The effects of age on CD4 upregulation and Treg distribution in a TAChR peptide-specific immune response (47.1)

Studies of age-related defects in T cell function have been complicated by the difficulty of identifying antigen-specific T cells early in the activation process. Thus, peptide-responsive T cells were identified and characterized by the upregulation of CD4, an early event following T cell receptor ligation. We focused on the Torpedo californica acetylcholine receptor (TAChR) peptide, p146-162, since responses to this peptide have been well defined in young mice. In old mice, the fine specificity of the TAChR response was preserved with age; p146-162 remained immunodominant. Yet, in vitro proliferative responses to p146-162 were diminished in a dose-dependent manner in lymph node cells (LNC) derived from old peptide-primed mice. When p146-162-specific Vβ6+CD4high T cells derived from young (2-5 months) and old (20-27 months) mice were examined, the upregulation of CD4 was maintained in old age but the frequency of Vβ6+CD4high T cells was often lower; reflecting fewer CD4+ LNC, changes in TCR repertoire selection and/or altered T cell regulation. Interestingly, Foxp3+CD25+CD4+ T regulatory cell (Treg) frequencies were elevated in the old peptide-responding populations. The Vβ6-CD4normal Treg phenotype predominated in both age groups, yet a unique "activated" CD4high Treg subpopulation was also identified. Future studies may help elucidate the potential role of these CD4high Tregs in promoting age-related immune dysfunction. Support: Myasthenia Gravis Foundation, Nathan Shock Aging Center, NIH R03 AG 14557 and San Antonio Area Foundation.

Acetylcholine receptor-reactive antibody induces nitric oxide production by a rat skeletal muscle cell line: influence of cytokine environment

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.

Myocytes respond in vivo to an antibody reactive with the acetylcholine receptor by upregulating interleukin-15: an interferon-gamma activator with the potential to influence the severity and course of experimental myasthenia gravis

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.

A monoclonal lewis rat myocyte line that responds to interferon-gamma: responsiveness with the potential to influence subsequent interactions with the immune system

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).

Myocytes respond to both interleukin-4 and interferon-gamma: cytokine responsiveness with the potential to influence the severity and course of experimental myasthenia gravis

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.

Chemokine production by rat myocytes exposed to interferon-gamma

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.

Lewis rats given antibodies against denatured acetylcholine receptor become resistant to induction of experimental autoimmune myasthenia gravis

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.

Evidence against chronic antigen-specific T lymphocyte activation in myasthenia gravis

Myasthenia gravis (MG) is an antigen-specific autoimmune disease caused by antibodies against acetylcholine receptors (AChR) at the post-synaptic membrane of the neuromuscular junction. Clinical and immunological data imply the involvement of AChR-specific T lymphocytes as helper cells for autoantibody production. Direct data to support this hypothesis, however, remain sparse. In the present study, a large population of MG patients was studied for evidence of peripheral blood T cell activation by several assays. Assays based on non-specific measurements of T cell activation as well as assays of antigen-specific clonal expansion were utilized. Levels of soluble IL-2 receptor in serum were modestly elevated in some patients, suggesting T cell activation. However, peripheral blood cells did not show evidence of IL-2 receptor expression or enhanced reactivity to IL-2 in culture. Clonable T cells selected for hypoxanthine phosphoribosyl transferase (hprt) mutation, another non-antigen-specific marker for T cell activation, were not seen with increased frequency except in patients treated with purine analogs. Antigen-specific T cell activation was measured by proliferation assays using heterologous and autologous sources of AChR. Antigen-restimulated peripheral blood cell cultures were cloned by limiting dilution. The vast majority of patients failed to show convincing evidence of AChR specific T cell activation or clonal expansion; only 2 of 44 patients demonstrated clonable autologous AChR-specific T cells. An alternative hypothesis of T cell involvement in MG is proposed in which T cell activation is discontinuous and predominantly directed at antigens other than AChR.

Identification of an idiotype associated with antibodies responsible for neuromuscular dysfunction in rats with experimental autoimmune myasthenia gravis

The primary goal of this study was to continue clarifying past observations made by this laboratory indicating that disease severity in experimentally induced myasthenia gravis in Lewis rats is directly determined by the responsiveness and antibody production of a small subset of the total population of acetylcholine receptor (AChR)-responsive B cells. This disease-causing subset of B cells was found to be associated, at least in part, with an idiotypic determinant recognized by a monoclonal anti-Id antibody (11E10) prepared in this laboratory. Since relationships between total AChR antibody titers and neuromuscular disease severity can be inconsistent both in human myasthenia gravis patients and in animal models of myasthenia gravis, the development of a simple serological test for the clonotypic/idiotypic subset(s) of anti-AChR antibody that is most directly responsible for inducing disease symptoms may point to more direct methods of diagnosing and monitoring disease.

Neonatal tolerance to an immunodominant T cell reactivity does not confer resistance to EAMG induction in Lewis rats

The overall goal of this study was to determine, during induction of experimental autoimmune myasthenia gravis (EAMG) in Lewis rats, the relative importance of acetylcholine receptor (AChR)-reactive helper T cells associated with one particular immunodominant fine specificity. Thus, experiments presented below were designed to evaluate the immunopathological role played by helper T cells with reactivity against the AChR alpha subunit region associated with amino acid residues 100-116 (i.e., alpha 100-116); in particular, the relationship between T cell reactivity with this specificity and disease induction was assessed. In order to examine the importance of this T cell reactivity, Lewis rat neonates were made T cell tolerant to a synthetic peptide alpha 100-116 and subsequently evaluated for anti-AChR antibody production and resulting neuromuscular dysfunction. Results indicated that although T cell reactivity against the alpha 100-116 peptide could be effectively removed from the Lewis T cell repertoire, tolerized Lewis rats immunized with AChR could undergo an active anti-AChR antibody response that produced symptoms of EAMG. Thus, other AChR T cell reactivities appeared capable of providing adequate help to B cells leading to production of anti-AChR antibodies with pathogenic potential.

