immune functions implies that the immune system feeds back information to the CNS. In fact, interleukins have neuroendocrine functions whether they are produced at the periphery by immune cells or at the CNS level by glial cells. Finally, the possible endocrine functions of lymphocytes are described and it is suggested that a complete regulatory loop between immune and neuro-endocrine systems exists. Studies in neuro-immunomodulation are of great importance from a theoretical point of view, the CNS-IS inter-relationships may not be considered only between the CNS and the periphery but also at the level of the immune micro-environment which may be considered as an immune-neuro-endocrine complex.

Theoretical mechanisms by which immunoglobulin therapy might benefit myasthenia gravis

The mechanisms underlying any clinical improvement observed in some patients with myasthenia gravis (MG) treated with normal immunoglobulin (Ig) are not defined. The pathologic alterations in the postsynaptic motor end plate in MG are likely due at least in part to one or more actions of antibodies against epitopes on the nicotinic acetylcholine receptor (anti-AChR Ab). Such anti-AChR Ab are secreted by B lymphocytes and are increased in the serum of MG patients but not of controls. The stimulus for anti-AChR Ab production in MG is unknown with evidence for a role of thymic abnormalities, immunoregulatory disturbances, and some possible molecular mimicry of exogenous antigens (microbial?). Postulated mechanisms underlying Ig effects in MG include: (i) competing with anti-AChR for binding to AChR; (ii) preventing attachment of Fc receptor-positive inflammatory cells to the anti-AChR Ab bound to the motor end plate; (iii) decreasing synthesis of anti-AChR Ab; and (iv) exerting an anti-idiotypic effect. Evidence for these mechanisms are discussed.

Cholinergic agonists selectively induce proliferative responses in the mature subpopulation of murine thymocytes

The incubation of murine thymocytes for 24 hr in the presence of cholinergic agonists induces selective proliferation of PNA- cells as measured by thymidine incorporation. The response of PNA- cells is mediated by the activation of nicotinic receptors. This conclusion is suggested by the inability of the muscarinic agonist, oxotremorine, to induce cell proliferation and by the inhibition exerted by the nicotinic antagonist, d-tubocurarine. The presence of cholinergic axons in the murine thymus adds biological interest to the selective expression of functional cholinergic receptors on mature thymocytes.

Desensitization of the nicotinic acetylcholine receptor: molecular mechanisms and effect of modulators

1. Loss of response after prolonged or repeated application of stimulus is generally termed desensitization. A wide variety of phenomena occurring in living organisms falls under this general definition of desensitization. There are two main types of desensitization processes: specific and non-specific. 2. Desensitization of the nicotinic acetylcholine receptor is triggered by prolonged or repeated exposure to agonists and results in inactivation of its ion channel. It is a case of specific desensitization and is an intrinsic molecular property of the receptor. 3. Desensitization of the nicotinic acetylcholine receptor at the neuromuscular junction was first reported by Katz and Thesleff in 1957. Desensitization of the receptor has been demonstrated by rapid kinetic techniques and also by the characteristic "burst kinetics" obtained from single-channel recordings of receptor activity in native as well as in reconstituted membranes. In spite of a number of studies, the detailed molecular mechanism of the nicotinic acetylcholine receptor desensitization is not known with certainty. The progress of desensitization is accompanied by an increase in affinity of the receptor for its agonist. This change in affinity is attributed to a conformational change of the receptor, as detected by spectroscopic and kinetic studies. A four-state general model is consistent with the major experimental observations. 4. Desensitization of the nicotinic acetylcholine receptor can be potentially modulated by exogenous and endogenous substances and by covalent modifications of the receptor structure. Modulators include the noncompetitive blockers, calcium, the thymic hormone peptides (thymopoietin and thymopentin), substance P, the calcitonin gene-related peptide, and receptor phosphorylation. Phosphorylation is an important posttranslational covalent modification that is correlated with the regulation and desensitization of the receptor through various protein kinases. 5. Although the physiological significance of desensitization of the nicotinic receptor is not yet fully understood, desensitization of receptors probably plays a significant role in the operation of the neuronal networks associated in memory and learning processes. Desensitization of the nicotinic receptor could also possibly be related to the neuromuscular disease, myasthenia gravis.

