[Show abstract][Hide abstract] ABSTRACT: Age-related changes in immune regulation are likely to account for the age-associated increase in serum autoantibody levels and in certain autoimmune disorders, such as myasthenia gravis (MG). To demonstrate directly a loss of immune tolerance in older individuals, responses to the acetylcholine receptor, the autoantigen in MG, were assessed in transgenic mice expressing the Torpedo californica acetylcholine receptor (TAChR) alpha-chain as a neo-self Ag. T cells from young transgenic mice had been shown to be tolerant to p146-162, the TAChR alpha-chain peptide that dominated young nontransgenic T cell responses in vitro. The immunodominance of p146-162 was not lost with age; fine specificity was preserved. Moreover, T cell tolerance to p146-162, as well as to other epitopes of the TAChR alpha-chain extracellular domain, was maintained in old transgenic mice. Even multiple TAChR immunizations coupled with the MG-enhancing cytokine, IL-12, did not break tolerance. In addition, T cells exhibiting CD4 upregulation, an early activation marker, were reduced in frequency equivalently in old and young transgenic animals, suggesting that immune regulation in this model was not impacted by aging. Moreover, B cell tolerance was also maintained with age. The persistence of immune tolerance was accompanied by an increase in the proportion of T regulatory cells; it is speculated that this may compensate for deficiencies in central tolerance that occur owing to thymic involution. In summary, our study reveals, for the first time, that some immune tolerance mechanisms do survive aging; this suggests that certain late-onset autoimmune disorders may be induced by a specific insult that disrupts immune homeostasis.
The Journal of Immunology 06/2010; 184(11):6067-75. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The study reported below describes increased expression of IL-4 receptor in cultured rat myocytes following exposure to an antibody reactive with the acetylcholine receptor (AChR). In addition, upon up-regulation of IL-4R, myocytes demonstrated an increased responsiveness to IL-4 by producing increased levels of IL-15. Moreover, following passive transfer of AChR antibody into Lewis rats, both the increased IL-4R expression and IL-15 production were also observed in intact skeletal muscle, co-localizing in particular individual muscle fibers; the same muscle fibers also produced the chemokine MCP-1 to which IL-4-producing T cells were attracted. A model is proposed in which these muscle activities participate in disease progression in experimental myasthenia gravis.
[Show abstract][Hide abstract] ABSTRACT: Reports from this laboratory suggested that expression of skeletal muscle-derived, inducible nitric oxide synthase (iNOS), is associated with resistance of a particular rat strain to the autoimmune model of myasthenia gravis (MG). The study reported below demonstrates a similar association between iNOS induction in skeletal muscle and disease-resistance when comparing different skeletal muscles originating from the same rat strain. Thus, soleus muscles, shown previously to be relatively resistant to disease even when obtained from disease-susceptible Lewis rats, were observed to express high levels of iNOS following exposure to antibody reactive with the nicotinic acetylcholine receptor (AChR). Increased iNOS expression appears to be associated with slow-twitch, type 1 fibers and would explain the relatively high iNOS expression in soleus muscles since they are dominated by this fiber type, compared to disease-susceptible EDL muscles which are dominated by fast-twitch, type 2 fibers.
[Show abstract][Hide abstract] ABSTRACT: A previous report from this laboratory suggested that expression of skeletal-muscle-derived, inducible nitric oxide synthase (iNOS), is associated with resistance to the autoimmune model of myasthenia gravis (MG) demonstrated by Wistar Furth rats following the passive transfer of antibody reactive with the nicotinic acetylcholine receptor (AChR). The study reported below demonstrates an association between increased expression of iNOS/NO in Wistar Furth rats and the induction of programmed cell death (apoptosis) in both macrophages and CD4+ T cells that attempt to traffic through targeted muscles. It is concluded that production of muscle-derived NO is protective in experimental MG, and in part, dictates the severity of eventual immunopathology.