V beta-specific immunotoxin selectively kills acetylcholine receptor-reactive T lymphocytes from mice with experimental autoimmune myasthenia gravis

Immunization of C57BL/6 mice with purified acetylcholine receptor (AChR) is known to induce a T cell-dependent antibody response that results in experimental autoimmune myasthenia gravis (EAMG). Since past observations link V beta 6+ T cells with a prominent AChR epitope specificity, a V beta 6-specific immunotoxin (VIT6) was tested in vitro for its ability to selectively kill monoclonal and polyclonal T cells that demonstrate reactivity against AChR. Results described below clearly demonstrate the ability to selectively kill AChR-reactive T cells based on their expression of a particular V beta-associated antigen receptor.

Evaluation of myosin-reactive antibodies from a panel of myasthenia gravis patients

In the study described below, 97 myasthenia gravis (MG) patients have been evaluated for antibody reactivity against muscle myosin. With few exceptions, we could clearly observe a positive correlation between the presence of circulating serum anti-myosin antibodies and disease severity. Unlike some studies of anti-striational antibodies in MG patients, no association with thymoma was apparent. Moreover, no relationships were revealed between the severity of disease symptoms demonstrated and absolute anti-myosin antibody titers or prominent IgG subclasses. Therefore, we suggest that expression of myosin reactivity may be one useful parameter for predicting disease severity in those patients, but it is not prerequisite for induction of MG.

Examination of characteristics that may distinguish disease-causing from benign AChR-reactive antibodies in experimental autoimmune myasthenia gravis

In summary, the strategies of the experimentation described above were designed to address the confusion resulting from observations concerning the lack of correlation between antibody titers and disease severity in MG patients. Lessons learned from these studies of EAMG suggest that if the proportion of the total expressed/produced anti-AChR antibody repertoire with disease-causing potential differs from patient-to-patient with MG, then assessment of the total antibody titer becomes meaningless unless a particular patient produces disease-causing reactivities that make up a major portion of the total titer. Not only may disease severity depend on the titer of a small subset of disease-causing antibody(s) reactive with a particular conformation-dependent AChR region, but may also depend on the relative contribution of additional subsets of antibody with functionally irrelevant or potentially protective activity. The key to exploiting the existence of antibody subsets with differing disease-causing potential will be to create probes that would allow the easy monitoring of the relevant reactivities. For instance, carefully selected anti-idiotypic antibodies (such as the 11E10 monoclonal antibody described above) may be of great value when specifically capable of recognizing idiotypes that are selectively associated with disease-causing anti-AChR antibodies and under-represented on antibodies lacking disease-causing capability. If, in addition, characteristics of helper T cells are identified that allow more accurate prediction of D+ Id production, exciting opportunities would become available to more directly evaluate disease mechanisms and to develop more highly efficacious immunotherapeutic strategies.

Antigen presentation and T cell specificity repertoire in determining responsiveness to an epitope important in experimental autoimmune myasthenia gravis

The overall goal of this study was to define, in experimental autoimmune myasthenia gravis (EAMG), immunological differences between helper T cells from two inbred rat strains that explain disease susceptibility on the one hand (in Lewis rats) and disease resistance on the other hand (in Wistar Furth rats). The working hypothesis for these studies was that the T cell compartment in Wistar Furth rats may lack the ability to activate responsiveness by existing B cells that have the potential to produce disease-causing antibodies; this quality may be related to a lack of T cell reactivity toward a determinant(s) associated with the alpha subunit sequence alpha 100-116 of the acetylcholine receptor (AChR) that demonstrates immunodominance in Lewis rats. Results presented below are consistent with the conclusion that there is a deficit in the Wistar Furth (WF) T cell specificity repertoire responsible for unresponsiveness to this important AChR epitope; this deficit exists despite the apparent ability of WF antigen presenting cells to bind and present the alpha 100-116 peptide, and is likely responsible for the inability of Wistar Furth T cells to drive an anti-AChR antibody response with disease-causing potential.

Inhibition of myosin ATPase activity by human myasthenia gravis antibodies reactive with the acetylcholine receptor

Antibodies, obtained from myasthenia gravis patients, with reactivity for an immunodominant region of the nicotinic acetylcholine receptor were found to also react with muscle myosin. Since amino acid sequence analyses have previously suggested possible serological relationships between AChR and a head region sequence of myosin heavy chain, cross-reactive antibodies were examined for their ability to interfere with ATPase activities associated with this region of myosin. Results indicated that AChR-specific antibodies purified from MG patient serum by binding to and elution from antigen columns were found to inhibit Ca(2+)-dependent, myosin-associated ATPase activity; interestingly, this inhibition appeared to be relatively selective in that neither K+(EDTA)-dependent nor Mg(2+)-dependent ATPase activities were sensitive to antibody-mediated interference.

Unexpected cross-reactivity between myosin and a main immunogenic region (MIR) of the acetylcholine receptor by antisera obtained from myasthenia gravis patients

Antibodies obtained from the plasma of patients with myasthenia gravis (MG) were found to contain reactivity against both the classic target antigen, the acetylcholine receptor, as well as muscle myosin. This observation was consistent with several previously published reports. However, it was also observed in the present study that much of the dual reactivity contained in MG plasma was due to the ability of individual clonotypic species of anti-receptor antibodies to also bind myosin. Furthermore, the cross-reactivity demonstrated by these antibodies appeared to involve a main immunogenic region of the acetylcholine receptor and an enzymatically important region in the head of the myosin heavy chain. This observation appears to provide new explanations for the epitope-restricted antibody response seen in MG patients.