Search for nicotinic acetylcholine receptors on human leukocytes: absence of alpha-bungarotoxin binding in studies of healthy individuals and myasthenia gravis patients

To investigate whether nicotinic acetylcholine receptors might be present on blood mononuclear cells we studied the binding [125I]alpha-bungarotoxin to mononuclear cells from three normal controls and seven myasthenia gravis patients. The medulloblastoma cell line, TE671, which expresses a functional nicotinic acetylcholine receptor having pharmacological properties similar to that of skeletal muscle receptor, was used as a positive control for alpha-bungarotoxin binding. None of the mononuclear cell samples studied exhibited specific binding of alpha-bungarotoxin.

Electrophoretic immunoblotting analysis of anti-thymus microsome antibodies in patients with myasthenia gravis

Anti-thymus microsome antibodies and anti-skeletal muscle microsome antibodies in sera from patients with myasthenia gravis (MG) were analyzed by means of immunoblotting, which was performed after SDS polyacrylamide gel electrophoresis of antigens to clarify the pathogenic role of the thymus in MG. Anti-thymus microsome antibodies were detected in 15 of the 20 cases of MG examined. The detection frequency (75%) was significantly higher than the corresponding frequency determined for anti-muscle microsome antibodies (35%) in the same group of patients. Thymic antigens with a molecular weight of 38 kilodaltons (KD), 60 KD and 220 KD were often recognized by antibodies in sera from MG patients studied here. The anti-thymus microsome antibodies were not cross-reactive with either thymic acetylcholine receptors or lymphocyte surfaces. These findings indicated that the specific antibodies were produced to the thymic microsomal fraction, and its frequency was higher than has been suspected in MG patients.

Secretory acetylcholinesterases from Brugia malayi adult and microfilarial parasites

Brugia malayi, a lymphatic filarial parasite, secretes acetylcholinesterase during in vitro cultivation. A significant amount of enzyme activity was detected both in culture media and somatic extracts of adult and microfilarial stages of the parasite. The microfilarial stage produces three times more enzyme than adult parasites as a proportion of total protein. The enzyme has true acetylcholinesterase (AChE) activity as hydrolysis of acetylthiocholine is three times faster than butyrylthiocholine and is inhibited by eserine, a specific inhibitor of AChE. Secretory enzyme from adult female parasite excretory-secretory material (ES) was enriched 23 fold using copper chelating and concanavalin A (Con A) affinity chromatography. The Con A eluate showed a major protein band of 100 kDa and a minor 200 kDa component. The ES enzyme is antigenic and cross reacts with antibodies raised in mice against AChE from electric eel by enzyme-linked immunosorbent assay and immunoprecipitation. Immunoprecipitation of 125I-labelled microfilarial ES and adult ES with anti-electric eel AChE antibodies revealed three proteins of 30, 40 and 200 kDa in microfilariae and two proteins of 100 and 200 kDa in adult female ES. It appears that filarial secretory AChE exists in multiple molecular forms.

Myasthenic sera recognize the human acetylcholine receptor bound to thymopoietin

The thymic hormone, thymopoietin (Tpo), from human (HTpo), bovine (BTpo) and from synthetic (sHTpo) origins bound to the acetylcholine receptor (AChR) solubilized by Triton 1.5% from human muscle. This binding was demonstrated either by inhibition of formation of radiolabeled alpha bungarotoxin (alpha Bgt)-AChR complexes measured after precipitation by ammonium sulfate or by a myasthenic serum containing a high concentration of anti-AChR antibodies, or directly by incubating the human AChR with radiolabeled sHTpo or BTpo. The 125I-labeled alpha Bgt-AChR complexes were totally inhibited by 10(-6) M sHTpo or BTpo. The complexes formed by AChR and the radiolabeled Tpo were recognized specifically by sera containing anti-AChR antibodies from myasthenic patients. The active pentapeptide derivative of Tpo, thymopentin, another thymic hormone, thymulin, as well as bovine insulin did not interfere with the specific binding of alpha Bgt to human AChR. Tpo and anti-AChR antibodies could participate together in the inhibition of neuromuscular conduction with Tpo modulating the depressive effect of the antibodies on the neuromuscular junction in myasthenia gravis.