[Show abstract][Hide abstract] ABSTRACT: In an attempt to identify mechanisms that explain the difference in susceptibility of two rat strains to the induction of experimental autoimmune myasthenia gravis (EAMG), acetylcholine receptor (AChR)-reactive antibodies were tested for their ability to up-regulate levels of inducible nitric oxide synthase (iNOS) in skeletal muscles of disease-sensitive Lewis rats and disease-resistant Wistar Furth (WF) rats. Initially, the WF muscle cell line, WE1, appeared to be more sensitive to antibody-stimulated iNOS induction and NO production than did the Lewis muscle cell line, LE1. Next, AChR-reactive antibody induced widespread iNOS production in skeletal muscles of WF rats, while iNOS production in muscles of Lewis rats was much less pronounced. Finally, inhibition of iNOS activity by administration of a specific iNOS inhibitor resulted in increased susceptibility to the induction of impaired muscle function in EAMG-resistant WF rats. It is speculated that nitric oxide production plays a protective immunomodulating role in WF rats.
[Show abstract][Hide abstract] ABSTRACT: Most patients with autoimmune myasthenia gravis (MG) produce autoantibodies against their muscle acetylcholine receptors (AChR), causing debilitating muscle weakness. Approximately 60% of MG patients first exhibit myasthenic symptoms after the age of 40. Yet, in the C57BL/6 mouse model of MG, older mice are resistant to induction of myasthenia gravis. To understand the immunological basis for this resistance, the effects of age on the B-cell responses to AChR from Torpedo californica, the inducing antigen, were addressed. As expected, the primary B-cell response was lower in 20-month-old mice than in 2-month-old mice; the isotype profile was not altered by age. When mice were re-immunized, the anti-T-AChR titers increased in both young and old animals, suggesting that a memory response was elicited. Importantly, memory B-cells activated in young animals were largely resistant to the age-associated loss of immune function and the recall memory response was vigorous. Furthermore, the antibodies produced in re-stimulated older mice were functional, as evidenced by the appearance of MG symptoms in some of these animals. Thus, by eliciting a recall memory response, the first examples of late onset MG in mice have been generated. By analogy, late onset MG in humans may be due to re-activation of B-cell responses initiated at a younger age.
Mechanisms of Ageing and Development 01/2003; 124(8-9):931-40. · 3.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Because it is one of the few autoimmune disorders in which the target autoantigen has been definitively identified, myasthenia gravis (MG) provides a unique opportunity for testing basic concepts of immune tolerance. In most MG patients, Abs against the acetylcholine receptors (AChR) at the neuromuscular junction can be readily identified and have been directly shown to cause muscle weakness. T cells have also been implicated and appear to play a role in regulating the pathogenic B cells. A murine MG model, generated by immunizing mice with heterologous AChR from the electric fish Torpedo californica, has been used extensively. In these animals, Abs cross-react with murine AChR; however, the T cells do not. Thus, to study tolerance to AChR, a transgenic mouse model was generated in which the immunodominant Torpedo AChR (T-AChR) alpha subunit is expressed in appropriate tissues. Upon immunization, these mice showed greatly reduced T cell responses to T-AChR and the immunodominant alpha-chain peptide. Limiting dilution assays suggest the likely mechanism of tolerance is deletion or anergy. Despite this tolerance, immunization with intact T-AChR induced anti-AChR Abs, including Abs against the alpha subunit, and the incidence of MG-like symptoms was similar to that of wild-type animals. Furthermore, evidence suggests that this B cell response to the alpha-chain receives help from T cells directed against the other AChR polypeptides (beta, gamma, or delta). This model offers a novel opportunity to elucidate mechanisms of tolerance regulation to muscle AChR and to clarify the role of T cells in MG.
The Journal of Immunology 01/2003; 169(11):6570-9. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Autoantibodies with reactivity against the postjunctional muscle receptor for acetylcholine receptor are able to interfere with contractile function of skeletal muscles and cause the symptoms of myasthenia gravis (MG) in humans, as well as in experimental animal models of MG. In the study described below using a rat model of MG, it was observed that exposure to acetylcholine receptor-reactive Abs also induced increased levels of chemokine (i.e., monocyte chemoattractant protein 1) production by skeletal muscle cells. This was true of both cultured rat myocytes exposed in vitro and rat muscle exposed in vivo following passive Ab transfer. Increased monocyte chemoattractant protein 1 production may explain the increased trafficking of leukocytes through muscle following Ab transfer described in this and other reports. These observations may also be relevant to the induction of disease symptoms in experimental animal models of MG, since numerous reports from this and other laboratories indicate that the cytokine environment provided by leukocytes trafficking through muscle may play a pivotal role in disease progression.