Preferential use of a T cell receptor V beta gene by acetylcholine receptor reactive T cells from myasthenia gravis-susceptible mice

Experimental autoimmune myasthenia gravis (EAMG) is an important model for testing current concepts in autoimmunity and novel immunotherapies for autoimmune diseases. The EAMG autoantigen, acethylcholine receptor (AChR), is structurally and immunologically complex, a potential obstacle to the application of therapeutic strategies aimed at oligoclonal T cell populations. Inasmuch as we had previously shown that the clonal heterogeneity of T cell epitope recognition in EAMG was unexpectedly limited, we examined TCR V beta expression. AChR primed lymph node T cells and established AChR reactive T cell clones from EAMG-susceptible C57BL/6 (B6; H-2b, Mls-1b) mice showed preferential utilization of the TCR V beta 6 segment of the TCR. After in vivo priming and in vitro restimulation for 7 days with AChR or a synthetic peptide bearing an immunodominant epitope, V beta 6 expressing lymph node cells (LNC) were expanded several-fold, accounting for up to 75% of recovered viable CD4+ cells. The LNC of B6.C-H-2bm12 (bm12; H-2bm12, Mls-1b) mice, which proliferated in response to AChR but not to the B6 immunodominant peptide, failed to expand V beta 6+ cells. Inasmuch as nonimmune bm12 and B6 animals had similar numbers of V beta 6+ LNC (4-5%), this suggested that structural requirements for TCR recognition of Ag/MHC complexes dictated V beta usage. Results concerning peptide reactivity and V beta 6 expression among T cells from (B6 x bm12)F1 animals also suggested that structure-function relationships, rather than negative selection or tolerance, accounted for the strain differences between B6 and bm12. To examine the potential effects of thymic negative selection of V beta 6+ cells on the T cell response to AChR, CB6F1 (H-2bxd, Mls-1b; V beta 6-expressing) and B6D2F1 (H-2bxd, Mls-1axb; V beta 6-deleting) strains were analyzed for AChR and peptide reactivity and V beta 6 expression. Both F1 strains responded well to AChR but the response of B6D2F1 mice to peptide was significantly reduced compared to CB6F1. Short and long term cultures of peptide-reactive B6D2F1 LNC showed no expansion of residual V beta 6+ cells, although similar cultures of CB6F1 LNC were composed of more than 60% V beta 6+ cells. The results from the F1 strains further indicated that the T cell repertoire for peptide was highly constrained and that non-V beta 6 expressing cells could only partially overcome Mls-mediated negative selection of V beta 6+ TCR capable of recognizing peptide.(ABSTRACT TRUNCATED AT 400 WORDS)

Preferential use of a T cell receptor V beta gene by acetylcholine receptor reactive T cells from myasthenia gravis-susceptible mice

Experimental autoimmune myasthenia gravis (EAMG) is an important model for testing current concepts in autoimmunity and novel immunotherapies for autoimmune diseases. The EAMG autoantigen, acethylcholine receptor (AChR), is structurally and immunologically complex, a potential obstacle to the application of therapeutic strategies aimed at oligoclonal T cell populations. Inasmuch as we had previously shown that the clonal heterogeneity of T cell epitope recognition in EAMG was unexpectedly limited, we examined TCR V beta expression. AChR primed lymph node T cells and established AChR reactive T cell clones from EAMG-susceptible C57BL/6 (B6; H-2b, Mls-1b) mice showed preferential utilization of the TCR V beta 6 segment of the TCR. After in vivo priming and in vitro restimulation for 7 days with AChR or a synthetic peptide bearing an immunodominant epitope, V beta 6 expressing lymph node cells (LNC) were expanded several-fold, accounting for up to 75% of recovered viable CD4+ cells. The LNC of B6.C-H-2bm12 (bm12; H-2bm12, Mls-1b) mice, which proliferated in response to AChR but not to the B6 immunodominant peptide, failed to expand V beta 6+ cells. Inasmuch as nonimmune bm12 and B6 animals had similar numbers of V beta 6+ LNC (4-5%), this suggested that structural requirements for TCR recognition of Ag/MHC complexes dictated V beta usage. Results concerning peptide reactivity and V beta 6 expression among T cells from (B6 x bm12)F1 animals also suggested that structure-function relationships, rather than negative selection or tolerance, accounted for the strain differences between B6 and bm12. To examine the potential effects of thymic negative selection of V beta 6+ cells on the T cell response to AChR, CB6F1 (H-2bxd, Mls-1b; V beta 6-expressing) and B6D2F1 (H-2bxd, Mls-1axb; V beta 6-deleting) strains were analyzed for AChR and peptide reactivity and V beta 6 expression. Both F1 strains responded well to AChR but the response of B6D2F1 mice to peptide was significantly reduced compared to CB6F1. Short and long term cultures of peptide-reactive B6D2F1 LNC showed no expansion of residual V beta 6+ cells, although similar cultures of CB6F1 LNC were composed of more than 60% V beta 6+ cells. The results from the F1 strains further indicated that the T cell repertoire for peptide was highly constrained and that non-V beta 6 expressing cells could only partially overcome Mls-mediated negative selection of V beta 6+ TCR capable of recognizing peptide.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine receptor-reactive antibodies in experimental autoimmune myasthenia gravis differing in disease-causing potential: subsetting of serum antibodies by preparative isoelectric focusing