Nicotine induces T-suppressor cells: modulation by the nicotinic antagonist D-tubocurarine and myasthenic serum

To further unravel the basic immunoregulatory defect present in myasthenia gravis, we undertook to study nicotinic acetylcholine receptor (AchR) activity on human peripheral blood leukocytes. A biphasic suppressive effect of nicotine was observed on lymphocyte proliferative responses to phytohemagglutinin, concanavalin A, and pokeweed mitogen with peaks at 10(-9) and 10(-5) M. Using a coculture approach, T cells preincubated with nicotine for 24 hr showed enhanced suppressor cell activity. This was partially blocked by serum from myasthenic patients and by the nicotinic antagonist d-tubocurarine. These studies suggest that suppressor T lymphocytes bear functional nicotinic AchR, which may be modulated by myasthenic serum, with possible relevance to the pathogenesis of myasthenia gravis.

In vitro anti-acetylcholine receptor antibody synthesis by myasthenia gravis patient lymphocytes: correlations with thymic histology and thymic epithelial-cell interactions

In vitro anti-acetylcholine receptor antibody (anti-AChR Ab) production by peripheral blood lymphocytes (PBL) and thymic lymphocytes was investigated in 52 patients with myasthenia gravis (MG). There was a positive correlation between in vitro anti-AChR Ab synthesis and in vivo titers. A relationship between the rates of synthesis by PBL and histological abnormalities of the thymus was also observed. Patients with hyperplastic thymus tended to produce the largest amounts in vitro, while those with an involuted thymus produced little or none. Production in thymoma patients is likely to correlate with the histological nature of the thymus associated with the tumor. In vitro Ab synthesis was modulated by the depletion of a cell subset for half of the patients tested. Finally, anti-AChR Ab production by thymocytes but not by PBL is enhanced by the addition of autologous or allogeneic thymic epithelial cells, suggesting a possible role of thymic epithelial cells in the autosensitization against AChR occurring in the thymus.

Increased binding of anti-acetylcholine receptor antibodies to thymic antigen in patients with myasthenia gravis and other autoimmune diseases, as compared to those with myasthenia gravis alone

We compared the binding activity against acetylcholine receptors solubilized from human muscle (AChRM) and human thymus (AChRT), of sera from patients with myasthenia gravis (MG) alone, to those of sera from patients with myasthenia gravis and associated autoimmune diseases (MG AD). The sera of the MG AD group bound relatively better to thymic antigen (86% vs. 62%). This group was found to contain a higher proportion of women over 40 years of age (more than 50% of the group). The expression of a particular AChR antigen in normal human thymus may be one of the factors involved in the pathogenesis of MG, especially when this disease is associated with other autoimmune disorders.

Expression of 3-fucosyl-N-acetyllactosamine on glia cells and its putative role in cell adhesion

Mouse monoclonal antibodies from five clones (MMA, 1G10, VIM C6, MC-1 and Tü9), elicited to human myeloid cells and reactive with the 3-fucosyl-N-acetyllactosamine sequence (also termed X-determinant), cross-react with glia cells from human and rat brain. In brain cell cultures from neonatal rats both astrocytes and oligodendrocytes express the X-determinant during the first period of the culture as shown by immunofluorescence tests. While the astrocytes, which exhibit signs of adhesion, permanently express the X-determinant, the oligodendrocytes lose the epitope nearly completely during culture. The oligodendrocytes preferentially grow on top of the astrocytic layer. After about 8-10 days of culture, numerous X-determinant-positive astrocytic membranes show oligodendrocyte-shaped negative print images underneath the galactocerebroside-positive oligodendrocytes. At this time, the oligodendrocytes are relatively firmly attached to the astrocytic layer. Since participation of the X-determinant in the compaction of the mouse 8-32 cell stage is being discussed, we conclude from our observations that the X-determinant may also play a role in the astrocyte-astrocyte and astrocyte-oligodendrocyte adhesion. It may represent the functionally active carbohydrate moiety of a heterotypic cell adhesion molecule of glia cells.