The Journal of Immunology 09/2002; 169(3):1579-86. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This review will address a paradox that has long fascinated scientists studying the effects of aging on the immune system. Although it has been clearly documented that B and T lymphocytes lose the ability to respond to antigenic or mitogenic stimulation with age, it has nonetheless been noted that the frequency of autoreactive antibodies is higher in older individuals. Given that the majority of the age-associated defects in immune regulation target the naïve T and B lymphocyte subsets, it has been presumed that this increase in antibodies specific for self antigens was due to changes in the B cell repertoire and/or to differences in the mechanisms responsible for generating immune tolerance in primary responses. However, in this review, we will address an alternative possibility that memory immune responses, first generated when the individual was young, may play a critical role in the appearance of serum autoantibodies by reactivation later in life (recall memory). It has recently been shown, in several different systems, that memory immunity can be maintained over the lifetime of the animal. Thus, memory B cells which are self-reactive may be harbored within an organism as it ages and the potential exists that they become re-activated at a later time, resulting in a vigorous autoreactive recall response. This may occur preferentially in older individuals due to several factors, including deficiencies in immune tolerance with age, progressive age-associated loss of tissue integrity yielding neo-self antigens, and possible re-exposure to an infectious agent which induces an autoimmune memory response through molecular mimicry. Thus, we propose that some of the autoantibodies seen in elderly patients and in older animals may have been produced by memory lymphocytes originally generated against antigens encountered during one's youth, but maintained in a tolerant (non reactive) state until a subsequent triggering event occurs. Possible implications of this model will be discussed.
Mechanisms of Ageing and Development 05/2002; 123(8):975-85. · 3.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The monoclonal Lewis rat skeletal muscle cell line, LE1, responded to the acetylcholine receptor (AChR)-reactive antibody mAb35 by up-regulating levels of mRNA for inducible nitric oxide synthase (iNOS/NOS-II), followed by levels of NO. Interferon-gamma (IFN-gamma) and interleukin-1 (IL-1) were also each capable of inducing iNOS message, and synergistically with mAb35. Finally, myocyte-derived NO was implicated as a possible source of immunomodulation in experimental autoimmune myasthenia gravis (EAMG), as shown by the ability of the culture fluids from IFN-gamma-activated LE1 cells to inhibit the proliferation of AChR-reactive T cells.
Journal of Neuroimmunology 12/2001; 120(1-2):103-11. · 3.03 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The monoclonal antibody, mAb35, which binds the main immunogenic region of the post-junctional muscle receptor for acetylcholine (AChR), results in contractile dysfunction and symptoms of experimental myasthenia gravis (EAMG). As described below, exposure to mAb35 also results in the production by muscle of increased levels of the interferon-gamma (IFN-gamma)-activating cytokine, interleukin-15. This effect is accompanied by the increased trafficking of leukocytes through muscle, some that produce IFN-gamma. These observations may be relevant to the induction of disease symptoms since numerous reports from other investigators indicate that IFN-gamma may play a pivotal role in this disease process.
Journal of Neuroimmunology 11/2001; 119(2):377-86. · 3.03 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Myasthenia gravis (MG) is an autoimmune disease caused by autoantibodies against the nicotinic acetylcholine receptor (AChR). Using phage-display technology we have characterized the largest panel of anti-AChR monoclonal antibodies thus far isolated from a single patient. Despite having been isolated with either Torpedo AChR or a human peptide, the recombinant antibodies shared with the donor's serum the ability to recognize human AChR expressed in its native configuration on the surface of TE671 cells. Their specificity for the main immunogenic region (MIR) of the AChR was demonstrated using a synthetic peptide corresponding to the region 67-76 of the human AChR alpha subunit and by inhibition of a highly pathogenic rat anti-MIR monoclonal antibody (mAb35). This work demonstrates the value of combinatorial libraries in isolating pathogenic autoantibodies from peripheral blood lymphocytes. Future genetic, structural, and functional analyses of the monoclonal antibodies reported herein should enhance our understanding of the pathogenesis of MG.