Antibodies obtained from the sera of Lewis rats demonstrating impaired neuromuscular function following immunization with purified acetylcholine receptor (AChR) were fractionated by preparative isoelectric focusing. Upon passive transfer of fractionated anti-receptor antibodies into immunologically naive, healthy recipient rats it was observed that two main subsets of AChR-specific antibody could be identified. One subset, representing about one-third of the expressed clonotypic antibody repertoire, was capable of directly perturbing AChR-dependent neuromuscular function following transfer. A second subset, demonstrated no detectable ability to induce disease symptoms following transfer. Although the anti-AChR antibodies were produced by immunization with Torpedo AChR, the inability of some antibody fractions to perturb AChR function was not explained by their inability to react with AChR of mammalian origin. Furthermore, the ability to transfer symptoms did not correspond with a particular antibody isotype (although the response was dominated by IgG2a) and did not depend solely on high relative binding avidity (benign reactivities of high relative binding avidity were also observed). Nonetheless, an anti-AChR antibody subset can be directly identified and purified from immune serum that is likely to contain reactivities that are most directly responsible for neuromuscular disease symptoms demonstrated by rats with experimental autoimmune myasthenia gravis.

Repetitive nerve stimulation vs. twitch tension in rats with EAMG

Two methods were compared with regard to their ability to detect acetylcholine receptor-dependent neuromuscular dysfunction in rats with experimental autoimmune myasthenia gravis. In both cases, detection of AChR impairment required amplification of symptoms by administration of the AChR antagonist curare and appeared to be directly related to increasing levels of circulating anti-AChR antibodies. First, in vivo evaluations of decremental compound motor action potentials following repetitive nerve stimulation were performed by electromyography. Impaired neuromuscular function (i.e., greater than 10% decrement) was noted only after rats had been immunized twice with AChR, requiring levels of circulating anti-AChR antibody greater than about 200 micrograms/mL in serum. In contrast, the direct in vitro evaluation of stimulated isometric twitch tension appeared to be more sensitive in that impaired AChR-dependent muscle contraction was clearly observed following a single AChR immunization, and, as shown previously, required anti-AChR antibody levels of about 50 micrograms/mL in serum. Further discussion is presented concerning the advantages and disadvantages associated with each method of monitoring disease.

Exacerbated muscle dysfunction by procainamide in rats with experimental myasthenia gravis

The induction of experimental autoimmune myasthenia gravis (EAMG) has long been shown to result in inefficient function of the acetylcholine receptor (AChR) and concomitant impairment of AChR-dependent neuromuscular communication. As an animal model of human myasthenia gravis, AChR-immunized rats demonstrate symptoms of MG very similar to those observed in human patients resulting from the presence of circulating anti-AChR antibodies which interfere with the normal function of the receptor. In addition to antibody antagonists of neuromuscular function, a variety of drugs have been observed to be associated with possible exacerbations of impaired neuromuscular function leading to myasthenic crisis in some MG patients. One drug, the cardiac anti-arrhythmic agent, procainamide, has been reported to cause both pre-synaptic and post-synaptic electrophysiologic effects at the neuromuscular junction. The study described below extends these observations to include the demonstration of perturbed AChR-dependent contractile muscle function in a rat model of MG.

Subsetting of acetylcholine receptor-reactive antibodies by preparative isoelectric focusing

The antibodies produced against most foreign antigens are composed of a family of immunoglobulins, a family composed of members that are of a number that often reflects the size/complexity of the molecule that stimulates their production. In other words, such responses involve the activation of a "polyclonal" B lymphocyte population. The antibody products of the B cells, although all capable of binding the original antigen, bind at various immunogenic sites (epitopes) on that antigen. Such differences in antigen-binding fine specificity is determined by amino acid residues in the antibody variable region domains found associated with the antigen combining site and tend to have a complimentary biochemistry with the molecule for which they are intended to interact. Furthermore, in addition to amino acid differences that dictate the isotypes and allotypes of antibody molecules, differences in the amino acids that compose the variable regions can produce differences in net charge of particular antibody molecules; thus, families of polyclonal antibodies, all reactive with the same antigen but with different fine specificities, can be separated and, as shown below, purified based on their isoelectric points by preparative isoelectric focusing (pIEF).

Determinant selection in murine experimental autoimmune myasthenia gravis. Effect of the bm12 mutation on T cell recognition of acetylcholine receptor epitopes

C57BL/6 (B6) mice respond to immunization with acetylcholine receptor (AChR) from Torpedo californica as measured by T cell proliferation, antibody production, and the development of muscle weakness resembling human myasthenia gravis. The congenic strain B6.C-H-2bm12 (bm12), which differs from B6 by three amino acid substitutions in the beta-chain of the MHC class II molecule I-A, develops a T cell proliferative response but does not produce antibody or develop muscle weakness. By examining the fine specificity of the B6 and bm12 T cell responses to AChR by using T cell clones and synthetic AChR peptides, we found key differences between the two strains in T cell epitope recognition. B6 T cells responded predominantly to the peptide representing alpha-subunit residues 146-162; this response was cross-reactive at the clonal level to peptide 111-126. Based on the sequence homology between these peptides and the T cell response to a set of truncated peptides, the major B6 T cell epitope was determined to be residues 148-152. The cross-reactivity of peptides 146-162 and 111-126 could also be demonstrated in vivo. Immunization of B6 mice with either peptide primed for T cell responses to both peptides. In contrast, immunization of bm12 mice with peptide 111-126 primed for an anti-peptide response, which did not cross-react with 146-162. Peptide-reactive T cells were not elicited after immunization of bm12 mice with 146-162. These results define a major T cell fine specificity in experimental autoimmune myasthenia gravis-susceptible B6 mice to be directed at alpha-subunit residues 148-152. T cells from disease-resistant bm12 mice fail to recognize this epitope but do recognize other portions of AChR. We postulate that alpha-148-152 is a disease-related epitope in murine experimental autoimmune myasthenia gravis. In this informative strain combination, MHC class II-associated determinant selection, rather than Ag responsiveness per se, may play a major role in determining disease susceptibility.