Primary cultures of human myasthenia gravis thymus and normal thymus. Studies of cell morphology, cell proliferative pattern and localization of alpha-bungarotoxin binding sites on cultured thymic cells

We have established primary cultures of human myasthenia gravis (MG) thymuses and normal thymuses. In cultures of 19 thymuses with hyperplasia among 23 MG thymuses and 12 thymuses among 13 normal thymuses, epithelial cells migrated in a mosaic-like arrangement and were maintained for more than 5-10 weeks. There were, among mononuclear epithelial cells, some multinucleated cells, some of which were considered to be derived from epithelial cells because they had a desmosome-like structure and contained tonofilaments in their cytoplasm. There was no significant difference in the morphology of epithelial cells between MG thymuses and normal thymuses. The growth rate of thymic epithelial cells was identified by [3H]thymidine autoradiography(ARG), labeling indices rising to a peak around a week and falling to low levels gradually. There was no significant difference in the growth rate of epithelial cells between MG thymuses and normal thymuses. An autoradiographic method with 125I-labeled alpha-bungarotoxin was used to detect the presence of acetylcholine receptor (AChR) on the cultured cells. ARG of human MG thymuses and normal thymuses, which were cultured for 4 weeks, revealed diffusely distributed silver grains on the epithelial cells. Toxin binding sites (AChRs) were considered to be present on the epithelial cells. There was no significant difference in the distribution of AChR on the epithelial cells between MG thymuses and normal thymuses.

Very late activation antigens (VLA) are human leukocyte-neuronal crossreactive cell surface antigens

The antigenic relationship between human neuronal and lymphocyte cell surface antigens has been analyzed using heteroantisera raised against human peripheral blood mononuclear cells (PBMC). The specificities of the crossreactive antigens were examined by immunoprecipitation of 125I-labeled SK-N-SH cultured neuronal cells using rabbit anti-PBMC (RAPBMC) sera and compared to known specificities using mAb. The predominant reactivity of each rabbit antiserum tested against SK-N-SH cells was with three molecules of 130,000, 160,000, and 180,000 Mr. These three chains comigrated with three molecules precipitated with the very late activation antigen (VLA)-specific mAb A-1A5. Sequential precipitations with mAb A-1A5 established that the three RAPBMC-precipitated bands were members of the VLA complex. This was confirmed by two-dimensional PAGE of the RAPBMC and A-1A5 immunoprecipitates, which were indistinguishable from one another. The two-dimensional pattern was more complex than was anticipated from the heterodimeric model of VLA chain association, and suggests an additional 130,000 Mr component of VLA. The three chains of the VLA complex precipitated by RAPBMC or mAb A-1A5 from SK-N-SH neurons closely resembled the VLA pattern present on activated T cells, including the 180,000 Mr activation-specific alpha 1 chain recognized by mAb TS2/7. Normal brain cell membranes also contain VLA molecules that are precipitated by RAPBMC and mAb A-1A5. Thus the VLA complex provides potentially important shared immunogens on human neurons and T cells.

An epitope shared by central nervous system myelin and peripheral blood macrophages

Lewis rats were immunized with a homogenate of human spinal cord. Splenocytes from the immunized rats were fused with cells from the SP2/0-Ag14 cell line to form hybrids that were subsequently screened immunohistochemically for secretion of antibodies against myelin. Thirty hybrids secreting anti-myelin antibodies were cloned. One secreted antibody (774) that immunohistochemically stained central nervous system (CNS) myelin but not peripheral nervous system (PNS) myelin also bound to the surface of peripheral blood macrophages. Hence we have identified an epitope that is shared by peripheral blood macrophages and CNS myelin.