[Show abstract][Hide abstract] ABSTRACT: Messenger RNA that encodes for monocyte chemotactic protein-1 (MCP-1), as well as its protein product, was observed to be constitutively expressed at low levels in a monoclonal Lewis rat skeletal muscle cell line (LE1). Immunohistochemical analyses of sections of skeletal muscle yielded similar results. Since interferon-gamma (IFN-gamma) has been reported to have a likely role in determining the severity of symptoms in the neuromuscular autoimmune disease experimental myasthenia gravis (EAMG), the hypothesis tested and proven true in these studies was that IFN-gamma would up-regulate the production of MCP-1 in LE1 cells. It was also observed that muscle-derived MCP-1 could be up-regulated in vivo in rats receiving a monoclonal anti-acetylcholine receptor antibody (mAb35), a potent inducer of symptoms of EAMG. Therefore, it is concluded that muscle may contribute to disease progression by producing factors that influence activities of the immune system.
[Show abstract][Hide abstract] ABSTRACT: Messenger RNA that encodes for interleukin-15 (IL-15) has been reported to be constitutively expressed in skeletal muscle, although the protein product is not generally observed. Furthermore, interferon-gamma (IFN-gamma) has been reported to exacerbate symptoms of experimental myasthenia gravis (EAMG). Therefore, since IL-15 is an activator of IFN-gamma-producing cells, the hypothesis that drove the study reported below proposes that muscle is not a passive participant in the development of disease symptoms in EAMG and, in fact, plays a very important active role by producing immunomodulating factors that can influence the eventual immunopathological impact of the immune system on muscle. Tests of this hypothesis, made using a monoclonal skeletal myocyte line from the Lewis rat, have indicated that myocytes produce IL-15 protein following exposure to interleukin-4 (IL-4), an interesting paradox in light of the usual anti-inflammatory role played by IL-4. Furthermore, the level of IL-15 also can be regulated by IFN-gamma itself. Although yet to be confirmed in vivo, IFN-gamma has been shown to be capable of activating cultured myocytes in a variety of ways that could influence the ongoing autoimmune response associated with EAMG.
[Show abstract][Hide abstract] ABSTRACT: In order to begin asking questions about immunopathology associated with the model of the neuromuscular disease experimental autoimmune myasthenia gravis, a monoclonal myocyte line, LE1, has been prepared from the Lewis rat. The LE1 myocyte clone was selected from among several clones produced based on its ease of maintenance in culture and for the stability of its phenotype, which is very similar to that reported for in vivo muscle and other cultured myocyte lines. Thus, LE1 cells were observed to produce, constitutively, the myocyte-associated neural cell adhesion molecule (CD56), the intracellular adhesion molecule (ICAM-1), and the acetylcholine receptor. LE1 cells were also observed to constitutively secrete relatively low levels of IL-6 and TGF-beta. Moreover, the LE1 cell line may be of use for predicting muscle responses to various immune mediators. For example, the inflammatory cytokine interferon-gamma (IFN-gamma) has been recently reported by others to play a role in experimental myasthenia gravis. Thus, it was of interest that LE1 cells could be activated by IFN-gamma to express increased levels of immunopathologically relevant membrane molecules such as ICAM-1 and Class II major histocompatibility molecules (i.e., RT-1B).
[Show abstract][Hide abstract] ABSTRACT: Experimental autoimmune myasthenia gravis (EAMG) in rats can be produced as the result of immunization with purified acetylcholine receptor (AChR). However, antibodies produced against an irreversibly denatured AChR were not capable of producing detectable AChR-dependent neuromuscular impairment such as that seen following immunization with AChR of intact conformation. This immunopathological difference was observed despite the fact that both immunizations resulted in the production of clonotypically heterogeneous antibodies with similar titers, isotype distribution, and relative binding avidities for conformationally intact AChR. Although they had no apparent disease-causing potential of their own, antibodies produced against denatured AChR could, however, bind AChR at the neuromuscular junction and mediate in vivo AChR-dependent neuromuscular impairment if a second anti-antibody was provided. Finally, immunization against denatured AChR, or administration to naive rats of antibodies obtained by immunization against denatured AChR, resulted in the recipient rats becoming resistant to the usual pathological effects of antibodies produced against intact AChR (either induced by active immunization or following passive antibody transfer). These observations suggest that disease severity in this system may be influenced by relationships between disease-causing and disease-abrogating antibodies.