Determinant selection in murine experimental autoimmune myasthenia gravis. Effect of the bm12 mutation on T cell recognition of acetylcholine receptor epitopes

C57BL/6 (B6) mice respond to immunization with acetylcholine receptor (AChR) from Torpedo californica as measured by T cell proliferation, antibody production, and the development of muscle weakness resembling human myasthenia gravis. The congenic strain B6.C-H-2bm12 (bm12), which differs from B6 by three amino acid substitutions in the beta-chain of the MHC class II molecule I-A, develops a T cell proliferative response but does not produce antibody or develop muscle weakness. By examining the fine specificity of the B6 and bm12 T cell responses to AChR by using T cell clones and synthetic AChR peptides, we found key differences between the two strains in T cell epitope recognition. B6 T cells responded predominantly to the peptide representing alpha-subunit residues 146-162; this response was cross-reactive at the clonal level to peptide 111-126. Based on the sequence homology between these peptides and the T cell response to a set of truncated peptides, the major B6 T cell epitope was determined to be residues 148-152. The cross-reactivity of peptides 146-162 and 111-126 could also be demonstrated in vivo. Immunization of B6 mice with either peptide primed for T cell responses to both peptides. In contrast, immunization of bm12 mice with peptide 111-126 primed for an anti-peptide response, which did not cross-react with 146-162. Peptide-reactive T cells were not elicited after immunization of bm12 mice with 146-162. These results define a major T cell fine specificity in experimental autoimmune myasthenia gravis-susceptible B6 mice to be directed at alpha-subunit residues 148-152. T cells from disease-resistant bm12 mice fail to recognize this epitope but do recognize other portions of AChR. We postulate that alpha-148-152 is a disease-related epitope in murine experimental autoimmune myasthenia gravis. In this informative strain combination, MHC class II-associated determinant selection, rather than Ag responsiveness per se, may play a major role in determining disease susceptibility.

Clonotypic analysis of anti-acetylcholine receptor antibodies from experimental autoimmune myasthenia gravis-sensitive Lewis rats and experimental autoimmune myasthenia gravis-resistant Wistar Furth rats

A single immunization of Lewis rats with purified acetylcholine receptor (AChR) emulsified in adjuvant typically stimulates the production of oligoclonal AChR-reactive antibodies (as demonstrated by IEF) dominated by the IgG2a subclass, of moderate but clonotypically heterogeneous relative Ag-binding avidity, and capable of inducing symptoms of experimental autoimmune myasthenia gravis. Although similar immunization of Wistar Furth rats produces AChR-reactive antibodies with similar characteristics of clonotypic heterogeneity, avidity, and isotype expression, no detectable signs of AChR-dependent muscle impairment is observed. This contrasts the ability to induce impaired AChR function upon the passive transfer of pre-formed Lewis anti-AChR antibodies into naive Wistar Furth rats, suggesting that disease resistance in this model is not conferred at the level of the AChR itself. Moreover, if more aggressive immunization protocols are used (i.e., multiple injections of AChR), a transient breakthrough of AChR-dependent muscle dysfunction can be induced directly in the Wistar Furth strain indicating that the potential for the production of disease-causing antibodies does exist in the Wistar Furth repertoire. IEF analysis of Wistar Furth anti-AChR antibodies has revealed that hyperimmunization results in modified antibody clonotype expression that might explain changing expression of disease symptoms; however, explanations for the apparent "resistance" of Wistar Furth rats to disease induction are likely to be complex.

Clonotypic analysis of anti-acetylcholine receptor antibodies from experimental autoimmune myasthenia gravis-sensitive Lewis rats and experimental autoimmune myasthenia gravis-resistant Wistar Furth rats

A single immunization of Lewis rats with purified acetylcholine receptor (AChR) emulsified in adjuvant typically stimulates the production of oligoclonal AChR-reactive antibodies (as demonstrated by IEF) dominated by the IgG2a subclass, of moderate but clonotypically heterogeneous relative Ag-binding avidity, and capable of inducing symptoms of experimental autoimmune myasthenia gravis. Although similar immunization of Wistar Furth rats produces AChR-reactive antibodies with similar characteristics of clonotypic heterogeneity, avidity, and isotype expression, no detectable signs of AChR-dependent muscle impairment is observed. This contrasts the ability to induce impaired AChR function upon the passive transfer of pre-formed Lewis anti-AChR antibodies into naive Wistar Furth rats, suggesting that disease resistance in this model is not conferred at the level of the AChR itself. Moreover, if more aggressive immunization protocols are used (i.e., multiple injections of AChR), a transient breakthrough of AChR-dependent muscle dysfunction can be induced directly in the Wistar Furth strain indicating that the potential for the production of disease-causing antibodies does exist in the Wistar Furth repertoire. IEF analysis of Wistar Furth anti-AChR antibodies has revealed that hyperimmunization results in modified antibody clonotype expression that might explain changing expression of disease symptoms; however, explanations for the apparent "resistance" of Wistar Furth rats to disease induction are likely to be complex.

T cells reactive with a small synthetic peptide of the acetylcholine receptor can provide help for a clonotypically heterogeneous antibody response and subsequently impaired muscle function

The influence of T cell specificity was evaluated with regard to its role in the antibody response against the acetylcholine receptor (AChR) and resulting AChR-dependent muscle dysfunction. The reactivity of immune Th cells was restricted to a small region of the AChR alpha-subunit (amino acid residues 100-116) reported to be highly immunogenic. T cells primed to this peptide were found to demonstrate significant proliferation when challenged in vitro with either the homologous peptide or the intact AChR. Adoptive transfer of the peptide-immune T cells into immunologically naive recipient rats followed by AChR challenge resulted in the production of anti-AChR antibodies very similar to those produced under the regulation of T cells immune to the entire intact AChR with regard to overall clonotypic heterogeneity (measured by IEF) and their ability to interfere with AChR-dependent muscle contraction. Interestingly, when the threonine at position 106 was substituted with a proline, the resulting peptide continued to be equally, if not exceedingly, capable of stimulating T cell-proliferative responses, but was found to be ineffective at stimulating the levels of anti-AChR antibodies necessary for producing neuromuscular dysfunction.