Natural killer cell activity in murine muscular dystrophy. III. NK-sensitive myoblast cells and lack of NK activity in beige/dystrophic hybrid mice

The NK-susceptibility of dystrophic mouse myoblast cells was investigated. Spleen cells from 8- to 10-week-old normal (+/+) and dystrophic (dy2J/dy2J) male C57BL/6J mice were fractionated on Percoll density gradients and the cells at each density interface were incubated with either 51Cr-labeled YAC-1 or myoblast cells in a 6 hr 51Cr-release assay. Myoblast target cells were obtained from either heterozygous (+/dy2J) or homozygous (dy2J/dy2J) muscle cultures or a transformed tetraploid myoblast line (M14D2). The data indicate that the interface between the 50 and 60% (1.060-1.075 g/ml) Percoll density fractions of spleen cells from either normal or dystrophic mice contains the largest proportion of asialo GM-1 positive and NK-1 positive cells displaying NK activity. Myoblast cells from either heterozygous (phenotypically normal) or homozygous dystrophic mice were not significantly different in susceptibility to NK-mediated lysis by Percoll enriched normal or dystrophic mouse NK cells. However, dystrophic mouse spleen cells had the highest NK activity against both myoblast targets as compared with normal mouse spleen cells. The transformed myoblast cell line, M14D2, was significantly less susceptible to NK-mediated lysis by dystrophic mouse spleen cells when compared with freshly cultured myoblast target cells. Target cell binding studies revealed that conjugate forming cells from the 50% Percoll density interface of dystrophic mouse spleen cells were approximately twofold greater than that of normal mouse spleen cells against either heterozygous or homozygous dystrophic mouse myoblast targets. Cold target inhibition studies revealed that the natural killing of dystrophic mouse myoblast cells was due to a YAC-1 reactive NK cell. Breeding experiments between C57BL/6J homozygous "beige" (bgJ/bgJ) mutant mice and dystrophic (dy2J/dy2J) mice produced beige/dystrophic hybrid mice which displayed clinical symptoms of the dystrophy process by 3 to 4 weeks of age. Spleen cells from these hybrid mice showed no significant differences in NK activity against YAC-1 target cells when compared with homozygous beige mice. Taken together, these results demonstrate the first reported evidence that murine myoblasts are susceptible to NK-mediated lysis. In addition, the data indicate that although dystrophic mouse NK cells recognize myoblast cells as targets, the NK cell studies with the beige/dystrophic hybrid mice do not indicate a direct in vivo role for NK cells in the dystrophy process.

Myasthenia gravis: immunohistological heterogeneity in microenvironmental organization of hyperplastic and neoplastic thymuses suggesting different mechanisms of tolerance breakdown

Four samples of thymoma obtained from patients affected by myasthenia gravis have been immunohistologically analysed on cryostat sections using a panel of antisera and monoclonal antibodies specific for antigens which define different stages of intrathymic lymphocyte differentiation and antigens specific for different types of thymic epithelial cells (cortical, medullary). When the thymoma samples were compared to age-matched normal thymuses and hyperplastic thymuses obtained from patients with myasthenia gravis some evident microenvironmental differences could be demonstrated using these reagents. In all the thymoma samples in fact the neoplastic lobules appeared as grossly enlarged cortical-type areas, formed by accumulations of T lymphocytes exhibiting the cortical immature phenotype (TdT+, T6+, etc.) within a network of putatively neoplastic epithelial cells characterized by cortical phenotype as defined by reactivity with various monoclonal antibodies (RFD4-, MR3+). These 'cortical' epithelia showed some abnormal features such as lack or irregular distribution of HLA-DR and enhanced keratin expression. Small areas of 'medullary' differentiation could be observed in 3/4 thymoma samples. In thymic hyperplasia, on the other hand, the cortical areas appeared somewhat compressed (but comparable to those observed in normal age-matched samples) by enlarged medullary areas. The expansion of medullary areas was due to the infiltration of 'peripheral' lymphoid tissue intruding through the extraparenchymal zone and forming organized B and T areas. These observations are discussed in the light of the clinical heterogeneity observed in myasthenia gravis.

Immunohistochemical recognition of human neuroepithelial tumors by anti-Leu 7 (HNK-1) monoclonal antibody

The immunoreactivity of the anti-Leu 7 (HNK-1) monoclonal antibody, a marker for natural killer cells, was evaluated with the peroxidase-anti-peroxidase (PAP) method on sections of human paraffin-embedded tissues from 135 tumors of the central nervous system and five esthesioneuroblastomas. As shown independently by others, the antibody was found to react with most types of neoplastic neuroepithelial cells. Our findings indicate that the reaction is most often localized on the cytoplasmic membranes. The immunoreactive cell membranes were generally those of well-differentiated tumor cells and of neoplastic cells found in tumors that usually were not embryonal in nature. Parallel immunostaining either of the same or of successive sections with an anti-glial fibrillary acidic protein serum was of considerable assistance in discriminating between different immunoreactive cells, e.g., between astrocytes and cells presumed to be oligodendrocytes. Despite its cross-recognition of cells of various histogenesis, the anti-Leu 7 monoclonal antibody can, in well-defined circumstances, elucidate specific differential diagnostic problems involving neurogenic neoplasms that cannot be resolved with routine staining techniques.

Human monoclonal anti-DNA antibodies react as lymphocytotoxic antibodies

Two out of 25 monoclonal anti-DNA autoantibodies that were produced by human-human hybridoma were found to have lymphocytotoxic activity. The antibodies reacted with normal B and T lymphocytes at cold (4 degrees C) as well as at warm (37 degrees C) temperatures. The lymphocytotoxic activity of the monoclonal anti-DNA antibodies could be inhibited by prior incubation of the antibodies with either polynucleotides, e.g. poly(I), poly(dT) or anti-idiotypic antibodies, that had been raised against a dominant anti-DNA antibody. The cross-reactivity between nuclear material and lymphocyte membrane raises the question whether these apparently diverse materials have a shared epitope. The cross-reactivity between anti-DNA antibodies and lymphocyte membrane may account in part for the lymphopenia observed in systemic lupus erythematosus patients.

A three-dimensional reconstruction of high endothelial venules in the mouse lymph node: an enzyme-histochemical study

A three-dimensional reconstruction of high endothelial venules (HE-venules) of an entire mouse lymph node is presented. The reconstruction has been made by means of the histochemical technique for alpha-naphthylacetate esterase. The course of the HE-venules is shown in coherence with lymphocytic aggregates (follicles and unit), which were concomitantly reconstructed. Carbonic anhydrase, glutamate-, and alpha-glycerophosphate dehydrogenase were found in the high endothelia, while calcium-stimulated NA+, K+ ATP-ase and the acetylcholinesterase were localized to the endothelia and/or to the perivascular sheath of the HE-venules and submarginal capillaries.

Shared antigenic determinants between human hemopoietic cells and nervous tissues and tumors