T cells reactive with a small synthetic peptide of the acetylcholine receptor can provide help for a clonotypically heterogeneous antibody response and subsequently impaired muscle function

The influence of T cell specificity was evaluated with regard to its role in the antibody response against the acetylcholine receptor (AChR) and resulting AChR-dependent muscle dysfunction. The reactivity of immune Th cells was restricted to a small region of the AChR alpha-subunit (amino acid residues 100-116) reported to be highly immunogenic. T cells primed to this peptide were found to demonstrate significant proliferation when challenged in vitro with either the homologous peptide or the intact AChR. Adoptive transfer of the peptide-immune T cells into immunologically naive recipient rats followed by AChR challenge resulted in the production of anti-AChR antibodies very similar to those produced under the regulation of T cells immune to the entire intact AChR with regard to overall clonotypic heterogeneity (measured by IEF) and their ability to interfere with AChR-dependent muscle contraction. Interestingly, when the threonine at position 106 was substituted with a proline, the resulting peptide continued to be equally, if not exceedingly, capable of stimulating T cell-proliferative responses, but was found to be ineffective at stimulating the levels of anti-AChR antibodies necessary for producing neuromuscular dysfunction.

Clonotypic analysis of anti-acetylcholine receptor antibodies produced against native and denatured antigen

Rats were immunized with either conformationally intact acetylcholine receptor (AChR) or reduced and sodium dodecyl sulfate (SDS)-denatured AChR. As expected, challenge with native AChR (nAChR) resulted in the production of serum antibodies reactive with native AChR; these antibodies were, as observed in earlier studies, oligoclonal, dominated by the rat IgG2a subclass, heterogeneous with respect to binding avidity, and importantly, able to interfere with normal AChR-dependent muscle contraction. Antibodies produced as a result of immunization with denatured AChR (dAChR) that were crossreactive with nAChR were similar but not identical to those produced directly against nAChR; in contrast, however, dAChR-stimulated antibodies were clearly incapable of causing detectable impairment of AChR-dependent muscle contractile function. This difference in disease-causing potential was demonstrated in spite of the observation that either nAChR or dAChR could generate similar levels of circulating antibodies that reacted with the native form of AChR. Moreover, the same difference in disease-causing potential was again observed upon passive intravenous administration of anti-AChR antibodies into naive recipient rats. IEF analyses demonstrated that antibodies stimulated by dAChR immunization expressed the same clonotypic heterogeneity and isotype distribution as those stimulated by nAChR immunization. However, an apparent shift was observed in the preferred clonotypes expressed in rats immunized with dAChR; antibodies with relatively lower binding avidities were more markedly represented than the higher avidity antibodies commonly accompanying immunization with nAChR. Furthermore, a distinct subset of high avidity clonotypes was expressed following immunization with dAChR not associated with nAChR immunization.

Selective elimination of autoreactive lymphocytes with immunotoxins

A variety of diseases are the result of identifiable cell types entering an abnormal state of development in which they escape existing mechanisms that regulate their growth or other functional activities. A variety of investigators interested in eliminating cells that have undergone malignant transformation have devised immunotherapeutic approaches based on the construction of hybrid molecules composed of highly toxic biological poisons covalently coupled with antibodies specific for membrane antigens expressed selectively by tumor cell targets. This strategy can be further exploited to eliminate any target cell with defined, selectively expressed membrane antigens. The following discussion describes possible uses of such an approach for achieving selective cytotoxicity of lymphocytes with undesirable immunoreactivities, such as those found in autoimmune disease and graft-versus-host disease.

Clonotypic analysis of the antibody response to the acetylcholine receptor in experimental autoimmune myasthenia gravis

Autoreactive B cells reactive with the acetylcholine receptor (AChR), and the antibodies produced by them, are proposed to play a primary role in the immunopathology of myasthenia gravis and its animal models. Therefore, the anti-AChR antibody response induced in rats was characterized for the clonotypic heterogeneity, isotype distribution, and affinity by isoelectric focusing (IEF) and affinity immunoblotting. It was determined that the rat anti-AChR serum antibody was relatively heterogeneous, reflecting the oligoclonality of the response. Furthermore, isotypic dominance by IgG2a was observed in that the majority of clonal products detected by IEF were of this isotype in both primary and secondary responses. Lastly, the clonotypic anti-AChR antibodies were of relatively low affinity (avidity) when compared to antibodies reactive with the highly immunogenic protein antigen, keyhole limpet hemocyanin; anti-AChR antibody avidity did not appear to increase when the antibodies in the secondary response were compared to antibodies in the primary response. These antibody characteristics are discussed in terms of their role in disease induction.

Selective idiotype suppression of an adoptive secondary antiacetylcholine receptor antibody response by immunotoxin treatment before transfer

Acetylcholine receptor (AChR)-immune lymph node cells were treated with Id-specific immunotoxin before their transfer and antigenic challenge in adoptive recipient rats. In contrast to untreated, AChR-immune lymph node cells that, when challenged, produced high titers of serum anti-AChR antibody, in vitro anti-Id-ricin A chain treatment significantly inhibited anti-AChR antibody responses upon adoptive transfer. The inhibition was specific in that control lymph node cells immune to keyhole limpet hemocyanin were unaffected and totally responsive after treatment by the same immunotoxin. Furthermore, evidence is presented by isoelectric focusing analysis that the anti-Id antibody preparation used in this study contains all of the specificities required to eliminate the entire spectrum of AChR-reactive B cell clones.