A panel of nine monoclonal antibodies raised against human hemopoietic cells was used for immunohistological labeling of frozen sections of human nervous tissues and tumors. Three antibodies showed a remarkably consistent labeling pattern when tested on 18 samples of normal or reactive tissue, on 31 neurogenic and 17 non-neurogenic tumors in an indirect immunofluorescence technique. VIM C6, an antibody recognizing cells of the granulocyte series, showed surface labeling of normal and reactive glial cells and of all types of glioma regardless of the grade of malignancy. VIT 13, an antibody recognizing activated T-cells, labeled the processes of normal, reactive, and neoplastic glia in a manner very similar to but not identical with glial fibrillary acidic protein (GFAP). VIB C5, an antibody recognizing B cells and granulocytes, showed surface labeling restricted to malignant cells (malignant gliomas and primitive neuroectodermal tumors) and fetal brain, thus recognizing, within the nervous system, an oncofetal antigen. Due to this operational specificity within the nervous system, some of the antibodies described here might have a role as diagnostic markers for CNS tumors. This study confirms and expands previous data that sharing of antigenic determinants by hemopoietic cells and nervous tissue or neurogenic tumors is common. However, the significance of such cross-recognition is still obscure. It is tempting to speculate that cross-reacting auto-antibodies might contribute to tissue damage in some immune-mediated neurologic diseases (myasthenia gravis, multiple sclerosis, CNS involvement in systemic lupus erythematosus) or to impairment of immunoregulation in multiple sclerosis or glioma patients. Furthermore, sharing of surface determinants might be responsible for the dual tissue tropism of some viruses, including the lymphotrophic virus (HTLV) in the encephalopathy of the acquired immune deficiency syndrome (AIDS).

Acetylcholine receptor antibody-producing cells in thymus and lymph nodes in myasthenia gravis

Eleven patients with myasthenia gravis (5 with thymoma) were studied and spontaneous production of antibody to acetylcholine receptor (AChR) in vitro was found by thymus cells in 10 (and in all 5 with thymoma) and by lymph node cells in 8 (and in 3 with thymoma). The rate of AChR antibody production by thymus cells was greater than that by lymph node cells (10.7 +/- 11.6 and 1.4 +/- 1.5 fmol/10(6) cells/week, respectively, mean +/- SD, P less than 0.05 by paired t test), although the B-cell population was always smaller in the thymus than in the lymph nodes (9.5 +/- 9.4 and 31 +/- 12.7%, P less than 0.001), suggesting the principal role of the thymus in AChR antibody production. It is suggested that lymph nodes can be one of the main sites of AChR antibody production in myasthenia gravis but the antibody-producing cells may originate in the thymus.

Murine monoclonal antibodies to the myelin-associated glycoprotein react with large granular lymphocytes of human blood

Monoclonal antibodies prepared to human myelin-associated glycoprotein were shown to react with a population of human peripheral blood mononuclear cells. The population is similar to the large granular lymphocytes or natural killer cells defined by antibody Leu 7 (also called HNK-1). The population also includes cells exhibiting the Leu 2 marker for suppressor/cytotoxic T cells. The results indicate a shared antigenicity between the nervous system and the immune system and may be relevant to the pathogenesis of demyelinating diseases.

A cholinergic receptor site on murine lymphocytes with novel binding characteristics

To further analyze functionally important cholinergic receptors on lymphocytes, we studied the binding of the muscarinic antagonist Quinuclidinyl benzilate (QNB) to murine splenic lymphocytes. Studies of displacement of [3H]QNB by unlabeled QNB on lymphocytes revealed at least two binding sites. Scatchard analysis of equilibrium binding isotherms also distinguished two sites with apparent Kds of 480 nM and 16 microM. There was greater specific QNB binding to B cell-enriched lymphocyte fractions than to T cell fractions. Lymphocyte binding demonstrated temperature-dependent dissociability, and specific binding occurred on isolated lymphocyte membranes as well. Both muscarinic and nicotinic ligands competed for QNB binding to lymphocytes with low and nearly equal affinity. Therefore, QNB binding sites on lymphocytes appear to be of low affinity and of mixed muscarinic and nicotinic character.

A human lymphocyte antigen is shared with a group of glycoproteins in peripheral nerve

The monoclonal antibody HNK-1 binds to a carbohydrate determinant in the myelin-associated glycoprotein (MAG) and other glycoproteins of human peripheral nerve. Some glycoproteins of lower Mr than the major P0 glycoprotein of myelin appear to bind more antibody than MAG. These glycoproteins electrophorese in the Mr range of 20,000 to 26,000 and are present in the purified myelin fraction. The results indicate that an antigen on the surface of a subset of lymphocytes is shared with a group of glycoproteins in human peripheral nerve. The antigen appears to be similar to that recognized by IgM paraproteins associated with a type of neuropathy.