Selective idiotype suppression of an adoptive secondary antiacetylcholine receptor antibody response by immunotoxin treatment before transfer

Acetylcholine receptor (AChR)-immune lymph node cells were treated with Id-specific immunotoxin before their transfer and antigenic challenge in adoptive recipient rats. In contrast to untreated, AChR-immune lymph node cells that, when challenged, produced high titers of serum anti-AChR antibody, in vitro anti-Id-ricin A chain treatment significantly inhibited anti-AChR antibody responses upon adoptive transfer. The inhibition was specific in that control lymph node cells immune to keyhole limpet hemocyanin were unaffected and totally responsive after treatment by the same immunotoxin. Furthermore, evidence is presented by isoelectric focusing analysis that the anti-Id antibody preparation used in this study contains all of the specificities required to eliminate the entire spectrum of AChR-reactive B cell clones.

Influence of T cell specificity on the heterogeneity and disease-causing capability of antibody against the acetylcholine receptor

Adoptive secondary anti-acetylcholine receptor (AChR) antibody responses were examined in rats to evaluate the influence of helper T cell specificity on the nature and disease-causing potential of antibody produced. Mixtures of B cells reactive with the intact AChR plus T cells reactive with purified AChR subunits (alpha, beta, gamma, delta) were transferred and antigen-challenged in immunologically naive recipient rats; the serum anti-AChR antibody produced was assessed by radioimmunoassay for differences in titers and by isoelectric focusing for differences in clonal heterogeneity as a function of the subunit specificity of T cells transferred. In addition, rats receiving different sources of AChR or AChR subunit-reactive T cells were examined for AChR-dependent muscle dysfunction. The results indicated a clear reduction in anti-AChR antibody concentrations and clonal heterogeneity in recipient rats receiving T cells of specificities restricted to individual subunits. However, except for a clear relationship between serum anti-AChR antibody concentration and disease induction, no particular AChR subunit-reactive helper T cell specificity appeared to preferentially cause muscle dysfunction. We conclude that if such relationships exists, T cells with specificities more restricted than those described here will have to be used.

Analysis of contractile properties of muscles from rats immunized with purified acetylcholine receptor

Experimental autoimmune myasthenia gravis (EAMG) was induced in rats by injection of purified acetylcholine receptor (AChR). In addition to detecting elevated serum titers of anti-AChR antibodies, we observed decreased twitch-tension at submaximal stimulation voltages and increased curare sensitivity by muscles obtained from immunized rats when compared to muscles obtained from nonimmune control rats. Furthermore, antibody-induced neuromuscular impairment was expressed to differing extents dependent on whether the diaphragm, soleus, or extensor digitorum longus muscle was examined. Thus, we conclude that potential antibody perturbation of AChR function will depend not only on the nature of the antibody, but also on the complex structure-function relationships that exist in individual muscles. This may partially explain the variable impairment of different muscle groups in patients with myasthenia.

Analysis of helper-T-cell function by acetylcholine receptor-reactive cell lines of defined AChR-subunit specificity

A small panel of cloned acetylcholine receptor (AChR)-reactive helper T cells were examined for their ability to proliferate when stimulated with AChR or purified AChR subunits. It was observed that all T-cell lines preferentially responded to the AChR alpha subunit, but that some also were stimulated by other subunits as well. This was interpreted as indicating that the alpha subunit plays a major role in anti-AChR T-cell responses, but that considerable potential cross-reactivity exists among the subunits recognized by T cells. Furthermore, a high level of "microheterogeneity" in the T-cell-specificity repertoire was suggested by the fact that even this small panel of cloned lines expressed several patterns of subunit reactivity. Finally, all cloned T-cell lines examined were found to be capable of functioning as regulatory helpers in vitro by providing the necessary signals to AChR-responsive B cells, resulting in anti-AChR antibody production.

T cell hybridomas reactive with the acetylcholine receptor and its subunits

A panel of thirty cloned rat-mouse T cell hybridomas was prepared by fusion of acetylcholine receptor (AChR)-reactive rat T cells with the mouse thymoma BW5147. The T cell hybrids were demonstrated to be AChR reactive by their ability to secrete IL 2 in response to either AChR itself or by purified AChR subunits (alpha,beta,gamma, or delta). Various patterns of AChR subunit reactivity were observed, suggesting a predominant recognition of the alpha subunit, and also a considerable cross-reactivity from one subunit to another.

T cell hybridomas reactive with the acetylcholine receptor and its subunits

A panel of thirty cloned rat-mouse T cell hybridomas was prepared by fusion of acetylcholine receptor (AChR)-reactive rat T cells with the mouse thymoma BW5147. The T cell hybrids were demonstrated to be AChR reactive by their ability to secrete IL 2 in response to either AChR itself or by purified AChR subunits (alpha,beta,gamma, or delta). Various patterns of AChR subunit reactivity were observed, suggesting a predominant recognition of the alpha subunit, and also a considerable cross-reactivity from one subunit to another.

An immunotoxin cytotoxic for breast cancer cells in vitro

A potent immunotoxin was formed by conjugating the murine monoclonal antibody 323/A3 to the A chain of ricin. The 323/A3 antibody recognizes an antigen expressed by most human breast cancers. When binding of 323/A3 is examined by enzyme-linked immunosorption assay, three human breast cell lines displayed strong binding, whereas two human breast cell lines and three non-breast cell lines displayed little or no binding. When the cell lines were tested at a concentration of 0.1 microgram/ml, those cell lines which displayed an abundance of antigen by enzyme-linked immunosorption assay were most sensitive to the effects of the 323/A3 immunotoxin. On the other hand, cell lines which displayed little or no antigen by enzyme-linked immunosorption assay were not inhibited by the immunotoxin at this concentration. Further examination of the effects of immunotoxin concentration on protein synthesis confirmed the sensitivity of those cell lines rich in the 323/A3 antigen over a broad dose range. Similarly, three cell lines which displayed little of the 323/A3 antigen demonstrated little inhibition of protein synthesis with various concentrations of 323/A3 immunotoxin. However, two cell lines which displayed little antigen were intermediate in their sensitivity to the 323/A3 immunotoxin. Preclinical evaluation of immunotoxins as potential therapeutic agents will require accurate and sensitive screening of a wide variety of cell types. The 323/A3 remains of interest in studying the effects of immunotoxin in a defined in vivo model system.

Selective in vitro inhibition of an antibody response to purified acetylcholine receptor by using anti-idiotypic antibodies coupled to the A chain of ricin

In vitro antibody responses by rat lymph node cells against purified acetylcholine receptor (AChR) were shown to be inhibitable by protein conjugates prepared with anti-idiotypic antibody and the toxic A chain of ricin. The idiotype specificity of the cytotoxicity was demonstrated by the inability of the same immunotoxin to inhibit an unrelated antibody response (anti-KLH) and by abrogation of specific toxicity in the presence of unconjugated anti-idiotype or antigen (AChR). Furthermore, immunotoxin prepared with an irrelevant antibody specificity failed to significantly inhibit either the anti-AChR or control antibody responses. Therefore, we suggest that idiotype-specific immunotoxins may be a useful addition or alternative to presently employed immunotherapies for autoimmune disease.

Selective in vitro inhibition of an antibody response to purified acetylcholine receptor by using anti-idiotypic antibodies coupled to the A chain of ricin

In vitro antibody responses by rat lymph node cells against purified acetylcholine receptor (AChR) were shown to be inhibitable by protein conjugates prepared with anti-idiotypic antibody and the toxic A chain of ricin. The idiotype specificity of the cytotoxicity was demonstrated by the inability of the same immunotoxin to inhibit an unrelated antibody response (anti-KLH) and by abrogation of specific toxicity in the presence of unconjugated anti-idiotype or antigen (AChR). Furthermore, immunotoxin prepared with an irrelevant antibody specificity failed to significantly inhibit either the anti-AChR or control antibody responses. Therefore, we suggest that idiotype-specific immunotoxins may be a useful addition or alternative to presently employed immunotherapies for autoimmune disease.

Influence of T cell specificity on the antibody response to the acetylcholine receptor

Lymph node T cells were obtained from rats immunized with purified acetylcholine receptor (AChR) or isolated receptor subunits (alpha, beta, gamma, or delta). The immune T cells were then analyzed for the ability to respond to native AChR or AChR subunit challenge in an in vitro proliferation assay, as well as to perform as helper T cells (TH) in an in vitro anti-AChR antibody response. Results indicated a significant degree of subunit-to-subunit crossreactivity at the T cell level. Moreover, helper function could be generated by stimulation of T cells immune to any of the AChR subunits, although alpha-immune TH cells appeared to provide a quantifiably increased level of specific antibody production by AChR-immune B cells in vitro when compared to antibody produced by the same B cells in conjunction when beta-, gamma-, or delta-immune TH cells.

Selective in vitro inhibition of an antibody response to purified acetylcholine receptor by using antigen-ricin A chain immunotoxin

Purified acetylcholine receptor (AChR) covalently coupled to the catalytically toxic A chain of ricin has been used to selectively eliminate rat lymph node cells involved in in vitro anti-AChR antibody responses. The resulting inhibition was specific in view of the lack of such inhibition of anti-Keyhole limpet hemocyanin antibody responses. Furthermore, when fractionated B cell or T cell populations were treated with AChR-A chain, both populations were found to be sensitive to the specific cytotoxicity. However, T cell cytotoxicity required higher concentrations of the immunotoxin. Furthermore, when AChR-immune lymphocytes were treated with AChR-A chain in vitro, they became unable to mediate secondary adoptive transfer responses in vivo. The abrogation of the anti-AChR adoptive response correlated with the lack of muscle weakness characteristic of experimental autoimmune myasthenia gravis. Thus, it is possible, in principle, to eliminate clones of antigen-reactive lymphocytes with antigen-ricin A chain immunotoxins. This lets open the possibility of using such agents in immunotherapeutic approaches to autoimmune disease.

Selective in vitro inhibition of an antibody response to purified acetylcholine receptor by using antigen-ricin A chain immunotoxin

Purified acetylcholine receptor (AChR) covalently coupled to the catalytically toxic A chain of ricin has been used to selectively eliminate rat lymph node cells involved in in vitro anti-AChR antibody responses. The resulting inhibition was specific in view of the lack of such inhibition of anti-Keyhole limpet hemocyanin antibody responses. Furthermore, when fractionated B cell or T cell populations were treated with AChR-A chain, both populations were found to be sensitive to the specific cytotoxicity. However, T cell cytotoxicity required higher concentrations of the immunotoxin. Furthermore, when AChR-immune lymphocytes were treated with AChR-A chain in vitro, they became unable to mediate secondary adoptive transfer responses in vivo. The abrogation of the anti-AChR adoptive response correlated with the lack of muscle weakness characteristic of experimental autoimmune myasthenia gravis. Thus, it is possible, in principle, to eliminate clones of antigen-reactive lymphocytes with antigen-ricin A chain immunotoxins. This lets open the possibility of using such agents in immunotherapeutic approaches to autoimmune disease.